IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-15 DOI: 10.1016/j.lithos.2024.107868

Wen-Xiang Zhang , Xing Zhang , Guang-Yan Zhou , Long Li , Huan Chang , Yuan-Bao Wu

Granitoids provide a vital window to probe the lithological configuration and chemical evolution of orogenic belts. In this contribution, we present an integrated study of mineral compositions, zircon UPb ages and HfO isotopes, titanite UPb ages and SmNd isotopes, as well as whole-rock element and Sr–Nd–Hf isotope compositions of the Liangwan granitic pluton in the northern Paleozoic accretionary orogenic unit of the Tongbai orogen, central China. The Liangwan pluton is composed mainly of monzogranites and contains abundant mafic microgranular enclaves (MMEs). The monzogranites have relatively high silica contents (SiO₂ = 67.40–69.91 wt%) and mainly exhibit shoshonite to high-K calc-alkaline and metaluminous features. The MMEs have similar mineral and geochemical compositions and zircon and titanite UPb ages of ca. 129 Ma to the monzogranites, suggesting that they are likely early-crystalized cumulates of the host monzogranites. The MMEs and monzogranites are both characterized by enrichment of large ion lithophile elements but depletion of high field-strength elements. The monzogranites have whole-rock initial Sr (I_sr) of 0.7069–0.7074, ε_Nd(t) of −14.2 to −13.7, and ε_Hf(t) of −17.5 to −17.2, zircon ε_Hf(t) of −17.8 to −17.0 and δ¹⁸O values of 5.27–5.98 ‰, and titanite ε_Nd(t) of −14.50 to −13.78. These features are distinct from the rocks in the northern Tongbai accretionary orogenic unit but similar to those of the post-collisional granitoids in the southern Tongbai collisional orogenic unit. The Liangwan pluton was likely stemmed from the subducted South China Block (SCB) underneath the northern segment of the Tongbai orogen. Our results show that the subducted continental mass can act as an alternative source for the magmatic rocks occurred in the accretionary unit.

花岗岩是探究造山带岩性构造和化学演化的重要窗口。在这篇论文中，我们综合研究了中国中部桐柏造山带北古生代增生造山单元梁湾花岗岩柱岩的矿物成分、锆石UPb年龄和HfO同位素、榍石UPb年龄和SmNd同位素，以及全岩元素和Sr-Nd-Hf同位素成分。梁湾花岗岩柱岩主要由单斜花岗岩组成，并含有丰富的黑云母微晶飞地（MMEs）。单斜花岗岩的二氧化硅含量相对较高（SiO2=67.40-69.91 wt%），主要表现为闪长岩至高K钙碱性和金属铝性特征。MMEs具有类似的矿物和地球化学成分，锆石和榍石的UPb年龄约为单斜花岗岩的129Ma，这表明它们很可能是主单斜花岗岩的早期晶化累积。MMEs和单斜长花岗岩都具有富集大离子亲岩元素但贫化高场强元素的特征。独居岩的全岩初始Sr（Isr）值为0.7069-0.7074，εNd（t）值为-14.2--13.7，εHf（t）值为-17.5--17.2，锆石εHf（t）值为-17.8--17.0，δ18O值为5.27--5.98‰，榍石εNd（t）值为-14.50--13.78。这些特征与桐柏北部增生造山单元的岩石不同，但与桐柏南部碰撞造山单元碰撞后花岗岩的特征相似。梁湾构造很可能源自桐柏造山带北段下俯冲的华南地块。我们的研究结果表明，俯冲大陆块可作为增生单元中岩浆岩的替代来源。

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引用次数: 0

Geochemical study of UHP serpentinites in southwestern Tianshan, China and its implications for trace elements deep recycling 中国天山西南部超高压蛇纹岩地球化学研究及其对微量元素深层循环的影响

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-15 DOI: 10.1016/j.lithos.2024.107867

Tingting Shen , José Alberto Padrón-Navarta , Thomas Bader , Congcong Lin , Tian Qiu , Jingsui Yang

Serpentinites play a crucial role in the recycling of elements and volatiles in subduction zones. We studied the geochemistry of Changawuzi serpentinites from Chinese southwestern Tianshan, which underwent ultrahigh-pressure (UHP) metamorphism. The bulk rock compositions of the serpentinites suggest that Changawuzi serpentinites originated from a variably depleted mantle and were subsequently enriched in fluid-mobile elements (FMEs) during initial serpentinization. Integrated analyses of trace element concentrations (Cs, U, As, and Sb), Sr–Nd–Pb isotopic compositions, and geological context collectively indicate that serpentinization likely occurred within the interior of the subducted slab. During the early stages of subduction, the concentrations of rare earth elements (REE), high-field-strength elements (HFSE), and other trace elements (such as Cs, Rb, Ba, Th, and U) decrease from low-grade lizardite to high-grade antigorite, as well as from primary clinopyroxene to metamorphic diopside. FMEs, particularly boron (B), are significantly enriched in lizardite, and the majority are liberated during prograde subduction, resulting in the metamorphic transformation from lizardite to antigorite. The uptake and variation of Sb and As in Changawuzi serpentinites are relatively minor. At peak metamorphic conditions, olivine, Ti-chondrodite and Ti-clinohumite become the main minerals hosting trace elements (such as REE, B, Sb, As and Li) that were released during partial antigorite dehydration and clinopyroxene re-equilibration. Ti-chondrodite/Ti-clinohumite as isolated grains or as lamellae within metamorphic olivine have the potential to carry HFSE, FMEs (particularly B and Li) and H₂O into the deeper mantle beyond the dehydration of serpentinites, potentially impacting arc magmatism and the global cycling of these elements.

蛇绿岩在俯冲带元素和挥发物的循环中发挥着至关重要的作用。我们对经历了超高压变质作用的中国西南天山长窝子蛇绿岩的地球化学进行了研究。蛇绿岩的大块岩石成分表明，长窝子蛇绿岩起源于不同程度的贫化地幔，并在最初的蛇绿岩化过程中富集了流体流动元素（FMEs）。对微量元素浓度（铯、铀、砷和锑）、锶-镎-铅同位素组成和地质背景的综合分析表明，蛇绿岩化很可能发生在俯冲板块内部。在俯冲的早期阶段，稀土元素（REE）、高场强元素（HFSE）和其他微量元素（如铯、铷、钡、钍和铀）的浓度从低品位蜥蜴石下降到高品位锑橄榄石，以及从原生霞石下降到变质闪长岩。矿物元素，尤其是硼（B），在蜥蜴岩中明显富集，而且大部分是在顺行俯冲过程中释放出来的，导致蜥蜴岩向锑辉石的变质转化。长窝子蛇绿岩中锑和砷的吸收和变化相对较小。在峰值变质条件下，橄榄石、钛刚玉和钛黝帘石成为承载微量元素（如 REE、B、Sb、As 和 Li）的主要矿物，这些微量元素是在部分黝帘石脱水和霞石再沸腾过程中释放出来的。作为孤立晶粒或变质橄榄石中的薄片的钛刚玉石/钛clinohumite有可能在蛇绿岩脱水之后将高频闪锌矿、全金属元素（尤其是硼和锂）以及H2O带入地幔深处，从而对弧岩浆活动和这些元素的全球循环产生潜在影响。

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引用次数: 0

U-Pb ages and Hf isotopic composition of detrital zircon in western Algarve Triassic sandstone (SW Iberia): Implications for crustal evolution, provenance, and paleogeography 阿尔加维西部三叠纪砂岩（伊比利亚西南部）中锆石碎片的 U-Pb 年龄和 Hf 同位素组成：对地壳演化、产地和古地理的影响

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-15 DOI: 10.1016/j.lithos.2024.107871

Manuel Francisco Pereira, Cristina Gama

The Triassic paleogeographic configuration before the Central Atlantic Ocean's opening and the Pangea's breakup establishes that Iberia was close to North America and North Africa. We present UPb and Hf isotope data of Triassic siliciclastic rocks of the Western Algarve basin (Southwest Iberia, Portugal) to draw inferences on their provenance to define the crustal evolution of the potential sources. Detrital zircon age populations of five samples of Triassic sandstones (68–80 % Neoproterozoic; 5–23 % Paleoproterozoic; 5–14 % Mesoproterozoic; <5 % Archaen and < 4 % Paleozoic) differ significantly from those of the underlying Carboniferous turbidites of the South Portuguese Zone suggesting provenance from outside present-day SW Iberia. Hf isotope signatures of the zircon grains from the western Algarve Triassic sandstones unravel a complex crustal evolution characterized by successive cycles of input of juvenile magmas and magmas derived from the reworking of older crust. Archean detrital zircon grains with positive εHf(t) values and model ages of 3.1–3 Ga indicate juvenile crust formation (Leonian event), while a grain dated at ca. 2.6 Ga showing negative εHf(t) values and model ages of 3.1 Ga suggests that the Archean crust became reworked later (Liberian event). Zircon grains dated between 2.4 and 2.5 Ga having positive to slightly negative εHf(t) values and model ages of 3.3–2.6 Ga model ages correspond to magmatism older than the Eburnean event known in the Reguibat shield, involving a juvenile component mixed with variable proportions of reworked Archean crust. Younger Paleoproterozoic grains (ca. 2.10 to 2.05 Ga; Eburnean-Birimian event) having positive εHf(t) values and model ages of 2.3–2.1 Ga and negative εHf(t) values and model ages of 3.6–2.6 Ga, also indicate interaction of juvenile sources with mixing of old crust. Mesoproterozoic grains show positive εHf(t) values and model ages of 2.3–2.1 Ga, suggesting juvenile crust formation and reworking of the Eburnean crust. Neoproterozoic (ca. 695–555 Ma) detrital zircon with positive εHf(t) values and model ages of 0.76–0.58 Ga point to juvenile crust formation (i.e. Cadomian/Pan-African and Avalonian arcs). They also have negative εHf(t) values in the range − 21.6 to −11.7 and model ages of 3.2–2.1 Ga, suggesting reworking of older crust. In summary, the εHf(t) values and UPb age pattern of the zircon grains from the Triassic siliciclastic rocks are similar to NW Africa and North America potential sources. Still, there is a notable gap in juvenile crust production during the Siderian in the peri-Eastern Laurentia, Avalonia, and Ganderia potential sources unknown in NW Africa. The lack of ca. 525–380 Ma and ca. 380–330 Ma detrital zircon in the western Algarve Triassic sandstones makes it challenging to admit an Atlantic margin of North America and SW Iberia provenance.

中大西洋开辟和泛大陆解体之前的三叠纪古地理格局确定了伊比利亚靠近北美洲和北非。我们提供了西阿尔加维盆地（葡萄牙伊比利亚西南部）三叠纪硅质碎屑岩的 UPb 和 Hf 同位素数据，以推断其来源，从而确定潜在来源的地壳演化。五个三叠纪砂岩样本的锆英石年龄群（68-80 % 新新生代；5-23 % 古新生代；5-14 % 中新生代；<5 % 古生代和<4 % 古生代）与南葡萄牙区石炭纪浊积岩下层的锆英石年龄群差异显著，表明其来源于当今伊比利亚西南部以外的地区。阿尔加维西部三叠纪砂岩中锆石颗粒的 Hf 同位素特征揭示了复杂的地壳演化过程，其特点是幼年岩浆和旧地壳再加工产生的岩浆的连续循环输入。具有正εHf(t)值和3.1-3 Ga模型年龄的Archean岩屑锆石颗粒表明地壳是由幼年岩浆形成的（Leonian事件），而一个年代为约2.6 Ga的锆石颗粒显示出负εHf(t)值和3.1 Ga模型年龄，这表明Archean岩壳在后来经过了再加工（Liberian事件）。年代在2.4-2.5 Ga之间的锆石颗粒，其εHf(t)值为正值到轻微的负值，模型年龄为3.3-2.6 Ga，对应于比雷吉巴特盾状区已知的埃伯恩事件更早的岩浆活动，包括混合了幼年成分和不同比例的再造阿切安地壳。较年轻的古近纪岩粒（约 2.10 至 2.05 Ga；埃伯恩-比里曼事件）具有正的εHf(t)值和 2.3 至 2.1 Ga 的模型年龄，以及负的εHf(t)值和 3.6 至 2.6 Ga 的模型年龄，也表明幼生源与旧地壳混合的相互作用。中新生代晶粒显示正的εHf(t)值和2.3-2.1 Ga的模型年龄，表明幼生代地壳的形成和埃伯恩地壳的再加工。新元古代（约695-555Ma）锆英石的εHf(t)值为正，模型年龄为0.76-0.58Ga，表明是幼壳形成（即Cadomian/泛非弧和Avalonian弧）。它们的εHf(t)值在-21.6到-11.7之间，模型年龄为3.2-2.1 Ga，表明是老地壳的再加工。总之，三叠纪硅质碎屑岩锆石晶粒的εHf(t)值和UPb年龄模式与非洲西北部和北美洲的潜在来源相似。然而，在西北非未知的近东劳伦西亚、阿瓦隆尼亚和甘德利亚潜在来源地区，西德纪的幼生地壳生成仍存在明显的差距。阿尔加维西部三叠纪砂岩中缺乏约 525-380 Ma 和约 380-330 Ma 的锆英石，这使得承认北美大西洋边缘和伊比利亚西南部的来源具有挑战性。

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引用次数: 0

Zinc and iron isotopic compositions of Cenozoic basalts in Inner Mongolia: New insights into deep carbon recycling related to Paleo-Asian slab subduction 内蒙古新生代玄武岩的锌和铁同位素组成：与古亚洲板块俯冲有关的深部碳循环新见解

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-15 DOI: 10.1016/j.lithos.2024.107866

Zhao-Xue Wang , Tianhao Wu , Sheng-Ao Liu

The origin of Cenozoic basalts in Inner Mongolia has been debated in recent years. Although the heavier-than-mantle zinc isotopic compositions indicate recycled carbonate in their sources, the recycled carbonate has been attributed to two different subducting oceanic slabs (Paleo-Asian vs. Paleo-Pacific). To further address this issue, Cenozoic basalts located in the west of the North-South Gravity Lineament (NSGL) in Inner Mongolia are investigated, and the sampling profile is approximately parallel to the NSGL (i.e., from southwest to northeast; SW-NE). These basalts have notably heavier zinc (δ⁶⁶Zn = 0.47–0.52 ‰) and iron (δ⁵⁶Fe = 0.18–0.24 ‰) isotopic compositions than those of the mantle, which cannot be interpreted by magmatic processes (differentiation and partial melting). Instead, the involvement of recycled carbonates in sources is a viable explanation for the high δ⁶⁶Zn characteristics, supported by high P₂O₅ contents and low Hf/Hf*. In addition, samples with high δ⁵⁶Fe also display high Fe/Mn (69–81) related to Cenozoic basalts from the east of the NSGL, indicating the existence of a pyroxenite component in sources in addition to carbonated peridotites. Combining with literature data, we found that basalts distributed in the SW-NE direction in Inner Mongolia have similarly heavy Zn and Fe isotopic compositions. This provides further constraints that mantle carbonate metasomatism in the west of the NSGL was most likely to have been caused by southeastward subduction of the Paleo-Asian oceanic slab, instead of northward subduction of the Paleo-Asian oceanic slab or subduction of the Paleo-Pacific oceanic slab.

近年来，关于内蒙古新生代玄武岩的成因一直存在争议。虽然重于幔锌同位素组成表明其来源为再生碳酸盐岩，但再生碳酸盐岩被认为是两种不同的俯冲洋板（古亚洲板块与古太平洋板块）。为了进一步解决这一问题，研究人员对位于内蒙古南北重力线（NSGL）西部的新生代玄武岩进行了调查，取样剖面与南北重力线大致平行（即从西南到东北；SW-NE）。这些玄武岩的锌（δ66Zn = 0.47-0.52 ‰）和铁（δ56Fe = 0.18-0.24 ‰）同位素组成明显重于地幔，这不能用岩浆过程（分异和部分熔融）来解释。相反，在高 P2O5 含量和低 Hf/Hf* 的支持下，来源中再生碳酸盐的参与是高δ66Zn 特征的一个可行解释。此外，具有高δ56Fe的样品还显示出与来自NSGL东部新生代玄武岩相关的高Fe/Mn（69-81），这表明除了碳酸盐化橄榄岩之外，岩源中还存在辉长岩成分。结合文献数据，我们发现内蒙古西南-东北方向分布的玄武岩具有类似的重锌、重铁同位素组成。这进一步证实了NSGL西部地幔碳酸盐变质作用很可能是由古亚洲大洋板块向东南俯冲造成的，而不是古亚洲大洋板块向北俯冲或古太平洋大洋板块俯冲造成的。

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引用次数: 0

Cumulate granites and extraction of interstitial high-silica melts: The case of leucogranites in the northern Tibetan Plateau 叠加花岗岩和间隙高硅熔体的提取：青藏高原北部白花岗岩的案例

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-14 DOI: 10.1016/j.lithos.2024.107869

Peng Wang , Xiangsong Wang , Guochun Zhao , Roberto F. Weinberg , Qian Liu

Accumulation of crystals and extraction of melt play a crucial role in generating diverse intermediate to felsic rocks. However, the process of separating crystals and melt in granitic rocks with high silica content remains a topic of debate. In this paper, detailed petrographic, geochemical, and isotopic observations reveal that the ca. 424 Ma Aoyiyayilake S-type granitic batholith, located in Eastern Kunlun of northern Tibetan Plateau, is composed of low- and high- SiO₂ units that resulted from crystal accumulation and melt extraction respectively. Petrographically, the presence of fractures filled with quartz and oligoclase indicates compaction and fracturing occurred in the presence of melt, resulting in the extraction of melts to produce the high-SiO₂ granites. Geochemically, the high-SiO₂ granites have higher depletions in Eu, lower light rare earth elements, large ion lithophile elements (e.g., Ba and Sr) and P content than the low-SiO₂ granites. This is due to the fractional crystallization of rock-forming minerals (e.g., oligoclase and orthoclase) and accessory minerals (e.g., apatite), consistent with the proportions of minerals in the two units, e.g., ∼0.3 % apatite in the low-SiO₂ granites and undetected apatite in the high-SiO₂ granites. Isotopically, the high-SiO₂ granites display lower δ¹¹B of −16.1 ‰ and − 17. compared to −15.7 ‰ to −7.14 ‰ in low-SiO₂ granite, which is attributed to the crystallization of muscovite. These characteristics serve as significant indicators of efficient magma fractionation during the formation of high-SiO₂ granites.

晶体的积累和熔体的提取在生成多种多样的中熔岩和长熔岩的过程中起着至关重要的作用。然而，在二氧化硅含量较高的花岗岩中，晶体和熔体的分离过程仍是一个争论不休的话题。本文通过详细的岩石学、地球化学和同位素观察，揭示了长约424 Ma的Aoyiyayil花岗岩中晶体和熔体的分离过程。位于青藏高原北部东昆仑的约 424 Ma Aoyiyayilake S 型花岗岩浴积岩由低二氧化硅和高二氧化硅单元组成，分别由晶体堆积和熔融萃取形成。从岩相学上看，裂隙中充满了石英和寡长石，表明在熔体存在的情况下发生了压实和断裂，导致熔体萃取产生了高SiO2花岗岩。在地球化学方面，与低二氧化硅花岗岩相比，高二氧化硅花岗岩的 Eu、低轻稀土元素、大离子亲岩元素（如 Ba 和 Sr）和 P 含量的贫化程度较高。这是由于成岩矿物（如低斜长石和正长石）和附属矿物（如磷灰石）的分馏结晶造成的，这与两个单元中矿物的比例一致，例如低二氧化硅花岗岩中磷灰石的比例为0.3%，而高二氧化硅花岗岩中未检测到磷灰石。从同位素角度来看，高二氧化硅花岗岩的δ11B 为-16.1 ‰和-17.，而低二氧化硅花岗岩的δ11B 为-15.7 ‰至-7.14 ‰，这归因于麝香石的结晶。这些特征是高二氧化硅花岗岩形成过程中岩浆有效分馏的重要指标。

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引用次数: 0

Magmatic differentiation of peralkaline granites: Constraints from iron isotope fractionation between Fe-bearing minerals 碱性花岗岩的岩浆分异：含铁矿物间铁同位素分馏的制约因素

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-12 DOI: 10.1016/j.lithos.2024.107863

De-Hong Du , Xiao-Lei Wang , Hang Xu , Shuo Wang , Ying-Ze Zhang , Weiqiang Li

Iron isotopes have been found useful in tracing magmatic processes of calc-alkaline granitic magmas, but its application in peralkaline granitic systems is hampered by the lack of information regarding the Fe isotope fractionation factors between alkali-rich ferromagnesian silicate minerals and FeTi oxides. To better understand the behavior of Fe isotopes during peralkaline magma differentiation, we carried out high-precision Fe isotope analyses on peralkaline and associated metaluminous high-silica granite rocks and Fe-bearing minerals separated from the rocks in Zhoushan archipelago, southeast China. The Fe-bearing mineral show a large dispersion in Fe isotope compositions, with δ⁵⁶Fe ranging from 0.03 ‰ to 0.70 ‰, following the sequence of K-feldspar ≥ magnetite > aegirine > arfvedsonite > ilmenite. The δ⁵⁶Fe differences between the mineral pairs are relatively consistent. Based on the magmatic temperatures defined by quartz-zircon oxygen isotopic geothermometer, the temperature-dependent equilibrium Fe isotope fractionation functions between following mineral pairs are obtained: Δ⁵⁶Fe_{aegirine-arfvedsonite} = 0.20 (± 0.07) × 10⁶/T², Δ⁵⁶Fe_{magnetite-arfvedsonite} = 0.38 (± 0.06) × 10⁶/T², and Δ⁵⁶Fe_{magnetite-aegirine} = 0.16 (± 0.04) × 10⁶/T². The bulk peralkaline granites have variable but generally high δ⁵⁶Fe values ranging from 0.28 ± 0.03 ‰ to 0.62 ± 0.04 ‰, with a mean of 0.42 ± 0.09 ‰ (1SD), which are higher than those of the associated metaluminous granitic samples (δ⁵⁶Fe = 0.22 ± 0.05 ‰, 1SD). Furthermore, δ⁵⁶Fe values of the peralkaline granites are negatively correlated with Sm/Yb and MnO, consistent with removal of isotopically light Fe-enriched arfvedsonite, implying that peralkaline granites experienced extensive magma differentiation regardless whether they were derived from differentiation of mantle-derived basaltic melts or partial melting of curst sources. Our results highlight a large Fe isotope fractionation between alkali ferromagnesian silicates and oxides, confirming Fe isotopes as a potential tool in tracking the differentiation processes of peralkaline magmas.

铁同位素被认为有助于追踪钙碱性花岗岩岩浆的岩浆过程，但由于缺乏有关富碱铁镁硅酸盐矿物与铁钛氧化物之间铁同位素分馏因子的信息，铁同位素在围岩花岗岩体系中的应用受到了阻碍。为了更好地了解围岩岩浆分异过程中铁同位素的行为，我们对中国东南部舟山群岛的围岩和伴生金属铝高硅花岗岩岩石以及从岩石中分离出来的含铁矿物进行了高精度的铁同位素分析。含铁矿物的铁同位素组成呈现出较大的分散性，δ56Fe从0.03‰到0.70‰不等，按照K长石≥磁铁矿>egirine>arfvedsonite>钛铁矿的顺序排列。矿物对之间的δ56Fe差异相对一致。根据石英-锆石氧同位素地温计确定的岩浆温度，可以得到以下矿物对之间与温度相关的平衡铁同位素分馏函数：Δ56Feaegirine-arfvedsonite = 0.20 (± 0.07) × 106/T2，Δ56Femagnetite-arfvedsonite = 0.38 (± 0.06) × 106/T2，Δ56Femagnetite-aegirine = 0.16 (± 0.04) × 106/T2。大块围岩花岗岩的δ56Fe值从0.28±0.03‰到0.62±0.04‰不等，平均值为0.42±0.09‰（1SD），但普遍较高，高于相关的金属铝质花岗岩样品（δ56Fe = 0.22 ± 0.05 ‰，1SD）。此外，碱性花岗岩的δ56Fe值与Sm/Yb和MnO呈负相关，这与富含同位素轻Fe的阿费维德松石被移除是一致的，这意味着碱性花岗岩经历了广泛的岩浆分异，无论它们是来自地幔玄武岩熔体的分异，还是来自凝灰岩源的部分熔融。我们的研究结果突显了碱性铁镁硅酸盐和氧化物之间存在着巨大的铁同位素分馏，证实了铁同位素是追踪围岩岩浆分异过程的潜在工具。

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引用次数: 0

Temporal variation in oxygen isotopes of peraluminous granites derived from sedimentary sources 沉积来源的过铝花岗岩氧同位素的时间变化

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-12 DOI: 10.1016/j.lithos.2024.107864

Claire E. Bucholz, Juan D. Hernández-Montenegro

The oxygen isotopic composition of magmatic rocks provides critical constraints on the contributions of crust versus mantle in their genesis. Peraluminous granites derived from partial melting of sedimentary rocks offer a unique archive to examine how the oxygen isotope composition of sedimentary rocks recycled into magmas has changed throughout Earth history. In this study, we explore this record through a two-pronged approach. First, we compile a comprehensive dataset of oxygen isotope bulk-rock and mineral analyses from globally distributed peraluminous granites and volcanic rocks ranging in age from 3.2 billion years to 6 million years. Second, we model the isotopic fractionation between sedimentary source rocks and derivative melts, as well as minerals in equilibrium with the melt during anatexis. Our compilation demonstrates a progressive increase in δ¹⁸O values of zircon and garnet from the Archean to Paleoproterozoic and again in the latest Neoproterozoic to Phanerozoic. Specifically, the average δ¹⁸O of zircon from peraluminous granites increases from 6.7 ± 1.0 ‰ to 9.5 ± 0.8 ‰ at ∼ 2.35 Ga, followed by another increase to 10.4 ± 0.7 ‰ after 600 Ma (errors are ± 1 s.d.). These observations align with the sedimentary rock record which suggests enhanced weathering and clay deposition resulting from tectonic and biological forcings. Furthermore, the increase in δ¹⁸O of peraluminous granites broadly mirrors similar secular increases in the δ¹⁸O values of siliciclastic sedimentary rocks. However, using our modeled fractionations between melt and source rock, the reconstructed source-rock δ¹⁸O values capture only the lower end of the siliciclastic sedimentary rock range, suggesting that sedimentary rocks recycled into magmas have, on average, lower δ¹⁸O values than coeval clay-rich shales. We propose that any global analyses of oxygen isotopes in magmatic rocks or zircon should use the average values of calculated source rocks for peraluminous granites in defining crustal contributions. Furthermore, our study highlights the broader implications of the observed trends, including the progressive contamination of the mantle and elevation of its δ¹⁸O values.

岩浆岩的氧同位素组成为地壳和地幔在岩浆岩形成过程中的作用提供了重要的制约因素。由沉积岩部分熔化而成的先铝花岗岩提供了一个独特的档案库，可用于研究在整个地球历史中，被回收到岩浆中的沉积岩的氧同位素组成是如何变化的。在本研究中，我们通过双管齐下的方法来探索这一记录。首先，我们汇编了一个全面的氧同位素大块岩石和矿物分析数据集，这些数据来自全球分布的年龄从32亿年到600万年不等的过铝花岗岩和火山岩。其次，我们模拟了沉积源岩和衍生物熔体之间的同位素分馏，以及在无定形过程中与熔体处于平衡状态的矿物。我们的研究结果表明，锆石和石榴石的δ18O值从奥陶纪到古近代逐渐增加，在新近纪到新生代再次增加。具体地说，过铝花岗岩中锆石的平均δ18O值在∼ 2.35 Ga时从6.7 ± 1.0 ‰增加到9.5 ± 0.8 ‰，600 Ma后又增加到10.4 ± 0.7 ‰（误差为± 1 s.d.）。这些观测结果与沉积岩记录相吻合，沉积岩记录表明构造和生物作用导致风化和粘土沉积增强。此外，过铝花岗岩δ18O值的增加大致反映了硅质沉积岩δ18O值的类似周期性增加。然而，利用我们所模拟的熔体与源岩之间的分馏，重建的源岩δ18O值仅捕捉到硅质沉积岩范围的下限，这表明回收到岩浆中的沉积岩的平均δ18O值低于同时期富含粘土的页岩。我们建议，在对岩浆岩或锆石中的氧同位素进行任何全球性分析时，应使用计算出的过铝花岗岩源岩的平均值来确定地壳的贡献。此外，我们的研究还强调了所观察到的趋势的广泛影响，包括地幔的逐渐污染及其δ18O值的升高。

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引用次数: 0

Pressure-Temperature-time paths from metapelites reveal Neoproterozoic continental crust underthrusting related to the West Gondwana amalgamation 来自元古岩的压力-温度-时间路径揭示了与西冈瓦纳混杂有关的新近纪大陆地壳下推作用

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-12 DOI: 10.1016/j.lithos.2024.107865

Alice Westin , Mahyra Tedeschi , Mario C. Campos Neto , George L. Luvizotto , Rafael G. Motta , Augusto G. Nobre , Rômulo A. Ando

In this contribution, we employed a petrochronological approach to investigate the tectonometamorphic evolution of Al-rich garnet-staurolite and garnet-staurolite-kyanite (biotite- and plagioclase-free) metapelites of the southernmost portion of the Neoproterozoic Brasília orogen. We have reconstructed the first prograde to peak pressure-temperature-time (P-T-t) paths reported for metamorphic units of the area, by combining petrographic analyses, quantitative compositional mapping of major elements, phase equilibrium modeling, and EPMA Th–U–Pb monazite chemical dating. The metamorphic reactions involved in the prograde metamorphic evolution are discussed, including the effects of garnet fractionation, exhaustion of reactants, and re-equilibration reactions on the major-element composition of garnet porphyroblasts, and their influence on P-T condition estimates. Raman spectroscopy on carbonaceous material (RSCM) thermometry provided insights into the synkinematic retrograde path. A steep prograde path marked by two stages is recorded by the garnet porphyroblasts of garnet-staurolite-muscovite (±kyanite) schists: (i) 555–585 °C and 0.60–0.90 GPa; (ii) 590–635 °C and 1.0–1.4 GPa. Monazite crystals record the prograde to peak path from ca. 630–625 Ma to ca. 605–595 Ma. Matrix graphite crystals suggest post-peak cooling to 400–500 °C concurrent with the late stages of development of the main foliation. The reconstructed P-T-t paths indicate an intermediate dT/dP metamorphism, and a burial rate of ∼0.55 km/Ma, with garnet compositional zoning suggesting that the high-pressure P-T-t path resulted from a single metamorphic event. The corresponding geothermal gradients, and in-situ ages, combined with regional evidence, suggest that peak metamorphic conditions were attained during collisional underthrusting of the continental crust related to the West Gondwana amalgamation.

在这篇论文中，我们采用岩石年代学方法研究了新新生代巴西利亚造山带最南端富铝石榴石-陶粒岩和石榴石-陶粒岩-榍石（不含生物岩和斜长石）变质岩的构造-变质演化。我们结合岩相分析、主要元素定量成分制图、相平衡建模和 EPMA Th-U-Pb monazite 化学年代测定，重建了该地区变质岩单位的首个从顺行到峰值的压力-温度-时间（P-T-t）路径。讨论了级变质演化过程中涉及的变质反应，包括石榴石分馏、反应物耗竭和再平衡反应对石榴石斑岩主要元素组成的影响，及其对 P-T 条件估算的影响。碳质材料上的拉曼光谱（RSCM）测温法提供了对同步逆行路径的深入了解。石榴石-白云石-莫斯卡维石（±斜长石）片岩的石榴石斑晶记录了两个阶段的陡峭逆行路径：(i) 555-585 °C，0.60-0.90 GPa；(ii) 590-635 °C，1.0-1.4 GPa。独居石晶体记录了从约 630-625 Ma 到约 605-595 Ma 的顺行至峰值路径。基质石墨晶体表明，峰后冷却至 400-500 °C，与主褶皱的后期发展阶段同时发生。重建的P-T-t路径显示了中间的dT/dP变质作用，埋藏率为∼0.55 km/Ma，石榴石成分分带表明高压P-T-t路径来自单一变质事件。相应的地热梯度和原位年龄，结合区域证据，表明变质峰值条件是在与西冈瓦纳混杂有关的大陆地壳碰撞下推过程中达到的。

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引用次数: 0

Tracking HFSE associated with high salinity fluid during HP metamorphism in the Zavkhan Terrane, Western Mongolia 追踪蒙古西部扎布汗地层在高压变质过程中与高盐度流体相关的高频震荡（HFSE

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-10 DOI: 10.1016/j.lithos.2024.107853

Manzshir Bayarbold , Atsushi Okamoto , Masaoki Uno , Otgonbayar Dandar , Mayuko Fukuyama , Geri Agroli , Noriyoshi Tsuchiya

Garnets often exhibit high concentrations of heavy rare-earth elements, which provide crucial insights into element mobility and fluid dynamics during metamorphism. This research reports on the distributions of trace and major elements in garnets from the Khungui eclogite of the Zavkhan Terrane in Western Mongolia. Within the eclogite sample, two types of garnets were identified, featuring dissimilar microstructures and compositional zoning: aggregate-type garnet with asymmetric zoning (Grt1) and euhedral garnet with concentric zoning (Grt2). Previous studies determined that Grt2 formation occurred in the pre-eclogite stage to eclogite facies (2.1–2.2 GPa and 580–610 °C), associated with the infiltration of high-saline fluids. The hexagonal-shaped pseudomorphs of Ti-bearing minerals associated with Grt1 suggest that the nucleation of titanite and garnet was simultaneously accelerated by the destabilization of Ti-augite during pre-eclogite metamorphism. This process could have contributed to the formation of aggregation textures, where Ti-bearing minerals are closely associated with Grt1 in the Khungui eclogite. Based on major divalent elemental composition zoning and trace element characteristics, both Grt1 and Grt2 in the Khungui eclogite are formed simultaneously from the pre-eclogite to eclogite stages. The cores (high Fe + Mg + Mn; Y + REE) of Grt1 and Grt2 are attributed to Rayleigh fractionation or a diffusion-limited uptake process. In contrast, the growth mechanisms of the Grt1 rim and Grt2 rim are distinct during the eclogite stage. The Grt1 rim is explained by a dissolution–reprecipitation, which resulted in the atoll texture observed in Grt1. The Grt2 rim (high Ca; low Y + REE) grew through a mechanism consistent with that of the Grt2 core. The major and trace element zonings of these garnets provide insights into element mobility related to Ti-bearing minerals and infiltration of high salinity fluids at different stages: (1) the mobilization of Ti and V increased under eclogite facies conditions (growth stage of garnet) compared to the pre-eclogite stage, with the mobility of Ti, Nb, Ta elements being pronounced under the exhumation stage (Rt–Ilm–Ttn2), possibly because of the infiltration of high-saline fluids and an increase in temperature, and (2) post-growth compositional modification of Grt1 was induced by a localized transport of Fe, Mg, Mn, and Ca elements in response to the replacement of ilmenite by titanite during decompression (0.1–0.5 GPa and 421–534 °C). The contrasting zoning of garnet in Khungui eclogite indicates dissimilar scales of element mobility under eclogite facies conditions (over a thin-section scale) and during decompression (up to several centimeters or beyond).

石榴石通常含有高浓度的重稀土元素，这为了解变质过程中元素的流动性和流体动力学提供了重要信息。本研究报告介绍了蒙古西部扎夫汗地层 Khungui 蚀变岩中石榴石的微量元素和主要元素的分布情况。在该斜长岩样本中，发现了两种类型的石榴石，它们具有不同的微观结构和成分分带：具有非对称分带的集合型石榴石（Grt1）和具有同心分带的八面体石榴石（Grt2）。之前的研究确定，Grt2 的形成是在夕闪岩前阶段到夕闪岩面（2.1-2.2 GPa 和 580-610 °C），与高碱性流体的渗入有关。与 Grt1 相关的六方形含钛矿物假象表明，在前沸石变质过程中，钛橄榄石和石榴石的成核同时被钛橄榄石的不稳定所加速。这一过程可能促成了聚集纹理的形成，在坤贵闪长岩中，含钛矿物与 Grt1 紧密相连。根据主要二价元素组成分带和微量元素特征，坤贵斜长岩中的Grt1和Grt2是在前斜长岩到斜长岩阶段同时形成的。Grt1和Grt2的核心（高铁+镁+锰；Y+稀土元素）归因于雷利分馏或扩散受限的吸收过程。相比之下，在辉绿岩阶段，Grt1 边缘和 Grt2 边缘的生长机制则截然不同。Grt1 边缘可解释为溶解再沉淀，这导致了在 Grt1 中观察到的环状纹理。Grt2 边缘（高 Ca；低 Y + REE）的生长机制与 Grt2 内核的生长机制一致。这些石榴石的主要元素和痕量元素分带提供了与含钛矿物和高盐度流体在不同阶段的渗透有关的元素流动性的见解：(1) 与前夕长岩阶段相比，在夕长岩面条件下（石榴石的生长阶段），Ti 和 V 元素的移动性增加，而在（Rt-Ilm-Ttn2）辉绿岩阶段，Ti、Nb、Ta 元素的移动性明显增加、(2) 在减压过程中，由于钛铁矿取代了钛铁矿，Fe、Mg、Mn 和 Ca 元素发生了局部迁移，从而引起了 Grt1 生长后成分的改变（0.1-0.5 GPa 和 421-534 °C）。坤贵斜长辉石中石榴石的对比分带表明，在斜长辉石面条件下（薄切片范围内）和减压过程中（长达几厘米或更远），元素移动的规模各不相同。

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引用次数: 0

Triassic–Jurassic alkaline magmatism in the Ivrea-Verbano Zone, Southern Alps: A zircon perspective on mantle sources and geodynamic significance 南阿尔卑斯山伊夫雷亚-韦尔巴诺区三叠纪-侏罗纪碱性岩浆活动：从锆石角度看地幔来源和地球动力学意义

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-11-08 DOI: 10.1016/j.lithos.2024.107854

Mattia Bonazzi , Abimbola C. Ogunyele , Tommaso Giovanardi , Maurizio Mazzucchelli , Alessandro Decarlis , Alessio Sanfilippo , Alberto Zanetti

The Ivrea-Verbano Zone (IVZ; western Southern Alps) consists of a distinctive sequence of the lower continental crust of the Adriatic plate, extending down to the subcontinental lithospheric mantle. It is characterized by a large variety of intrusive bodies of variable geochemical composition and age, offering a unique insight into the evolution of mantle-derived magmatism in post-collisional and extensional geodynamic settings. In this study, we characterize a suite of alkaline dykes intruding a mantle massif – the Finero Phlogopite Peridotite in northern IVZ. These dykes include zircon-bearing diorites and anorthosites, mainly composed by HFSE-rich amphibole and phlogopite, albite (>90 vol% in anorthosites) and apatite. Zircon, monazite, ilmenite, titanite, Nb-rich oxides, and carbonates are common accessory minerals. Additionally, a “composite” diorite dyke containing both HFSE-rich and HFSE-poor amphiboles was investigated. The study is aimed at providing new trace element, U-Pb geochronological and Lu-Hf isotopes dataset on zircon from these alkaline dykes, to refine the understanding of their mantle source characteristics, emplacement age and geodynamic implications. The trace element composition of zircons from the studied dykes points to segregation from melts with alkaline to ultra-alkaline affinity. Concordia U-Pb ages of zircon from the alkaline diorite dykes span from 221 to 191 Ma, which are interpreted as the result of multiple crystallization/recrystallization stages related to different magmatic pulses. Conversely, zircon from anorthosite and composite diorite dykes yield a narrow time range of 198–202 Ma, highlighting the occurrence of a magmatic pulse around ca. 200 Ma. The εHf_(t) values (+13.4 to +5.7) of zircon from the alkaline diorite dykes are significantly more positive compared to the values in those from anorthosite and composite diorite dykes (+4.2 to −0.4), suggesting that the parental melts were derived from heterogeneous asthenospheric mantle sources with low to moderate amount of recycled continental crust components. Our data and reappraisal of the literature indicate that the IVZ experienced a protracted period of alkaline magmatism from ca. 235 Ma to 185 Ma. The melts migrated along mantle shear zones during the Triassic-Jurassic lithospheric extension. Different pulses of alkaline magmatism were associated with relevant extensional tectonic stages recorded by the continental crust, presumably triggering a passive uplift of heterogenous asthenospheric reservoirs over a front of at least 500 km. This tectono-magmatic cycle is a precursor to the focused rifting stage which caused the opening of the Jurassic Alpine Tethys, enhancing Pangea fragmentation.

伊夫雷亚-韦尔巴诺区（Ivrea-Verbano Zone，南阿尔卑斯山西部）由亚得里亚海板块下部大陆地壳的一个独特序列组成，一直延伸到次大陆岩石圈地幔。其特点是有大量不同地球化学成分和年龄的侵入体，为了解碰撞后和伸展地球动力环境中地幔岩浆的演变提供了独特的视角。在这项研究中，我们描述了一套侵入地幔块体--位于IVZ北部的Finero辉绿岩橄榄岩--的碱性岩体的特征。这些岩体包括含锆石的闪长岩和正长岩，主要由富含HFSE的闪长岩和辉长岩、白云石（在正长岩中占90%）和磷灰石组成。锆石、独居石、钛铁矿、榍石、富铌氧化物和碳酸盐是常见的附属矿物。此外，还研究了一个 "复合 "闪长岩斜长岩，其中包含富含高频闪长岩和贫含高频闪长岩的闪长岩。该研究旨在为这些碱性岩堤中的锆石提供新的痕量元素、U-Pb地质年代和Lu-Hf同位素数据集，以完善对其地幔源特征、成岩年龄和地球动力学影响的认识。所研究堤坝中锆石的微量元素组成表明，这些锆石是从具有碱性至超碱性亲和力的熔体中分离出来的。来自碱性闪长岩堤的锆石的康科迪亚 U-Pb 年龄跨度为 221 至 191 Ma，可解释为与不同岩浆脉冲有关的多个结晶/再结晶阶段的结果。相反，从正长岩和复合闪长岩岩体中提取的锆石的时间范围很窄，为198-202 Ma，突显了大约200 Ma的岩浆脉冲。碱性闪长岩岩体锆石的εHf(t)值（+13.4至+5.7）与正长岩和复合闪长岩岩体锆石的εHf(t)值（+4.2至-0.4）相比明显偏正，表明母体熔体来自异质天体层地幔源，含有少量至中等量的再循环大陆地壳成分。我们的数据和对文献的重新评估表明，IVZ经历了从约235Ma到185Ma的漫长碱性岩浆活动期。在三叠纪-侏罗纪岩石圈延伸期间，熔融物沿着地幔剪切带迁移。不同的碱性岩浆活动脉冲与大陆地壳记录的相关延伸构造阶段相关联，可能引发了异质星震层储层在至少 500 公里的前沿被动隆升。这一构造-岩浆循环是造成侏罗纪阿尔卑斯特提斯开裂的集中裂解阶段的前兆，加剧了泛大陆的分裂。

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