Rick Verberne, Hugo W. van Schrojenstein Lantman, Steven M. Reddy, Matteo Alvaro, David Wallis, Denis Fougerouse, Antonio Langone, David W. Saxey, William D. A. Rickard
The trace-element composition of rutile is commonly used to constrain P–T–t conditions for a wide range of metamorphic systems. However, recent studies have demonstrated the redistribution of trace elements in rutile via high-diffusivity pathways and dislocation-impurity associations related to the formation and evolution of microstructures. Here, we investigate trace-element migration in low-angle boundaries formed by dislocation creep in rutile within an omphacite vein of the Lago di Cignana unit (Western Alps, Italy). Zr-in-rutile thermometry and inclusions of quartz in rutile and of coesite in omphacite constrain the conditions of rutile deformation to around the prograde boundary from high pressure to ultra-high pressure (~2.7 GPa) at temperatures of 500–565°C. Crystal-plastic deformation of a large rutile grain results in low-angle boundaries that generate a total misorientation of ~25°. Dislocations constituting one of these low-angle boundaries are enriched in common and uncommon trace elements, including Fe and Ca, providing evidence for the diffusion and trapping of trace elements along the dislocation cores. The role of dislocation microstructures as fast-diffusion pathways must be evaluated when applying high-resolution analytical procedures as compositional disturbances might lead to erroneous interpretations for Ca and Fe. In contrast, our results indicate a trapping mechanism for Zr.
金红石的微量元素组成通常用于限制各种变质系统的P–T–T条件。然而,最近的研究表明,金红石中微量元素通过高扩散率途径和位错-杂质缔合物的重新分布与微观结构的形成和演化有关。在这里,我们研究了微量元素在低角度边界中的迁移,该边界是由Lago di Cignana单元(意大利西阿尔卑斯)的绿辉石脉内金红石的位错蠕变形成的。Zr在金红石中的测温以及金红石中石英和绿辉石中柯石英的包裹体将金红石变形的条件限制在500–565°C温度下从高压到超高压(~2.7GPa)的前进边界附近。大金红石晶粒的晶体塑性变形导致低角度边界,产生约25°的总取向差。构成这些低角度边界之一的位错富含常见和不常见的微量元素,包括Fe和Ca,为微量元素沿位错核的扩散和捕获提供了证据。在应用高分辨率分析程序时,必须评估位错微观结构作为快速扩散途径的作用,因为成分扰动可能导致对Ca和Fe的错误解释。相反,我们的结果表明了Zr的俘获机制。
{"title":"Trace-element heterogeneity in rutile linked to dislocation structures: Implications for Zr-in-rutile geothermometry","authors":"Rick Verberne, Hugo W. van Schrojenstein Lantman, Steven M. Reddy, Matteo Alvaro, David Wallis, Denis Fougerouse, Antonio Langone, David W. Saxey, William D. A. Rickard","doi":"10.1111/jmg.12686","DOIUrl":"10.1111/jmg.12686","url":null,"abstract":"<p>The trace-element composition of rutile is commonly used to constrain <i>P</i>–<i>T</i>–<i>t</i> conditions for a wide range of metamorphic systems. However, recent studies have demonstrated the redistribution of trace elements in rutile via high-diffusivity pathways and dislocation-impurity associations related to the formation and evolution of microstructures. Here, we investigate trace-element migration in low-angle boundaries formed by dislocation creep in rutile within an omphacite vein of the Lago di Cignana unit (Western Alps, Italy). Zr-in-rutile thermometry and inclusions of quartz in rutile and of coesite in omphacite constrain the conditions of rutile deformation to around the prograde boundary from high pressure to ultra-high pressure (~2.7 GPa) at temperatures of 500–565°C. Crystal-plastic deformation of a large rutile grain results in low-angle boundaries that generate a total misorientation of ~25°. Dislocations constituting one of these low-angle boundaries are enriched in common and uncommon trace elements, including Fe and Ca, providing evidence for the diffusion and trapping of trace elements along the dislocation cores. The role of dislocation microstructures as fast-diffusion pathways must be evaluated when applying high-resolution analytical procedures as compositional disturbances might lead to erroneous interpretations for Ca and Fe. In contrast, our results indicate a trapping mechanism for Zr.</p>","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2022-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42846995","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}
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.
{"title":"Effects of Fe3+ in sillimanite on mineral stabilities and parageneses in ultrahigh-temperature metapelites","authors":"Bin Wang, 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":null,"pages":null},"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}
Alejandro Cisneros de León, Axel K. Schmitt, Bodo Weber
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 (ZrO2), 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
{"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, Axel K. Schmitt, Bodo Weber","doi":"10.1111/jmg.12683","DOIUrl":"10.1111/jmg.12683","url":null,"abstract":"<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","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":null,"pages":null},"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}
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.
{"title":"Tectonic erosion and deep subduction in Central Tibet: Evidence from the discovery of retrograde eclogites in the Amdo microcontinent","authors":"Yinbiao Peng, Shengyao Yu, Sanzhong Li, Yongjiang Liu, M. Santosh, Pei Lv, Yunshuai Li, Chuanzhi Li, 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 >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":null,"pages":null},"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}
Håkon Austrheim, Ane K. Engvik, Morgan Ganerød, Kristina G. Dunkel, Mari Roen Velo
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, Ane K. Engvik, Morgan Ganerød, Kristina G. Dunkel, Mari Roen Velo","doi":"10.1111/jmg.12682","DOIUrl":"10.1111/jmg.12682","url":null,"abstract":"<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","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":null,"pages":null},"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}
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.
{"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, Hao Cheng, Besim Dragovic, Kai-Yang Du, 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 (<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":null,"pages":null},"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}
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.
{"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, Josef Ježek, 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":null,"pages":null},"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}
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.
{"title":"Thermodynamic constraints on the composition of orogenically thickened lower crust","authors":"Yi-Bing Li, Yu-Wen Wu, Bin Su, Si Chen, Qing-Hua Zhang, 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> (>50.2 wt%), X<sub>Mg</sub> (>0.70), X<sub>Ca</sub> (>0.49), or low X<sub>Al</sub> (<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 >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":null,"pages":null},"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}
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.
{"title":"Garnet crystallization mechanisms and localized polymetamorphism in the southwestern Meguma Terrane, Nova Scotia, Canada","authors":"Alexandra B. Nagurney, Mark J. Caddick, 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 <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":null,"pages":null},"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}
Sebastián O. Verdecchia, Carlos D. Ramacciotti, Cesar Casquet, Edgardo G. Baldo, Juan A. Murra, Robert J. Pankhurst
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 (M1) is assigned to the youngest Grenvillian metamorphic event recognized in this basement at c. 1035 Ma, whereas the Rinconada metamorphism (M2) 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 M1 and M2 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 M2 event which was of the Barrovian type (±kyanite). Part of the metamorphic P–T 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 P–T history. M1 is represented by preservation of Grt1 ± Kfs ± Sil, with peak P–T condition of 790°C and 5.2 kbar, that is, granulite facies. This early metamorphic event was related to a deformational D1 episode represented by a relict S1 foliation. The latter is preserved as aligned inclusions in staurolite porphyroblasts and as relics of an older crenulated foliation in microlithons from the matrix. M2 followed a clockwise P–T path with three mineral growth stages. The earliest occurred at ~585°C and ~8.7 kbar and is represented by Grt2 ± St1 ± Bt1 + Qz. Grt2 was partially coeval with growth of St1, which was stable at ~625°C and 9.0 kbar. Grt2 + St1 are syn-kinematic to the main S2 foliation (D2 episode). Subsequently, decompression (D3) started as St2 (+ Bt2 + Ms1 + Qz + Pl) crystallized, and garnet was partially consumed at ~612–620°C and ~7.3–7.7 kbar. St3 + Grt3 crystallized at ~608°C and ~6.8 kbar at the end of D3. Increasing P–T conditions during the earlier M2 growth stage suggest burial of the Maz Metasedimentary Series, probably linked to tectonic thickening by underthrusting (tectonic phase D2). Peak metamorphic conditions were attained during thrust stacking. The tec
{"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, Carlos D. Ramacciotti, Cesar Casquet, Edgardo G. Baldo, Juan A. Murra, Robert J. Pankhurst","doi":"10.1111/jmg.12677","DOIUrl":"10.1111/jmg.12677","url":null,"abstract":"<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","PeriodicalId":16472,"journal":{"name":"Journal of Metamorphic Geology","volume":null,"pages":null},"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}