Geological Society of America Bulletin最新文献

{"title":"Erosion and dust emission driven by alternatively episodic water- and wind-dominated environments in the stony Hami Basin, East Asia","authors":"Dehai Zhang, Guocan Wang, Jordan T. Abell, Alex Pullen, Feng Cheng, Tianyi Shen, Junliang Ji","doi":"10.1130/b38004.1","DOIUrl":"https://doi.org/10.1130/b38004.1","url":null,"abstract":"Wind is one of the most dominant agents of erosion and dust production in arid basins within the continental interior of central Asia. However, the interactions between water and wind erosion in landscape evolution and dust production in stony deserts remain unclear. We present an integrated geomorphologic, sedimentologic, and chronologic study from the stony Hami Basin and propose a hypothesis on dust production that may apply to other stony East Asian deserts. We propose that precipitation-driven water erosion contributed to lowering the basin floor and dust emissions. A 10Be depth profile from an isolated terrace (TN3) yields an exposure age of 198.3 +17.9/−23.9 ka which is geologically consistent with the electron spin resonance ages of the lower elevation terraces (TN2 and TS2), suggesting that higher precipitation during interglacials led to the water erosion of the higher elevation terrace and deposition of the lower terrace during the late Pleistocene. Integrated with field investigation, we thus infer that recurrent water erosion plays an important role in exposing friable strata, releasing loose sediments from consolidated bedrock, and increasing the availability of fine particles for the wind to pick up. Intense wind, especially during glacial periods, lowered the basin floor and transported the eroded materials out of the intermontane internally drained basin. Our results show that alternately episodic wind erosion (during glacial periods) and water erosion (during interglacial periods) driven by climatic cycles jointly contributed to the lowering of the basin floor and dust production in the Hami Basin.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147382152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effusive volcanic microcosm of a regional ignimbrite flare-up: Prolonged life cycle of the Chaxas Complex, northern Chile, and its influence on modern volcanic arc character","authors":"Charles Lewis, Shanaka L. de Silva, Alejandro Cisneros de León, Dale Burns, Mattias Villarroel","doi":"10.1130/b37909.1","DOIUrl":"https://doi.org/10.1130/b37909.1","url":null,"abstract":"Abstract Volcanological and temporal development of the Chaxas Complex on the western edge of the Altiplano-Puna Volcanic Complex of northern Chile is reported here in full for the first time. The Chaxas Complex is a collection of spatially and chronologically related lava domes and associated volcaniclastic deposits that was thought to be constructed between 8.35 Ma and 1.09 Ma, spanning almost the entire duration of the Altiplano-Puna Volcanic Complex flare-up. Prior studies also suggested that the 4.18 ± 0.03 Ma Puripicar ignimbrite was discharged from a vent near the Chaxas Complex. However, development of the Chaxas Complex has not been detailed until now. Redefined stratigraphy and volcanic history indicate a younger and shorter history for the Chaxas Complex than previously thought. The oldest unit described is the 5.44 ± 0.01 Ma Agua Perdida Rhyolite, which immediately underlies the 4.18 ± 0.03 Ma Puripicar ignimbrite that was sourced from buried vents to the north of the Chaxas Complex. Puripicar is in turn overlain by the 3.73 ± 0.02 Ma Embaucador Rhyolite. Following eruption of the Embaucador, the Chaxas Complex produced effusive domes, a sequence of local ignimbrites, block-and-ash flows, debris avalanches, and lahars between 3.54 ± 0.33 Ma and 1.242 ± 0.049 Ma. The 0.98 ± 0.03 Ma Purico ignimbrite caps the Chaxas sequence in the southeast. Stacked on top of the Chaxas Complex and the buried Puripicar source vent to the west and north is a thick (up to 1 km) pile of dacitic (62%–66% SiO2) coulées and lava flows (the arc platform lavas) that form a basal platform to the 23-km-long Sairecabur-Escalante-Colorados-Putana arc volcano cluster, which define an unusually spatially dense zone of composite edifices. Based on mineralogy and geochemistry of the arc platform lavas, they are identified as a transitional sequence between the end of the Chaxas Complex and the development of the modern arc. U-Pb zircon ages of the arc platform lavas are as young as 0.07 ± 0.01 Ma but also carry zircon crystal cargo that chronologically overlaps with those in eruptions of the Chaxas Complex, connoting that intrusions of the Puripicar-Chaxas magmatic system are being sampled by younger arc magmas. The anomalously dense spatial density of this volcano cluster may reflect the filtering effect of a now solidified intrusive complex that birthed the Puripicar supereruption. Crustal priming by large silicic systems followed by focused “steady-state” arc activity is posited as a primary mechanism to overprint characteristic volcano spacing in the Central Volcanic Zone.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"137 5-6","pages":"2596-2618"},"PeriodicalIF":0.0,"publicationDate":"2025-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147915956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Brecciation and epithermal mineralization in the Baia Mare ore district (Romania): The Wilhelm deposit","authors":"Călin Gabriel Tămaş","doi":"10.1130/b37585.1","DOIUrl":"https://doi.org/10.1130/b37585.1","url":null,"abstract":"Abstract The Wilhelm deposit is part of an intermediate-sulfidation polymetallic Zn-Pb-Ag-Au vein system in the Baia Mare ore district of the Eastern Carpathians, Romania, where left-lateral tectonic displacement in an E–W-dominated fault system controlled the epithermal mineralization. The Wilhelm deposit consists of tens of vein sets, including the sub-parallel Complex veins (1–7), and is hosted by the ca. 11.6 Ma Ulmoasa dacite. The 7 Complex vein is composed of sub-vertical breccia, including marginal fine-grained rock flour breccia (Fgb), which is matrix-supported and cemented by minor interstitially precipitated minerals. This breccia is cut and re-brecciated multiple times by a clast-supported breccia (Csb) cemented by four hydrothermal mineralization stages comprising the economic ore, i.e., gray quartz–pyrite (M1); sphalerite–galena–pyrite–freibergite (M2); white calcite–electrum–freibergite (M3); and gray-blue quartz–freibergite with an unnamed Ag-mineral (Ag,Cu)8SbS5 (M4). Each mineralization stage follows its distinct brecciation event (B1 to B4). This clast-supported breccia is comminuted near contacts with unbrecciated dacitic host rock to a matrix-supported breccia with rock flour enclosing small ore and host-rock fragments (Ofb). The rounded shape of fragments originating in the underlying sedimentary rock basement indicates the upward transport of Fgb by incipient phreatomagmatic activity. The dominant ore and gangue minerals of Csb suggest dominant hydrothermal fluid flow during ore formation. The gradual contact of Csb with Ofb and its clasts indicate that Ofb was formed by tectonic movement during the waning stage of hydrothermal activity, because both breccias are cut by pink calcite veins (mineralization stage M5). A similar evolution from phreatomagmatic breccias through repeated hydrothermal brecciation and mineralization to late tectonic brecciation is characteristic of the entire Baia Mare district. Its consistent relation to coeval calc-alkaline magmatism indicates that magmatic fluids played an essential role in ore formation. Resulting steep thermal gradients with or without mixing with surface water created a metal zonation with deep Cu-rich zones, intermediate Pb-Zn zones, and Au-rich bonanza zones due to shallow fluid boiling. The local presence of Au-rich ores also at greater depth indicates fluid de-sulfidation as an alternative mechanism for Au precipitation.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"137 5-6","pages":"1927-1944"},"PeriodicalIF":0.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147919503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pervasive Neoarchean melting of subducted sediments generating sanukitoid and associated magmatism in the North China Craton, with implications for the operation of plate tectonics","authors":"Jialiang Li, Shengwen Liu, Haibo Ma, Chen Wu, Di‐Cheng Zhu, Jingao Liu","doi":"10.1130/b37279.1","DOIUrl":"https://doi.org/10.1130/b37279.1","url":null,"abstract":"The Mesoarchean to Neoarchean period (ca. 3.0−2.5 Ga) is the most important stage during the emergence and evolution of plate tectonics. However, plate subduction at this time may have been less stable and perhaps more susceptible to the lubrication effect of sediments than the modern counterpart. Such predictions have not yet been verified by field-based investigations. In this work, we identified two types of rock units (i.e., sanukitoids and associated adakitic suites, exposed in the Eastern Hebei Complex of the North China Craton) and illustrated their petrogenesis and tectonic context through field, geochronologic, geochemical, and isotopic investigations. Laser ablation−inductively coupled plasma−mass spectrometry zircon U-Pb analyses suggest that the two magmatic suites formed within a relatively short time span of ca. 2596−2544 Ma and ca. 2559−2533 Ma, respectively. The sanukitoids are composed of meta-andesites and diorite porphyrites and characterized by relatively high MgO (3.94−5.62 wt%), Mg# (50−61), Cr (73−343 ppm), and Ni (37−111 ppm) values. The adakitic rocks are composed of granodiorite-granite gneisses and have relatively high Sr (316−1001 ppm) and low Y (7−13 ppm) and Yb (0.83−1.37 ppm) contents, and relatively high Sr/Y (36−89) and La/Yb (16−45) ratios. Rocks from both suites exhibit depletions of Nb, Ta, and Ti and have similar Sr-Nd-Hf-Zn isotopes: variable (87Sr/86Sr)i (0.7002−0.7053), weakly positive εNd(t) (+0.3 to +1.7) and εHf(t) (+1.8 to +6.8), and slightly heavy δ66Zn (0.30‰−0.36‰). These geochemical characteristics indicate that the sanukitoids were derived from the melting of subducted sediments followed by melt-mantle interaction, whereas the adakitic rocks were produced by direct partial melting of subducted plate (including tonalite-trondjhemite-granodiorite melts) under a garnet stability field with minor sediments. Such distinct magmatic rock associations, together with the coeval charnockites and tholeiites with diverse compositions in the adjacent area, can be best explained by a slab breakoff model. Further, events associated with slab breakoff are likely to represent a transition of a quasi-plate tectonic regime, characterized by multiple, continuous, and stagnant attempts to start the modern-style subduction on Earth. In addition, the emergence of sanukitoids and associated magmas symbolized the onset of supracrustal recycling into the mantle. Combined with the Nd-Hf-Zn isotopes of diverse magmatic rocks in the North China Craton that are comparable to other Precambrian magmatic rock suites worldwide, we suggest that supracrustal recycling symbolized the onset of plate tectonics since ca. 3.0 Ga, and by inference played a key role in the development of subduction-driven plate tectonics in addition to Earth’s secular cooling.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"52 8","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139447887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Metamorphic evolution of high-pressure and ultrahigh-temperature granulites from the Alxa Block, North China Craton: Implications for the collision and exhumation of Paleoproterozoic orogenic belts","authors":"Lei Zou, Jing-Hui Guo, Li-Fei Zhang, Guangyu Huang, Shu‐Juan Jiao, Zhong-Hua Tian, Ping-Hua Liu","doi":"10.1130/b37120.1","DOIUrl":"https://doi.org/10.1130/b37120.1","url":null,"abstract":"High-pressure (HP) and ultrahigh-temperature (UHT) granulites with a high geothermal gradient (greater than 500 °C/GPa) are prominent features of Paleoproterozoic orogenic belts and may represent paired metamorphic belts present during the early stages of plate tectonics. Understanding their pressure−temperature−time (P-T-t) paths and metamorphic evolutionary relationships could provide valuable constraints on the tectonic processes of Paleoproterozoic orogenic belts. Here, we describe garnet mafic and clinopyroxene-orthopyroxene (Cpx-Opx) granulites from the Diebusige area of the Alxa Block in the western part of the Khondalite Belt, North China Craton. Through detailed petrographic, phase equilibrium modeling, and Ti-in-amphibole thermometric studies, we obtained the preserved peak mineral assemblages of two types of mafic granulites: garnet + clinopyroxene + amphibole + plagioclase + quartz + ilmenite, and clinopyroxene + orthopyroxene + plagioclase + amphibole + garnet (rare) + ilmenite. The preserved peak P-T conditions were determined to be 850−890 °C/11.4−13.2 kbar (HP granulite-facies) and 950−970 °C/8.2−9.2 kbar (UHT conditions), with thermal gradients of ∼70 °C/kbar (moderate differential temperature/differential pressure, dT/dP) and ∼110 °C/kbar (high dT/dP), respectively. Using sensitive high-resolution ion microprobe U-Pb dating and rare earth element analysis of zircons, we found that the garnet mafic granulite recorded an HP granulite-facies metamorphic age of ca. 1.95 Ga and a retrograde cooling age of ca. 1.8 Ga, while the Cpx-Opx granulite recorded a consistent retrograde cooling age of ca. 1.8 Ga. By combining these results with the metamorphic evolution and timing (ca. 1.92−1.91 Ga) of UHT rocks from the Khondalite Belt, we suggest that the garnet (HP) mafic and Cpx-Opx (UHT) granulites may represent different stages of the same metamorphic event, shedding light on the processes involved in the collision and subsequent exhumation of Paleoproterozoic orogenic belts.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"8 3","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138951928","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Origin of Early Cretaceous mafic volcanic rocks from the Erlian Basin west of the Great Xing’an Range of North China: Implications for the tectono-magmatic evolution of East Asia","authors":"Jianzhou Tang, Zhicheng Zhang, Mark B. Allen, Shuguang Song, Cong Ding, Ke Li, Yan Chen","doi":"10.1130/b37068.1","DOIUrl":"https://doi.org/10.1130/b37068.1","url":null,"abstract":"Early Cretaceous intraplate volcanic rocks are widespread in NE Asia, but their origin remains controversial. This work presents zircon U-Pb ages, whole-rock element and Sr-Nd isotope data for mafic volcanic rocks from the Erlian Basin, a wide rift basin in NE Asia. There were two episodes of Early Cretaceous mafic volcanism in the Erlian Basin, and the eruptions show contrasting geochemical compositions. The early mafic volcanic rocks, with U-Pb ages of ca. 140−135 Ma, show slightly depleted Sr-Nd isotope compositions (ISr(t) = 0.7042−0.7052; εNd(t) = +0.82 to +3.0) and arc-like trace-element compositions, which are derived from subduction-related fluid/melt metasomatized lithosphere mantle. The late mafic volcanic rocks (dated at ca. 125 Ma) have enriched Sr-Nd isotopes (ISr(t) = 0.7055−0.7077; εNd(t) = −0.50 to −2.67) and oceanic-island basalt (OIB)-like trace-element compositions, revealing the metasomatism of melts from crustal materials and asthenosphere mantle. The two types of mafic volcanic rocks may record the interactions of the mantle and melts from the subducted paleo-Pacific oceanic slab at different depths. The landward-then-oceanward migration pattern of the Mesozoic volcanism from NE Asia can be explained by the flat subduction and subsequent slab roll-back of the Paleo-Pacific Ocean, consistent with migration patterns from the North China Craton and South China Block, implying similar Jurassic−Cretaceous subduction evolution along the entire East Asia margin. Some Late Jurassic to Early Cretaceous dates from east Mongolia and the southern margin of the Erlian Basin diverge from this trajectory. In combination with previous studies, we suggest that the Early Cretaceous pervasive intraplate volcanism in the Erlian Basin and adjacent areas of NE Asia mainly resulted from the slab roll-back of the Paleo-Pacific Ocean with a combined effect from the post-collision extension of the Mongol-Okhotsk orogen.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"76 17","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138957899","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ordovician−Early Devonian granitic magmatism as the consequence of intracontinental orogenic activity along the Qinhang belt in South China","authors":"Xinchen Yuan, Junlai Liu, Qijun Yang, Baojun Zhou, Yong Lv, Jiwen Wu","doi":"10.1130/b36992.1","DOIUrl":"https://doi.org/10.1130/b36992.1","url":null,"abstract":"The early Paleozoic tectono-magmatic activity within the South China block, which is well illustrated by Ordovician−Devonian granites in the western Qinhang belt, was the response to closure of the Proto-Tethys Ocean and convergence of continental blocks. The spatiotemporal distribution and source characteristics of the granites provide us the opportunity to understand the processes and driving mechanisms of intracontinental orogeny. As an example, the Miaoershan-Yuechengling granite batholith in northern Guangxi, located along the western margin of the Qinhang orogenic belt, is mainly composed of quartz monzonite and monzogranite. All the granitic rocks from Miaoershan-Yuechengling batholith are composed of K-feldspar, quartz, plagioclase, biotite, and hornblende. Geochronologic dating indicates that the Miaoershan-Yuechengling batholith was emplaced during the late Silurian and Early Devonian, respectively. The rocks have high SiO2, with an average value of 73.29 wt%, and total alkalis (Na2O + K2O = 7.21−10.03 wt%), but low Al2O3 (12.96−15.51 wt%), showing characteristics of the high-potassium calc-alkaline series of S-type peraluminous granites (Al2O3/[CaO + Na2O + K2O] = 1.03−1.22). Trace elements in the Miaoershan-Yuechengling granitic rocks are characterized by enrichment of large ion lithophile elements and depletion of high field strength elements. Their rare earth element (REE) trends are characterized by relatively flat distribution patterns with weak light REE enrichment, weak heavy REE fractionation, and negative Eu anomalies. Zircons from the rocks have negative εHf(t) values ranging from −13.24 to −5.1, with crustal model ages (THf2) of 2.2−1.7 Ga. These features indicate that they are S-type granites with parental magmas originating from partial melting of sandy argillaceous sources of Paleoproterozoic lower continental crust. The thermal budget for Ordovician to Early Devonian magmatism is attributed either to crustal thickening in relation to intracontinental orogenic compression or to crustal thinning due to postorogenic tectonic extension during assembly and breakup of Greater Gondwana. This study reveals that the change in mantle convection systems during plate interactions acted as a major driving force for the early orogenic processes, late collapse of the orogenic belt, and massive syncollisional to postorogenic magmatism.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"34 4","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138957230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Permian−Triassic magmatism above a slab window in the Eastern Tianshan: Implications for the evolution of the southern Altaids","authors":"M. Muhtar, Wenjiao Xiao, M. Brzozowski, Q. Mao, He Yang, Changzhi Wu","doi":"10.1130/b37133.1","DOIUrl":"https://doi.org/10.1130/b37133.1","url":null,"abstract":"Permian−Triassic metaluminous−peraluminous granitoids, mafic−ultramafic plutons, and Ni-Cu and Au deposits are prominent features in the Eastern Tianshan of the southern Altaids. However, the genetic relationship between coeval granitoids and mafic−ultramafic intrusions, and the geodynamics of magmatism and related mineralization, remain ambiguous. To address these ambiguities, we present petrological, geochemical, and bulk-rock Sr-Nd-Fe and zircon U-Pb-Hf isotope analyses of granitoids from the Shuangchagou Complex and gabbros from the Huangshandong Complex in the Eastern Tianshan. Zircon U-Pb ages demonstrate that the Huangshandong gabbro was emplaced at ca. 277.8 ± 1.4 Ma. In contrast, U-Pb ages determined from zircons in the granitic rocks of the Shuangchagou Complex suggest that the complex crystallized from three stages of magmatism: (1) strongly peraluminous S-type granitic magma represented by early-stage gneiss and granitic veins (ca. 289 Ma), (2) metaluminous to weakly peraluminous I-type granitic magmas represented by the intermediate-stage granitoids (ca. 283−261 Ma), and (3) late-stage granitoids (ca. 250−241 Ma). The intermediate- and late-stage granitoids (ca. 283−241 Ma) show clear enrichments in the light rare earth elements and large ion lithophile elements (e.g., Rb, Th, and U), and depletions in high field strength elements (e.g., Nb, Ta, and Ti), similar to arc magmas, which indicates that the North Tianshan oceanic plate was still subducting during the Middle Triassic. Considering the diversity of magmatic rocks (e.g., mid-oceanic-ridge−type mafic rocks, and I-, S- and A-type igneous rocks), mineralization styles (e.g., Alaskan-type Ni-Cu sulfide deposits and orogenic gold deposits), and the dextral strike-slip faults (e.g., Kanggur Fault) that occurred concurrently in the Eastern Tianshan during the Early Permian to Middle Triassic, we suggest that splitting of the subducted portion of the North Tianshan oceanic plate created a slab window that allowed the upwelling and partial melting of asthenospheric mantle to form the mafic−ultramafic intrusions and related Ni-Cu sulfide deposits. Sustained migration of magma provided the heat necessary to induce partial melting, devolatilization, and desulfurization of crustal materials, producing the Permian−Triassic, high-K to calc-alkaline I- and S-type granitoids, and associated orogenic gold deposits. By integrating the results of this study with published work regarding the Kanggur Accretionary Complex, we suggest that the subduction of the North Tianshan Ocean may have lasted until the Late Triassic.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"102 52","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138958653","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An experimental investigation of the characteristics of cataclastic bands in high-porosity sandstones","authors":"Mingming Jiang, Xiaofei Fu, Zicheng Wang","doi":"10.1130/b36801.1","DOIUrl":"https://doi.org/10.1130/b36801.1","url":null,"abstract":"Cataclastic bands in high-porosity sandstones significantly influence fluid flow, thus impacting the exploration and development of oil and gas. However, little experimental research has been conducted on the main factors controlling the formation, evolution, and physical properties of cataclastic bands. Moreover, it is difficult to use field surveys to discern variations and trends in the structural and physical properties of cataclastic bands formed during different deformation processes. In this study, we used a high-pressure and low-velocity ring-shear apparatus to analyze high-porosity, pure sandstone. Multiple sets of ring-shear experiments were carried out using the effective normal stress or shear displacement as a single variable. The experimental samples were analyzed based on physical property tests and thin sections. Our results indicate that the particles in the cataclastic bands generally have better roundness and are smaller (by at least two to three orders of magnitude) than the host rock. The porosity and permeability of the cataclastic bands are ∼70% lower and two to three orders of magnitude lower than those of the host rock, respectively. The characteristics of the cataclastic bands are controlled by two main factors, namely, the effective normal stress and shear displacement. The effective normal stress controls the intensity of the cataclasis, and the shear displacement controls the physical properties of the grains and indirectly controls the evolutionary stage, which corresponds to the intensity of cataclasis. As the effective normal stress or shear displacement increases, the cataclasis in the cataclastic bands intensifies, and the grain size decreases; then, the decrease in the porosity gradually declines, and the permeability decrease and thickness increase and then plateau. The results of this study reveal the evolutionary mechanisms of the structural and physical properties of cataclastic bands in high-porosity sandstones and lay a theoretical foundation for determining the effect of these bands on fluid flow in oil and gas reservoirs.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"114 25","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138959619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleocene oceanic-island basalt−type magmatism in the Lhasa Block attests to decoupled mantle-crust deformation during Indian-Asian collision","authors":"Yun-Chuan Zeng, Ji-feng Xu, Jian‐Lin Chen, Bao-di Wang, F. Huang, Hongxia Yu","doi":"10.1130/b37289.1","DOIUrl":"https://doi.org/10.1130/b37289.1","url":null,"abstract":"The post-collisional evolution of the Tibetan lithosphere is of paramount significance to our understanding of collisional orogeny. It is generally postulated that the Lhasa lithospheric mantle was horizontally shortened and thickened coherently with the overlying crust to form a physical barrier, preventing Indian subduction beneath Tibet until the thickened mantle root was foundered during the Miocene. This study first identifies post-collisional oceanic-island basalt (OIB)-type magmatism in the Lhasa Block (LB), as attested by zircon U-Pb age (ca. 58 Ma) and geochemistry—positive Nb-Ta anomalies, high La/Yb, and depleted bulk-rock Sr-Nd and zircon Hf isotopes, of diabase in the northern (inboard relative to Indus Suture) part of this block. Coupled with extensive early Paleogene arc-type magmatism in the southern-central LB and thermodynamic modeling, we suggest that these diabases were formed by partially molten upwelling asthenosphere near the base of continental crust, where much of the underlying lithospheric mantle had been removed due to Neo-Tethyan slab rollback and lithospheric delamination. Compared to OIB-type magmatism worldwide, the diabases investigated here were emplaced peculiarly in a region where the continental crust was under horizontal compression and shortening by coeval thrusting. Our study thus implies a decoupled deformation between the crust and mantle of the LB during the early Indian-Asian collision.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"82 4","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138995359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}