首页 > 最新文献

Journal of Metamorphic Geology最新文献

英文 中文
Multi-episodic formation of baddeleyite and zircon in polymetamorphic anorthosite and rutile-bearing ilmenitite from the Chiapas Massif Complex, Mexico 墨西哥恰帕斯地块杂岩多变质斜长岩和含金红石钛铁矿中坏辉石和锆石的多期形成
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-06-28 DOI: 10.1111/jmg.12683
Alejandro Cisneros de León, Axel K. Schmitt, Bodo Weber
<p>Massif-type anorthosite and comagmatic associations of rutile-bearing ilmenitite (RBI) and oxide-apatite-rich amphibolite (OARA) from the Chiapas Massif Complex (CMC) in southeastern Mexico display a protracted billion-year accessory mineral record encompassing magmatic crystallization at c. 1.0 Ga to recent ductile shear deformation at c. 3.0 Ma. Multiple discrete zircon populations between these age end-members resulted from neoformation/recrystallization during local to regional metamorphism that affected the southeastern portion of the CMC. The ubiquitous presence of relict baddeleyite (ZrO<sub>2</sub>), along with various zircon generations spatially associated with pristine to partly retrogressed Zr-bearing igneous and metamorphic minerals (e.g., ilmenite, rutile, högbomite and garnet), suggests significant Zr diffusive re-equilibration (exsolution) during slow cooling and mineral breakdown followed by crystallization of baddeleyite. The subsequent transformation of baddeleyite into zircon was likely driven by reaction with Si-bearing fluids in several geochronologically identified metamorphic stages. Strikingly contrasting compositional signatures in coeval zircon from anorthosite (silicate-dominated) and comagmatic RBI (Ti-Fe-oxide-dominated) indicate a major role of fluids locally equilibrating with the rock matrix, as indicated by distinct zircon trace element and oxygen isotopic compositions. A high-grade metamorphic event at c. 950 Ma is likely responsible for the formation of coarse-grained rutile (~0.1–10 mm in diameter), srilankite, zircon and garnet with rutile inclusions as well as metamorphic högbomite surrounding Fe-Mg spinel. Zr-in-rutile minimum temperatures suggest >730°C for this event, which may correlate to rutile-forming granulite facies metamorphism in other Grenvillian-aged basement rocks in Mexico and northern South America. A younger generation of baddeleyite exsolution occurred during post-peak cooling of coarse-grained rutile, reflected in rimward Zr depletion and formation of discontinuous baddeleyite coronas. Baddeleyite around rutile was then transformed into zircon possibly during subsequent metamorphism at c. 920 or 620 Ma, resulting from syn-kinematic and contact metamorphism, respectively. Regional metamorphism at c. 450 and 250 Ma extensively overprinted the existing zircon population, especially during the Triassic event, as suggested by a significant presence of zircon with this age. Nearly pristine baddeleyite occurring interstitial to ilmenite yielded an isochron age of c. 232 Ma according to in situ U–Pb secondary ion mass spectrometry (SIMS), suggesting either formation during metamorphic peak conditions or post-peak cooling. Zircon with ages of c. 80–100 Ma in anorthosite is identified for the first time within the CMC and coincides with cooling ages of c. 100 Ma for coarse-grained rutile. This age is similar to those of rocks occurring ~200 km further to the east in Guatemala, which are also b
墨西哥东南部恰帕斯地块杂岩(CMC)中含金红石的钛铁矿(RBI)和富含氧化磷灰石的角闪岩(OARA)的地块型斜长岩和岩浆组合显示了一段长达10亿年的辅助矿物记录,包括1.0 Ga的岩浆结晶和3.0 Ma的近期韧性剪切变形。在这些年龄端元之间的多个离散锆石种群是由局部到区域变质作用期间的新形成/再结晶造成的,这些变质作用影响了CMC的东南部。残余坏辉石(ZrO2)的普遍存在,以及与原始到部分退变含锆火成岩和变质矿物(如钛铁矿、金红石、högbomite和石榴石)相关的各种锆石代,表明在缓慢冷却和矿物分解过程中,锆的扩散再平衡(析出)显著,然后是坏辉石的结晶。在地质年代学上确定的几个变质期中,变质岩与含硅流体的反应可能导致了变质岩向锆石的转化。从锆石微量元素和氧同位素组成可以看出,同时期的斜长岩(硅酸盐为主)和岩浆型RBI(钛铁氧化物为主)锆石的组成特征明显不同,表明流体在与岩石基质的局部平衡中起主要作用。c. 950 Ma的高变质事件可能形成了粗粒金红石(直径~0.1 ~ 10mm)、含金红石包裹体的硅蓝石、锆石和石榴石,以及围绕铁镁尖晶石的变质岩högbomite。金红石中锆的最低温度为>730°C,这可能与墨西哥和南美洲北部其他格伦维里亚时代基底岩石中的金红石形成麻粒岩相变质有关。粗粒金红石峰后冷却过程中出现了较年轻一代的坏辉石析出,表现为Zr向内耗竭和不连续坏辉石日冕的形成。金红石周围的坏辉石可能在随后的约920或620 Ma变质作用中转化为锆石,分别是同步变质作用和接触变质作用的结果。c. 450和250 Ma的区域变质作用广泛地覆盖了现有的锆石种群,特别是在三叠纪事件期间,这表明这个时代的锆石大量存在。根据原位U-Pb二次离子质谱分析(SIMS),在钛铁矿与钛铁矿之间出现的近乎原始的坏辉石的等时线年龄为c. 232 Ma,表明它可能是在变质峰条件下形成的,也可能是峰后冷却形成的。斜长岩的锆石年龄在80 ~ 100 Ma之间,与粗晶金红石的冷却年龄在100 Ma之间一致。这一年龄与危地马拉东部约200公里的岩石年龄相似,这些岩石也被波洛奇断裂系统所束缚,但被榴辉岩相变质作用所覆盖。然而,在200ma之后在中压中心南部发生的高压事件目前还没有得到支持。尽管与普通火成岩相比,CMC斜长岩组合中金红石和钛铁矿的丰度异常高,但这里记录的反应仍然强调了这些相在广泛的变质条件下产生含锌副矿物的重要性。
{"title":"Multi-episodic formation of baddeleyite and zircon in polymetamorphic anorthosite and rutile-bearing ilmenitite from the Chiapas Massif Complex, Mexico","authors":"Alejandro Cisneros de León,&nbsp;Axel K. Schmitt,&nbsp;Bodo Weber","doi":"10.1111/jmg.12683","DOIUrl":"10.1111/jmg.12683","url":null,"abstract":"&lt;p&gt;Massif-type anorthosite and comagmatic associations of rutile-bearing ilmenitite (RBI) and oxide-apatite-rich amphibolite (OARA) from the Chiapas Massif Complex (CMC) in southeastern Mexico display a protracted billion-year accessory mineral record encompassing magmatic crystallization at c. 1.0 Ga to recent ductile shear deformation at c. 3.0 Ma. Multiple discrete zircon populations between these age end-members resulted from neoformation/recrystallization during local to regional metamorphism that affected the southeastern portion of the CMC. The ubiquitous presence of relict baddeleyite (ZrO&lt;sub&gt;2&lt;/sub&gt;), along with various zircon generations spatially associated with pristine to partly retrogressed Zr-bearing igneous and metamorphic minerals (e.g., ilmenite, rutile, högbomite and garnet), suggests significant Zr diffusive re-equilibration (exsolution) during slow cooling and mineral breakdown followed by crystallization of baddeleyite. The subsequent transformation of baddeleyite into zircon was likely driven by reaction with Si-bearing fluids in several geochronologically identified metamorphic stages. Strikingly contrasting compositional signatures in coeval zircon from anorthosite (silicate-dominated) and comagmatic RBI (Ti-Fe-oxide-dominated) indicate a major role of fluids locally equilibrating with the rock matrix, as indicated by distinct zircon trace element and oxygen isotopic compositions. A high-grade metamorphic event at c. 950 Ma is likely responsible for the formation of coarse-grained rutile (~0.1–10 mm in diameter), srilankite, zircon and garnet with rutile inclusions as well as metamorphic högbomite surrounding Fe-Mg spinel. Zr-in-rutile minimum temperatures suggest &gt;730°C for this event, which may correlate to rutile-forming granulite facies metamorphism in other Grenvillian-aged basement rocks in Mexico and northern South America. A younger generation of baddeleyite exsolution occurred during post-peak cooling of coarse-grained rutile, reflected in rimward Zr depletion and formation of discontinuous baddeleyite coronas. Baddeleyite around rutile was then transformed into zircon possibly during subsequent metamorphism at c. 920 or 620 Ma, resulting from syn-kinematic and contact metamorphism, respectively. Regional metamorphism at c. 450 and 250 Ma extensively overprinted the existing zircon population, especially during the Triassic event, as suggested by a significant presence of zircon with this age. Nearly pristine baddeleyite occurring interstitial to ilmenite yielded an isochron age of c. 232 Ma according to in situ U–Pb secondary ion mass spectrometry (SIMS), suggesting either formation during metamorphic peak conditions or post-peak cooling. Zircon with ages of c. 80–100 Ma in anorthosite is identified for the first time within the CMC and coincides with cooling ages of c. 100 Ma for coarse-grained rutile. This age is similar to those of rocks occurring ~200 km further to the east in Guatemala, which are also b","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 9","pages":"1493-1527"},"PeriodicalIF":3.4,"publicationDate":"2022-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.12683","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42669261","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Tectonic erosion and deep subduction in Central Tibet: Evidence from the discovery of retrograde eclogites in the Amdo microcontinent 西藏中部构造侵蚀与深俯冲:来自安多微大陆逆行榴辉岩发现的证据
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-06-28 DOI: 10.1111/jmg.12685
Yinbiao Peng, Shengyao Yu, Sanzhong Li, Yongjiang Liu, M. Santosh, Pei Lv, Yunshuai Li, Chuanzhi Li, Yiming Liu

The Amdo microcontinent which separates the Qiangtang terrane to the north and the Lhasa terrane to the south is a key terrane for reconstructing the tectonic evolution of Central Tibet. We report the new finding of retrograde eclogites within the Amdo microcontinent in this study. The eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, rutile and quartz and underwent a four-stage metamorphic evolution, including a peak eclogite facies stage (M1) at ~20–24 kbar and 580–620°C, followed by an HP granulite facies decompression stage (M2) at ~13–15 kbar and 750–780°C, a subsequent MP-UHT granulite facies heating stage (M3) at 8–10 kbar and >840°C and a final amphibolite facies retrogression (M4) at 5.3–6.0 kbar and 560–580°C. The eclogites exhibit rare earth element distribution patterns and trace element abundances similar to those of N-MORB and arc-related volcanics, with depleted whole-rock εNd(t) values of 3.4 to 4.2, and are inferred to have formed in a back-arc basin tectonic setting. Zircon and rutile U–Pb dating yields a protolith age of 226 ± 5 Ma, a peak eclogite facies metamorphic age of 190 ± 1 Ma, an HP granulite facies metamorphic age of 179 ± 1 Ma and an amphibolite facies retrograde age of 172 ± 1 Ma. The clockwise P–T–t paths and the oceanic protolith signature of retrograde eclogites suggest that part of the back arc basin was subducted to depths of ~80 km. Tectonic erosion associated with the subduction of the Amdo microcontinent beneath the Tethys Ocean accounts for the deep subduction of the back-arc basin and the absence of arc magmatic rocks in the northern Amdo microcontinent.

安多微大陆北隔羌塘地体,南隔拉萨地体,是重建西藏中部构造演化的关键地体。本文报道了在安多微大陆内发现的逆行榴辉岩的新发现。榴辉岩以石榴石、辉长石、金红石和石英的变质峰矿物组合为特征,经历了4期变质演化,包括~20 ~ 24 kbar和580 ~ 620℃的榴辉岩相峰阶段(M1)、~13 ~ 15 kbar和750 ~ 780℃的高压麻粒岩相减压阶段(M2)、8 ~ 10 kbar和>840℃的MP-UHT麻粒岩相加热阶段(M3)和5.3 ~ 6.0 kbar和560 ~ 580℃的角闪岩相退变阶段(M4)。榴辉岩稀土元素分布模式和微量元素丰度与N-MORB和弧缘火山岩相似,全岩亏缺εNd(t)值为3.4 ~ 4.2,形成于弧后盆地构造环境。锆石和金红石U-Pb定年结果表明,原岩年龄为226±5 Ma,榴辉岩相峰变质年龄为190±1 Ma,高压麻粒岩相变质年龄为179±1 Ma,角闪岩相逆变质年龄为172±1 Ma。顺时针P-T-t路径和逆行榴辉岩的海洋原岩特征表明,部分弧后盆地俯冲至~80 km深度。与特提斯洋下安多微大陆俯冲有关的构造侵蚀作用,是导致安多微大陆北部弧后盆地深俯冲和弧后岩浆岩缺失的主要原因。
{"title":"Tectonic erosion and deep subduction in Central Tibet: Evidence from the discovery of retrograde eclogites in the Amdo microcontinent","authors":"Yinbiao Peng,&nbsp;Shengyao Yu,&nbsp;Sanzhong Li,&nbsp;Yongjiang Liu,&nbsp;M. Santosh,&nbsp;Pei Lv,&nbsp;Yunshuai Li,&nbsp;Chuanzhi Li,&nbsp;Yiming Liu","doi":"10.1111/jmg.12685","DOIUrl":"10.1111/jmg.12685","url":null,"abstract":"<p>The Amdo microcontinent which separates the Qiangtang terrane to the north and the Lhasa terrane to the south is a key terrane for reconstructing the tectonic evolution of Central Tibet. We report the new finding of retrograde eclogites within the Amdo microcontinent in this study. The eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, rutile and quartz and underwent a four-stage metamorphic evolution, including a peak eclogite facies stage (M<sub>1</sub>) at ~20–24 kbar and 580–620°C, followed by an HP granulite facies decompression stage (M<sub>2</sub>) at ~13–15 kbar and 750–780°C, a subsequent MP-UHT granulite facies heating stage (M<sub>3</sub>) at 8–10 kbar and &gt;840°C and a final amphibolite facies retrogression (M<sub>4</sub>) at 5.3–6.0 kbar and 560–580°C. The eclogites exhibit rare earth element distribution patterns and trace element abundances similar to those of N-MORB and arc-related volcanics, with depleted whole-rock ε<sub>Nd</sub>(t) values of 3.4 to 4.2, and are inferred to have formed in a back-arc basin tectonic setting. Zircon and rutile U–Pb dating yields a protolith age of 226 ± 5 Ma, a peak eclogite facies metamorphic age of 190 ± 1 Ma, an HP granulite facies metamorphic age of 179 ± 1 Ma and an amphibolite facies retrograde age of 172 ± 1 Ma. The clockwise P–T–t paths and the oceanic protolith signature of retrograde eclogites suggest that part of the back arc basin was subducted to depths of ~80 km. Tectonic erosion associated with the subduction of the Amdo microcontinent beneath the Tethys Ocean accounts for the deep subduction of the back-arc basin and the absence of arc magmatic rocks in the northern Amdo microcontinent.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 9","pages":"1545-1572"},"PeriodicalIF":3.4,"publicationDate":"2022-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44104880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 3
Effects of Fe3+ in sillimanite on mineral stabilities and parageneses in ultrahigh-temperature metapelites 硅线石中Fe3+对超高温变质长岩矿物稳定性和共生矿的影响
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-06-28 DOI: 10.1111/jmg.12684
Bin Wang, Chunjing Wei
Based on the nature of ferric sillimanite, an activity model for sillimanite containing Fe3+ is constructed, tested and adopted to calculate phase equilibria of pelitic compositions under ultrahigh‐temperature (UHT) conditions. The calculated P–T projections and pseudosections suggest that the incorporation of Fe3+ into sillimanite can fairly solve the current imperfectly topological match between thermodynamic calculations and synthetic experiments, especially at high oxygen fugacity. Fe3+ in sillimanite remarkably elevates the temperature to switch the parageneses of orthopyroxene + sillimanite (Opx + Sil) and sapphirine + quartz (Spr + Qz) in oxidized metapelites, with an increment around 50–70°C. The calculated compatibility diagrams show that the widely approbatory UHT‐diagnostic mineral assemblages of Opx + Sil and Spr + Qz usually occur in metapelites with high Mg/Fe2+ ratios, which depend on both bulk‐rock MgO and oxygen fugacity, whereas the metapelites with low Mg/Fe2+ ratios are characterized by the assemblage of Garnet + sillimanite (Grt + Sil) with or without spinel (Spl) in UHT conditions. Moreover, comprehensive comparisons suggest that the essential petrogenetic framework of natural UHT metapelites is mostly governed by the two metamorphic reactions of Opx + Sil = Spr + Grt and Grt + Sil = Spl + Spr.
根据含铁硅线石的性质,建立了含Fe3+硅线石的活度模型,并对其进行了测试,并应用于超高温条件下泥质组分的相平衡计算。计算得到的P-T投影和伪截面表明,将Fe3+掺入硅线石中可以较好地解决目前热力学计算和合成实验之间不完美的拓扑匹配,特别是在高氧逸度下。硅线石中的Fe3+显著升高了氧化偏长岩中正辉石+硅线石(Opx + Sil)和蓝宝石+石英(Spr + Qz)的共生关系,升高幅度在50 ~ 70℃左右。计算的配伍图表明,广泛认可的超高温诊断矿物组合Opx + Sil和Spr + Qz通常出现在高Mg/Fe2+比值的偏长岩中,这取决于整体岩石的MgO和氧逸度,而低Mg/Fe2+比值的偏长岩则以石榴石+硅线石(Grt + Sil)组合为特征,在超高温条件下有或没有尖晶石(Spl)。综合比较表明,天然超高温变质岩的基本成岩格架主要受Opx + Sil = Spr + Grt和Grt + Sil = Spl + Spr两个变质反应控制。
{"title":"Effects of Fe3+ in sillimanite on mineral stabilities and parageneses in ultrahigh-temperature metapelites","authors":"Bin Wang,&nbsp;Chunjing Wei","doi":"10.1111/jmg.12684","DOIUrl":"10.1111/jmg.12684","url":null,"abstract":"Based on the nature of ferric sillimanite, an activity model for sillimanite containing Fe3+ is constructed, tested and adopted to calculate phase equilibria of pelitic compositions under ultrahigh‐temperature (UHT) conditions. The calculated P–T projections and pseudosections suggest that the incorporation of Fe3+ into sillimanite can fairly solve the current imperfectly topological match between thermodynamic calculations and synthetic experiments, especially at high oxygen fugacity. Fe3+ in sillimanite remarkably elevates the temperature to switch the parageneses of orthopyroxene + sillimanite (Opx + Sil) and sapphirine + quartz (Spr + Qz) in oxidized metapelites, with an increment around 50–70°C. The calculated compatibility diagrams show that the widely approbatory UHT‐diagnostic mineral assemblages of Opx + Sil and Spr + Qz usually occur in metapelites with high Mg/Fe2+ ratios, which depend on both bulk‐rock MgO and oxygen fugacity, whereas the metapelites with low Mg/Fe2+ ratios are characterized by the assemblage of Garnet + sillimanite (Grt + Sil) with or without spinel (Spl) in UHT conditions. Moreover, comprehensive comparisons suggest that the essential petrogenetic framework of natural UHT metapelites is mostly governed by the two metamorphic reactions of Opx + Sil = Spr + Grt and Grt + Sil = Spl + Spr.","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 9","pages":"1529-1544"},"PeriodicalIF":3.4,"publicationDate":"2022-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41983885","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 2
Low-grade prehnite-pumpellyite facies metamorphism and metasomatism in basement rocks adjacent to the Permian Oslo rift: The importance of displacive reactions 二叠系奥斯陆裂谷附近基岩低品位前黑岩-泵状岩相变质与交代作用:驱替反应的重要性
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-06-23 DOI: 10.1111/jmg.12682
Håkon Austrheim, Ane K. Engvik, Morgan Ganerød, Kristina G. Dunkel, Mari Roen Velo
<p>The Kongsberg and Bamble lithotectonic domains of SE-Norway are known as classical Precambrian high-grade metamorphic terrains. The area has undergone extensive metasomatism with formation of albitites and scapolite-rich rocks and numbers of previously economically important deposits including the Kongsberg Silver and the Modum Cobalt mines. We demonstrate here that the central part of the Bamble lithotectonic domain (Kragerø area) has locally developed low-grade metamorphic minerals (prehnite, pumpellyite, analcime, stilpnomelane and thomsonite) belonging to the prehnite-pumpellyite and zeolite facies. Structurally, the low-grade minerals occur as fracture fills, in the alteration selvages around fractures where the rock is albitized, and along shear zones and cataclastic zones. The fracture fill and the alteration selvages vary from millimetres scale to 1 m in thickness. The fractures with low-grade minerals are part of larger fracture systems. The low-grade minerals typically formed by both displacive (swelling) and replacive reactions and in a combination of these. Prehnite together with albite, K-feldspar, quartz, epidote and hydrogarnet form lenses along (001) faces in biotite and chlorite leading to bending of the sheet silicates through a displacive reaction mechanism. Numerous replacement reactions including the earlier minerals as well as the low-grade minerals occur. As albite, K-feldspar, talc, quartz, actinolite, titanite, calcite and hydrogrossular form in the same veins and in the same biotite grain as the classical low-grade minerals, they probably belong to the low-grade assemblage and some of the albitization in the region presumably occurred at low-grade conditions. Alteration of olivine (Fo69) at low-grade conditions results in the formation of clay minerals including ferroan saponite. Reconnaissance studies at the east (Idefjord lithotectonic domain) and the northwest (Kongsberg lithotectonic domain) sides of the Oslo rift together with reports of low-grade assemblages in south-western Sweden along the continuation of the rift into Skagerrak suggest that the low grade assembles occur in rocks adjacent to the Oslo rift along its full extent. Ar-Ar dating of K-feldspar from the low-grade assemblages gave an age of 265.2 ± 0.4 Ma (MSWD = 0.514 and P = 0.766), suggesting that the low-grade metamorphism and some of the metasomatism is induced by fluids and heat from the magmatic activity of the Permian Oslo rift, which requires transport of fluid over distances of several kilometres. The metamorphic conditions are constrained by stability fields of prehnite, pumpellyite and analcime to be less than 250°C and at a pressure less than 5 kbars. The displacive reactions created micro-fractures and porosity in the adjacent minerals that enhance fluid flow and low-grade mineral formation on a local scale. On a thin section scale, the displacive growth of albite in biotite results in a local volume increase of several 100%. Whether the
挪威东南部的Kongsberg和Bamble岩石构造域是典型的前寒武纪高变质构造域。该地区经历了广泛的交代作用,形成了富含钠长石和角长石的岩石,以及许多以前具有重要经济意义的矿床,包括Kongsberg银矿和Modum钴矿。本研究表明,班布尔岩体构造域中部(Kragerø地区)局部发育低品位变质矿物(前黝岩、泵柱岩、铝镁石、铁镁石和thomsonite),属于前黝岩-泵柱岩和沸石相。在构造上,低品位矿物以裂隙填充物、裂隙周围的蚀变边缘以及剪切带和碎裂带的形式赋存。裂缝充填体和蚀变边缘厚度从毫米级到1米级不等。含低品位矿物的裂缝是较大裂缝系统的一部分。低品位矿物,通常由驱替(溶胀)和替代反应以及两者的结合形成。前辉石与钠长石、钾长石、石英、绿帘石和水榴石沿黑云母和绿泥石的(001)面形成透镜,通过位移反应机制导致硅酸片弯曲。发生了许多替代反应,包括早期矿物和低品位矿物。由于钠长石、钾长石、滑石、石英、放线石、钛矿、方解石和水镁石与经典低品位矿物在同一脉脉和同一黑云母颗粒中形成,它们可能属于低品位组合,该地区的部分钠长石化可能发生在低品位条件下。在低品位条件下,橄榄石(Fo69)蚀变形成了包括铁皂石在内的粘土矿物。在奥斯陆裂谷东侧(Idefjord岩石构造域)和西北侧(Kongsberg岩石构造域)进行的勘测研究,以及在瑞典西南部沿着裂谷延伸至Skagerrak的低品位组合的报道表明,低品位组合出现在奥斯陆裂谷完整范围内邻近的岩石中。低品位组合钾长石的Ar-Ar年龄为265.2±0.4 Ma (MSWD = 0.514, P = 0.766),表明低品位变质作用和部分交代作用是由二叠纪奥斯陆裂谷岩浆活动的流体和热量引起的,这需要流体在几公里的距离上进行输送。变质条件受前辉石、泵辉石和铝矿稳定场的限制,在小于250℃和小于5 kbar的压力下。驱替代性反应在邻近矿物中产生微裂缝和孔隙,从而增强了局部范围内的流体流动和低品位矿物形成。在薄片尺度上,钠长石在黑云母中的置换生长导致局部体积增加数100%。是否需要打开更大的、水平导向的裂缝系统,将流体输送到几公里的距离,这也是驱替反应的结果,目前尚不清楚。低变质作用和交代作用形成于奥斯陆裂谷肩部,可能对其隆升起了作用。
{"title":"Low-grade prehnite-pumpellyite facies metamorphism and metasomatism in basement rocks adjacent to the Permian Oslo rift: The importance of displacive reactions","authors":"Håkon Austrheim,&nbsp;Ane K. Engvik,&nbsp;Morgan Ganerød,&nbsp;Kristina G. Dunkel,&nbsp;Mari Roen Velo","doi":"10.1111/jmg.12682","DOIUrl":"10.1111/jmg.12682","url":null,"abstract":"&lt;p&gt;The Kongsberg and Bamble lithotectonic domains of SE-Norway are known as classical Precambrian high-grade metamorphic terrains. The area has undergone extensive metasomatism with formation of albitites and scapolite-rich rocks and numbers of previously economically important deposits including the Kongsberg Silver and the Modum Cobalt mines. We demonstrate here that the central part of the Bamble lithotectonic domain (Kragerø area) has locally developed low-grade metamorphic minerals (prehnite, pumpellyite, analcime, stilpnomelane and thomsonite) belonging to the prehnite-pumpellyite and zeolite facies. Structurally, the low-grade minerals occur as fracture fills, in the alteration selvages around fractures where the rock is albitized, and along shear zones and cataclastic zones. The fracture fill and the alteration selvages vary from millimetres scale to 1 m in thickness. The fractures with low-grade minerals are part of larger fracture systems. The low-grade minerals typically formed by both displacive (swelling) and replacive reactions and in a combination of these. Prehnite together with albite, K-feldspar, quartz, epidote and hydrogarnet form lenses along (001) faces in biotite and chlorite leading to bending of the sheet silicates through a displacive reaction mechanism. Numerous replacement reactions including the earlier minerals as well as the low-grade minerals occur. As albite, K-feldspar, talc, quartz, actinolite, titanite, calcite and hydrogrossular form in the same veins and in the same biotite grain as the classical low-grade minerals, they probably belong to the low-grade assemblage and some of the albitization in the region presumably occurred at low-grade conditions. Alteration of olivine (Fo69) at low-grade conditions results in the formation of clay minerals including ferroan saponite. Reconnaissance studies at the east (Idefjord lithotectonic domain) and the northwest (Kongsberg lithotectonic domain) sides of the Oslo rift together with reports of low-grade assemblages in south-western Sweden along the continuation of the rift into Skagerrak suggest that the low grade assembles occur in rocks adjacent to the Oslo rift along its full extent. Ar-Ar dating of K-feldspar from the low-grade assemblages gave an age of 265.2 ± 0.4 Ma (MSWD = 0.514 and P = 0.766), suggesting that the low-grade metamorphism and some of the metasomatism is induced by fluids and heat from the magmatic activity of the Permian Oslo rift, which requires transport of fluid over distances of several kilometres. The metamorphic conditions are constrained by stability fields of prehnite, pumpellyite and analcime to be less than 250°C and at a pressure less than 5 kbars. The displacive reactions created micro-fractures and porosity in the adjacent minerals that enhance fluid flow and low-grade mineral formation on a local scale. On a thin section scale, the displacive growth of albite in biotite results in a local volume increase of several 100%. Whether the","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 9","pages":"1467-1492"},"PeriodicalIF":3.4,"publicationDate":"2022-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.12682","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43711489","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 3
Multi-mineral petrochronology on a high-pressure mafic granulite reveals short-lived high-temperature metamorphism in the North China Craton 华北克拉通高压基性麻粒岩多矿物岩石年代学揭示了华北克拉通短暂高温变质作用
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-06-14 DOI: 10.1111/jmg.12681
Xiao-Meng Li, Hao Cheng, Besim Dragovic, Kai-Yang Du, Ying Zhou

Accurately defining the peak ages and timescales of high-temperature metamorphism is fundamental to unravelling tectonic dynamics. However, metamorphic constraints are frequently hampered by a large spread of zircon U–Pb ages without explicit textural relationships. Integrated garnet and zircon petrochronology may clarify ambiguous ages retrieved from ancient high-temperature metamorphic rocks. There is a long-standing debate on the interpretation of the spread of zircon ages from c. 2.5–1.8 Ga for the granulites of the North China Craton. In order to clarify the timing and duration of (ultra)high-temperature metamorphism in the North China Craton, we investigated a mafic granulite and the adjoining gneiss from the Yinshan Block of the North China Craton using zircon and titanite U–Pb geochronology combined with garnet Lu–Hf and Sm–Nd geochronology. Pseudosection modelling and conventional thermobarometric calculations constrain the peak metamorphic conditions to be ~1.0 GPa and ~850°C. The near-complete lack of major-element zoning in garnet, aside from ~2 μm diffusion profiles at crystal rims, suggests complete re-equilibration at peak temperatures followed by fast cooling from high temperatures. The Lu–Hf garnet age of 1870 ± 4 Ma and Sm–Nd age of 1870 ± 7 Ma, determined on the same garnet fractions, are indistinguishable from the zircon U–Pb age of 1866 ± 11 Ma obtained from zircon that grew contemporaneously with garnet, evidenced by the chemical equilibrium of coexisting garnet and zircon, and are additionally consistent with a titanite U–Pb age of 1876 ± 7 Ma. We interpret this close agreement of ages, within uncertainty, coupled to the existence of flat Sm–Nd–Hf profiles in garnet that also has well-preserved Lu zoning, to reflect a short-lived high-temperature metamorphic event that was terminated by rapid exhumation and cooling. The short-lived (<4 Myr) high-temperature metamorphism may be generated in the lowermost parts of the crust through magmatic underplating/intraplating during extension that follows collision of the Ordos and the Yinshan Blocks.

准确确定高温变质作用的峰值年龄和时间尺度是揭示构造动力学的基础。然而,由于锆石U-Pb年龄分布广泛,没有明确的结构关系,变质约束常常受到阻碍。综合石榴石和锆石岩石年代学可以澄清从古代高温变质岩中获得的模糊年龄。关于华北克拉通麻粒岩中约2.5 ~ 1.8 Ga锆石分布的解释一直存在争议。为了明确华北克拉通(超)高温变质作用的时间和持续时间,利用锆石和钛矿U-Pb年代学方法,结合石榴石u - hf和Sm-Nd年代学方法,对华北克拉通阴山地块的一块基性麻粒岩及其毗邻片麻岩进行了研究。伪剖面模拟和常规热气压计算限制了变质峰条件为~1.0 GPa和~850℃。在石榴石中,除了在晶缘处有~2 μm的扩散分布外,几乎完全没有主元素分带,这表明石榴石在峰值温度下完全重新平衡,然后从高温快速冷却。在同一石榴石组分上测定的Lu-Hf年龄(1870±4 Ma)和Sm-Nd年龄(1870±7 Ma)与在与石榴石同时生长的锆石中测定的锆石U-Pb年龄(1866±11 Ma)难以区分,石榴石和锆石共存的化学平衡证明了这一点,并且与钛矿的U-Pb年龄(1876±7 Ma)一致。我们解释这种年龄的紧密一致,在不确定的范围内,加上石榴石中存在平坦的Sm-Nd-Hf剖面,也保存完好的Lu分带,反映了一个短暂的高温变质事件,该事件被快速挖掘和冷却所终止。短期(< 4myr)高温变质作用可能发生在地壳最下部,是鄂尔多斯与阴山地块碰撞后伸展过程中岩浆的下镀/内镀作用。
{"title":"Multi-mineral petrochronology on a high-pressure mafic granulite reveals short-lived high-temperature metamorphism in the North China Craton","authors":"Xiao-Meng Li,&nbsp;Hao Cheng,&nbsp;Besim Dragovic,&nbsp;Kai-Yang Du,&nbsp;Ying Zhou","doi":"10.1111/jmg.12681","DOIUrl":"10.1111/jmg.12681","url":null,"abstract":"<p>Accurately defining the peak ages and timescales of high-temperature metamorphism is fundamental to unravelling tectonic dynamics. However, metamorphic constraints are frequently hampered by a large spread of zircon U–Pb ages without explicit textural relationships. Integrated garnet and zircon petrochronology may clarify ambiguous ages retrieved from ancient high-temperature metamorphic rocks. There is a long-standing debate on the interpretation of the spread of zircon ages from <i>c</i>. 2.5–1.8 Ga for the granulites of the North China Craton. In order to clarify the timing and duration of (ultra)high-temperature metamorphism in the North China Craton, we investigated a mafic granulite and the adjoining gneiss from the Yinshan Block of the North China Craton using zircon and titanite U–Pb geochronology combined with garnet Lu–Hf and Sm–Nd geochronology. Pseudosection modelling and conventional thermobarometric calculations constrain the peak metamorphic conditions to be ~1.0 GPa and ~850°C. The near-complete lack of major-element zoning in garnet, aside from ~2 μm diffusion profiles at crystal rims, suggests complete re-equilibration at peak temperatures followed by fast cooling from high temperatures. The Lu–Hf garnet age of 1870 ± 4 Ma and Sm–Nd age of 1870 ± 7 Ma, determined on the same garnet fractions, are indistinguishable from the zircon U–Pb age of 1866 ± 11 Ma obtained from zircon that grew contemporaneously with garnet, evidenced by the chemical equilibrium of coexisting garnet and zircon, and are additionally consistent with a titanite U–Pb age of 1876 ± 7 Ma. We interpret this close agreement of ages, within uncertainty, coupled to the existence of flat Sm–Nd–Hf profiles in garnet that also has well-preserved Lu zoning, to reflect a short-lived high-temperature metamorphic event that was terminated by rapid exhumation and cooling. The short-lived (&lt;4 Myr) high-temperature metamorphism may be generated in the lowermost parts of the crust through magmatic underplating/intraplating during extension that follows collision of the Ordos and the Yinshan Blocks.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 9","pages":"1447-1466"},"PeriodicalIF":3.4,"publicationDate":"2022-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45815679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 4
Constraining the P–T path of (U)HP rocks with reaction overstepping during subduction; example from the Western Gneiss Region (Norway) 俯冲过程中反应越级对(U)HP岩石P-T路径的约束西片麻岩地区(挪威)的例子
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-06-10 DOI: 10.1111/jmg.12680
Shah Wali Faryad, Josef Ježek, Jan Kulhánek

This paper presents the results of petrological observations and diffusion modelling on garnet from high-pressure to ultrahigh-pressure ((U)HP) metamorphic rocks of the Western Gneiss Region in the Nordfjord. Garnet from kyanite-bearing micaschist preserves two generations of garnet growth that are related to the Pre-Caledonian granulite facies and Caledonian eclogite facies metamorphic events. Mafic eclogite, forming lenses in the micaschist, contains only eclogite facies assemblages with partial recrystallization under amphibolite facies conditions. Caledonian garnet in both the micaschist and hosting eclogite indicates reaction overstepping and nucleation near or above 550°C/2.0 GPa. Maximum pressure and temperature, calculated using pseudosection modelling for the eclogite facies event, were ~2.6 GPa and 650°C. The interface between the Pre-Caledonian and Caledonian garnet in the micaschist shows a strong compositional gradient or possibly a compositional jump. The preservation of such a gradient together with the hummocky-shaped composition profiles in the Caledonian garnet from the eclogite indicates either no relaxation or a short-time of relaxation of the rocks at their peak temperature conditions, as well as their exhumation by cooling. Possibly, heating or exhuming of the rocks by isothermal decompression could have easily modified such compositional irregularities along the garnet profiles. A cooling rate of ~187°C/Ma and exhumation rate in the vertical direction of ~2.5 cm/year for the HP rocks were obtained by considering that the temperature and transport distance changes from their maximum depth and peak temperature to the surface were proportional to the time (3.5 Ma) calculated by modelling for the garnet.

本文介绍了北峡湾西片麻岩区高压-超高压(U)HP)变质岩中石榴石的岩石学观测和扩散模拟结果。含蓝晶石云母岩中的石榴石保存了与前加里东期麻粒岩相和加里东期榴辉岩相变质事件有关的两代石榴石生长。在云母片岩中形成透镜体的基性榴辉岩,在角闪岩相条件下仅含有部分再结晶的榴辉岩相组合。云母岩和赋矿榴辉岩中的加里东期石榴石在550℃/2.0 GPa附近或以上均显示出反应越界和成核。根据榴辉岩相事件的拟剖面模型计算,最大压力和温度分别为~2.6 GPa和650℃。在云母岩中,前加里东期和加里东期石榴石的界面显示出强烈的成分梯度或可能的成分跳跃。这种梯度的保存以及加里东期榴辉岩石榴石的丘状成分剖面表明,岩石在其峰值温度条件下没有松弛或有短时间的松弛,以及通过冷却将其挖掘出来。或许,通过等温减压加热或挖掘岩石可以很容易地改变石榴石剖面上的这种成分不规则性。考虑到从最大深度和峰值温度到地表的温度和运输距离变化与石榴石模型计算的时间(3.5 Ma)成正比,得出HP岩石的冷却速率为~187°C/Ma,垂直方向的挖掘速率为~2.5 cm/年。
{"title":"Constraining the P–T path of (U)HP rocks with reaction overstepping during subduction; example from the Western Gneiss Region (Norway)","authors":"Shah Wali Faryad,&nbsp;Josef Ježek,&nbsp;Jan Kulhánek","doi":"10.1111/jmg.12680","DOIUrl":"10.1111/jmg.12680","url":null,"abstract":"<p>This paper presents the results of petrological observations and diffusion modelling on garnet from high-pressure to ultrahigh-pressure ((U)HP) metamorphic rocks of the Western Gneiss Region in the Nordfjord. Garnet from kyanite-bearing micaschist preserves two generations of garnet growth that are related to the Pre-Caledonian granulite facies and Caledonian eclogite facies metamorphic events. Mafic eclogite, forming lenses in the micaschist, contains only eclogite facies assemblages with partial recrystallization under amphibolite facies conditions. Caledonian garnet in both the micaschist and hosting eclogite indicates reaction overstepping and nucleation near or above 550°C/2.0 GPa. Maximum pressure and temperature, calculated using pseudosection modelling for the eclogite facies event, were ~2.6 GPa and 650°C. The interface between the Pre-Caledonian and Caledonian garnet in the micaschist shows a strong compositional gradient or possibly a compositional jump. The preservation of such a gradient together with the hummocky-shaped composition profiles in the Caledonian garnet from the eclogite indicates either no relaxation or a short-time of relaxation of the rocks at their peak temperature conditions, as well as their exhumation by cooling. Possibly, heating or exhuming of the rocks by isothermal decompression could have easily modified such compositional irregularities along the garnet profiles. A cooling rate of ~187°C/Ma and exhumation rate in the vertical direction of ~2.5 cm/year for the HP rocks were obtained by considering that the temperature and transport distance changes from their maximum depth and peak temperature to the surface were proportional to the time (3.5 Ma) calculated by modelling for the garnet.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 9","pages":"1427-1446"},"PeriodicalIF":3.4,"publicationDate":"2022-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47905807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 5
Thermodynamic constraints on the composition of orogenically thickened lower crust 造山增厚下地壳组成的热力学约束
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-06-09 DOI: 10.1111/jmg.12679
Yi-Bing Li, Yu-Wen Wu, Bin Su, Si Chen, Qing-Hua Zhang, Yi Chen

Orogenically thickened lower crust is the key site of crustal differentiation, crustal deformation, and Moho modification. However, the composition of thickened lower crust is still highly debated. Here, we calculate a set of pseudosections with mafic lower crust compositions in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 (NCKFMASHTO) system. Our modelling results show that the maximum thickness of the mafic lower crust increases with the Moho temperature (TMoho). In addition, the lithologies of stable mafic crust are characterized by medium-pressure (MP) to high-pressure (HP) granulites at 40–50 km, HP granulites and garnet-omphacite granulites at 50–60 km, and garnet-omphacite granulites at 60–70 km. Under the Pamir geothermal conditions, mafic rocks with high SiO2 (>50.2 wt%), XMg (>0.70), XCa (>0.49), or low XAl (<0.11) could be stable at 70 km; however, only ~10% of global mafic granulite xenoliths lie within this compositional range. Further modelling indicates that if TMoho reaches 900–1000°C, neither the lower crust nor the upper mantle has significant strength relative to the upper crust and that only ~5–37% of mafic materials are gravitationally stable at 70 km. This implies that the base of doubly thickened (70 km) crust is dominated by intermediate-felsic rocks, consistent with the low Vp and Vp/Vs values seismically observed in young orogenic crustal roots. Thus, most mafic materials at >70 km could delaminate into the deep mantle. Our results provide insights on the formation of extremely thick crust with a predominantly intermediate-felsic base and the crustal thickness variation in continental collision zones.

造山增厚下地壳是地壳分异、地壳变形和莫霍变质的关键部位。然而,增厚下地壳的组成仍有很大争议。在此,我们计算了na20 - cao - k20 - feo - mgo - al2o3 - sio2 - h2o - tio2 - o2 (NCKFMASHTO)体系中一组具有基性下地壳组成的伪截面。模拟结果表明,基性下地壳的最大厚度随着莫霍温度(TMoho)的升高而增大。稳定基性地壳岩性以40 ~ 50 km范围内的中压—高压麻粒岩、50 ~ 60 km范围内的高压麻粒岩和石榴石—辉石麻粒岩、60 ~ 70 km范围内的石榴石—辉石麻粒岩为特征。在帕米尔地热条件下,高SiO2 (>50.2 wt%)、XMg (>0.70)、XCa (>0.49)或低XAl (<0.11)的基性岩石在70 km处稳定存在;然而,全球基性麻粒岩捕虏体中只有约10%在这一成分范围内。进一步的模拟表明,当TMoho达到900-1000°C时,下地壳和上地幔相对于上地壳都没有明显的强度,只有~ 5-37%的基性物质在70 km处引力稳定。这表明双增厚(70 km)地壳基底以中长英质岩石为主,与地震观测到的年轻造山带地壳根的低Vp值和Vp/Vs值一致。因此,在70公里处的大多数镁质物质都可以分解到地幔深处。我们的研究结果提供了对以中长英质基底为主的极厚地壳的形成和大陆碰撞带地壳厚度变化的见解。
{"title":"Thermodynamic constraints on the composition of orogenically thickened lower crust","authors":"Yi-Bing Li,&nbsp;Yu-Wen Wu,&nbsp;Bin Su,&nbsp;Si Chen,&nbsp;Qing-Hua Zhang,&nbsp;Yi Chen","doi":"10.1111/jmg.12679","DOIUrl":"10.1111/jmg.12679","url":null,"abstract":"<p>Orogenically thickened lower crust is the key site of crustal differentiation, crustal deformation, and Moho modification. However, the composition of thickened lower crust is still highly debated. Here, we calculate a set of pseudosections with mafic lower crust compositions in the Na<sub>2</sub>O–CaO–K<sub>2</sub>O–FeO–MgO–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub>–H<sub>2</sub>O–TiO<sub>2</sub>–O<sub>2</sub> (NCKFMASHTO) system. Our modelling results show that the maximum thickness of the mafic lower crust increases with the Moho temperature (<i>T</i><sub>Moho</sub>). In addition, the lithologies of stable mafic crust are characterized by medium-pressure (MP) to high-pressure (HP) granulites at 40–50 km, HP granulites and garnet-omphacite granulites at 50–60 km, and garnet-omphacite granulites at 60–70 km. Under the Pamir geothermal conditions, mafic rocks with high SiO<sub>2</sub> (&gt;50.2 wt%), X<sub>Mg</sub> (&gt;0.70), X<sub>Ca</sub> (&gt;0.49), or low X<sub>Al</sub> (&lt;0.11) could be stable at 70 km; however, only ~10% of global mafic granulite xenoliths lie within this compositional range. Further modelling indicates that if <i>T</i><sub>Moho</sub> reaches 900–1000°C, neither the lower crust nor the upper mantle has significant strength relative to the upper crust and that only ~5–37% of mafic materials are gravitationally stable at 70 km. This implies that the base of doubly thickened (70 km) crust is dominated by intermediate-felsic rocks, consistent with the low <i>V</i><sub><i>p</i></sub> and <i>V</i><sub><i>p</i></sub>/<i>V</i><sub><i>s</i></sub> values seismically observed in young orogenic crustal roots. Thus, most mafic materials at &gt;70 km could delaminate into the deep mantle. Our results provide insights on the formation of extremely thick crust with a predominantly intermediate-felsic base and the crustal thickness variation in continental collision zones.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 8","pages":"1405-1426"},"PeriodicalIF":3.4,"publicationDate":"2022-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42265281","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Garnet crystallization mechanisms and localized polymetamorphism in the southwestern Meguma Terrane, Nova Scotia, Canada 加拿大新斯科舍省Meguma地块西南部石榴石结晶机制及局部多变质作用
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-05-20 DOI: 10.1111/jmg.12678
Alexandra B. Nagurney, Mark J. Caddick, Chris E. White

We present data on the pressure and temperature (P–T) conditions experienced by metamorphic rocks of the Meguma Terrane, Nova Scotia, Canada, also utilizing three-dimensional microstructural data on one sample to better constrain the mechanisms that controlled garnet crystallization. Inverse and forward thermodynamic modelling place peak P–T conditions in the southwestern Meguma Terrane at ~650°C and 4.5 kbar. Interpretation of these results with petrographic observations and previous P–T constraints across the terrane suggests that amphibolite facies metamorphism occurred during the Devonian Neoacadian orogeny (406–388 Ma). Integration of quantitative 3D textural data with an estimated metamorphic heating rate of <5°C/Myr is consistent with amphibolite facies metamorphism resulting from tectonic loading during the Neoacadian orogeny, though the exact nature of the orogeny is still not well understood. Further, the intrusion of granitic plutons into the Meguma metasediments at 373 Ma likely locally drove metamorphic recrystallization (polymetamorphism). The 3D size, shape, and location of garnet crystals in one sample reveal that the rate-limiting step for garnet crystallization was likely the diffusion of aluminium through the intergranular matrix at length scales less than the mean nearest neighbour distance between garnet crystals. Nucleation was aided by epitaxial overgrowth onto a muscovite substrate, though it appears there may have been a decoupling between minerals providing a substrate and those providing nutrients during garnet growth.

我们提供了加拿大新斯科舍省Meguma Terrane变质岩所经历的压力和温度(P-T)条件的数据,并利用一个样品的三维微观结构数据来更好地约束控制石榴石结晶的机制。反演和正演热力学模拟表明,在~650°C和4.5 kbar时,Meguma地块西南部的P-T条件达到峰值。这些结果与岩石学观测和以往跨地体的P-T约束解释表明,泥盆纪-新阿卡德造山运动(406-388 Ma)期间发生了角闪岩相变质作用。定量三维纹理数据与估计的5°C/Myr的变质升温速率相结合,与新阿卡德造山运动期间构造负荷导致的角闪岩相变质相一致,尽管造山运动的确切性质仍未得到很好的了解。此外,373 Ma花岗岩岩体侵入Meguma变质沉积层可能局部驱动了变质再结晶(多变质作用)。一个样品中石榴石晶体的三维尺寸、形状和位置表明,石榴石结晶的限速步骤可能是铝在小于石榴石晶体之间平均最近邻距离的长度尺度上通过晶间基体的扩散。在白云母基底上的外延过度生长有助于成核,尽管在石榴石生长过程中,提供基底的矿物和提供营养物质的矿物之间似乎存在解耦。
{"title":"Garnet crystallization mechanisms and localized polymetamorphism in the southwestern Meguma Terrane, Nova Scotia, Canada","authors":"Alexandra B. Nagurney,&nbsp;Mark J. Caddick,&nbsp;Chris E. White","doi":"10.1111/jmg.12678","DOIUrl":"10.1111/jmg.12678","url":null,"abstract":"<p>We present data on the pressure and temperature (<i>P–T</i>) conditions experienced by metamorphic rocks of the Meguma Terrane, Nova Scotia, Canada, also utilizing three-dimensional microstructural data on one sample to better constrain the mechanisms that controlled garnet crystallization. Inverse and forward thermodynamic modelling place peak <i>P–T</i> conditions in the southwestern Meguma Terrane at ~650°C and 4.5 kbar. Interpretation of these results with petrographic observations and previous <i>P–T</i> constraints across the terrane suggests that amphibolite facies metamorphism occurred during the Devonian Neoacadian orogeny (406–388 Ma). Integration of quantitative 3D textural data with an estimated metamorphic heating rate of &lt;5°C/Myr is consistent with amphibolite facies metamorphism resulting from tectonic loading during the Neoacadian orogeny, though the exact nature of the orogeny is still not well understood. Further, the intrusion of granitic plutons into the Meguma metasediments at 373 Ma likely locally drove metamorphic recrystallization (polymetamorphism). The 3D size, shape, and location of garnet crystals in one sample reveal that the rate-limiting step for garnet crystallization was likely the diffusion of aluminium through the intergranular matrix at length scales less than the mean nearest neighbour distance between garnet crystals. Nucleation was aided by epitaxial overgrowth onto a muscovite substrate, though it appears there may have been a decoupling between minerals providing a substrate and those providing nutrients during garnet growth.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 8","pages":"1383-1404"},"PeriodicalIF":3.4,"publicationDate":"2022-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46022517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Late Famatinian (440–410 Ma) overprint of Grenvillian metamorphism in Grt-St schists from the Sierra de Maz (Argentina): Phase equilibrium modelling, geochronology, and tectonic significance 阿根廷马兹山Grt-St片岩中晚法马世(440-410 Ma)格伦维利亚变质作用的叠加:相平衡模拟、地质年代学和构造意义
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-05-18 DOI: 10.1111/jmg.12677
Sebastián O. Verdecchia, Carlos D. Ramacciotti, Cesar Casquet, Edgardo G. Baldo, Juan A. Murra, Robert J. Pankhurst
<p>The analysis of major and trace elements in zoned minerals is useful for deciphering parts of the tectonothermal evolution of polymetamorphic tarrain. We applied this approach to the Maz Metasedimentary Series in Western Sierras Pampeanas of Argentina, where polymetamorphism resulted in the overprinting of a Grenvillian basement (the Maz Complex) during the pervasive Rinconada tectonic phase of the Famatinian orogeny. The older metamorphism (M<sub>1</sub>) is assigned to the youngest Grenvillian metamorphic event recognized in this basement at c. 1035 Ma, whereas the Rinconada metamorphism (M<sub>2</sub>) was Silurian to early Devonian, essentially between 440 and 410 Ma. The latter resulted from oceanward migration of the orogenic front relative to earlier late Cambrian to Ordovician (490–470 Ma) tectonic phases of the Famatinian orogeny. The M<sub>1</sub> and M<sub>2</sub> metamorphic events have been recognized in a staurolite-garnet schist from the Maz Metasedimentary Series. Most metamorphic minerals from this rock were formed during the M<sub>2</sub> event which was of the Barrovian type (±kyanite). Part of the metamorphic <i>P–T</i> evolution is recorded in the complex compositional zoning of garnet porphyroblasts. Three types of garnet were identified based on texture and chemistry, including trace elements (REEs). Phase equilibrium analysis, compositional isopleth, and multi-equilibrium thermobarometry were applied in order to establish the <i>P–T</i> history. M<sub>1</sub> is represented by preservation of Grt<sub>1</sub> ± Kfs ± Sil, with peak <i>P–T</i> condition of 790°C and 5.2 kbar, that is, granulite facies. This early metamorphic event was related to a deformational D<sub>1</sub> episode represented by a relict S<sub>1</sub> foliation. The latter is preserved as aligned inclusions in staurolite porphyroblasts and as relics of an older crenulated foliation in microlithons from the matrix. M<sub>2</sub> followed a clockwise <i>P–T</i> path with three mineral growth stages. The earliest occurred at <i>~</i>585°C and <i>~</i>8.7 kbar and is represented by Grt<sub>2</sub> ± St<sub>1</sub> ± Bt<sub>1</sub> + Qz. Grt<sub>2</sub> was partially coeval with growth of St<sub>1</sub>, which was stable at ~625°C and 9.0 kbar. Grt<sub>2</sub> + St<sub>1</sub> are syn-kinematic to the main S<sub>2</sub> foliation (D<sub>2</sub> episode). Subsequently, decompression (D<sub>3</sub>) started as St<sub>2</sub> (+ Bt<sub>2</sub> + Ms<sub>1</sub> + Qz + Pl) crystallized, and garnet was partially consumed at <i>~</i>612–620°C and <i>~</i>7.3–7.7 kbar. St<sub>3</sub> + Grt<sub>3</sub> crystallized at <i>~</i>608°C and <i>~</i>6.8 kbar at the end of D<sub>3</sub>. Increasing <i>P–T</i> conditions during the earlier M<sub>2</sub> growth stage suggest burial of the Maz Metasedimentary Series, probably linked to tectonic thickening by underthrusting (tectonic phase D<sub>2</sub>). Peak metamorphic conditions were attained during thrust stacking. The tec
分带矿物中主微量元素的分析有助于破译多变质岩体的部分构造-热演化过程。我们将这一方法应用于阿根廷西帕米亚山脉的马兹变质沉积系,在famatian造山运动的普遍Rinconada构造阶段,该地区的多变质作用导致了Grenvillian基底(马兹杂岩)的叠加。其中,较老变质作用(M1)为该基底最年轻的Grenvillian变质作用(约1035 Ma),而Rinconada变质作用(M2)为志留纪至早泥盆世,主要在440 ~ 410 Ma之间。后者是相对于晚寒武世早期至奥陶世(490-470 Ma)法马纪造山构造阶段造山锋向海洋迁移的结果。在马兹变质岩系的一颗星辉岩-石榴石片岩中发现了M1和M2变质事件。其中大部分变质矿物形成于M2事件,为巴罗威型(±蓝晶石)。部分变质P-T演化记录在石榴石卟啉母细胞的复杂成分分带中。根据石榴石的结构和化学成分(包括微量元素)鉴定出三种类型的石榴石。为了建立P-T历史,采用了相平衡分析、成分等线和多平衡热压法。M1以Grt1±Kfs±Sil保存为代表,峰值P-T条件为790℃,5.2 kbar,为麻粒岩相。这一早期变质事件与以残余S1片理为代表的D1期变形有关。后者以排列的包裹体的形式保存在橄榄岩卟卟母细胞中,并作为一个更古老的圆纹叶理的遗迹保存在基质的微石中。M2沿顺时针P-T路径生长,有三个矿物生长阶段。最早发生在~585℃,~8.7 kbar,表现为Grt2±St1±Bt1 + Qz。Grt2部分与St1生长同步,St1在~625℃和9.0 kbar下稳定生长。Grt2 + St1与主要的S2叶理(D2片段)同步运动。随后,St2 (+ Bt2 + Ms1 + Qz + Pl)结晶开始减压(D3),石榴石在~612 ~ 620℃和~7.3 ~ 7.7 kbar下被部分消耗。St3 + Grt3在~608℃和~6.8 kbar的温度下在D3末端结晶。M2生长早期P-T条件的增加表明马兹变质沉积系的埋藏,可能与逆冲作用下的构造增厚有关(构造期D2)。在逆冲叠合过程中,变质条件达到高峰。S2片理主要发生在D2构造期,在各个尺度上都具有渗透作用。近等温减压路径与发掘相一致,可能是由于沿离散剪切带(构造期D3)伸展而形成糜棱岩片理S3。
{"title":"Late Famatinian (440–410 Ma) overprint of Grenvillian metamorphism in Grt-St schists from the Sierra de Maz (Argentina): Phase equilibrium modelling, geochronology, and tectonic significance","authors":"Sebastián O. Verdecchia,&nbsp;Carlos D. Ramacciotti,&nbsp;Cesar Casquet,&nbsp;Edgardo G. Baldo,&nbsp;Juan A. Murra,&nbsp;Robert J. Pankhurst","doi":"10.1111/jmg.12677","DOIUrl":"10.1111/jmg.12677","url":null,"abstract":"&lt;p&gt;The analysis of major and trace elements in zoned minerals is useful for deciphering parts of the tectonothermal evolution of polymetamorphic tarrain. We applied this approach to the Maz Metasedimentary Series in Western Sierras Pampeanas of Argentina, where polymetamorphism resulted in the overprinting of a Grenvillian basement (the Maz Complex) during the pervasive Rinconada tectonic phase of the Famatinian orogeny. The older metamorphism (M&lt;sub&gt;1&lt;/sub&gt;) is assigned to the youngest Grenvillian metamorphic event recognized in this basement at c. 1035 Ma, whereas the Rinconada metamorphism (M&lt;sub&gt;2&lt;/sub&gt;) was Silurian to early Devonian, essentially between 440 and 410 Ma. The latter resulted from oceanward migration of the orogenic front relative to earlier late Cambrian to Ordovician (490–470 Ma) tectonic phases of the Famatinian orogeny. The M&lt;sub&gt;1&lt;/sub&gt; and M&lt;sub&gt;2&lt;/sub&gt; metamorphic events have been recognized in a staurolite-garnet schist from the Maz Metasedimentary Series. Most metamorphic minerals from this rock were formed during the M&lt;sub&gt;2&lt;/sub&gt; event which was of the Barrovian type (±kyanite). Part of the metamorphic &lt;i&gt;P–T&lt;/i&gt; evolution is recorded in the complex compositional zoning of garnet porphyroblasts. Three types of garnet were identified based on texture and chemistry, including trace elements (REEs). Phase equilibrium analysis, compositional isopleth, and multi-equilibrium thermobarometry were applied in order to establish the &lt;i&gt;P–T&lt;/i&gt; history. M&lt;sub&gt;1&lt;/sub&gt; is represented by preservation of Grt&lt;sub&gt;1&lt;/sub&gt; ± Kfs ± Sil, with peak &lt;i&gt;P–T&lt;/i&gt; condition of 790°C and 5.2 kbar, that is, granulite facies. This early metamorphic event was related to a deformational D&lt;sub&gt;1&lt;/sub&gt; episode represented by a relict S&lt;sub&gt;1&lt;/sub&gt; foliation. The latter is preserved as aligned inclusions in staurolite porphyroblasts and as relics of an older crenulated foliation in microlithons from the matrix. M&lt;sub&gt;2&lt;/sub&gt; followed a clockwise &lt;i&gt;P–T&lt;/i&gt; path with three mineral growth stages. The earliest occurred at &lt;i&gt;~&lt;/i&gt;585°C and &lt;i&gt;~&lt;/i&gt;8.7 kbar and is represented by Grt&lt;sub&gt;2&lt;/sub&gt; ± St&lt;sub&gt;1&lt;/sub&gt; ± Bt&lt;sub&gt;1&lt;/sub&gt; + Qz. Grt&lt;sub&gt;2&lt;/sub&gt; was partially coeval with growth of St&lt;sub&gt;1&lt;/sub&gt;, which was stable at ~625°C and 9.0 kbar. Grt&lt;sub&gt;2&lt;/sub&gt; + St&lt;sub&gt;1&lt;/sub&gt; are syn-kinematic to the main S&lt;sub&gt;2&lt;/sub&gt; foliation (D&lt;sub&gt;2&lt;/sub&gt; episode). Subsequently, decompression (D&lt;sub&gt;3&lt;/sub&gt;) started as St&lt;sub&gt;2&lt;/sub&gt; (+ Bt&lt;sub&gt;2&lt;/sub&gt; + Ms&lt;sub&gt;1&lt;/sub&gt; + Qz + Pl) crystallized, and garnet was partially consumed at &lt;i&gt;~&lt;/i&gt;612–620°C and &lt;i&gt;~&lt;/i&gt;7.3–7.7 kbar. St&lt;sub&gt;3&lt;/sub&gt; + Grt&lt;sub&gt;3&lt;/sub&gt; crystallized at &lt;i&gt;~&lt;/i&gt;608°C and &lt;i&gt;~&lt;/i&gt;6.8 kbar at the end of D&lt;sub&gt;3&lt;/sub&gt;. Increasing &lt;i&gt;P–T&lt;/i&gt; conditions during the earlier M&lt;sub&gt;2&lt;/sub&gt; growth stage suggest burial of the Maz Metasedimentary Series, probably linked to tectonic thickening by underthrusting (tectonic phase D&lt;sub&gt;2&lt;/sub&gt;). Peak metamorphic conditions were attained during thrust stacking. The tec","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 8","pages":"1347-1381"},"PeriodicalIF":3.4,"publicationDate":"2022-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46468112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 4
Garnet, zircon, and monazite age and REE signatures in (ultra)high-temperature and high-pressure rocks: Examples from the Caledonides and the Pamir (超)高温高压岩石中的石榴石、锆石和独居石年龄及稀土元素特征:以加里东泥质和帕米尔高原为例
IF 3.4 2区 地球科学 Q1 GEOLOGY Pub Date : 2022-05-09 DOI: 10.1111/jmg.12667
Lorraine Tual, Matthijs A. Smit, Ellen Kooijman, Melanie Kielman-Schmitt, Lothar Ratschbacher
<p>Rare earth element (REE) signatures of high-U/Pb and high-Th/Pb accessory minerals are typically used to link their ages to specific petrological processes (‘petrochronology’)—most notably the growth or breakdown of garnet. Although this approach is powerful, gaps in our understandings of REE systematics in high-grade rocks exist, particularly regarding the degree to which these minerals chemically equilibrate at extreme conditions. To investigate this, we performed comparative chronology and REE analysis of garnet, zircon, and monazite in (1) a fluid-rich, ultrahigh-pressure (UHP) migmatite from the Western Gneiss Region, Norway, and (2) dry felsic granulite xenoliths from the Pamir, Tajikistan. Zircon and monazite from the hydrous migmatite provided ages of 450–370 Ma and a range of Gd/Yb values across this time span. A Lu-Hf garnet age of 422 ± 2 Ma coincides with the age at which zircon and monazite exhibit the highest Gd/Yb values, as well as the largest range therein. The degree of dispersion in these values is substantial, especially for monazite. Zircon and monazite in the dry xenoliths provide age clusters between 50 and 11 Ma, recording pulsed growth and recrystallization. The Lu/Hf garnet ages for these samples are 41–38 Ma. The accessory minerals of that age are texturally associated with garnet, yet have the lowest, not the highest, Gd/Yb values. In both cases, there is evidence that co-genetic garnet and accessory minerals achieved REE equilibrium during growth. However, the age and compositional record of chronometric accessory minerals that were co-genetic with garnet are distinctly different between the two case examples. In the hydrous migmatite, supply-limited garnet growth in the presence of fluid phase resulted in strongly zoned garnet and a correspondingly large range in Gd/Yb values among co-genetic zircon and monazite. The range in Gd/Yb values match among these phases and collectively capture the strong fluctuations in the REE composition of matrix micro-domains caused by garnet growth. In this case, it is the range in Gd/Yb values, rather than a specific composition that is diagnostic for garnet growth. In the felsic granulites, garnet and accessory minerals growth occurred in a fluid-limited regime, in which short fluid pulses triggered reactions that had been likely significantly overstepped. The seemingly contradictory pattern of increasing Gd/Yb <i>after</i> garnet growth in these samples is the result of garnet having high Gd/Yb and continued zircon growth forcing further HREE depletion of the matrix with time. The situation that high, rather than low, Gd/Yb values in zircon and monazite indicate equilibrium with garnet may be common in dry granulites and other anhydrous high-temperature rocks. Our findings provide an improved framework for the reliable identification of the accessory minerals that equilibrated with garnet, even when the REE-age record of these minerals is complex, dispersed, and seemingly contra
高u /Pb和高th /Pb副矿物的稀土元素(REE)特征通常用于将它们的年龄与特定的岩石学过程(“岩石年代学”)联系起来——最明显的是石榴石的生长或分解。虽然这种方法很强大,但我们对高品位岩石中稀土元素系统的理解仍存在空白,特别是这些矿物在极端条件下的化学平衡程度。为了研究这一点,我们对(1)挪威西部片麻岩地区的富流体、超高压(UHP)混辉岩和(2)塔吉克斯坦帕米尔的干长英质麻粒岩捕虏体中的石榴石、锆石和独一石进行了比较年代学和稀土元素分析。含水杂岩中的锆石和独居石提供了450-370 Ma的年龄和Gd/Yb值范围。Lu-Hf石榴石年龄为422±2 Ma,与锆石和独居石Gd/Yb值最高的年龄一致,且变化幅度最大。这些值的分散程度很大,特别是对独居石。干捕虏体中的锆石和独居石年龄在50 ~ 11 Ma之间,记录了脉冲生长和再结晶。这些样品的Lu/Hf石榴石年龄为41 ~ 38 Ma。该年代的副矿物在结构上与石榴石相关,但Gd/Yb值最低,而不是最高。在这两种情况下,均有证据表明共生石榴石及其附属矿物在生长过程中达到稀土平衡。然而,与石榴石共成因的年代辅助矿物的年代和组成记录在两例中有明显差异。在含水杂岩中,由于流体相的存在,石榴石的生长受到限制,形成了强烈的石榴石分带,并在同生锆石和独居石之间形成了较大的Gd/Yb值范围。Gd/Yb值的变化范围在这些相之间匹配,并共同捕获了石榴石生长引起的基体微畴REE组成的强烈波动。在这种情况下,Gd/Yb值的范围,而不是诊断石榴石生长的特定成分。在长英质麻粒岩中,石榴石和副矿物的生长是在流体受限的条件下进行的,在这种条件下,短流体脉冲引发的反应可能被明显地超越了。这些样品中石榴石生长后Gd/Yb增加的看似矛盾的模式是石榴石具有高Gd/Yb和锆石持续生长的结果,迫使基体随着时间的推移进一步耗尽HREE。锆石和独居石中Gd/Yb值偏高而不是偏低的情况表明与石榴石平衡,这种情况可能在干麻粒岩和其他无水高温岩石中普遍存在。我们的发现为可靠地鉴定与石榴石平衡的辅助矿物提供了一个改进的框架,即使这些矿物的ree年龄记录复杂,分散,并且看似矛盾。此外,结合锆石、独居石、石榴石年龄和稀土元素记录,改进了我们样品的区域构造解释。
{"title":"Garnet, zircon, and monazite age and REE signatures in (ultra)high-temperature and high-pressure rocks: Examples from the Caledonides and the Pamir","authors":"Lorraine Tual,&nbsp;Matthijs A. Smit,&nbsp;Ellen Kooijman,&nbsp;Melanie Kielman-Schmitt,&nbsp;Lothar Ratschbacher","doi":"10.1111/jmg.12667","DOIUrl":"10.1111/jmg.12667","url":null,"abstract":"&lt;p&gt;Rare earth element (REE) signatures of high-U/Pb and high-Th/Pb accessory minerals are typically used to link their ages to specific petrological processes (‘petrochronology’)—most notably the growth or breakdown of garnet. Although this approach is powerful, gaps in our understandings of REE systematics in high-grade rocks exist, particularly regarding the degree to which these minerals chemically equilibrate at extreme conditions. To investigate this, we performed comparative chronology and REE analysis of garnet, zircon, and monazite in (1) a fluid-rich, ultrahigh-pressure (UHP) migmatite from the Western Gneiss Region, Norway, and (2) dry felsic granulite xenoliths from the Pamir, Tajikistan. Zircon and monazite from the hydrous migmatite provided ages of 450–370 Ma and a range of Gd/Yb values across this time span. A Lu-Hf garnet age of 422 ± 2 Ma coincides with the age at which zircon and monazite exhibit the highest Gd/Yb values, as well as the largest range therein. The degree of dispersion in these values is substantial, especially for monazite. Zircon and monazite in the dry xenoliths provide age clusters between 50 and 11 Ma, recording pulsed growth and recrystallization. The Lu/Hf garnet ages for these samples are 41–38 Ma. The accessory minerals of that age are texturally associated with garnet, yet have the lowest, not the highest, Gd/Yb values. In both cases, there is evidence that co-genetic garnet and accessory minerals achieved REE equilibrium during growth. However, the age and compositional record of chronometric accessory minerals that were co-genetic with garnet are distinctly different between the two case examples. In the hydrous migmatite, supply-limited garnet growth in the presence of fluid phase resulted in strongly zoned garnet and a correspondingly large range in Gd/Yb values among co-genetic zircon and monazite. The range in Gd/Yb values match among these phases and collectively capture the strong fluctuations in the REE composition of matrix micro-domains caused by garnet growth. In this case, it is the range in Gd/Yb values, rather than a specific composition that is diagnostic for garnet growth. In the felsic granulites, garnet and accessory minerals growth occurred in a fluid-limited regime, in which short fluid pulses triggered reactions that had been likely significantly overstepped. The seemingly contradictory pattern of increasing Gd/Yb &lt;i&gt;after&lt;/i&gt; garnet growth in these samples is the result of garnet having high Gd/Yb and continued zircon growth forcing further HREE depletion of the matrix with time. The situation that high, rather than low, Gd/Yb values in zircon and monazite indicate equilibrium with garnet may be common in dry granulites and other anhydrous high-temperature rocks. Our findings provide an improved framework for the reliable identification of the accessory minerals that equilibrated with garnet, even when the REE-age record of these minerals is complex, dispersed, and seemingly contra","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":"40 8","pages":"1321-1346"},"PeriodicalIF":3.4,"publicationDate":"2022-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/jmg.12667","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48064372","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 8
期刊
Journal of Metamorphic Geology
全部 Acc. Chem. Res. ACS Applied Bio Materials ACS Appl. Electron. Mater. ACS Appl. Energy Mater. ACS Appl. Mater. Interfaces ACS Appl. Nano Mater. ACS Appl. Polym. Mater. ACS BIOMATER-SCI ENG ACS Catal. ACS Cent. Sci. ACS Chem. Biol. ACS Chemical Health & Safety ACS Chem. Neurosci. ACS Comb. Sci. ACS Earth Space Chem. ACS Energy Lett. ACS Infect. Dis. ACS Macro Lett. ACS Mater. Lett. ACS Med. Chem. Lett. ACS Nano ACS Omega ACS Photonics ACS Sens. ACS Sustainable Chem. Eng. ACS Synth. Biol. Anal. Chem. BIOCHEMISTRY-US Bioconjugate Chem. BIOMACROMOLECULES Chem. Res. Toxicol. Chem. Rev. Chem. Mater. CRYST GROWTH DES ENERG FUEL Environ. Sci. Technol. Environ. Sci. Technol. Lett. Eur. J. Inorg. Chem. IND ENG CHEM RES Inorg. Chem. J. Agric. Food. Chem. J. Chem. Eng. Data J. Chem. Educ. J. Chem. Inf. Model. J. Chem. Theory Comput. J. Med. Chem. J. Nat. Prod. J PROTEOME RES J. Am. Chem. Soc. LANGMUIR MACROMOLECULES Mol. Pharmaceutics Nano Lett. Org. Lett. ORG PROCESS RES DEV ORGANOMETALLICS J. Org. Chem. J. Phys. Chem. J. Phys. Chem. A J. Phys. Chem. B J. Phys. Chem. C J. Phys. Chem. Lett. Analyst Anal. Methods Biomater. Sci. Catal. Sci. Technol. Chem. Commun. Chem. Soc. Rev. CHEM EDUC RES PRACT CRYSTENGCOMM Dalton Trans. Energy Environ. Sci. ENVIRON SCI-NANO ENVIRON SCI-PROC IMP ENVIRON SCI-WAT RES Faraday Discuss. Food Funct. Green Chem. Inorg. Chem. Front. Integr. Biol. J. Anal. At. Spectrom. J. Mater. Chem. A J. Mater. Chem. B J. Mater. Chem. C Lab Chip Mater. Chem. Front. Mater. Horiz. MEDCHEMCOMM Metallomics Mol. Biosyst. Mol. Syst. Des. Eng. Nanoscale Nanoscale Horiz. Nat. Prod. Rep. New J. Chem. Org. Biomol. Chem. Org. Chem. Front. PHOTOCH PHOTOBIO SCI PCCP Polym. Chem.
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
0
微信
客服QQ
Book学术公众号 扫码关注我们
反馈
×
意见反馈
请填写您的意见或建议
请填写您的手机或邮箱
×
提示
您的信息不完整,为了账户安全,请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
现在去查看 取消
×
提示
确定
Book学术官方微信
Book学术文献互助
Book学术文献互助群
群 号:481959085
Book学术
文献互助 智能选刊 最新文献 互助须知 联系我们:info@booksci.cn
Book学术提供免费学术资源搜索服务,方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。
Copyright © 2023 Book学术 All rights reserved.
ghs 京公网安备 11010802042870号 京ICP备2023020795号-1