Geological Society of America Bulletin最新文献

{"title":"High-resolution X-ray fluorescence-based provenance mapping of Eocene fluvial distributary fans that fed ancient Gosiute Lake, Wyoming, USA","authors":"M.E. Smith, H. Gregorich, L. Gipson, R.C. Krueger, A.R. Carroll, E.C. Parrish, A.P. Walters, S. Honig, C. Schwaderer, S. Meyers, B.S. Singer, T.K. Lowenstein, W. Arnuk","doi":"10.1130/b37207.1","DOIUrl":"https://doi.org/10.1130/b37207.1","url":null,"abstract":"The Green River Formation of Wyoming, USA, is host to the world’s largest known lacustrine sodium carbonate deposits, which accumulated in a closed basin during the early Eocene greenhouse. Alkaline brines are hypothesized to have been delivered to ancient Gosiute Lake by the Aspen paleoriver that flowed from the Colorado Mineral Belt. To precisely trace fluvial provenance in the resulting deposits, we conducted X-ray fluorescence analyses and petrographic studies across a suite of well-dated sandstone marker beds of the Wilkins Peak Member of the Green River Formation. Principal component analysis reveals strong correlation among elemental abundances, grain composition, and sedimentary lithofacies. To isolate a detrital signal, elements least affected by authigenic minerals, weathering, and other processes were included in a principal component analysis, the results of which are consistent with petrographic sandstone modes and detrital zircon chronofacies of the basin. Sandstone marker beds formed during eccentricity-paced lacustrine lowstands and record the migration of fluvial distributary channel networks from multiple catchments around a migrating depocenter, including two major paleorivers. The depositional topography of these convergent fluvial fans would have inversely defined bathymetric lows during subsequent phases of lacustrine inundation, locations where trona could accumulate below a thermocline. Provenance mapping verifies fluvial connectivity to the Aspen paleoriver and to sources of alkalinity in the Colorado Mineral Belt across Wilkins Peak Member deposition, and shows that the greatest volumes of sediment were delivered from the Aspen paleoriver during deposition of marker beds A, B, D, and I, each of which were deposited coincident with prominent “hyperthermal” isotopic excursions documented in oceanic cores.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":" 47","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138616800","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":"When did the Indus River of South-Central Asia take on its “modern” drainage configuration?","authors":"Y. Najman, Guangsheng Zhuang, Andrew Carter, Lorenzo Gemignani, Ian Millar, Jan Wijbrans","doi":"10.1130/b36596.1","DOIUrl":"https://doi.org/10.1130/b36596.1","url":null,"abstract":"For sedimentary archives to be used as a record of hinterland evolution, the factors affecting the archive must be known. In addition to tectonics, a number of factors, such as changes in climate and paleodrainage, as well as the degree of diagenesis, influence basin sediments. The Indus River delta-fan system of South-Central Asia records a history of Himalayan evolution, and both the onshore and offshore sedimentary repositories have been studied extensively to research orogenesis. However, a number of unknowns remain regarding this system. This paper seeks to elucidate the paleodrainage of the Indus River, in particular when it took on its modern drainage configuration with respect to conjoinment of the main Himalayan (Punjabi) tributary system with the Indus trunk river. We leverage the fact that the Punjabi tributary system has a significantly different provenance signature than the main trunk Indus River, draining mainly the Indian plate. Therefore, after the Punjabi tributary system joined the Indus River, the proportion of Indian plate material in the repositories downstream of the confluence should have been higher than in the upstream repository. We compared bulk Sr-Nd data and detrital zircon U-Pb data from the Cenozoic upstream peripheral foreland basin and downstream Indus delta and Indus Fan repositories. We determined that throughout Neogene times, repositories below the confluence had a higher proportion of material from the Indian plate than those above the confluence. Therefore, we conclude that the Indus River took on its current configuration, with the Punjabi tributary system draining into the Indus trunk river in the Paleogene, early in the history of the orogen. The exact time when the tributary system joined the Indus should correlate with a shift to more Indian plate input in the downstream repositories only. While the upstream repository records no change in Indian plate input from Eocene to Neogene times, a shift to increased material from the Indian plate occurs at the Eocene−Oligocene boundary in the delta, but sometime between 50 Ma and 40 Ma in the fan. Though further work is required to understand the discrepancy between the two downstream repositories, we can conclude that the tributary system joined the Indus trunk river at or before the start of the Oligocene.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"108 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139200463","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":"Late Miocene to present synchronous extension and contraction in the eastern Pamir: Insights from inversion of thermochronologic data across the southern Muztaghata dome","authors":"Shenqiang Chen, M. Fellin, Sean D. Willett, Colin Maden, M. Guillong, Hanlin Chen, Yaguang Chen","doi":"10.1130/b36953.1","DOIUrl":"https://doi.org/10.1130/b36953.1","url":null,"abstract":"Late Cenozoic gneiss domes cover ∼30% of the surface of the Pamir salient in the northwestern end of the India−Asia collision zone. The highest peaks of the Pamir are in the east, where the ∼250-km-long, ∼N−S-trending Kongur Shan extensional system controls the topography. We combined 115 new apatite (U-Th-Sm)/He and zircon (U-Th)/He single-grain dates from 18 samples and previous thermochronologic data with three-dimensional thermokinematic models to constrain the thermo-tectonic history of the southern portion of the Muztaghata dome, one of the largest gneiss domes in the eastern Pamir. The new cooling dates from the western boundary of the southern Muztaghata dome generally increase with distance from the southern Kongur Shan fault and are related to normal faulting along the fault at near-surface levels over the last 6.5 m.y. The new dates across the central−eastern portion of the dome outline the previously recorded U-shaped date pattern at a higher spatial resolution. The modeling indicates that this pattern is most likely the result of uplift and erosion above a flat-ramp-flat thrust fault at depth over the last 7 m.y. Modeling does not resolve how topographic changes may have affected the observed distribution of cooling dates, but it indicates a faster thrust-slip rate associated with an increase in relief and a slower one associated with steady-state topography. Our results suggest that the modern topography along the southern Muztaghata dome, similar to the rest of the eastern Pamir salient, is shaped by normal faulting at shallow depth, but its growth may still be governed by contraction and crustal thickening at depth.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"438 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139211631","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":"Cenozoic dextral transpressional tectonics in the northwestern Qaidam Basin, northern Tibet: Evidence from paleomagnetic and kinematic analysis of the arcuate belts","authors":"Luying Peng, Xiangjiang Yu, Baochun Huang, Feng Cheng, Yizhou Yang, Jiawei Wu, Kexin Yi, Zhaojie Guo","doi":"10.1130/b37075.1","DOIUrl":"https://doi.org/10.1130/b37075.1","url":null,"abstract":"The mechanisms by which complex intracontinental deformation in the northern Tibetan Plateau was accommodated since the India-Asia collision remain debated. Characterization of the formation of arcuate structures in northern Tibet provides important constraints on this debate. We conducted a new paleomagnetic study on the mid- to late Miocene strata along the curved Lenghu-Nanbaxian and Eboliang-Hulushan belts of the Qaidam Basin, northern Tibet. Our results revealed that there is nonsignificant relative rotation within localities along these arcuate belts, which yielded a common mean direction of declination (D) = 3.6°, inclination (I) = 35.7° (α95 = 2.4°) after tilt correction, suggesting negligible Neogene vertical-axis rotation along the arcuate belts in the Qaidam Basin. Outcropped fault striations and the positive flower structures indicate dextral strike-slip−dominated motion along the faults since the mid- to late Miocene. By integrating the paleomagnetic results with the kinematics of these associated faults, we ruled out the possibility that these curved belts formed due to the frictional drag of the Altyn Tagh fault or due to differential shortening across the Qaidam Basin. Instead, we attribute the formation of these nonrotational arcuate belts to dextral transpressional deformation occurring within the basin since the mid- to late Miocene. Different from the orogenic belts in the northern Tibetan Plateau that absorbed postcollisional convergence through block rotation, crustal shortening, and lateral extrusion, the Qaidam Basin has also accommodated significant intracontinental deformation in the northern Tibetan Plateau through transpressional deformation within the basin. This inference underscores the importance of recognizing crustal extrusion within rigid blocks as a record of intracontinental deformation in the northern Tibetan Plateau.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"35 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139214945","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":"Germanium-rich nanoparticles in Cu-poor sphalerite: A new mechanism for Ge enrichment","authors":"Guotao Sun, Jia-xi Zhou, Alexandre Cugerone, Mei-fu Zhou, Lingli Zhou","doi":"10.1130/b37014.1","DOIUrl":"https://doi.org/10.1130/b37014.1","url":null,"abstract":"Germanium (Ge) is a critical raw material used in high-technology industry (i.e., optical industry) applications, and it is predominantly concentrated in coals and Zn-rich deposits. Previous studies on Zn-rich deposits have documented a correlation between Ge enrichment and the Cu, Ag, and/or Pb-Mn contents in the sphalerite crystal lattice. In this study, we observed Ge-rich nanoparticles hosted in Cu-poor sphalerite from the Banbianjie Zn-Ge deposit (>800 t graded at ∼100 ppm Ge), located in southwest China. Laser-ablation−inductively coupled plasma−mass spectroscopy (LA-ICP-MS) analyses revealed that sphalerite contains very heterogeneous Ge contents (172−1553 ppm). Germanium contents showed positive correlations with Fe, Mn, and Pb contents and negative correlations with Cd contents. Higher Ge contents were detected in the darker zones, whereas the lighter zones showed systematically low Ge contents and were enriched in Cd. Using transmission electron microscopy (TEM), Zn-Ge-Pb-S nanoparticles were identified in the darker zones of sphalerite. These nanoparticles exhibited Ge/Pb ratios (0.48−1.96) very similar to those measured in sphalerite (0.36−2.04), suggesting that Ge could be essentially hosted within the nanoparticles. We propose that the amounts of Zn-Ge-Pb-S nanoparticles are related to a self-organization model induced by rapid crystal growth. This self-organization processes may control the fluctuations of element concentrations in the boundary layer. This study highlights the importance of studying the nanoscale expression of critical elements to understand their incorporation mechanisms into natural materials.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"61 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139230905","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":"In situ U-Pb dating of carbonate veins in Cambrian shales constrains fluid flow and hydrocarbon evolution at the southeastern margin of the Upper Yangtze platform, southwestern China","authors":"Qing-zhong Fan, Da-Quan Liu, Wei Du, Yiming Li, Feng Liang, Fuping Zhao, Xia Feng, Yi Chen, Ziya Zhang, Yuxiang Zhang, Chen Zhang","doi":"10.1130/b36893.1","DOIUrl":"https://doi.org/10.1130/b36893.1","url":null,"abstract":"Fluid flow in sedimentary basins not only impacts redistribution of the geothermal cycle and precipitation of ore deposits, but also exerts control on hydrocarbon migration and accumulation. However, reconstructing the history of fluid flow in basins that have experienced multiple tectonic deformation events is exceedingly difficult. Here, we examined petrography, in situ U-Pb geochronology, and rare earth element (REE) and C-O isotope geochemistry, as well as fluid inclusion microthermometry of fracture fillings within the Cambrian Niutitang Formation shales at the southeastern margin of the Upper Yangtze platform, southwestern China. The results show that four main fluid flow pulses are identified based on cathodoluminescence images, U-Pb ages, and geochemical data, namely, 446−428 Ma (fibrous calcite and barytocalcite), 343−329 Ma (calcite I), 113 Ma (calcite II), and 63 Ma (calcite III). The fibrous calcite (ca. 446 Ma) and barytocalcite (ca. 428 Ma) veins, corresponding to the late Caledonian Orogeny, show significantly positive Eu-Y anomalies, negative Ce anomalies, and enrichment in heavy REE, similar to their host rocks, suggesting that the mineral-forming fluids were derived mainly from dissolution of the host rocks. An abundance of bitumen inclusions with homogenization temperatures (Th) of 93.1−137.4 °C and high salinities (5−8 wt%) indicate that the first fluid flow pulse occurred during the oil generation stage in a closed fluid system. Calcite I (ca. 343−329 Ma) exhibits REE depletion and high Y/Ho ratios, a low fluid inclusion salinity (2−10 wt%) with Th = 78.4−125.8 °C, and C-O isotopic compositions similar to the underlying marine carbonates. This suggests that calcite I formed in an open fluid system, which was related to the transition from compression to extension during the Hercynian Orogeny. The pre-existing faults were reactivated and opened, resulting in the leakage and reconstruction of hydrocarbon reservoirs. Calcite II (ca. 113.4 Ma) has similar REE+Y patterns and C-O isotopic compositions to the host rocks. It contains abundant single-phase hydrocarbon gas (CH4) inclusions with high Th (164.1−211.1 °C) and salinity (6−14 wt%) values, indicating that the third phase fluid was derived largely from the host rocks and migrated during the early Yanshanian Orogeny. Lastly, calcite III (ca. 62.7 Ma) exhibits extremely low REE concentrations, low δ13CPDB [Peedee belemnite] values (−6.74‰), and low fluid inclusion salinities (0.3−7.0 wt%) with Th = 61.9−97.1 °C, suggesting that the fourth fluid flow pulse was affected by meteoric water to some extent. This can be interpreted to represent an open fluid system, which caused gas dispersion in the Niutitang Formation shales. Our findings provide important references for reconstructing the history of fluid flow in tectonically complex basins worldwide.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"67 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139263494","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":"New biogeochemical insights into Mesozoic terrestrial paleoecology and evidence for omnivory in troodontid dinosaurs","authors":"Thomas M. Cullen, Brian L. Cousens","doi":"10.1130/b37077.1","DOIUrl":"https://doi.org/10.1130/b37077.1","url":null,"abstract":"The Cretaceous paleocommunities of North America preserve a rich record of biodiversity that suggests many species occupied narrow biogeographic ranges in comparison to their ecological equivalents in extant systems. How taxa in these systems partitioned their niches and structured their communities can be difficult to determine from fossils alone, which has led to a variety of hypotheses concerning diets and habitat use. Here, we examine element ratios (Sr/Ca, Ba/Ca) in the enamel of a suite of co-occurring vertebrate taxa sampled from a spatiotemporally constrained interval in the Oldman Formation of Alberta, Canada, to reconstruct trophic structure, and use δ13C, δ18O, and 87Sr/86Sr compositions to test for niche partitioning and habitat use among hadrosaurids, ceratopsids, and ankylosaurs. We also test previously proposed dietary hypotheses of troodontid theropods. In large ornithischians, we find Ba/Ca and Sr/Ca ratios that are consistent with herbivory, with hadrosaurs distinct from ceratopsids and ankylosaurids in their 87Sr/86Sr ranges, a pattern that is indicative of differences in habitat use/breadth, dietary plant sources, and feeding height. The sampled mammals, varanoid lizards, dromaeosaurids, and tyrannosaurids preserve a gradient of lower Sr/Ca and Ba/Ca ratios that is consistent with animal-dominant omnivorous to faunivorous diets. Troodontids, which have been variably hypothesized as either faunivorous, omnivorous, or herbivorous due to their distinct and unusual dentition, preserve Sr/Ca and Ba/Ca ratios that fall between those of the ornithischians and the dromaeosaurids. From these multi-proxy data, we interpret troodontids as mixed-feeding to plant-dominant omnivores. These proxies represent a valuable tool for understanding the trophic and community ecology of Cretaceous ecosystems and hold enormous potential for future research in paleobiology.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"51 12","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139271043","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":"Two-stage crust-mantle interactions from oceanic subduction to post-collisional extension in the northern margin of the North China Craton: Insights from Paleozoic to Mesozoic magmatism","authors":"Yingsuo Zhang, Yong-Mei Zhang, Xue-Xiang Gu, Jia-Lin Wang, Bo Yao, Haidong Sui","doi":"10.1130/b37209.1","DOIUrl":"https://doi.org/10.1130/b37209.1","url":null,"abstract":"The northern margin of the North China Craton experienced prolonged tectono-magmatic evolution during the late Paleozoic−early Mesozoic in response to the southward subduction and closure of the Paleo-Asian Ocean. However, details about the subduction process and the timing of the tectonic transition from subduction to post-collision are still poorly constrained. Here, we identify two-stage crust-mantle interactions in the Wulashan area and report new geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopic data for magmatic rocks that record such processes following the subduction and closure of the Paleo-Asian Ocean. The early Carboniferous Xiguanjing pluton features a bimodal suite of gabbro (ca. 333 Ma) and syenogranite (ca. 331 Ma). The gabbros have arc-like geochemical affinities, with low Nb/La (0.31−0.40) and La/Ba (0.04−0.09) ratios, and variable Rb/Y (1.22−2.94) ratios, as well as enriched, mantle-like Sr-Nd-Pb (87Sr/86Sri = 0.7046−0.7047; εNd(t) = −3.8 to −3.5; 206Pb/204Pbi = 17.078−17.141) and enriched to depleted Hf (εHf(t) = −4.5 to +6.2) isotopic values. Such geochemical signatures indicate that they were derived from partial melting of the subcontinental lithospheric mantle that was metasomatized by slab-derived fluids, with minor involvement of asthenospheric components. In contrast, the contemporaneous syenogranites are characterized by lower negative εNd(t) (−13.5 to −12.1) and εHf(t) values (−16.3 to −8.2), which suggests that they were formed by partial melting of the lower crust. Late Triassic Shadegai and Xishadegai plutons are mainly composed of enclave-bearing syenogranite, and both mafic microgranular enclaves and syenogranites crystallized at ca. 233−231 Ma. The mafic microgranular enclaves have geochemical features similar to those of the early Carboniferous gabbros, and also have moderately enriched isotopic compositions (εNd(t) = −9.7 to −8.4; εHf(t) = −9.2 to −0.3), which suggests that they originated from interaction between mantle-derived magma and overlying crust-derived magma, with minor additions of asthenospheric melts in their sources. Field and petrological observations, coupled with the similar ages of the host granites and mafic microgranular enclaves, suggest a magmatic mingling process. Isotopic mixing models suggest that minor amounts (∼10%−20%) of lower crustal materials were mixed during the formation of the mafic microgranular enclaves. The host syenogranites display calc-alkaline to alkalic and metaluminous to weakly peraluminous compositions, and negative εNd(t) (−15.0 to −12.1) and εHf(t) values (−16.4 to −9.8), which indicates that they were mainly derived from partial melting of the lower crust and experienced the injection of deep mantle-derived magmas. Our new data, along with previously published data for magmatic rocks in the northern margin of the North China Craton, suggest that the early Carboniferous bimodal intrusive rocks formed in a localized back-arc extensional regime that was probably","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"38 2","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139275770","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":"A 5000 yr record of coastal uplift and subsidence reveals multiple source faults for past earthquakes on the central Hikurangi margin, New Zealand","authors":"CharlotteOlivia Pizer, K. Clark, Jamie Howarth, A. Howell, Jaime Delano, Bruce W. Hayward, Nicola J. Litchfield","doi":"10.1130/b36995.1","DOIUrl":"https://doi.org/10.1130/b36995.1","url":null,"abstract":"Prehistoric records of subduction earthquakes are often distinguished by evidence of synchronous widespread coastal deformation, the extent of which negates the plausibility of alternative source faults. At the Hikurangi subduction margin in New Zealand, untangling the record of subduction interface ruptures is complicated. Large earthquake age uncertainties inhibit unique solutions of along-strike correlations, and complex patterns of coastal deformation caused by upper-plate faulting prevent reliable indication of source faults. In this work, we improved paleoearthquake reconstructions on the central Hikurangi margin with a new, well-constrained 5000 yr earthquake record from Pakuratahi Valley near Napier, North Island, New Zealand. Evidence of laterally extensive paleoenvironmental changes is consistent with coseismic subsidence and coseismic uplift in large earthquakes. Radiocarbon dates on fragile terrestrial macrofossils and tephra isochrons were used to construct robust age models that yielded earthquake ages of 4839−4601 calibrated (cal.) yr B.P., 3630−3564 cal. yr B.P., 2687−2439 cal. yr B.P., and 1228−823 cal. yr B.P. Integration of these ages with refined earthquake chronology from nearby Ahuriri Lagoon indicated that the next large earthquake impacting the Napier area is more likely to cause coastal subsidence than uplift. Drawing on correlations with cotemporal evidence elsewhere on the central margin, we infer that the overall patterns of coseismic deformation could be generated by either rupture of the subduction interface or upper-plate faults, or both. This inability to separate source faults for past earthquakes limits the efficiency of forecasting future earthquakes. Similar problems of intertwined paleoearthquake signatures likely apply to other plate boundaries, where we recommend cautious interpretation of coastal deformation to accurately address the hazard from both types of source faults.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"81 3-4","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139272718","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":"Intra−Neo-Tethyan subduction initiation inferred from the Indawgyi mafic rocks in the Central Ophiolite Belt, Myanmar","authors":"Qinghua Zhang, Yi Chen, Si Chen, Bin Su, Yibing Li, Kaihui Shi, Me M. Aung, Kyaing Sein","doi":"10.1130/b37076.1","DOIUrl":"https://doi.org/10.1130/b37076.1","url":null,"abstract":"Geological evidence has demonstrated the presence of an intra−Neo-Tethyan subduction system during the Cretaceous. However, when and how this intra-oceanic subduction was initiated, especially for the eastern Neo-Tethys, are still not well constrained. Here we present geochemical and geochronological analyses of the Indawgyi mafic rocks from the Central Ophiolite Belt in the West Burma Block (Myanmar), which record early forearc spreading during the intra−Neo-Tethyan subduction initiation. Zircon U-Pb ages of gabbros indicate the ophiolitic crust formation at ca. 120 Ma. Gabbros show mid-oceanic-ridge basalt−like rare earth element patterns and depleted Sr-Nd-Pb isotopic compositions with negative anomalies of high field strength elements (e.g., Nb, Ta, Zr, and Hf), similar to forearc basalt characteristics. Basalts show more slab-derived component signatures than the gabbros and represent mantle wedge magmas most likely formed between forearc spreading and arc maturation. These data, together with regional geological records and geophysical observations, suggest that the Indawgyi gabbros were derived from an intra−Neo-Tethyan forearc setting during the early stage of subduction initiation. Considering the timing of supra-subduction zone ophiolites and metamorphic sole in the Indo-Burma Range, we propose that spontaneous subduction initiation and sinking of the eastern Neo-Tethyan lithosphere during the Early Cretaceous (ca. 120 Ma) led to formation of the Indawgyi forearc crust, whereas subsequent mature subduction resulted in the Middle Cretaceous (ca. 108‒90 Ma) arc magmatism in the West Burma Block. These findings confirm the double-subduction model of the Neo-Tethys Ocean and shed new light on the intra−Neo-Tethyan subduction initiation.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"30 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135390363","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}