Pub Date : 2024-10-25DOI: 10.1016/j.lithos.2024.107838
Guochao Chen , Xiaofei Zhang , Xianzhi Pei , Ruibao Li , Zuochen Li , Junqi Wei , Rongzhen Zhang
The petrogenesis and tectonic setting of early Paleozoic adakites and granitic pegmatites in the North Qinling orogenic belt are highly debated issues. Zircon UPb dating revealed that the Huichizi pluton is composed of the Early Silurian granodiorites, Late Silurian granodiorites, and Early Devonian granitic pegmatite dikes. The average εHf(t) value of pegmatite dikes was −2.8, which is lower than those of the Early Silurian (4.8) and Late Silurian granodiorites (5.1). It is worth noting that the Early Silurian and Late Silurian granodiorites exhibited adakitic characteristics and were formed through the partial melting of a thickened juvenile mafic lower crust. In addition, the Early Devonian pegmatite dikes displayed a substantial fractional crystallization. They were derived from the partial melting of mixed sources, including the crustal and mantle materials. The early Paleozoic adakitic rocks in the North Qinling orogenic belt can be categorized into four groups according to their c geochemical characteristics. The adakitic rocks of the first group (496–458 Ma) were rich in Na and exhibited extremely high εHf(t) values. They were formed by the partial melting of the Erlangping back-arc oceanic crust. The adakitic rocks of the second group (454–420 Ma) exhibited enriched Na or K contents and varying εHf(t) values. They were derived from the partial melting of a thickened lower crust with various mantle components, underplated by mafic magma formed during the subduction of the Shangdan Ocean. The adakites of the third (420–410 Ma) and fourth (410–400 Ma) groups were formed by the partial melting of a thickened lower crust under collisional and post-collisional settings, respectively.
{"title":"Silurian-devonian adakites and granitic pegmatitic dikes in North Qinling, China: Multi-stage magmatism and implications for the tectonic evolution","authors":"Guochao Chen , Xiaofei Zhang , Xianzhi Pei , Ruibao Li , Zuochen Li , Junqi Wei , Rongzhen Zhang","doi":"10.1016/j.lithos.2024.107838","DOIUrl":"10.1016/j.lithos.2024.107838","url":null,"abstract":"<div><div>The petrogenesis and tectonic setting of early Paleozoic adakites and granitic pegmatites in the North Qinling orogenic belt are highly debated issues. Zircon U<img>Pb dating revealed that the Huichizi pluton is composed of the Early Silurian granodiorites, Late Silurian granodiorites, and Early Devonian granitic pegmatite dikes. The average ε<sub>Hf</sub>(<em>t</em>) value of pegmatite dikes was −2.8, which is lower than those of the Early Silurian (4.8) and Late Silurian granodiorites (5.1). It is worth noting that the Early Silurian and Late Silurian granodiorites exhibited adakitic characteristics and were formed through the partial melting of a thickened juvenile mafic lower crust. In addition, the Early Devonian pegmatite dikes displayed a substantial fractional crystallization. They were derived from the partial melting of mixed sources, including the crustal and mantle materials. The early Paleozoic adakitic rocks in the North Qinling orogenic belt can be categorized into four groups according to their c geochemical characteristics. The adakitic rocks of the first group (496–458 Ma) were rich in Na and exhibited extremely high ε<sub>Hf</sub>(<em>t</em>) values. They were formed by the partial melting of the Erlangping back-arc oceanic crust. The adakitic rocks of the second group (454–420 Ma) exhibited enriched Na or K contents and varying ε<sub>Hf</sub>(<em>t</em>) values. They were derived from the partial melting of a thickened lower crust with various mantle components, underplated by mafic magma formed during the subduction of the Shangdan Ocean. The adakites of the third (420–410 Ma) and fourth (410–400 Ma) groups were formed by the partial melting of a thickened lower crust under collisional and post-collisional settings, respectively.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"490 ","pages":"Article 107838"},"PeriodicalIF":2.9,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658366","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}
Pub Date : 2024-10-24DOI: 10.1016/j.lithos.2024.107843
C.G.C. Patten , M. Junge , R. Coltat , A.P. Jesus , A. Beranoaguire , P. Tropper , J. Alt
Seafloor massive sulfide (SMS) deposits at slow and ultra-slow spreading ridges are often spatially related to, or hosted in oceanic core complexes (OCCs). The specific oceanic crust architecture, magmatism, hydrothermal fluid circulation and lithologies at OCCs, however, imply different S and metal (e.g. Cu, Zn, Co, Ni) fluxes relative to well-structured oceanic crust at-fast spreading ridges and which are not yet fully constrained. The study of S and metal distribution in the ODP Hole 735B deep drill core from the Atlantis bank allows to understand these fluxes along detachment faults and to better constrain the source zone of S and metals for OCC-related SMS deposits. Significant depletion of S, Cu, Zn and Ni are observed within the upper 250 m of the drill core where intense deformation and hydrothermal fluid circulation occurred. During the complex tectono-magmatic-hydrothermal evolution of the Atlantis Bank, four important stages are recognized for S and metal mobilization: 1) magmatic stratification leading to a higher proportion of sulfide-rich and S, Cu, Zn and Co fertile oxide gabbros in the root zone of the Atlantis Bank detachment, 2) high temperature ductile deformation leading to magmatic sulfide reworking and onset of sulfide leaching with limited metal mobilization, 3) extensive sulfide leaching and metal mobilization during amphibolite to greenschist facies metasomatism and, 4) late stage secondary sulfide precipitation and S enrichment during low temperature fluid circulation. Mass balance calculations from the source zones of the Atlantis Bank detachment highlights that metal mobilization during hydrothermal alteration of gabbroic rocks along detachment faults can fully account for the formation of OCC-related SMS deposits at slow and ultraslow spreading ridges. The Atlantis Bank detachment system, however, is gabbroic-dominated and represent the magmatic end-member of OCCs and further work is necessary for understanding metal fluxes in ultramafic-dominated detachment systems.
慢扩张海脊和超慢扩张海脊的海底块状硫化物（SMS）矿床通常与大洋核心复合体（OCCs）在空间上相关，或位于大洋核心复合体中。然而，大洋核心复合体的特定大洋地壳结构、岩浆活动、热液循环和岩性，意味着与快速扩张海脊上结构良好的大洋地壳相比，具有不同的S和金属（如铜、锌、钴、镍）通量，而这些通量尚未得到充分制约。通过对亚特兰蒂斯岩滩 ODP 735B 号钻孔深部岩芯中的锰和金属分布的研究，可以了解沿脱落断层的锰和金属通量，更好地确定与 OCC 有关的 SMS 沉积的锰和金属源区。在钻探岩芯上部 250 米处观察到了 S、Cu、Zn 和 Ni 的严重损耗，这里发生了强烈的变形和热液循环。在亚特兰蒂斯岩滩复杂的构造-岩浆-热液演化过程中，S 和金属的移动分为四个重要阶段：1）岩浆分层导致亚特兰蒂斯岩滩脱离体根部区域富含硫化物和 S、Cu、Zn 和 Co 的肥沃氧化辉长岩比例增加；2）高温韧性变形导致岩浆硫化物再加工和硫化物浸出的开始，但金属移动有限；3）广泛的硫化物浸出和热液循环导致亚特兰蒂斯岩滩脱离体根部区域富含硫化物和 S、Cu、Zn 和 Co 的肥沃氧化辉长岩比例增加、3) 在闪长岩向绿泥石岩相变质过程中，硫化物广泛沥滤并动员金属；以及 4) 在低温流体循环过程中，晚期次生硫化物沉淀和 S 富集。对亚特兰蒂斯岸剥离源区进行的质量平衡计算表明，沿剥离断层的辉长岩热液蚀变过程中的金属移动完全可以解释慢速和超慢速扩张脊上与 OCC 有关的 SMS 矿床的形成。然而，亚特兰蒂斯岸剥离系统以辉长岩为主，代表了OCC的岩浆末端成分，要了解以超基性岩为主的剥离系统中的金属通量，还需要开展进一步的工作。
{"title":"Sulfur and metal mobilization during the life cycle of an oceanic core complex: Implications for seafloor massive sulfide deposits formation at slow and ultra-slow spreading ridges","authors":"C.G.C. Patten , M. Junge , R. Coltat , A.P. Jesus , A. Beranoaguire , P. Tropper , J. Alt","doi":"10.1016/j.lithos.2024.107843","DOIUrl":"10.1016/j.lithos.2024.107843","url":null,"abstract":"<div><div>Seafloor massive sulfide (SMS) deposits at slow and ultra-slow spreading ridges are often spatially related to, or hosted in oceanic core complexes (OCCs). The specific oceanic crust architecture, magmatism, hydrothermal fluid circulation and lithologies at OCCs, however, imply different S and metal (e.g. Cu, Zn, Co, Ni) fluxes relative to well-structured oceanic crust at-fast spreading ridges and which are not yet fully constrained. The study of S and metal distribution in the ODP Hole 735B deep drill core from the Atlantis bank allows to understand these fluxes along detachment faults and to better constrain the source zone of S and metals for OCC-related SMS deposits. Significant depletion of S, Cu, Zn and Ni are observed within the upper 250 m of the drill core where intense deformation and hydrothermal fluid circulation occurred. During the complex tectono-magmatic-hydrothermal evolution of the Atlantis Bank, four important stages are recognized for S and metal mobilization: 1) magmatic stratification leading to a higher proportion of sulfide-rich and S, Cu, Zn and Co fertile oxide gabbros in the root zone of the Atlantis Bank detachment, 2) high temperature ductile deformation leading to magmatic sulfide reworking and onset of sulfide leaching with limited metal mobilization, 3) extensive sulfide leaching and metal mobilization during amphibolite to greenschist facies metasomatism and, 4) late stage secondary sulfide precipitation and S enrichment during low temperature fluid circulation. Mass balance calculations from the source zones of the Atlantis Bank detachment highlights that metal mobilization during hydrothermal alteration of gabbroic rocks along detachment faults can fully account for the formation of OCC-related SMS deposits at slow and ultraslow spreading ridges. The Atlantis Bank detachment system, however, is gabbroic-dominated and represent the magmatic end-member of OCCs and further work is necessary for understanding metal fluxes in ultramafic-dominated detachment systems.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"490 ","pages":"Article 107843"},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572700","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}
Pub Date : 2024-10-24DOI: 10.1016/j.lithos.2024.107839
Anna Nikolenko , Christian Schmidt , Melanie J. Sieber , Valby van Schijndel , Ilya V. Veksler
Eudialyte-group minerals (EGM) are unique tracers of peralkaline silica-undersaturated melts. They receive global interest as potential resources for high-field-strength elements (HFSE, e.g., Zr, Nb, Ta) and rare-earth elements (REE), which are critical materials for modern technologies. The main condition for magmatic crystallization of EGM in general is that the concentration of Zr in the parental melt should reach saturation. The solubility of EGM in peralkaline melts from the system Na2O–CaO–Al2O3–SiO2 ± H2O at temperatures between 750 and 1000 °C and pressures of 100 and 200 MPa was investigated. Newly formed crystalline phases in the run products are EGM grains, parakeldyshite and albite. EGM are stable between 750 and 900 °C, and melt incongruently to parakeldyshite between 900 and 1000 °C. EGM crystallization from peralkaline silica-undersaturated melts at nominally dry conditions and 750–850 °C requires a minimum of 0.2–0.22 wt% ZrO2 in the melt. In experiments with the addition of H2O, saturation is attained at much higher ZrO2 concentrations (1.1–2.85 wt%) in the same temperature interval. REE and HFSE are strongly compatible with eudialyte-group minerals as the EGM-melt distribution coefficients (D) vary from 2 to 90 with falling temperature. The lowest D values are observed in experiments with the highest Zr solubility, i.e., at high temperature and in hydrated compositions. Light REE and especially La tend to have lower D values than the heavy REE.
{"title":"Magmatic stability of eudialyte-group minerals (EGM) and element distribution between EGM and peralkaline silica-undersaturated melts","authors":"Anna Nikolenko , Christian Schmidt , Melanie J. Sieber , Valby van Schijndel , Ilya V. Veksler","doi":"10.1016/j.lithos.2024.107839","DOIUrl":"10.1016/j.lithos.2024.107839","url":null,"abstract":"<div><div>Eudialyte-group minerals (EGM) are unique tracers of peralkaline silica-undersaturated melts. They receive global interest as potential resources for high-field-strength elements (HFSE, e.g., Zr, Nb, Ta) and rare-earth elements (REE), which are critical materials for modern technologies. The main condition for magmatic crystallization of EGM in general is that the concentration of Zr in the parental melt should reach saturation. The solubility of EGM in peralkaline melts from the system Na<sub>2</sub>O–CaO–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> ± H<sub>2</sub>O at temperatures between 750 and 1000 °C and pressures of 100 and 200 MPa was investigated. Newly formed crystalline phases in the run products are EGM grains, parakeldyshite and albite. EGM are stable between 750 and 900 °C, and melt incongruently to parakeldyshite between 900 and 1000 °C. EGM crystallization from peralkaline silica-undersaturated melts at nominally dry conditions and 750–850 °C requires a minimum of 0.2–0.22 wt% ZrO<sub>2</sub> in the melt. In experiments with the addition of H<sub>2</sub>O, saturation is attained at much higher ZrO<sub>2</sub> concentrations (1.1–2.85 wt%) in the same temperature interval. REE and HFSE are strongly compatible with eudialyte-group minerals as the EGM-melt distribution coefficients (<em>D</em>) vary from 2 to 90 with falling temperature. The lowest <em>D</em> values are observed in experiments with the highest Zr solubility, i.e., at high temperature and in hydrated compositions. Light REE and especially La tend to have lower <em>D</em> values than the heavy REE.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"490 ","pages":"Article 107839"},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593514","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}
Pub Date : 2024-10-24DOI: 10.1016/j.lithos.2024.107842
Thi Huong Ngo , Tatyana V. Svetlitskaya , Tuan Anh Tran , Andrey E. Izokh , Peter A. Nevolko , Trong Hoa Tran , Hoàng Ly Vũ , Thi Phuong Ngo
The Song Hien region is located at the southern margin of the South China Block and includes Early–Middle Triassic mafic suites. The petrogenesis and tectonic context of these rocks are important to comprehending one of the most challenging periods in the tectonic evolution of northern Vietnam related to the South China–Indochina collision. In the present study, we provide the first systematic examination of whole-rock geochemical and SrNd isotopic compositions of mafic suites from the NE Vietnam. The studied Early–Middle Triassic suites are dominated by basalts. The rocks are enriched in LILEs, U, and Th and depleted in Nb and Ta and show a wide range of geochemical and SrNd isotopic compositions ((La/Yb)CN = 0.4–4.6; Dy/Dy⁎ = 0.7–1.3; (87Sr/86Sr)i = 0.7053–0.7125; εNd(t) = (+3.7)–(−8.0)). They all originated from shallow melting of a subduction-modified lithospheric mantle, and the compositional diversity of these basalts is attributed mainly to geochemical and Nd-isotopic heterogeneity in the mantle source. The geochemical and SrNd isotopic features of the studied mafic suites indicate a negligible contribution of the asthenospheric mantle to magma generation and differ significantly from those of the Emeishan plume-related basalts. A model in which Early–Middle Triassic mafic magmatic activity in the NE Vietnam region is the result of decompression melting driven by convective thinning of the South China mantle lithosphere during the 250–240 Ma period is discussed in the study. This period corresponds to the South China–Indochina continental collision. In the NE Vietman region, the Early–Middle Triassic syn-collisional magmatism has an important metallogenic context, controlling NiCu sulfide and Sn(Cu) mineralizations.
{"title":"Indosinian magmatism in NE Vietnam: Petrogenesis and geodynamic implications of Triassic mafic suites from the Song Hien region","authors":"Thi Huong Ngo , Tatyana V. Svetlitskaya , Tuan Anh Tran , Andrey E. Izokh , Peter A. Nevolko , Trong Hoa Tran , Hoàng Ly Vũ , Thi Phuong Ngo","doi":"10.1016/j.lithos.2024.107842","DOIUrl":"10.1016/j.lithos.2024.107842","url":null,"abstract":"<div><div>The Song Hien region is located at the southern margin of the South China Block and includes Early–Middle Triassic mafic suites. The petrogenesis and tectonic context of these rocks are important to comprehending one of the most challenging periods in the tectonic evolution of northern Vietnam related to the South China–Indochina collision. In the present study, we provide the first systematic examination of whole-rock geochemical and Sr<img>Nd isotopic compositions of mafic suites from the NE Vietnam. The studied Early–Middle Triassic suites are dominated by basalts. The rocks are enriched in LILEs, U, and Th and depleted in Nb and Ta and show a wide range of geochemical and Sr<img>Nd isotopic compositions ((La/Yb)<sub>CN</sub> = 0.4–4.6; Dy/Dy<sup>⁎</sup> = 0.7–1.3; (<sup>87</sup>Sr/<sup>86</sup>Sr)<em>i</em> = 0.7053–0.7125; <em>ε</em>Nd(t) = (+3.7)–(−8.0)). They all originated from shallow melting of a subduction-modified lithospheric mantle, and the compositional diversity of these basalts is attributed mainly to geochemical and Nd-isotopic heterogeneity in the mantle source. The geochemical and Sr<img>Nd isotopic features of the studied mafic suites indicate a negligible contribution of the asthenospheric mantle to magma generation and differ significantly from those of the Emeishan plume-related basalts. A model in which Early–Middle Triassic mafic magmatic activity in the NE Vietnam region is the result of decompression melting driven by convective thinning of the South China mantle lithosphere during the 250–240 Ma period is discussed in the study. This period corresponds to the South China–Indochina continental collision. In the NE Vietman region, the Early–Middle Triassic <em>syn</em>-collisional magmatism has an important metallogenic context, controlling Ni<img>Cu sulfide and Sn(<img>Cu) mineralizations.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107842"},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142551923","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}
Pub Date : 2024-10-24DOI: 10.1016/j.lithos.2024.107841
Stefano Tenuta , Katy A. Evans , Steven M. Reddy , David W. Saxey , Tommaso Tacchetto , Denis Fougerouse , Xiao Sun
Serpentinites record processes that redistribute major and trace elements between mantle and crust. Platinum Group Elements (PGEs) are trace elements in serpentinites hosted in sulphides and alloys. Alloys are challenging to find, and most analytical techniques lack the spatial resolution to analyse them. This research adopts automatic mineral mapping technique to detect PGM grains in a sample from the Wadi Tayin (Oman) peridotite and uses atom probe tomography, a nanoscale quantitative analytical technique, to analyse the grain. This work applies and assesses the applicability of atom probe tomography to measure the 187Os/188Os isotopic ratio of natural alloys and uses the ratio to constrain the source of Os. A novel algorithm is used to automatically determine the number of counts of the 187Os and 188Os peaks, to calculate the isotopic 187Os/188Os ratio and the analytical uncertainty. The 187Os/188Os ratio is 0.126 ± 0.003, consistent with the isotopic composition reported by literature in the dunite of the Main Mantle Section of the Wadi Tayin ophiolite.
The analytical uncertainty is one order of magnitude higher than conventional bulk rock techniques, such as negative-thermal ionisation mass spectrometry (N-TIMS) and inductively coupled plasma mass spectrometry (ICP-MS). However, the precision is sufficient to conclude that the non-radiogenic 187Os/188Os ratio is compatible with a mantle origin for the alloy. Decreasing whole-rock Re with increasing LOI and the overprinting of magmatic pentlandite by magnetite demonstrate that progressive serpentinisation may have modified the Re budget. The results indicate that atom probe tomography can analyse 187Os/188Os ratio quantitatively in micron-sized natural alloys and provide insights into natural processes.
蛇绿岩记录了主要元素和微量元素在地幔和地壳之间重新分布的过程。铂族元素（PGEs）是蛇纹岩中以硫化物和合金形式存在的微量元素。合金的发现具有挑战性，大多数分析技术缺乏分析合金的空间分辨率。本研究采用自动矿物制图技术检测瓦迪塔因（阿曼）橄榄岩样本中的 PGM 晶粒，并使用纳米级定量分析技术原子探针断层扫描来分析晶粒。这项工作应用原子探针层析技术测量天然合金的 187Os/188Os 同位素比值，并对其适用性进行了评估。研究采用了一种新颖的算法，自动确定 187Os 和 188Os 峰的计数次数，计算出同位素 187Os/188Os 比率和分析不确定性。187Os/188Os 比率为 0.126 ± 0.003，与文献报道的瓦迪塔伊因蛇绿岩主幔段云英岩的同位素组成一致。分析不确定性比传统的块岩技术（如负热电离质谱法（N-TIMS）和电感耦合等离子体质谱法（ICP-MS））高一个数量级。然而，精确度足以得出结论：非辐射成因的 187Os/188Os 比值与合金的地幔成因相符。全岩 Re 随 LOI 的增加而降低，以及磁铁矿对岩浆戊铁矿的覆盖，表明蛇绿岩化可能改变了 Re 的预算。研究结果表明，原子探针层析技术可以定量分析微米级天然合金中的 187Os/188Os 比率，并提供对天然过程的深入了解。
{"title":"Nanoscale Os isotopic quantification of Wadi Tayin dunite platinum group minerals by atom probe tomography","authors":"Stefano Tenuta , Katy A. Evans , Steven M. Reddy , David W. Saxey , Tommaso Tacchetto , Denis Fougerouse , Xiao Sun","doi":"10.1016/j.lithos.2024.107841","DOIUrl":"10.1016/j.lithos.2024.107841","url":null,"abstract":"<div><div>Serpentinites record processes that redistribute major and trace elements between mantle and crust. Platinum Group Elements (PGEs) are trace elements in serpentinites hosted in sulphides and alloys. Alloys are challenging to find, and most analytical techniques lack the spatial resolution to analyse them. This research adopts automatic mineral mapping technique to detect PGM grains in a sample from the Wadi Tayin (Oman) peridotite and uses atom probe tomography, a nanoscale quantitative analytical technique, to analyse the grain. This work applies and assesses the applicability of atom probe tomography to measure the <sup>187</sup>Os/<sup>188</sup>Os isotopic ratio of natural alloys and uses the ratio to constrain the source of Os. A novel algorithm is used to automatically determine the number of counts of the <sup>187</sup>Os and <sup>188</sup>Os peaks, to calculate the isotopic <sup>187</sup>Os/<sup>188</sup>Os ratio and the analytical uncertainty. The <sup>187</sup>Os/<sup>188</sup>Os ratio is 0.126 ± 0.003, consistent with the isotopic composition reported by literature in the dunite of the Main Mantle Section of the Wadi Tayin ophiolite.</div><div>The analytical uncertainty is one order of magnitude higher than conventional bulk rock techniques, such as negative-thermal ionisation mass spectrometry (N-TIMS) and inductively coupled plasma mass spectrometry (ICP-MS). However, the precision is sufficient to conclude that the non-radiogenic <sup>187</sup>Os/<sup>188</sup>Os ratio is compatible with a mantle origin for the alloy. Decreasing whole-rock Re with increasing LOI and the overprinting of magmatic pentlandite by magnetite demonstrate that progressive serpentinisation may have modified the Re budget. The results indicate that atom probe tomography can analyse <sup>187</sup>Os/<sup>188</sup>Os ratio quantitatively in micron-sized natural alloys and provide insights into natural processes.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107841"},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142552113","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}
Pub Date : 2024-10-24DOI: 10.1016/j.lithos.2024.107844
Yu Zhang , Qichao Zhang , Xin Wang
The Western Kunlun Orogenic Belt (WKOB), along the northwestern margin of the Qinghai–Xizang Plateau, was formed by the collision of Gondwana-derived terranes to the south and the Tarim Block to the north and was closely associated with closure of the Proto-Tethys Ocean during the late Neoproterozoic to early Paleozoic. We present a combined zircon UPb geochronology, whole-rock composition, and Sr–Nd–Hf isotopic study of syn-collisional granitoid plutons and mafic microgranular enclaves (MMEs) in the region. Zircon UPb dating yields ages of 443.8 ± 4.4, 451.9 ± 4.2, 462.9 ± 3.5, and 456 ± 4.2 Ma for the Tongayoupuagezi, Shanjie, and Pishigai plutons and MMEs from the Pishigai pluton, respectively. The granitoids are metaluminous to weakly peraluminous (A/CNK = 1.00–1.17) and belong to the high-K calc-alkaline series. They have (87Sr/86Sr)i ratios of 0.7058–0.7154, εNd(t) values of −8.78 to −0.93, and εHf(t) values of −19.72 to +6.87. The MMEs have variable SiO2 contents (45.7–60.2 wt%) and are more mafic than the host granitoids, but have similar Sr–Nd–Hf isotopic compositions to the host granitoids [(87Sr/86Sr)i = 0.7102–0.7110; εNd(t) = −6.57 to −3.56; εHf(t) = −7.17 to −1.81]. The MMEs are fragments of cumulates formed during the early stages of magma evolution. The granitoids were produced by the partial melting of a mélange source. The new data support the view that the Middle–Late Ordovician syn-collisional granitoids with MMEs distributed along the WKOB represent a magmatic response to terrane collision. This suggests that juvenile crustal growth in older orogenic systems, which occurs by arc addition, also involves some vertical addition during the final stage of orogenic collision. Our study suggests that mélange diaper melting is a key mechanism of crustal growth during the syn-collision stage in continental collision zones, associated with slab breakoff.
西昆仑造山带（WKOB）位于青藏高原西北边缘，由南面的冈瓦纳地块和北面的塔里木地块碰撞形成，与新元古代晚期至古生代早期原特提斯洋的关闭密切相关。我们对该地区的同步碰撞花岗岩柱岩和岩浆岩微晶飞地（MMEs）进行了锆石UPb地质年代、全岩成分和Sr-Nd-Hf同位素综合研究。锆石UPb测年结果显示，汤峪铺盖子、上街和皮石盖岩块体以及来自皮石盖岩块体的MMEs的年龄分别为443.8±4.4、451.9±4.2、462.9±3.5和456±4.2Ma。这些花岗岩为金属铝质至弱过铝质（A/CNK = 1.00-1.17），属于高K钙碱性系列。它们的（87Sr/86Sr）i比值为0.7058-0.7154，εNd（t）值为-8.78至-0.93，εHf（t）值为-19.72至+6.87。MMEs具有不同的SiO2含量（45.7-60.2 wt%），比主花岗岩的岩浆性更强，但具有与主花岗岩相似的Sr-Nd-Hf同位素组成[(87Sr/86Sr)i = 0.7102-0.7110; εNd(t) = -6.57 to -3.56; εHf(t) = -7.17 to -1.81] 。MMEs是岩浆演化早期形成的堆积物碎片。花岗岩是由混合岩源部分熔融产生的。新数据支持这样一种观点，即沿西九龙龙骨山脉分布的中-晚奥陶世同碰撞花岗岩与MMEs是岩浆对陆相碰撞的反应。这表明，在造山运动的最后阶段，老造山运动系统中的幼年地壳增长（通过弧加成发生）也涉及一些垂直加成。我们的研究表明，在大陆碰撞带的同步碰撞阶段，与板块断裂相关的熔岩蜕变是地壳生长的一个关键机制。
{"title":"Petrogenesis of early Paleozoic syn-collisional granitoids and enclaves in Western Kunlun, Northwest China: Implications for the growth of continental crust","authors":"Yu Zhang , Qichao Zhang , Xin Wang","doi":"10.1016/j.lithos.2024.107844","DOIUrl":"10.1016/j.lithos.2024.107844","url":null,"abstract":"<div><div>The Western Kunlun Orogenic Belt (WKOB), along the northwestern margin of the Qinghai–Xizang Plateau, was formed by the collision of Gondwana-derived terranes to the south and the Tarim Block to the north and was closely associated with closure of the Proto-Tethys Ocean during the late Neoproterozoic to early Paleozoic. We present a combined zircon U<img>Pb geochronology, whole-rock composition, and Sr–Nd–Hf isotopic study of syn-collisional granitoid plutons and mafic microgranular enclaves (MMEs) in the region. Zircon U<img>Pb dating yields ages of 443.8 ± 4.4, 451.9 ± 4.2, 462.9 ± 3.5, and 456 ± 4.2 Ma for the Tongayoupuagezi, Shanjie, and Pishigai plutons and MMEs from the Pishigai pluton, respectively. The granitoids are metaluminous to weakly peraluminous (A/CNK = 1.00–1.17) and belong to the high-K calc-alkaline series. They have (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub> ratios of 0.7058–0.7154, ε<sub>Nd</sub>(t) values of −8.78 to −0.93, and ε<sub>Hf</sub>(t) values of −19.72 to +6.87. The MMEs have variable SiO<sub>2</sub> contents (45.7–60.2 wt%) and are more mafic than the host granitoids, but have similar Sr–Nd–Hf isotopic compositions to the host granitoids [(<sup>87</sup>Sr/<sup>86</sup>Sr)<sub><em>i</em></sub> = 0.7102–0.7110; ε<sub>Nd</sub>(t) = −6.57 to −3.56; ε<sub>Hf</sub>(t) = −7.17 to −1.81]. The MMEs are fragments of cumulates formed during the early stages of magma evolution. The granitoids were produced by the partial melting of a mélange source. The new data support the view that the Middle–Late Ordovician syn-collisional granitoids with MMEs distributed along the WKOB represent a magmatic response to terrane collision. This suggests that juvenile crustal growth in older orogenic systems, which occurs by arc addition, also involves some vertical addition during the final stage of orogenic collision. Our study suggests that mélange diaper melting is a key mechanism of crustal growth during the syn-collision stage in continental collision zones, associated with slab breakoff.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107844"},"PeriodicalIF":2.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142551922","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}
<div><div>The Howley Islands intrusions consist of three coarse-grained amphibole-phlogopite/biotite quartz gabbro dykes and one medium-grained amphibole-biotite quartz diorite body that cut rocks of the Exploits Subzone in central Newfoundland along strike from the multi-million-ounce Valentine gold deposits. The petrogeneses and ages of these rocks were investigated to better constrain the process evolution of the orogenic gold belt that extends for more than 200 km across central Newfoundland.</div><div>The quartz gabbro dykes are composed of magnesio-ferri-hornblende-cummingtonite-phlogopite/biotite macrocrysts mantled by plagioclase (labradorite to oligoclase)-quartz coronas. The gabbros are LILE- and LREE-enriched, transitional arc-like rocks that formed from a different melt source and parental magma than the quartz diorite body. The quartz diorite is plagioclase-rich (50 modal % andesine), contains only trace cummingtonite, lacks phlogopite, and preserves rare diopside overgrown by magnesio-ferri-hornblende. This intrusion is more alkaline and OIB-like than the quartz gabbros and exhibits the influence of a deeper, more enriched mantle component, although both melts variably interacted with deep lithosphere. The quartz gabbro dykes and quartz diorite body may represent melts of the lower lithosphere and upper asthenosphere, respectively.</div><div>The abundance of coarse- to medium-grained amphibole and phlogopite/biotite in the samples is consistent with crystallization of hydrous magmas and rapid, water-enhanced crystal growth, with cooling paths recorded by chemically zoned grains of magnesio-ferri-hornblende and plagioclase. One quartz gabbro displays reverse core to rim chemical zoning of plagioclase from andesine to labradorite, which may reflect decreasing pressure during magma ascent and crystallization, magma mixing of evolved and more primitive magmas, and/or fluctuations in H<sub>2</sub>O content. The presence of cummingtonite suggests crystallization at relatively low temperatures in shallow, low-pressure, upper crustal magma chambers. The quartz gabbros may represent melts equivalent to the nearby Howley Islands gabbro body, whereas the quartz diorite may represent a plagioclase cumulate along the margin of another melt chamber.</div><div>U-Pb CA-ID-TIMS zircon geochronology yielded ages of ca. 400.3 Ma for the gabbro dykes and 399.9 Ma for the quartz diorite intrusion, within the ca. 410–377 Ma age range for mineralization of the nearby Valentine gold deposits. The ca. 400 Ma intrusions, when considered in conjunction with regional models, reflect melting and hydrous magmatism in the mantle wedge above a retreating Avalonian slab that was dehydrating during the Acadian orogenic cycle. The coincidence of Pridoli (ca. 422 Ma) to Emsian (ca. 400 Ma) bimodal magmatism and orogenic gold mineralization in central Newfoundland reflects more than twenty million years of high geothermal gradients and fluid flow, which when combined w
{"title":"Petrogenesis and high-precision U-Pb zircon geochronology of the Howley Islands intrusions, Central Newfoundland Appalachians: Hydrous magmatism of Emsian age (ca. 400 Ma) along a multi-million-ounce orogenic gold belt","authors":"I.W. Honsberger , H.A.I. Sandeman , S.L. Kamo , W. Bleeker","doi":"10.1016/j.lithos.2024.107837","DOIUrl":"10.1016/j.lithos.2024.107837","url":null,"abstract":"<div><div>The Howley Islands intrusions consist of three coarse-grained amphibole-phlogopite/biotite quartz gabbro dykes and one medium-grained amphibole-biotite quartz diorite body that cut rocks of the Exploits Subzone in central Newfoundland along strike from the multi-million-ounce Valentine gold deposits. The petrogeneses and ages of these rocks were investigated to better constrain the process evolution of the orogenic gold belt that extends for more than 200 km across central Newfoundland.</div><div>The quartz gabbro dykes are composed of magnesio-ferri-hornblende-cummingtonite-phlogopite/biotite macrocrysts mantled by plagioclase (labradorite to oligoclase)-quartz coronas. The gabbros are LILE- and LREE-enriched, transitional arc-like rocks that formed from a different melt source and parental magma than the quartz diorite body. The quartz diorite is plagioclase-rich (50 modal % andesine), contains only trace cummingtonite, lacks phlogopite, and preserves rare diopside overgrown by magnesio-ferri-hornblende. This intrusion is more alkaline and OIB-like than the quartz gabbros and exhibits the influence of a deeper, more enriched mantle component, although both melts variably interacted with deep lithosphere. The quartz gabbro dykes and quartz diorite body may represent melts of the lower lithosphere and upper asthenosphere, respectively.</div><div>The abundance of coarse- to medium-grained amphibole and phlogopite/biotite in the samples is consistent with crystallization of hydrous magmas and rapid, water-enhanced crystal growth, with cooling paths recorded by chemically zoned grains of magnesio-ferri-hornblende and plagioclase. One quartz gabbro displays reverse core to rim chemical zoning of plagioclase from andesine to labradorite, which may reflect decreasing pressure during magma ascent and crystallization, magma mixing of evolved and more primitive magmas, and/or fluctuations in H<sub>2</sub>O content. The presence of cummingtonite suggests crystallization at relatively low temperatures in shallow, low-pressure, upper crustal magma chambers. The quartz gabbros may represent melts equivalent to the nearby Howley Islands gabbro body, whereas the quartz diorite may represent a plagioclase cumulate along the margin of another melt chamber.</div><div>U-Pb CA-ID-TIMS zircon geochronology yielded ages of ca. 400.3 Ma for the gabbro dykes and 399.9 Ma for the quartz diorite intrusion, within the ca. 410–377 Ma age range for mineralization of the nearby Valentine gold deposits. The ca. 400 Ma intrusions, when considered in conjunction with regional models, reflect melting and hydrous magmatism in the mantle wedge above a retreating Avalonian slab that was dehydrating during the Acadian orogenic cycle. The coincidence of Pridoli (ca. 422 Ma) to Emsian (ca. 400 Ma) bimodal magmatism and orogenic gold mineralization in central Newfoundland reflects more than twenty million years of high geothermal gradients and fluid flow, which when combined w","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107837"},"PeriodicalIF":2.9,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142551880","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}
Pub Date : 2024-10-22DOI: 10.1016/j.lithos.2024.107840
Wiktoria Gmochowska , Ewa Słaby , Anna Gumsley , Gabriela A. Kozub-Budzyń , Sourabh Bhattacharya
Titanite is often used to describe the path of igneous, metamorphic, and hydrothermal processes. Therefore, titanite can unravel the multistage magmatic and post-magmatic evolution of granitoids. In this study, we present a comprehensive study of the ca. 2.57–2.51 Ga Closepet Batholith in the Dharwar Craton of southern India using titanite. This granitoid body provides a unique opportunity as various structural levels of the batholith are continuously outcropping. The textural and geochemical studies of titanite, supported by UPb isotopic dating, allowed us to distinguish five generations of magmatic and hydrothermal titanite. Three types of magmatic titanite demonstrate stage-growth crystallization (type I) and a change from reduced, high-temperature (type II) to oxidised, low-temperature conditions (type III). Hydrothermal titanite is recorded as altered titanite with zoned to patchy textures and secondary fractures and veinlets (type IV) and titanite inclusions within biotite (type V). Hydrothermal titanite (type IV) shows depletion in rare earth elements and high-field strength elements, indicating mobilization of those elements by a fluid. UPb dating by LA-ICP-MS of magmatic titanite type I yielded ages of ca. 2.5 Ga, consistent with the timing of formation of the Closepet Batholith. The relationship between titanite textures and chemistry indicates that titanite serves as a recorder of the multistage magmatic and post-magmatic evolution of the Closepet Batholith. In addition, our study shows that hydrothermal activity affected a large area, with fluids circulating over long distances within the upper structural levels of the Closepet Batholith.
{"title":"Multistage magmatic and post-magmatic evolution of the Neoarchaean Closepet Batholith of Dharwar Craton in southern India - insights from the texture and chemical composition of titanite","authors":"Wiktoria Gmochowska , Ewa Słaby , Anna Gumsley , Gabriela A. Kozub-Budzyń , Sourabh Bhattacharya","doi":"10.1016/j.lithos.2024.107840","DOIUrl":"10.1016/j.lithos.2024.107840","url":null,"abstract":"<div><div>Titanite is often used to describe the path of igneous, metamorphic, and hydrothermal processes. Therefore, titanite can unravel the multistage magmatic and post-magmatic evolution of granitoids. In this study, we present a comprehensive study of the ca. 2.57–2.51 Ga Closepet Batholith in the Dharwar Craton of southern India using titanite. This granitoid body provides a unique opportunity as various structural levels of the batholith are continuously outcropping. The textural and geochemical studies of titanite, supported by U<img>Pb isotopic dating, allowed us to distinguish five generations of magmatic and hydrothermal titanite. Three types of magmatic titanite demonstrate stage-growth crystallization (type I) and a change from reduced, high-temperature (type II) to oxidised, low-temperature conditions (type III). Hydrothermal titanite is recorded as altered titanite with zoned to patchy textures and secondary fractures and veinlets (type IV) and titanite inclusions within biotite (type V). Hydrothermal titanite (type IV) shows depletion in rare earth elements and high-field strength elements, indicating mobilization of those elements by a fluid. U<img>Pb dating by LA-ICP-MS of magmatic titanite type I yielded ages of ca. 2.5 Ga, consistent with the timing of formation of the Closepet Batholith. The relationship between titanite textures and chemistry indicates that titanite serves as a recorder of the multistage magmatic and post-magmatic evolution of the Closepet Batholith. In addition, our study shows that hydrothermal activity affected a large area, with fluids circulating over long distances within the upper structural levels of the Closepet Batholith.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107840"},"PeriodicalIF":2.9,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536320","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}
Pub Date : 2024-10-19DOI: 10.1016/j.lithos.2024.107836
Jing-Yuan Chen , Jin-Hui Yang , Ji-Heng Zhang , Yu-Sheng Zhu , Jin-Feng Sun , Shao-Wei Zhao
Water plays a crucial role in determining the crystallization sequence of magma, which subsequently influences the chemical compositions of magmatic rocks across different tectonic settings. In this study, we compared the evolutionary features of granitic rocks along the coast and inland areas of southeast China, aiming to identify the key factors influencing their evolution. Our work indicates that multiple granitic intrusions formed between 126 and 142 Ma in the coastal region of southeastern China, which is consistent with the formation ages of large-scale granitoids in the inland Gan-Hang Belt. Isotopic characteristics suggest that the granitic rocks in southern Fujian originated from the melting of juvenile crust, while those in northern Fujian and eastern Zhejiang were formed from the partial melting of ancient crustal rocks, incorporating mafic magma evolved from the mantle. Most of the granitoids from the coastal region of southeastern China exhibit low zircon saturation temperatures (680–800 °C) and Zr/Sr ratios (<1), suggesting their origin from a cold, wet magma reservoir. The porphyritic quartz diorite and porphyritic monzogranite represent the residual cumulate rocks of this hydrous magma reservoir, whereas the granitic porphyry and high-silica equigranular alkali feldspar granite evolved from the felsic melts extracted from the same reservoir. In contrast, most of the Early Cretaceous granitoids in the Gan-Hang Belt, located in the inland areas of southeast China, display high zircon saturation temperatures (800–900 °C) and Zr/Sr ratios (>1), indicating their origin from hot, water-poor magma reservoirs. The porphyritic granites in this region represent residual cumulate rocks formed in water-poor magma reservoirs, whereas the high-silica equigranular granites evolved from hot felsic melts extracted from similar magma reservoirs. In the Early Cretaceous, the coastal region of southeastern China was closer to the Late Mesozoic paleo-Pacific subduction zone, where crystal-melt segregation within cold, wet magma reservoirs predominantly influenced magma evolution. Conversely, the granitoids in the Gan-Hang Belt in the inland region, located farther from the Late Mesozoic paleo-Pacific subduction zone, were associated with a rift tectonic setting and formed through crystal-melt segregation within hot, water-poor magma reservoirs. Our study underscores the critical role of water content in magma reservoirs in shaping the chemical composition of granitic rocks through crystal-melt segregation, thereby deepening our understanding of crustal formation processes across diverse tectonic environments.
{"title":"Water content drives distinct evolution trajectory of Early Cretaceous granitoids in inland and coastal southeast China","authors":"Jing-Yuan Chen , Jin-Hui Yang , Ji-Heng Zhang , Yu-Sheng Zhu , Jin-Feng Sun , Shao-Wei Zhao","doi":"10.1016/j.lithos.2024.107836","DOIUrl":"10.1016/j.lithos.2024.107836","url":null,"abstract":"<div><div>Water plays a crucial role in determining the crystallization sequence of magma, which subsequently influences the chemical compositions of magmatic rocks across different tectonic settings. In this study, we compared the evolutionary features of granitic rocks along the coast and inland areas of southeast China, aiming to identify the key factors influencing their evolution. Our work indicates that multiple granitic intrusions formed between 126 and 142 Ma in the coastal region of southeastern China, which is consistent with the formation ages of large-scale granitoids in the inland Gan-Hang Belt. Isotopic characteristics suggest that the granitic rocks in southern Fujian originated from the melting of juvenile crust, while those in northern Fujian and eastern Zhejiang were formed from the partial melting of ancient crustal rocks, incorporating mafic magma evolved from the mantle. Most of the granitoids from the coastal region of southeastern China exhibit low zircon saturation temperatures (680–800 °C) and Zr/Sr ratios (<1), suggesting their origin from a cold, wet magma reservoir. The porphyritic quartz diorite and porphyritic monzogranite represent the residual cumulate rocks of this hydrous magma reservoir, whereas the granitic porphyry and high-silica equigranular alkali feldspar granite evolved from the felsic melts extracted from the same reservoir. In contrast, most of the Early Cretaceous granitoids in the Gan-Hang Belt, located in the inland areas of southeast China, display high zircon saturation temperatures (800–900 °C) and Zr/Sr ratios (>1), indicating their origin from hot, water-poor magma reservoirs. The porphyritic granites in this region represent residual cumulate rocks formed in water-poor magma reservoirs, whereas the high-silica equigranular granites evolved from hot felsic melts extracted from similar magma reservoirs. In the Early Cretaceous, the coastal region of southeastern China was closer to the Late Mesozoic paleo-Pacific subduction zone, where crystal-melt segregation within cold, wet magma reservoirs predominantly influenced magma evolution. Conversely, the granitoids in the Gan-Hang Belt in the inland region, located farther from the Late Mesozoic paleo-Pacific subduction zone, were associated with a rift tectonic setting and formed through crystal-melt segregation within hot, water-poor magma reservoirs. Our study underscores the critical role of water content in magma reservoirs in shaping the chemical composition of granitic rocks through crystal-melt segregation, thereby deepening our understanding of crustal formation processes across diverse tectonic environments.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107836"},"PeriodicalIF":2.9,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536319","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}
Pub Date : 2024-10-17DOI: 10.1016/j.lithos.2024.107835
Yongsheng Gai, Tuo Ma, Liang Liu, Xiaoying Liao, Lei Kang, Chao Wang, Wenqiang Yang
The partial melting of HP–UHP rocks plays a crucial role in facilitating the exhumation of deeply subducted rocks. However, accurately determining the P–T–t conditions of the initial melting and subsequent crystallization is often challenging, which can hamper our understanding of the relationship between partial melting and exhumation. We present a detailed investigation of granitic veins in the (U)HP felsic gneiss in the eastern South Altyn Tagh (SAT), northwest China. These granitic veins have similar whole rock geochemical characteristics to those of the felsic gneiss: high K2O (5.01–9.95 wt%) and Rb contents, and low Sr contents, with negative correlations between Rb/Sr ratios and Ba or Sr contents. This suggests that the veins were generated by muscovite-dehydration melting of the felsic gneiss. Garnet crystals in the felsic gneiss contain many titanite and multiphase solid inclusions in their mantles. Using the compositions of the garnet mantles and granitic veins, alongside pseudosection modelling of the felsic gneiss, we estimate that the initial melting conditions of the felsic gneiss occurred at 2.57–2.61 GPa and 1000 °C, just above the solidus. In situ UPb dating of titanite inclusions in the garnet mantles yields an initial melting age of ∼485 Ma. Furthermore, anatectic zircon grains in the granitic veins yield UPb ages of 488–484 Ma. Using Ti-in-zircon thermometry and 176Lu/177Hf-in-zircon geobarometry, we estimate that the anatectic zircon grains crystallized at 647–872 °C and 0.16–0.82 GPa. The estimated P–T–t path from the initial melting of the felsic gneiss to the crystallization of the granitic veins indicates rapid exhumation from ∼2.6 to 0.16–0.82 GPa. This exhumation can be attributed to partial melting, which weakened the rocks and enabled their ascent to shallower depths. Moreover, the potassic melts derived from partial melting of the felsic gneiss provide new insights into the genesis of potassic granitoids in subduction zones.
{"title":"Partial melting of HP–UHP felsic gneiss in the South Altyn Tagh reveals the rapid exhumation of a deeply subducted slab","authors":"Yongsheng Gai, Tuo Ma, Liang Liu, Xiaoying Liao, Lei Kang, Chao Wang, Wenqiang Yang","doi":"10.1016/j.lithos.2024.107835","DOIUrl":"10.1016/j.lithos.2024.107835","url":null,"abstract":"<div><div>The partial melting of HP–UHP rocks plays a crucial role in facilitating the exhumation of deeply subducted rocks. However, accurately determining the <em>P–T–t</em> conditions of the initial melting and subsequent crystallization is often challenging, which can hamper our understanding of the relationship between partial melting and exhumation. We present a detailed investigation of granitic veins in the (U)HP felsic gneiss in the eastern South Altyn Tagh (SAT), northwest China. These granitic veins have similar whole rock geochemical characteristics to those of the felsic gneiss: high K<sub>2</sub>O (5.01–9.95 wt%) and Rb contents, and low Sr contents, with negative correlations between Rb/Sr ratios and Ba or Sr contents. This suggests that the veins were generated by muscovite-dehydration melting of the felsic gneiss. Garnet crystals in the felsic gneiss contain many titanite and multiphase solid inclusions in their mantles. Using the compositions of the garnet mantles and granitic veins, alongside pseudosection modelling of the felsic gneiss, we estimate that the initial melting conditions of the felsic gneiss occurred at 2.57–2.61 GPa and 1000 °C, just above the solidus. In situ U<img>Pb dating of titanite inclusions in the garnet mantles yields an initial melting age of ∼485 Ma. Furthermore, anatectic zircon grains in the granitic veins yield U<img>Pb ages of 488–484 Ma. Using Ti-in-zircon thermometry and <sup>176</sup>Lu/<sup>177</sup>Hf-in-zircon geobarometry, we estimate that the anatectic zircon grains crystallized at 647–872 °C and 0.16–0.82 GPa. The estimated <em>P–T–t</em> path from the initial melting of the felsic gneiss to the crystallization of the granitic veins indicates rapid exhumation from ∼2.6 to 0.16–0.82 GPa. This exhumation can be attributed to partial melting, which weakened the rocks and enabled their ascent to shallower depths. Moreover, the potassic melts derived from partial melting of the felsic gneiss provide new insights into the genesis of potassic granitoids in subduction zones.</div></div>","PeriodicalId":18070,"journal":{"name":"Lithos","volume":"488 ","pages":"Article 107835"},"PeriodicalIF":2.9,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142536318","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}
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