Numerical simulations of the paleostress field during a period of tectonic fracture formation and rock failure criteria are used to quantitatively predict the development and occurrence of tectonic fractures induced by the formation of the SB18 fault zone in the Middle Ordovician Yijianfang Formation of the Shunnan area, Tarim Basin, China. The results of acoustic emission experiments, mechanical property measurements, and tectonic fracture occurrence observations obtained from core descriptions and fullbore formation microimager logs are combined with the Andersonian model of faulting and the finite element method, which is widely used for the numerical simulation of stress fields, to investigate the paleotectonic and in situ stress fields via numerical simulation. The quantitative prediction of the opening pressure and opening sequence of tectonic fractures is based on the occurrence of tectonic fracture, numerical simulation of in situ stresses, and coordinate system conversion. The results show that the width of the fracture zone induced by strike-slip faulting is ∼310 m. The degree of fracture development is significantly increased when the Young’s modulus, paleostress difference, and paleostress difference coefficient of the rock are elevated. The current horizontal principal stress is positively correlated with the distance from the fault, and the elevated areal density of the secondary faults causes a clockwise deflection of the horizontal stress direction. SSE-striking shear fractures with orientations ranging from 140° to 150° and two sets of tensional fractures with orientations ranging from −40° to −35° and 55° to 60° are preferentially opened in the water injection development stage of the reservoir. As the horizontal stress difference, horizontal stress difference coefficient, and angle between the maximum horizontal principal stress and a fracture decrease, the fracture opening pressure decreases. At the structural highs (burial depths <6225 m) and lows (burial depths >6225 m), the fracture burial depth is positively and negatively correlated with the opening pressure, respectively. Quantitative prediction of tectonic fracture developmental characteristics, opening pressure, and the opening sequence and investigation of the main factors that control their development can help to identify and support opportunities for hydrocarbon exploration and development of fractured carbonate reservoirs.
{"title":"Tectonic fractures induced by strike-slip faulting in intracratonic ultradeep carbonate rocks: Insights from the finite element method and self-adaptive constraints computational model for boundary conditions","authors":"Yuntao Li, Wenlong Ding, Jun Han, Xuyun Chen, Cheng Huang, Jingtian Li, Shihao Ding","doi":"10.1130/b37196.1","DOIUrl":"https://doi.org/10.1130/b37196.1","url":null,"abstract":"Numerical simulations of the paleostress field during a period of tectonic fracture formation and rock failure criteria are used to quantitatively predict the development and occurrence of tectonic fractures induced by the formation of the SB18 fault zone in the Middle Ordovician Yijianfang Formation of the Shunnan area, Tarim Basin, China. The results of acoustic emission experiments, mechanical property measurements, and tectonic fracture occurrence observations obtained from core descriptions and fullbore formation microimager logs are combined with the Andersonian model of faulting and the finite element method, which is widely used for the numerical simulation of stress fields, to investigate the paleotectonic and in situ stress fields via numerical simulation. The quantitative prediction of the opening pressure and opening sequence of tectonic fractures is based on the occurrence of tectonic fracture, numerical simulation of in situ stresses, and coordinate system conversion. The results show that the width of the fracture zone induced by strike-slip faulting is ∼310 m. The degree of fracture development is significantly increased when the Young’s modulus, paleostress difference, and paleostress difference coefficient of the rock are elevated. The current horizontal principal stress is positively correlated with the distance from the fault, and the elevated areal density of the secondary faults causes a clockwise deflection of the horizontal stress direction. SSE-striking shear fractures with orientations ranging from 140° to 150° and two sets of tensional fractures with orientations ranging from −40° to −35° and 55° to 60° are preferentially opened in the water injection development stage of the reservoir. As the horizontal stress difference, horizontal stress difference coefficient, and angle between the maximum horizontal principal stress and a fracture decrease, the fracture opening pressure decreases. At the structural highs (burial depths <6225 m) and lows (burial depths >6225 m), the fracture burial depth is positively and negatively correlated with the opening pressure, respectively. Quantitative prediction of tectonic fracture developmental characteristics, opening pressure, and the opening sequence and investigation of the main factors that control their development can help to identify and support opportunities for hydrocarbon exploration and development of fractured carbonate reservoirs.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"110 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140709091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Although abundant Neoproterozoic igneous rocks exposed along the periphery of the Yangtze Block of the South China Craton record the tectonic processes of the assembly and breakup of the Rodinia supercontinent, the mechanism that induced the rifting of the South China Craton from Rodinia and reconstruction of the paleogeographic position of the South China Craton in Rodinia remain controversial. We document two episodes of bimodal intrusions with emplacement ages of ca. 785 Ma and ca. 750 Ma in the Diancangshan Massif that provide critical constraints on the rifting processes and mechanisms. The rock association and the elemental and Hf-O isotopic signatures of these two episodes of bimodal intrusions illustrate that they are an important component of the Panxi-Hannan magmatic arc in the western Yangtze Block. The spatial pattern of Neoproterozoic sedimentary rocks to the west of the Panxi-Hannan arc and their provenance indicate that intra-arc rifting promoted the separation of microplates such as the Xuelongshan and Diancangshan massifs and even the Yidun Block from the western Yangtze Block and the mechanism induced synchronous deposits in these regions.
{"title":"Intra-arc rifting induced the fragmentation of microplate from the continental margin","authors":"Limin Wu, Guochun Zhao, Jianfeng Gao, Xiaohan Dong, Aimei Zhang, Touping Peng","doi":"10.1130/b37397.1","DOIUrl":"https://doi.org/10.1130/b37397.1","url":null,"abstract":"Although abundant Neoproterozoic igneous rocks exposed along the periphery of the Yangtze Block of the South China Craton record the tectonic processes of the assembly and breakup of the Rodinia supercontinent, the mechanism that induced the rifting of the South China Craton from Rodinia and reconstruction of the paleogeographic position of the South China Craton in Rodinia remain controversial. We document two episodes of bimodal intrusions with emplacement ages of ca. 785 Ma and ca. 750 Ma in the Diancangshan Massif that provide critical constraints on the rifting processes and mechanisms. The rock association and the elemental and Hf-O isotopic signatures of these two episodes of bimodal intrusions illustrate that they are an important component of the Panxi-Hannan magmatic arc in the western Yangtze Block. The spatial pattern of Neoproterozoic sedimentary rocks to the west of the Panxi-Hannan arc and their provenance indicate that intra-arc rifting promoted the separation of microplates such as the Xuelongshan and Diancangshan massifs and even the Yidun Block from the western Yangtze Block and the mechanism induced synchronous deposits in these regions.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"6 20","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140710618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wangchao Li, Changqing Yin, C. Yakymchuk, Lin Ding, Shun Li, J. Qian, Peng Gao, Yanling Zhang
We report an integrated comprehensive dataset composed of petrography, pressure-temperature (P-T) calculations, monazite U-Th-Pb ages, and trace-element data from pelitic schists in the eastern Indus-Yarlung suture zone in the Milin area of the eastern Himalaya. These rocks represent the exposure of subduction-related rocks within the eastern Indus-Yarlung suture zone accretionary complex. The dominant mineral assemblages of the pelitic schists are garnet + kyanite + staurolite + biotite + quartz and garnet + kyanite + staurolite + biotite + paragonite + sillimanite with quartz, plagioclase, and ilmenite assemblages. Phase equilibrium modeling of sillimanite-bearing pelitic schists yielded peak P-T conditions of ∼670−680 °C at ∼8.6 kbar, similar to that of kyanite-bearing schists (∼670 °C, ∼8.8 kbar). Monazite grains with complex internal structures retained variable ages ranging from 28 Ma to 15 Ma, which correlate systematically with changes in the concentrations of Y, Th, U, and heavy rare earth elements and ratios of Th/U. Combined with petrologic analysis, we conclude that the pelitic schists experienced a long-lived prograde metamorphism from ca. 28 Ma to ca. 22 Ma. Peak metamorphism occurred in the period 22−21 Ma, followed by quasi-isothermal decompression until 15 Ma. The discrepancies among metamorphic P-T-t paths in the eastern Indus-Yarlung suture zone indicate the presence of not only collision-related regional metamorphism at medium P-T conditions, but also subduction-related high-pressure−low-temperature terranes in the Milin region. These two domains experienced different P-T evolution and tectonic histories and were juxtaposed in the early Neogene during the India-Asia continental collision.
我们报告了喜马拉雅山东部米林地区东印度河-雅鲁藏布江断裂带辉长岩的岩石学、压力-温度（P-T）计算、独居石U-Th-Pb年龄和痕量元素数据组成的综合数据集。这些岩石代表了印度河-雅鲁藏布江东缝合带增生复合体中与俯冲有关的岩石的出露。辉绿岩片岩的主要矿物组合为石榴石+闪长岩+辉长岩+生物锂辉石+石英和石榴石+闪长岩+辉长岩+生物锂辉石+副长石+矽线石，以及石英、斜长石和钛铁矿组合。对含菱锰矿的辉长岩片岩进行相平衡建模后发现，其峰值 P-T 条件为 ∼670-680 °C，温度为 ∼8.6 千巴，与含闪长岩片岩的峰值 P-T 条件相似（∼670 °C，温度为 ∼8.8 千巴）。具有复杂内部结构的独居石晶粒保留了从 28 Ma 到 15 Ma 的不同年龄，这些年龄与 Y、Th、U 和重稀土元素浓度的变化以及 Th/U 的比率系统地相关。结合岩石学分析，我们得出结论，钾长石片岩经历了从约 28 Ma 到约 22 Ma 的长期顺变质作用。变质作用的峰值出现在 22-21 Ma 期间，随后是直到 15 Ma 的准等温减压作用。印度河-雅鲁藏布江断裂带东部变质P-T-t路径的差异表明，在中等P-T条件下，不仅存在与碰撞相关的区域变质作用，而且在米林地区还存在与俯冲相关的高压低温地层。这两个区域经历了不同的P-T演化和构造历史，在新近纪早期印度-亚洲大陆碰撞过程中并置在一起。
{"title":"Pressure-temperature-time evolution of the Milin pelitic schists: Implications for the tectonic evolution of the eastern Indus-Yarlung suture zone, eastern Himalaya","authors":"Wangchao Li, Changqing Yin, C. Yakymchuk, Lin Ding, Shun Li, J. Qian, Peng Gao, Yanling Zhang","doi":"10.1130/b36978.1","DOIUrl":"https://doi.org/10.1130/b36978.1","url":null,"abstract":"We report an integrated comprehensive dataset composed of petrography, pressure-temperature (P-T) calculations, monazite U-Th-Pb ages, and trace-element data from pelitic schists in the eastern Indus-Yarlung suture zone in the Milin area of the eastern Himalaya. These rocks represent the exposure of subduction-related rocks within the eastern Indus-Yarlung suture zone accretionary complex. The dominant mineral assemblages of the pelitic schists are garnet + kyanite + staurolite + biotite + quartz and garnet + kyanite + staurolite + biotite + paragonite + sillimanite with quartz, plagioclase, and ilmenite assemblages. Phase equilibrium modeling of sillimanite-bearing pelitic schists yielded peak P-T conditions of ∼670−680 °C at ∼8.6 kbar, similar to that of kyanite-bearing schists (∼670 °C, ∼8.8 kbar). Monazite grains with complex internal structures retained variable ages ranging from 28 Ma to 15 Ma, which correlate systematically with changes in the concentrations of Y, Th, U, and heavy rare earth elements and ratios of Th/U. Combined with petrologic analysis, we conclude that the pelitic schists experienced a long-lived prograde metamorphism from ca. 28 Ma to ca. 22 Ma. Peak metamorphism occurred in the period 22−21 Ma, followed by quasi-isothermal decompression until 15 Ma. The discrepancies among metamorphic P-T-t paths in the eastern Indus-Yarlung suture zone indicate the presence of not only collision-related regional metamorphism at medium P-T conditions, but also subduction-related high-pressure−low-temperature terranes in the Milin region. These two domains experienced different P-T evolution and tectonic histories and were juxtaposed in the early Neogene during the India-Asia continental collision.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"90 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140717910","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
As a robust accessory mineral in igneous rocks, the mineralogical and geochemical characteristics of zircon can record the lithological differentiation and magmatic−hydrothermal evolution of highly evolved granitic systems. The F-Rb−rich, highly evolved Baishitouquan pluton of NW China exhibits gradual lithological changes from leucogranite, amazonite-bearing granite, and amazonite granite in the lower levels of the pluton to topaz-bearing amazonite granite, topaz albite granite, and pegmatite in the upper levels. In this study, three types of zircon grains were identified in five lithological zones based on textural and chemical characteristics. Type I zircon, which mostly occurs in leucogranite and amazonite-bearing granite, exhibits oscillatory zoning in cathodoluminescence images and experienced low degrees of radiation damage (0.21−0.68 × 1015 α-decay events/mg), which is indicative of its magmatic origin. Type II zircon, which mostly occurs in amazonite granite and amazonite pegmatite, exhibits textures that are indicative of hydrothermal alteration (e.g., spongy texture, porosity, and microcracks), and has elevated concentrations of some cations, such as Ca and Al. Type II zircon contains a higher concentration of non-formula elements, including rare earth elements (REEs), and Hf, Th, and U, than Type I and III zircons. Additionally, Type II zircon exhibits a significant M-type lanthanide tetrad effect and experienced varying levels of radiation damage (3.75−11.72 × 1015 α-decay events/mg). These characteristics suggest that Type II zircon has a hydrothermally altered origin. Type III zircon, which is restricted to the topaz-albite granite, has the smallest crystal size among all types of zircon grains, shows a euhedral to anhedral mottled appearance, and is characterized by patchy, cloudy, or irregular zoning, with numerous fluid inclusions. This type of zircon contains higher concentrations of Ti (110−1030 μg/g) than other types of zircon grains. Additionally, this type of zircon experienced limited radiation damage (2.18−3.69 × 1015 α-decay events/mg), and has a smooth surface and homogeneous internal textures. These characteristics suggest that Type III zircon is the product of fluid interaction with hydrothermally altered Type II zircon. Accordingly, this type of zircon crystallized directly from a Zr-saturated hydrothermal fluid during the later stages of magmatic−hydrothermal evolution. These contrasting textural and compositional features of the three types of zircon grains are indicative of three stages of magmatic−hydrothermal evolution of the Baishitouquan pluton: magmatic, magmatic−hydrothermal transition, and hydrothermal. These magmatic and hydrothermal processes were involved in the enrichment, transport, and precipitation of rare metals, such as Rb. Accordingly, this contribution demonstrates that the textures and chemistry of zircon grains can serve as petrogenetic indicators for assessing magmatic−hydrothermal evolution a
锆石是火成岩中一种坚固的附属矿物，其矿物学和地球化学特征可以记录高度演化花岗岩系统的岩性分异和岩浆-热液演化过程。中国西北部富含F-Rb、高度演化的白石头泉岩体呈现出岩性渐变的特征，从岩体下部的白花岗岩、含芒花岗岩和芒花岗岩，到岩体上部的含黄玉芒花岗岩、黄玉白云母花岗岩和伟晶岩。在这项研究中，根据纹理和化学特征，在五个岩性带中确定了三种类型的锆石颗粒。Ⅰ型锆石主要分布在白云母花岗岩和含亚马孙岩的花岗岩中，在阴极荧光图像中呈现振荡带状，受到的辐射损伤程度较低（0.21-0.68 × 1015 α-衰变事件/mg），表明其来源于岩浆。第二类锆石主要出现在亚马逊花岗岩和亚马逊伟晶岩中，其纹理显示出热液蚀变的特征（如海绵状纹理、多孔性和微裂缝），并且某些阳离子（如钙和铝）的浓度较高。与 I 型和 III 型锆石相比，II 型锆石含有更高浓度的非公式元素，包括稀土元素 (REE)、Hf、Th 和 U。此外，II型锆石表现出明显的M型镧系元素四射效应，并经历了不同程度的辐射损伤（3.75-11.72 × 1015 α-衰变事件/mg）。这些特征表明，II 型锆石起源于热液蚀变。III型锆石仅限于黄玉-黑云母花岗岩，在所有类型的锆石晶粒中晶体尺寸最小，外观呈正八面体至正八面体斑驳状，特征为斑块状、浑浊状或不规则带状，并含有大量流体包裹体。与其他类型的锆石晶粒相比，这类锆石含有更高浓度的 Ti（110-1030 微克/克）。此外，这类锆石经历的辐射损伤有限（2.18-3.69 × 1015 α-衰变事件/mg），表面光滑，内部纹理均匀。这些特征表明，III 型锆石是流体与热液蚀变 II 型锆石相互作用的产物。因此，这种类型的锆石是在岩浆-热液演化的后期阶段从Zr饱和的热液中直接结晶出来的。三类锆石晶粒在质地和成分上的这些对比特征表明了白石头泉岩浆-热液演化的三个阶段：岩浆期、岩浆-热液转换期和热液期。这些岩浆和热液过程参与了稀有金属（如铷）的富集、迁移和沉淀。因此，这项研究表明，锆石晶粒的纹理和化学成分可作为岩石成因指标，用于评估高度演化花岗岩系统中的岩浆-热液演化和稀有金属矿化。此外，本研究还通过锆石的视角，提出了一个富含F的高度演化花岗岩体系的岩浆-热液演化模型。
{"title":"Magmatic−hydrothermal evolutionary processes in highly evolved granitic systems: Insights from zircons of the Baishitouquan pluton, NW China","authors":"Zhen-Hua Wang, R. Lei, M. Brzozowski, Changzhi Wu","doi":"10.1130/b37425.1","DOIUrl":"https://doi.org/10.1130/b37425.1","url":null,"abstract":"As a robust accessory mineral in igneous rocks, the mineralogical and geochemical characteristics of zircon can record the lithological differentiation and magmatic−hydrothermal evolution of highly evolved granitic systems. The F-Rb−rich, highly evolved Baishitouquan pluton of NW China exhibits gradual lithological changes from leucogranite, amazonite-bearing granite, and amazonite granite in the lower levels of the pluton to topaz-bearing amazonite granite, topaz albite granite, and pegmatite in the upper levels. In this study, three types of zircon grains were identified in five lithological zones based on textural and chemical characteristics. Type I zircon, which mostly occurs in leucogranite and amazonite-bearing granite, exhibits oscillatory zoning in cathodoluminescence images and experienced low degrees of radiation damage (0.21−0.68 × 1015 α-decay events/mg), which is indicative of its magmatic origin. Type II zircon, which mostly occurs in amazonite granite and amazonite pegmatite, exhibits textures that are indicative of hydrothermal alteration (e.g., spongy texture, porosity, and microcracks), and has elevated concentrations of some cations, such as Ca and Al. Type II zircon contains a higher concentration of non-formula elements, including rare earth elements (REEs), and Hf, Th, and U, than Type I and III zircons. Additionally, Type II zircon exhibits a significant M-type lanthanide tetrad effect and experienced varying levels of radiation damage (3.75−11.72 × 1015 α-decay events/mg). These characteristics suggest that Type II zircon has a hydrothermally altered origin. Type III zircon, which is restricted to the topaz-albite granite, has the smallest crystal size among all types of zircon grains, shows a euhedral to anhedral mottled appearance, and is characterized by patchy, cloudy, or irregular zoning, with numerous fluid inclusions. This type of zircon contains higher concentrations of Ti (110−1030 μg/g) than other types of zircon grains. Additionally, this type of zircon experienced limited radiation damage (2.18−3.69 × 1015 α-decay events/mg), and has a smooth surface and homogeneous internal textures. These characteristics suggest that Type III zircon is the product of fluid interaction with hydrothermally altered Type II zircon. Accordingly, this type of zircon crystallized directly from a Zr-saturated hydrothermal fluid during the later stages of magmatic−hydrothermal evolution. These contrasting textural and compositional features of the three types of zircon grains are indicative of three stages of magmatic−hydrothermal evolution of the Baishitouquan pluton: magmatic, magmatic−hydrothermal transition, and hydrothermal. These magmatic and hydrothermal processes were involved in the enrichment, transport, and precipitation of rare metals, such as Rb. Accordingly, this contribution demonstrates that the textures and chemistry of zircon grains can serve as petrogenetic indicators for assessing magmatic−hydrothermal evolution a","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140717453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hong-Yan Wang, Jian‐Bo Zhou, S. A. Wilde, Gong-Yu Li, Bin Fu
Since the Paleozoic, the tectonic evolution of northeastern Eurasia has been dominated by the Paleo-Asian Ocean and the Paleo-Pacific Ocean tectonic domains. However, the spatiotemporal framework and the timing of tectonic transition between these two oceanic domains remain enigmatic. To address this issue, we report petrological, geochronological, and geochemical data for eight sandstone samples deposited along the convergent margin between the Northeast China terranes and the North China craton in central Jilin Province, China. The results show that these sandstones are immature graywackes with a maximum depositional age of Early Triassic (248 ± 1 Ma), and their sediments were largely derived from coeval magmatic rocks in a juvenile continental arc. According to our new results and previous studies, we identified a sedimentary basin (most likely an intra-arc or forearc basin) intimately associated with one or more continental arcs along the northeastern edge of the North China craton, and we suggest that the southwestward subduction of the Jilin-Heilongjiang Ocean in the early Mesozoic accounts for this continental arc setting. There is a distinct temporal gap between the closure of the Paleo-Asian Ocean (ca. 260 Ma) and the onset of Paleo-Pacific plate subduction (234−220 Ma), which is essentially coeval with the southwestward subduction of the Jilin-Heilongjiang Ocean between 256 Ma and 239 Ma, meaning the latter is a key link that marks the transition between these two tectonic domains.
自古生代以来，欧亚大陆东北部的构造演化一直由古生代亚洲洋构造域和古生代太平洋构造域主导。然而，这两个大洋构造域之间的时空框架和构造转换时间仍然是个谜。为了解决这个问题，我们报告了中国吉林省中部沿中国东北陆相与华北克拉通交汇边缘沉积的八个砂岩样本的岩石学、地质年代学和地球化学数据。结果表明，这些砂岩属于未成熟灰岩，最大沉积年龄为早三叠世（248±1Ma），其沉积物主要来源于幼年大陆弧中的共生岩浆岩。根据新的研究结果和以往的研究，我们在华北克拉通东北边缘发现了一个与一个或多个大陆弧密切相关的沉积盆地（很可能是弧内盆地或弧前盆地），并认为中生代早期吉林-黑龙江洋的西南俯冲是造成这种大陆弧环境的原因。古亚洲洋的关闭（约 260 Ma）与古太平洋板块俯冲的开始（234-220 Ma）之间存在明显的时间差，这与吉林-黑龙江洋在 256 Ma 至 239 Ma 之间的西南向俯冲基本上是共时的，这意味着后者是标志这两个构造域之间过渡的关键环节。
{"title":"Mesozoic intra-arc basin records the tectonic transition from the Paleo-Asian Ocean to the Paleo-Pacific Ocean in northeastern Eurasia","authors":"Hong-Yan Wang, Jian‐Bo Zhou, S. A. Wilde, Gong-Yu Li, Bin Fu","doi":"10.1130/b37244.1","DOIUrl":"https://doi.org/10.1130/b37244.1","url":null,"abstract":"Since the Paleozoic, the tectonic evolution of northeastern Eurasia has been dominated by the Paleo-Asian Ocean and the Paleo-Pacific Ocean tectonic domains. However, the spatiotemporal framework and the timing of tectonic transition between these two oceanic domains remain enigmatic. To address this issue, we report petrological, geochronological, and geochemical data for eight sandstone samples deposited along the convergent margin between the Northeast China terranes and the North China craton in central Jilin Province, China. The results show that these sandstones are immature graywackes with a maximum depositional age of Early Triassic (248 ± 1 Ma), and their sediments were largely derived from coeval magmatic rocks in a juvenile continental arc. According to our new results and previous studies, we identified a sedimentary basin (most likely an intra-arc or forearc basin) intimately associated with one or more continental arcs along the northeastern edge of the North China craton, and we suggest that the southwestward subduction of the Jilin-Heilongjiang Ocean in the early Mesozoic accounts for this continental arc setting. There is a distinct temporal gap between the closure of the Paleo-Asian Ocean (ca. 260 Ma) and the onset of Paleo-Pacific plate subduction (234−220 Ma), which is essentially coeval with the southwestward subduction of the Jilin-Heilongjiang Ocean between 256 Ma and 239 Ma, meaning the latter is a key link that marks the transition between these two tectonic domains.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"28 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140720444","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhaoliang Hou, Kun-Feng Qiu, A. Rogowitz, Richard A. Schultz, Hao-Cheng Yu, Bernhard Grasemann
Stylolites are common dissolution structures in carbonate rocks in the upper crust and document a coupled physical-chemical feedback during pressure solution in rocks. By applying high-resolution electron-based analysis we investigate a rare example of stylolites in cryptocrystalline quartz (novaculite) from western Sichuan Basin, China. The investigated stylolites exhibit an increased amplitude from the tip toward the center, which correlates with the maturity of stylolites and thus provides an excellent opportunity to infer the dynamic processes operating during stylolite formation. Microstructurally, stylolites are characterized by a concentration of biotite and hematite, dissolving irregular quartz grains, and the occurrence of dissolution porosity. By investigating the progressive co-variations between stylolite amplitude and microstructure characteristics from the stylolite tip toward the center, we demonstrate, for the first time, the evidence of stylolite growth through anticracks. It is inferred that stylolites in cryptocrystalline quartz originate from the propagation of mode I micro-cracks around pre-existing biotite, followed by pore-scale dissolution. Both processes, micro-cracking and dissolution, are interacting and co-evolving via a self-organization fashion during shortening. Our study contributes to the ongoing debate about whether stylolites are conduits or barriers for fluid flow.
水帘洞是上地壳碳酸盐岩中常见的溶解结构，记录了岩石压力溶解过程中的物理化学耦合反馈。通过应用高分辨率电子分析方法，我们研究了中国四川盆地西部隐晶质石英（黝帘石）中的一个罕见的花柱石实例。所研究的水云母表现出从顶端向中心的振幅增大，这与水云母的成熟度相关，从而为推断水云母形成过程中的动态过程提供了极好的机会。从微观结构上看，水云母的特点是生物铁矿和赤铁矿集中、溶解不规则石英颗粒以及出现溶解孔隙。通过研究水云母振幅与微观结构特征之间从水云母顶端向中心的渐进共变关系，我们首次证明了水云母通过反裂缝生长的证据。据此推断，隐晶质石英中的水云母源于模式 I 微裂缝在预先存在的生物沸石周围的传播，然后是孔隙尺度的溶解。在缩短过程中，微裂纹和溶解这两个过程通过自组织方式相互作用、共同演化。我们的研究为正在进行的关于水云母是流体流动的通道还是障碍的争论做出了贡献。
{"title":"Progressive development of stylolites in cryptocrystalline quartz","authors":"Zhaoliang Hou, Kun-Feng Qiu, A. Rogowitz, Richard A. Schultz, Hao-Cheng Yu, Bernhard Grasemann","doi":"10.1130/b37461.1","DOIUrl":"https://doi.org/10.1130/b37461.1","url":null,"abstract":"Stylolites are common dissolution structures in carbonate rocks in the upper crust and document a coupled physical-chemical feedback during pressure solution in rocks. By applying high-resolution electron-based analysis we investigate a rare example of stylolites in cryptocrystalline quartz (novaculite) from western Sichuan Basin, China. The investigated stylolites exhibit an increased amplitude from the tip toward the center, which correlates with the maturity of stylolites and thus provides an excellent opportunity to infer the dynamic processes operating during stylolite formation. Microstructurally, stylolites are characterized by a concentration of biotite and hematite, dissolving irregular quartz grains, and the occurrence of dissolution porosity. By investigating the progressive co-variations between stylolite amplitude and microstructure characteristics from the stylolite tip toward the center, we demonstrate, for the first time, the evidence of stylolite growth through anticracks. It is inferred that stylolites in cryptocrystalline quartz originate from the propagation of mode I micro-cracks around pre-existing biotite, followed by pore-scale dissolution. Both processes, micro-cracking and dissolution, are interacting and co-evolving via a self-organization fashion during shortening. Our study contributes to the ongoing debate about whether stylolites are conduits or barriers for fluid flow.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"33 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140727322","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. B. Watts, C. Xu, M. P. Searle, C. Jurkowski, R. Shail
A new compilation of Bouguer gravity anomaly data has been used, together with forward and inverse modeling, to reappraise the structure, volume, and state of isostasy of the Cornubian batholith of SW England. We show the individual plutons that comprise the batholith are, on average, ∼10−11 km thick, are outward-sloping in their upper 2−3 km, and are underlain by roots which protrude downward into the middle crust. The batholith volume is estimated within the range of 76,367 ± 17,286 km3, significantly larger than previous estimates. Granite outcrops correlate with elevated topography, and mass balance calculations show that the mass deficiency of the granites relative to their host metasedimentary rocks is approximately equal to the mass excess of the topography relative to air. The existence of roots beneath individual plutons is in general agreement with predictions of an Airy model of isostasy and a depth of compensation that is within the crust rather than at the Moho. In addition, a middle crust compensation depth is compatible with the origin of the granites by heating and melting of metasedimentary rocks and with data from experimental rock mechanics which suggest that at the melting temperature and pressure of granite formation, deformation is likely to be plastic and controlled by glide along dislocations. During pluton emplacement the middle crust would, therefore, have acted as a mechanically weak layer, effectively decoupling the topography from any support it might otherwise have received from the lower crust and/or upper mantle.
{"title":"The Permian Cornubian granite batholith, SW England; Part 2: Gravity anomalies, structure, and state of isostasy","authors":"A. B. Watts, C. Xu, M. P. Searle, C. Jurkowski, R. Shail","doi":"10.1130/b37459.1","DOIUrl":"https://doi.org/10.1130/b37459.1","url":null,"abstract":"A new compilation of Bouguer gravity anomaly data has been used, together with forward and inverse modeling, to reappraise the structure, volume, and state of isostasy of the Cornubian batholith of SW England. We show the individual plutons that comprise the batholith are, on average, ∼10−11 km thick, are outward-sloping in their upper 2−3 km, and are underlain by roots which protrude downward into the middle crust. The batholith volume is estimated within the range of 76,367 ± 17,286 km3, significantly larger than previous estimates. Granite outcrops correlate with elevated topography, and mass balance calculations show that the mass deficiency of the granites relative to their host metasedimentary rocks is approximately equal to the mass excess of the topography relative to air. The existence of roots beneath individual plutons is in general agreement with predictions of an Airy model of isostasy and a depth of compensation that is within the crust rather than at the Moho. In addition, a middle crust compensation depth is compatible with the origin of the granites by heating and melting of metasedimentary rocks and with data from experimental rock mechanics which suggest that at the melting temperature and pressure of granite formation, deformation is likely to be plastic and controlled by glide along dislocations. During pluton emplacement the middle crust would, therefore, have acted as a mechanically weak layer, effectively decoupling the topography from any support it might otherwise have received from the lower crust and/or upper mantle.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"49 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140739602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The correct citation for Figures 1A and 1B was mistakenly left out of the original paper. See PDF file for details.
原论文中错误地遗漏了图 1A 和图 1B 的正确引用。详见 PDF 文件。
{"title":"ERRATUM: Mineralization and genesis of the orogenic gold system in the Kalamaili area, East Junggar, Xinjiang, northwestern China","authors":"Xuexiang Gu, Yongmei Zhang, Zhanling Ge, Weizhi Chen","doi":"10.1130/b36650e.1","DOIUrl":"https://doi.org/10.1130/b36650e.1","url":null,"abstract":"The correct citation for Figures 1A and 1B was mistakenly left out of the original paper. See PDF file for details.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"15 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140736902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fang-Fang An, Tian Qiu, Hong Zhang, Honglin Yuan, Yongfeng Zhu
A 300 Ma magmatic hydrothermal ore-forming process is identified in the Hatu gold belt in west Junggar, northwest China, based on precise age constraint by secondary ion mass spectroscopy U-Pb dating of hydrothermal zircon and Ar-Ar dating of muscovite. The gold deposits in the Hatu belt (Hatu, Qi-V, Huilvshan, etc.) are similar in geology, with NE- and NW-trending orebodies composed of gold-bearing quartz veins and auriferous altered tuffaceous wall-rocks. Hydrothermal zircon grains separated from gold-bearing quartz veins in the Qi-V gold deposit provide a concordia age of 299.6 Ma and a nearly identical weighted mean 206Pb/238U age of 300 ± 2 Ma. Muscovite samples also from the gold-bearing quartz veins yield 40Ar/39Ar plateau ages of 299.6 ± 1.7 Ma, 299.9 ± 1.8 Ma, and 300.6 ± 1.9 Ma. By comprehensive compilation of geological and geochemical characteristics, tectonic evolution, and geochronology of the gold deposits in the Hatu gold belt, our new precise age data confirm that the gold deposits in the Hatu belt formed simultaneously at ca. 300 Ma, and likely formed during a post-collisional extensional setting by magmatic hydrothermal fluid from cooling magmatic sources.
根据热液锆石的二次离子质谱 U-Pb 测年和黝帘石的 Ar-Ar 测年的精确年龄约束，确定了中国西北准噶尔西部哈图金矿带的 300 Ma 岩浆热液成矿过程。哈图带（哈图、七五、会儿山等）的金矿床地质相似，矿体呈东北和西北走向，由含金石英脉和含金蚀变凝灰岩壁岩组成。从 Qi-V 金矿床含金石英脉中分离出的热液锆石颗粒提供了 299.6 Ma 的一致年龄和几乎相同的加权平均 206Pb/238U 年龄（300 ± 2 Ma）。同样来自含金石英矿脉的白云母样品的 40Ar/39Ar 高原年龄分别为 299.6 ± 1.7 Ma、299.9 ± 1.8 Ma 和 300.6 ± 1.9 Ma。通过对哈图金矿带金矿床的地质和地球化学特征、构造演化和地质年代的综合整理，我们新的精确年龄数据证实，哈图金矿带的金矿床是在大约 300 Ma 时同时形成的，并且很可能是在一个隆升时期形成的。我们新的精确年龄数据证实，哈图金矿带的金矿床是在大约 300 Ma 时同时形成的，并且很可能是在碰撞后的延伸环境中由来自冷却岩浆源的岩浆热液形成的。
{"title":"New precise age constraints of the Hatu gold belt, west Junggar, NW China: Implications for a 300 Ma magmatic hydrothermal event in post-collisional setting","authors":"Fang-Fang An, Tian Qiu, Hong Zhang, Honglin Yuan, Yongfeng Zhu","doi":"10.1130/b37148.1","DOIUrl":"https://doi.org/10.1130/b37148.1","url":null,"abstract":"A 300 Ma magmatic hydrothermal ore-forming process is identified in the Hatu gold belt in west Junggar, northwest China, based on precise age constraint by secondary ion mass spectroscopy U-Pb dating of hydrothermal zircon and Ar-Ar dating of muscovite. The gold deposits in the Hatu belt (Hatu, Qi-V, Huilvshan, etc.) are similar in geology, with NE- and NW-trending orebodies composed of gold-bearing quartz veins and auriferous altered tuffaceous wall-rocks. Hydrothermal zircon grains separated from gold-bearing quartz veins in the Qi-V gold deposit provide a concordia age of 299.6 Ma and a nearly identical weighted mean 206Pb/238U age of 300 ± 2 Ma. Muscovite samples also from the gold-bearing quartz veins yield 40Ar/39Ar plateau ages of 299.6 ± 1.7 Ma, 299.9 ± 1.8 Ma, and 300.6 ± 1.9 Ma. By comprehensive compilation of geological and geochemical characteristics, tectonic evolution, and geochronology of the gold deposits in the Hatu gold belt, our new precise age data confirm that the gold deposits in the Hatu belt formed simultaneously at ca. 300 Ma, and likely formed during a post-collisional extensional setting by magmatic hydrothermal fluid from cooling magmatic sources.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"43 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140736836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pleistocene outburst floods from the drainage of glacial Lake Missoula carved bedrock canyons into the Columbia Plateau in eastern Washington, USA, forming the Channeled Scabland. However, rates of bedrock incision by outburst floods are largely unconstrained, which hinders the ability to link flood hydrology with landscape evolution in the Channeled Scabland and other flood-carved landscapes. We used long profiles of hanging tributaries to reconstruct the pre-flood topography of the two largest Channeled Scabland canyons, upper Grand Coulee and Moses Coulee, and a smaller flood-eroded channel, Wilson Creek. The topographic reconstruction indicates floods eroded 67.8 km3, 14.5 km3, and 1.6 km3 of rock from upper Grand Coulee, Moses Coulee, and Wilson Creek, respectively, which corresponds to an average incision depth of 169 m, 56 m, and 10 m in each flood route. We simulated flood discharge over the reconstructed, pre-flood topography and found that high-water evidence was emplaced in each of these channels by flow discharges of 3.1 × 106 m3 s−1, 0.65−0.9 × 106 m3 s−1, and 0.65−0.9 × 106 m3 s−1, respectively. These discharges are a fraction of those predicted under the assumption that post-flood topography was filled to high-water marks for Grand and Moses Coulees. However, both methods yield similar results for Wilson Creek, where there was less erosion. Sediment transport rates based on these discharges imply that the largest canyons could have formed in only about six or fewer floods, based on the time required to transport the eroded rock from each canyon, with associated rates of knickpoint propagation on the order of several km per day. Overall, our results indicate that a small number of outburst floods, with discharges much lower than commonly assumed, can cause extensive erosion and canyon formation in fractured bedrock.
{"title":"Rates of bedrock canyon incision by megafloods, Channeled Scabland, eastern Washington, USA","authors":"K. Lehnigk, Isaac J. Larsen, M. P. Lamb, S. David","doi":"10.1130/b36975.1","DOIUrl":"https://doi.org/10.1130/b36975.1","url":null,"abstract":"Pleistocene outburst floods from the drainage of glacial Lake Missoula carved bedrock canyons into the Columbia Plateau in eastern Washington, USA, forming the Channeled Scabland. However, rates of bedrock incision by outburst floods are largely unconstrained, which hinders the ability to link flood hydrology with landscape evolution in the Channeled Scabland and other flood-carved landscapes. We used long profiles of hanging tributaries to reconstruct the pre-flood topography of the two largest Channeled Scabland canyons, upper Grand Coulee and Moses Coulee, and a smaller flood-eroded channel, Wilson Creek. The topographic reconstruction indicates floods eroded 67.8 km3, 14.5 km3, and 1.6 km3 of rock from upper Grand Coulee, Moses Coulee, and Wilson Creek, respectively, which corresponds to an average incision depth of 169 m, 56 m, and 10 m in each flood route. We simulated flood discharge over the reconstructed, pre-flood topography and found that high-water evidence was emplaced in each of these channels by flow discharges of 3.1 × 106 m3 s−1, 0.65−0.9 × 106 m3 s−1, and 0.65−0.9 × 106 m3 s−1, respectively. These discharges are a fraction of those predicted under the assumption that post-flood topography was filled to high-water marks for Grand and Moses Coulees. However, both methods yield similar results for Wilson Creek, where there was less erosion. Sediment transport rates based on these discharges imply that the largest canyons could have formed in only about six or fewer floods, based on the time required to transport the eroded rock from each canyon, with associated rates of knickpoint propagation on the order of several km per day. Overall, our results indicate that a small number of outburst floods, with discharges much lower than commonly assumed, can cause extensive erosion and canyon formation in fractured bedrock.","PeriodicalId":508784,"journal":{"name":"Geological Society of America Bulletin","volume":"2 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140735640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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