Geological Society of America Bulletin最新文献

{"title":"Pre- and postsettlement depositional processes and environments of the 3rd- to 5th-order White Clay Creek watershed, Piedmont Province, Pennsylvania and Delaware, USA","authors":"J. Pizzuto, M. E. Huffman, E. Symes","doi":"10.1130/b37032.1","DOIUrl":"https://doi.org/10.1130/b37032.1","url":null,"abstract":"We extend two hypotheses based on studies of 1st- to 3rd-order Piedmont watersheds of southeastern Pennsylvania, USA, by collecting data in a larger 3rd- to 5th-order watershed nearby. One hypothesis posits that presettlement river corridors were dominated by wetlands, and the other suggests that river valleys were filled by millpond sedimentation following European settlement. Both hypotheses support new river restoration practices, so their generality is important to assess. Ten lithofacies indicate depositional environments, while pedostratigraphic criteria and 14C dating define presettlement and postsettlement stratigraphic units. Basal gravels similar to modern stream bed sediments represent presettlement channels with active bedload transport. Wedge-shaped gravel deposits resembling modern bars further document presettlement bedload transport by channelized flows. Extensive presettlement and postsettlement units of massive, organic-poor, fine-grained sediment formed when overbank flows inundated floodplains. Peat deposits, exposed at a single site (but absent elsewhere), represent a presettlement wetland. Decimeter-thick, discontinuous, massive carbonaceous fine-grained sediments occasionally overlie basal gravels; these may represent localized wetlands adjacent to presettlement channels or hydraulic backwater environments. Laminated sand and mud accumulated behind one 3-m-high mill dam, but these millpond deposits are absent at other sites. Instead of being dominated by wetlands, presettlement river corridors are better described as a complex mosaic of riparian environments including older colluvial landforms, floodplains (some of which may have been seasonally inundated wetlands), primary (and possibly secondary) channels, and depending on geomorphic setting, either localized or valley-spanning wetlands. After European settlement, millponds were important locally, but their deposits represent a minor component of the stratigraphic record.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46658263","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":"FTIR study of H2O in silicate minerals and mineral inclusions in chromite from the peridotite zone of the Stillwater complex (Montana, USA): Evidence for chromitite formation in an H2O-rich environment","authors":"Yang Bai, Mengmeng Cui, B. Su, Xia Liu, Yan Xiao, P. Robinson, X. Gu","doi":"10.1130/b36733.1","DOIUrl":"https://doi.org/10.1130/b36733.1","url":null,"abstract":"Although the involvement of hydrous fluids has been frequently invoked in the formation of stratiform chromitites in layered intrusions, there is a lack of natural evidence to signify their presence and mechanism. Here, Fourier-transform infrared spectroscopy (FTIR) of H2O in silicate minerals in the lowermost layer and G chromitite layer of the Stillwater complex, Montana, USA, shows that olivine grains have 20−55 ppm H2O, orthopyroxene has 30−45 ppm H2O, and clinopyroxene has 144−489 ppm H2O. The jointly increasing H2O contents of olivine and orthopyroxene in silicate cumulates along with magma differentiation record a negative correlation in chromitites. On the basis of poikilitic clinopyroxene, we calculated that the interstitial melts had averages of 1.3 wt% and 2.3 wt% H2O in dunite and chromitite, respectively, showing significant differences between chromitites and silicate cumulates. More than 10% of the chromite grains contained polymineralic inclusions up to 100 μm in size that were composed mainly of orthopyroxene, hornblende, plagioclase, and phlogopite. Most of these minerals were characterized by higher MgO and fluid-mobile element contents, such as Na and K, than minerals in associated silicates. Based on the mineral modes of the hydrous phases and their compositions, the trapped fluids contained ∼2.6 wt% H2O, consistent with the FTIR estimates, indicating the inclusion compositions represent interstitial melts instead of parental magmas. These observations indicate that the chromite microlites collected fluids during early crystallization, leading to a heterogeneous fluid redistribution in the melt. The fluids were collected on the surface of chromite grains during crystallization and then dissolved into poikilitic pyroxene. Chromite grains could also be efficiently floated by these fluids, causing them to migrate away from the silicate minerals in the magma channel and leading to the formation of nearly monomineralic chromitite seams. This process serves as a kinetic model indicating that chromite could be completely separated from silicates during mechanical sorting in layered intrusions.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48401670","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":"The formation of a giant post-collision porphyry copper system: A case study of the Jiama deposit, Tibet","authors":"Miao Sun, Junwu Tang, R. Klemd, Bin Lin, Pan Tang, Zebin Zhang, Wei Chen, Fa-qiao Li, Jing Qi, Han Chen, Feng-hua Gu","doi":"10.1130/b36924.1","DOIUrl":"https://doi.org/10.1130/b36924.1","url":null,"abstract":"The large magma reservoirs underlying world-class porphyry deposits are one of the key factors in their formation, which thus led to the present study focusing on the unmineralized intrusive rocks underlying the porphyry molybdenum-copper orebody of the post-collisional Jiama porphyry-skarn copper-polymetallic deposit in southern Tibet. The Jiama porphyry intrusion comprises intermediate-silica quartz diorite, monzogranite, and granodiorite porphyries, as well a high-silica granite porphyry. The intrusive rocks suite exhibits similar whole-rock Sr-Nd isotopic compositions [εNd(t) = −3.9 to −0.8], suggesting a common, non-radiogenic magma source. Yet, these rocks have distinct geochemical characteristics. The intermediate-silica rocks are relatively enriched in Ba and Sr with minor Eu anomalies, and show adakite-like geochemical characteristics. In contrast, the high-silica granite porphyry is strongly depleted in Ba, Sr, and Eu, and lacks adakite-like geochemical characteristics. We propose that the high-silica granite porphyry represents highly fractionated melt extracted from a silicic mush reservoir (crystallinity of ∼40%−65%), and that the monzogranite and granodiorite porphyries constitute the complementary residual silicic cumulates. High crystallinity facilitates the formation of connected fluid pathways, allowing the efficient removal of volatiles from the remaining silicic melt and a rapid flux of the ore-forming fluids toward the apical parts of the large magma reservoir. Less-evolved mafic melt is believed to have repeatedly intruded the base of the magma reservoir, thereby releasing volatiles and water into the silicic mush systems. The volatiles migrated upward through the fluid channels and accumulated in the apical part of the magma reservoir, subsequently, as a result of the overpressure in the roof zone, ore-forming fluids and successive batches of magma were expelled together, thereby forming the Jiama porphyry-skarn deposit.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49369587","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":"Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life","authors":"S. Slotznick, N. Swanson‐Hysell, Yiming Zhang, Katherine E. Clayton, C. Wellman, N. Tosca, P. Strother","doi":"10.1130/b36634.1","DOIUrl":"https://doi.org/10.1130/b36634.1","url":null,"abstract":"The Nonesuch Formation microbiota provide a window into ca. 1075 Ma life within the interior of ancient North America. The Nonesuch water body formed following the cessation of widespread volcanism within the Midcontinent Rift as the basin continued to subside. In northern Michigan and Wisconsin, USA, the Copper Harbor Conglomerate records terrestrial alluvial fan and fluvial plain environments that transitioned into subaqueous lacustrine deposition of the Nonesuch Formation. These units thin toward a paleotopographic high associated with the Brownstone Falls angular unconformity. Due to these “Brownstone Highlands,” we were able to explore the paleoenvironment laterally at different depths in contemporaneous deposits. Rock magnetic data constrain that when the lake was shallow, it was oxygenated as evidenced by an oxidized mineral assemblage. Oxygen levels were lower at greater depth—in the deepest portions of the water body, anoxic conditions are recorded. An intermediate facies in depth and redox between these endmembers preserves detrital magnetite and hematite, which can be present in high abundance due to the proximal volcanic highlands. This magnetic facies enabled the development of a paleomagnetic pole based on both detrital magnetite and hematite that constrains the paleolatitude of the lake to 7.1 ± 2.8°N. Sediments of the intermediate facies preserve exquisite organic-walled microfossils, with microfossils being less diverse to absent in the anoxic facies where amorphous organic matter is more likely to be preserved. The assemblage of cyanobacteria and eukaryotes (both photoautotrophs and heterotrophs) lived within the oxygenated waters of this tropical Mesoproterozoic water body.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48365003","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":"High-temperature altered oceanic crust recycling into oceanic-island basalt−like mantle produces alkaline continental crust driven by mélange diapirs: Insights from isotopic tracing and numerical modeling","authors":"Huichuan Liu, Pengpeng Huangfu, G. Zhu","doi":"10.1130/b36961.1","DOIUrl":"https://doi.org/10.1130/b36961.1","url":null,"abstract":"Genesis of the large-volume alkaline crust at active continental margin is still enigmatic for geologists worldwide. The point at issue is whether or not subducted oceanic crusts get involved and how they interact with the mantle source of the alkaline crust. Late Mesozoic juvenile alkaline crusts with high εNd(t)-εHf(t) values are widely distributed in the Great Xing’an Range of NE China, as parts of an arc magmatic belt related to the Mongol-Okhotsk Ocean closure. We carried out multi-isotope analyses and 2-D high-resolution numerical modeling to trace the mantle source nature of the alkaline crust. The alkaline rocks show similar trace elements with the I-type enriched mantle and are originated from an upwelling oceanic-island basalt−like mantle. Their high field strength element depleted arc features indicate the crustal material addition in the source region. Low δ18O, mantle-like Sr-Nd-Hf and light Mg isotope compositions, limited δ7Li variations, no Nd-Hf decoupling, and our mixing calculation preclude continental crustal assimilation, marine-sediment melt and/or altered oceanic crust (AOC)−fluid metasomatism, and bulk marine sediment involvement, and provide evidence of the bulk AOC addition in the mantle source. Lower δ18O values than the mantle and relatively low δ7Li values further confirmed the involved AOC to be a high-temperature (high-T) AOC. Our multi-isotope tracing successfully fingerprints the recycled high-T AOC into the source region of the alkaline juvenile crust. Then, our 2-D high-resolution numerical modeling reconstructs the high-T AOC recycling processes driven by mélange melting.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44805886","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":"Interseismic creep of carbonate-hosted seismogenic normal faults: Insights from central Italy","authors":"L. Del Sole, S. Mazzoli, M. Carafa, Giovanni Toffol, G. Pennacchioni, G. Giuli, C. Invernizzi, E. Tondi","doi":"10.1130/b36954.1","DOIUrl":"https://doi.org/10.1130/b36954.1","url":null,"abstract":"Understanding fault behavior in carbonates is critical because they represent loci of earthquake nucleation. Models of fault-slip mode generally assume: (1) seismic sliding and aseismic sliding occur in different fault patches, (2) creep is restricted to lithology-controlled weak domains, and (3) rate-weakening patches are interseismically locked. We studied three carbonate-hosted seismogenic normal faults in central Italy by combining (micro)structural and geochemical analyses of fault rocks integrated with new seismic coupling estimates. The (upper bound) seismic coupling was estimated to be ∼0.75, which indicates that at least 25% of the long-term deformation in the study area is released aseismically in the upper crust. Microscopy and electron-backscatter diffraction analyses revealed that whereas the localized principal slip zone records seismic slip (as ultracataclastic material, calcite crystallographic preferred orientation (CPO), and truncated clasts), the bulk fault rock below behaves differently. Cataclasites in massive limestones deform by cataclastic flow, pressure solution, and crystal plasticity, along with CPO development. Foliated tectonites in micritic limestones deform by pressure solution and frictional sliding, with CPO development. We suggest these mechanisms accommodate on-fault interseismic creep. This is consistent with experimental results reporting velocity-strengthening behavior at low slip rates. We present multiscale evidence of coexisting seismic and aseismic slip along the same fault in limestones during the seismic cycle. Our results imply that on-fault aseismic motion must be added to seismic slip to reconcile the long-term deformation rates and that creep is not exclusive to phyllosilicate-bearing units. Our work constitutes a step forward in understanding fault behavior and the seismic cycle in carbonates, and it may profoundly impact future studies on seismogenic potential and earthquake hazard assessment.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44256621","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":"Examining the influence of disequilibrium landscape on millennial-scale erosion rates in the San Bernardino Mountains, California, USA","authors":"M. Argueta, S. Moon, K. Blisniuk, N. Brown, L. Corbett, P. Bierman, S. Zimmerman","doi":"10.1130/b36734.1","DOIUrl":"https://doi.org/10.1130/b36734.1","url":null,"abstract":"Temporal and spatial variations of tectonic rock uplift are generally thought to be the main controls on long-term erosion rates in various landscapes. However, rivers continuously lengthen and capture drainages in strike-slip fault systems due to ongoing motion across the fault, which can induce changes in landscape forms, drainage networks, and local erosion rates. Located along the restraining bend of the San Andreas Fault, the San Bernardino Mountains provide a suitable location for assessing the influence of topographic disequilibrium from perturbations by tectonic forcing and channel reorganization on measured erosion rates. In this study, we measured 17 new basin-averaged erosion rates using cosmogenic 10Be in river sands (hereafter, 10Be-derived erosion rates) and compiled 31 10Be-derived erosion rates from previous work. We quantify the degree of topographic disequilibrium using topographic analysis by examining hillslope and channel decoupling, the areal extent of pre-uplift surface, and drainage divide asymmetry across various landscapes. Similar to previous work, we find that erosion rates generally increase from north to south across the San Bernardino Mountains, reflecting a southward increase in tectonic activity. However, a comparison between 10Be-derived erosion rates and various topographic metrics in the southern San Bernardino Mountains suggests that the presence of transient landscape features such as relict topography and drainage-divide migration may explain local variations in 10Be-derived erosion rates. Our work shows that coupled analysis of erosion rates and topographic metrics provides tools for assessing the influence of tectonic uplift and channel reorganization on landscape evolution and 10Be-derived erosion rates in an evolving strike-slip restraining bend.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41542037","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":"Vanished evaporites, halokinetic structure, and Zn-Pb mineralization in the world-class Angouran deposit, northwestern Iran","authors":"Liang-liang Zhuang, Yucai Song, D. Leach, Yingchao Liu, Z. Hou, M. Fard","doi":"10.1130/b36910.1","DOIUrl":"https://doi.org/10.1130/b36910.1","url":null,"abstract":"The Angouran deposit (19.3 Mt at 23.4% Zn and 4% Pb) is the second-largest Zn-Pb deposit in Iran. The deposit is hosted in a Neoproterozoic−Cambrian marble-schist sequence within a breccia pipe in a domal structure, with sulfide mineralization under low-temperature hydrothermal conditions (<200 ºC). The features of the ore-hosting breccias are similar to known halokinetic diapir breccias in the world but evaporite minerals are subtle. The common types of breccia clasts in the Angouran breccia pipe include a matrix-supported angular clast (float breccia) with highly variable sizes and orientations and exotic volcanic clasts. The volcanic clasts were derived from the underlying Miocene volcanic rocks, evidenced by the consistent petrography and zircon U-Pb ages dated at 20−19 Ma. Abundant smithsonite pseudomorphs after anhydrite and anhydrite inclusions within sphalerite and pre-ore marcasite in the breccia matrix indicate that the breccia pipe contains abundant anhydrite prior to the Zn-Pb mineralization. The enrichment of evaporite is also supported by the occurrence of considerable double-terminated quartz crystals that contain spherical and tabular carbonate inclusions and anomalously high Li, Na, and K concentrations, relatively high B concentration, and high δ18O values (up to 28.3‰). These observations suggest the Angouran deposit formed in a former halokinetic diapir breccia pipe. The halokinetic diapirism was possibly triggered by thrust loading of the marble-schist sequence over the Miocene evaporite beds during the Arabia-Eurasia continental collision. Halokinetic structures elsewhere in the Angouran region warrant this consideration. Most of the evaporite minerals in the breccia pipe were dissolved and replaced before and/or during subsequent Zn-Pb sulfide and smithsonite mineralization events. This study provides a good example for the identification of vanished evaporites, halokinetic structure, and associated Mississippi Valley-type mineralization.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46837911","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":"Tracing Oligocene−Miocene source-to-sink systems in the deep Levant Basin: A sandstone provenance study","authors":"Adar Glazer, D. Avigad, N. Morag, A. Gerdes","doi":"10.1130/b36864.1","DOIUrl":"https://doi.org/10.1130/b36864.1","url":null,"abstract":"The Levant Basin in the Eastern Mediterranean contains an ∼3-km-thick, predominantly siliciclastic section of Oligocene−Miocene age, which hosts large hydrocarbon reservoirs (“Tamar Sands Play”). Here, we present a provenance study of Oligocene−Miocene sandstones based on detrital zircon U-Pb-Hf and heavy mineral assemblages. Samples were retrieved from four boreholes across the Levant Basin: Myra-1, Dolphin-1, Leviathan-1, and Karish North-1. Our investigations revealed that the sediments are dominated by Neoproterozoic and older Precambrian zircons with variable Hf isotopic composition, indicating that they were mainly reworked from Paleozoic−Mesozoic sandstones of African-Arabian provenance, with minor derivation from the Neoproterozoic basement of the Arabian-Nubian Shield. Variations in the proportions of pre−900 Ma zircons were encountered in various levels of the siliciclastic section. These zircons were markedly enriched (44%−57%) in the Rupelian and Aquitanian−Burdigalian intervals, accompanied by abundant detrital apatite peloids in the heavy mineral fraction, and relatively sparse (21%−38%) in the Chattian−Aquitanian and Langhian−Tortonian intervals, alongside scarce Mesozoic−Cenozoic zircons. These findings allow us to associate the deep-basin detrital record with two sedimentary transport systems that reached the Levant Basin from both NE Africa and Arabia simultaneously until the late Miocene, when sediment transport from Arabia ceased. While Rupelian and Aquitanian−Burdigalian sediments, including the main section of the “Tamar Sands,” were derived mainly from Arabian sources via the Levant continental margin, Chattian−Aquitanian and Langhian−Tortonian sediments were primarily sourced from NE Africa via the Nile Delta. Detrital contribution from the Eurasian side of the Eastern Mediterranean was not identified, suggesting that sand originating in the Arabia-Eurasia collision belt did not reach the Levant Basin.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43360236","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":"Post-rift magmatism controlled by detachment faults in a microplate, northwestern South China Sea","authors":"Chang Wang, Qiliang Sun, C. Morley, Haibo Huang","doi":"10.1130/b36981.1","DOIUrl":"https://doi.org/10.1130/b36981.1","url":null,"abstract":"Post-rift magmatism along continental margins is usually focused on highly stretched basins or aborted rifts. Adjacent microplates with relatively thick lithosphere are not expected to exhibit intense post-rift magmatism. This study identifies 20 mounded structures and associated pathways using two-dimensional, multichannel seismic data and ocean bottom seismometer (OBS) data across the southeastern Xisha Massif of the northwestern South China Sea. This massif is a relatively thick (>20 km) region of crust that forms a microplate between two rift branches. The mounded structures are interpreted as volcanoes, based on their seismic reflections and morphological characteristics. Detachment faults that extend into the middle crust captured the magma and provided pathways for vertical migration. During the rise of magma into the sedimentary stratum, detachment faults still served as the main channels of magmatic migration. The rigidity differences between the basement and the overlying sediments, as well as the stress field, facilitated subordinate pathways for magmatic migration, particularly at the depocenters and flanks of half-grabens. Consequently, larger volcanoes are present above the basement highs, while smaller volcanoes are located in the centers of half-grabens. This study provides criteria for identifying submarine mounded structures of different origins that are applicable beyond the study area. Moreover, this study highlights that detachment faults play a key role in the volcanic systems of the relatively rigid microplates of heterogeneous crustal structure. It also promotes our understanding of post-rift magmatism and the dynamic evolution of continental margins, and the results could be applicable to other areas with similar geological settings.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48756247","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}