American Journal of Science最新文献

{"title":"Weathering intensity and lithium isotopes: A reactive transport perspective","authors":"M. Winnick, J. Druhan, K. Maher","doi":"10.2475/05.2022.01","DOIUrl":"https://doi.org/10.2475/05.2022.01","url":null,"abstract":"Lithium isotopes have emerged as a powerful tool to probe the response of global weathering to changes in climate. Due to the preferential incorporation of 6Li into clay minerals during chemical weathering, the isotope ratio δ7Li may be used to interrogate the balance of primary mineral dissolution and clay precipitation. This balance has been linked to relative rates of chemical and physical denudation, such that dissolved δ7Li (δ7Lidiss) is highest at moderate weathering intensities when chemical and physical denudation are comparable. However, we argue that current theory linking δ7Li to weathering regimes through fluid travel times are unable to explain observations of low δ7Li and high Li concentrations in rapidly eroding settings. In this study, we re-examine the relationships between δ7Li, Li concentration, and weathering regime by incorporating Li isotopes into simulations of weathering profiles using a reactive transport model (CrunchFlow) that includes advective fluxes of regolith to simulate variable erosion rates in response to uplift. In these simulations, fractionation is implemented through a kinetic fractionation factor during clay precipitation, which allows the δ7Li of dissolved and suspended loads in the model to vary as a function of Li/Al ratios in primary and secondary minerals. When the model is run over a range of infiltration and erosion rates, simulations reproduce observed global patterns of δ7Lidiss and suspended load δ7Li as a function of weathering intensity, controlled primarily by water travel times and mineral residence times in weathered bedrock. We find that reduced water travel times at low weathering intensity, however, are inconsistent with observations of high Li concentrations. As an alternative, we demonstrate how the rapid weathering of soluble, Li-rich minerals such as chlorite under low weathering intensities may resolve this apparent discrepancy between data and theory. We also suggest that observed patterns are consistent with geothermal Li sources under low weathering intensities. This work offers a foundation guiding future studies in testing potential mechanisms underlying global riverine δ7Lidiss.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"647 - 682"},"PeriodicalIF":2.9,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44313854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 Idria serpentinite protrusion, Diablo Range, California: From upper mantle to the surface","authors":"R. Coleman, J. Gooley, R. Gregory, S. Graham","doi":"10.2475/04.2022.01","DOIUrl":"https://doi.org/10.2475/04.2022.01","url":null,"abstract":"The New Idria serpentinite body in the Coast Ranges of California is a diapir that resulted from the interaction of the migrating Mendocino trench-ridge-transform fault triple junction, transpression, metasomatic fluids, and previously subducted oceanic crust and mantle. Northward propagation of the San Andreas fault progressively eliminated the original subduction zone, allowing seawater to penetrate into the formerly subducting abyssal peridotite mantle, triggering serpentinization. The associated physical changes in density, volume, and strength yielded an expanding, buoyantly rising serpentinite protrusion, facilitated by transpression along the San Andreas fault. Sedimentary facies and intrusion of minor cross cutting syenite and alkali basalt dikes indicate that the serpentinization-driven diapir buoyantly rose and widely breached the surface by ca. 14 Ma, attending migration of the Mendocino Triple Junction past the latitude of New Idria.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"533 - 560"},"PeriodicalIF":2.9,"publicationDate":"2022-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43198975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 petrogenesis and tectonic setting of the New Hampshire Plutonic Suite: Towards a more comprehensive model for the magmatism of the Acadian Orogeny","authors":"M. Dorais","doi":"10.2475/03.2022.03","DOIUrl":"https://doi.org/10.2475/03.2022.03","url":null,"abstract":"The Wamsutta and Nineteenmile Brook Diorites, two small plutons located in the White Mountains of New Hampshire, have bearing on the tectonic setting of magmatism between 410 and 407 Ma in this portion of the northern Appalachians. The unmetamorphosed, undated Nineteenmile Brook pluton has arc basalt affinities, produced in the same arc as the mafic magmas that were mingled with the ∼410 Ma Meredeth Porphyric Granite of central New Hampshire. These volcanic arc magmas from a westerly dipping subduction zone contributed both heat and mass to the petrogenesis of the New Hampshire Plutonic Suite (NHPS), producing the high temperature melts of the Kinsman Granodiorite of the NHPS. These peraluminous NHPS magmas were emplaced during collision of Avalonia with Laurentia, forming the bases of Acadian thrust sheets. The ∼408 Ma Wamsutta Diorite has appinite-like textures and chemically is a low SiO2 adakite, with Sr/Y ratios of ∼ 400 and (La/Yb)N between 80 and 130. These magmas were generated after flat slab, subduction erosion mixed basaltic rocks into the mantle wedge and partially melted the mafic rocks in the garnet stability field. The melts interacted with the surrounding peridotite to attain the low SiO2 adakite characteristics. At this same time, the ∼407 Ma Exeter Diorite and other arc plutons were emplaced in the Merrimack belt of southeastern New Hampshire. By 400 Ma, continued westerly dipping subduction provided mafic magma underplating to partially melt lower crustal amphibolites, generating the Spaulding Tonalite. Subsequently, lower crustal delamination and asthenospheric upwelling provided the heat source that produced a younger, post-tectonic suite of magmas between 390 and 370 Ma that, while having arc signatures because of the heritage of their crustal source rocks, are not arc magmas because subduction is thought to have ceased by this time. These plutons include the mafic rocks of the Northeast Kingdom of Vermont and the Mooselookmeguntic Igneous Complex of NH and ME. This same heat source may have contributed to melting lower to midcrustal metasediments to produce the widespread peraluminous Concord Granite of Vermont, New Hampshire, and western Maine.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"493 - 531"},"PeriodicalIF":2.9,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44798434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 complex response of continental silicate rock weathering to the colonization of the continents by vascular plants in the Devonian","authors":"P. Maffre, Y. Goddéris, A. Pohl, Y. Donnadieu, S. Carretier, Guillaume Le Hir","doi":"10.2475/03.2022.02","DOIUrl":"https://doi.org/10.2475/03.2022.02","url":null,"abstract":"The first forests appeared on the continents during the Givetian stage of the Devonian. The fossil record shows that, by the end of the Devonian, vascular plants and forests were common and widespread in the wet lowlands. Although the impact of this major event on chemical weathering of the continents is reasonably known, the coeval change in physical erosion has never been explored. Here, we build a mathematical description of the coupled response of the physical erosion and chemical weathering on the continents, to the colonization by vascular plants over the course of the Devonian. This spatially-resolved erosion model is coupled to the GEOCLIM model to simulate the response of the global carbon and alkalinity cycles, and of climate, to the colonization phase. A set of simulations is described, assuming an increased weatherability of the continental surface, and a change in physical erosion which can be either a decrease or an increase in response to the spreading of vascular plants. We explore first the initial pre-colonization and the final post-colonization steady states of the surficial Earth system. Then, we simulate the transient states of the Earth system in response to theoretical randomized scenarios for the colonization. We find that the pathways of the colonization have a major impact on the CO2 history through the Devonian. Depending on the magnitude of the change in physical erodibility and chemical weatherability, and on the colonization scenario, atmospheric CO2 evolution may display contrasting behaviors: from a uniform CO2 decrease over the Devonian, to more complex patterns characterized first by a global warming from the end of the Givetian into the Frasnian, and then by a final cooling, in first order agreement with the proxy data for CO2 and reconstructed climate evolution.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"461 - 492"},"PeriodicalIF":2.9,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47564169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 PATCH Lab v1.0: A database and workspace for Cenozoic terrestrial paleoclimate and environment reconstruction","authors":"T. Kukla, J. Rugenstein, E. Driscoll, D. Ibarra, C. Chamberlain","doi":"10.31223/x5pk9w","DOIUrl":"https://doi.org/10.31223/x5pk9w","url":null,"abstract":"In the last two decades, analytical advances and a growing interest in relevant research questions has brought a rapid increase in the amount of stable isotope data used for reconstructing terrestrial paleoclimates and environments. As the spatial and temporal resolution of proxy data continues to improve, the quantitative interpretation of these data is becoming increasingly common. These advances in data resolution and theory bring opportunities for multi-proxy comparisons, synthesis and modeling of large datasets, integration with paleoecological datasets, improved climate model benchmarking, and more. Here, in an effort to support these growing avenues of research, we present The PATCH Lab (Paleo-Analysis of Terrestrial Climate and Hydrology)—an online portal to discover, download, and quantitatively analyze deep time (>1 Ma) terrestrial stable isotope data. The PATCH Lab portal hosts a new database that currently includes 27009 stable isotope measurements from 211 publications spanning multiple terrestrial proxies, and quantitative models for interpreting water isotope and soil carbonate data. Data query, download, and modeling results are organized into user-friendly graphical interfaces that export datasets as .csv files. New data can be easily submitted to the PATCH Lab curators through the portal by completing a data submission template. The PATCH Lab, with the help of community engagement, serves as a resource for archiving terrestrial stable isotope data, building paleo “isoscapes”, and increasing accessibility to quantitative methods of investigating terrestrial stable isotopes in paleoclimate.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"1124 - 1158"},"PeriodicalIF":2.9,"publicationDate":"2022-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46613815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 early Paleozoic active continental margin basin along the southern Chinese Altai: Evidence from high-grade paragneisses in the Fuyun region","authors":"X. Cui, M. Sun, Guochun Zhao, Jinlong Yao, Yunying Zhang, Yigui Han","doi":"10.2475/02.2022.04","DOIUrl":"https://doi.org/10.2475/02.2022.04","url":null,"abstract":"High-grade gneisses are widespread in the Chinese segment of the Altai orogen, but their nature is not yet well-constrained with interpretations varying from Precambrian basement to Paleozoic meta-sediments. Such a controversy has hindered our understanding of the early Paleozoic geologic history of the Altai orogen. This study presents whole-rock geochemistry, zircon U-Pb and Hf isotopic data for paragneisses from the Qiongkuer Domain of the southern Chinese Altai, aiming to reveal their sedimentary and metamorphic history and shed light on the geodynamics of the Altai orogen. The paragneisses contain detrital zircons with mostly euhedral shapes, which, together with their weak HREE fractionation and Zr-Hf depletion relative to continental crust, may imply short-distance transport and low maturity of the sediments. In addition, these rocks have felsic compositions, high Rb contents and negative Eu anomalies, as well as low La/Sc and high Co/Th ratios, possibly indicating an acidic-intermediate igneous provenance. Our results show that the detrital zircons from the paragneisses are dominantly ca. 535 to 435 Ma old, some have Neoproterozoic ages, and only a few have Mesoproterozoic or Archean ages. Since the youngest detrital zircon population record an early Silurian weighted mean age of 441 Ma, and an early Devonian (411 Ma) granite intruded these paragneisses, we infer that their protoliths were deposited in the Silurian. The cumulative distribution curves of zircon age spectra of the paragneisses are comparable to those of sediments at convergent continental margins. The large spread of εHf(t) values (−9.5 to +12.9) of the predominant Paleozoic zircons also reflects possible active margin settings which contain both juvenile and reworked materials in the source. Therefore, the protoliths of the studied paragneisses were immature sediments mostly deposited at an active continental margin during the early Paleozoic and sourced mainly from proximal igneous rocks. Similar detrital zircon age spectra of early Paleozoic sequences from the Chinese Altai, Mongolia Altai, and Khovd Zone support the existence of a large accretionary wedge developed along the western margin of the Ikh-Mongol Arc system, resulting from continuous northeast-dipping oceanic subduction.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"190 - 224"},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47204862","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 carboniferous continental arc magmatism in the southeastern Central Asian Orogenic Belt: insights from the Erenhot granitic pluton, Inner Mongolia","authors":"Bingqing Xu, Guochun Zhao, Jinlong Yao, Peng Wang, Yanhong He, Yigui Han, H. Zhou, Bo Wang","doi":"10.2475/02.2022.08","DOIUrl":"https://doi.org/10.2475/02.2022.08","url":null,"abstract":"The closure time of the Hegenshan Ocean and its suturing scenario is debated, which hinders our understanding of the architecture and tectonic evolution of the southeastern Central Asian Orogenic Belt. We present an integrated study of in-situ zircon U-Pb isotopic ages and Hf isotope compositions, whole-rock geochemistry and Sr-Nd isotopes on the less-studied Erenhot granitic pluton in central Inner Mongolia. The ca. 303 to 300 Ma Erenhot pluton is composed of monzogranites, which are high-K calc-alkaline rocks and show I-type affinities. Moreover, positive correlation between Ba and Sr, along with the notably positive Rb and Pb anomalies, negative δEu and depletion in Ba, Eu, Nb and Ti, imply crystal fractionation played an important role in the magma evolution. The pluton also shows relative enrichment in light rare earth elements and large ion lithophile elements and depletion in high field strength elements, typical features of subduction-related magma. Isotopically, predominantly positive whole-rock εNd(t) (0.9–3.8) and zircon εHf(t) (4.50–13.66) values indicate a dominant juvenile crustal source with minor older crustal contamination. Given the mostly Proterozoic model ages (1318–543 Ma) and the presence of xenocrystic zircons, we infer that the Erenhot pluton probably was formed in a continental arc setting. Combined with the available published data, it is proposed that an east-west trending continental arc developed and was accreted onto the Uliastai Continental Margin in the Carboniferous, resulting from the northward subduction of the Hegenshan Ocean. The late Carboniferous continental arc-related magmatism (ca. 303–300 Ma) at Erenhot probably witnessed the waning stage of Hegenshan oceanic lithosphere subduction beneath the Uliastai Continental Margin.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"351 - 379"},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48444665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleo- to Mesoarchean crustal growth in the Karwar block, southern India: Constraints on TTG genesis and Archean tectonics","authors":"C. Ishwar-Kumar, K. Sajeev, M. Satish‐Kumar, I. Williams, S. Wilde, T. Hokada, B. Windley","doi":"10.2475/02.2022.02","DOIUrl":"https://doi.org/10.2475/02.2022.02","url":null,"abstract":"In this study we present field relations, petrology, whole-rock major, trace and rare earth element geochemistry, zircon U-Pb ages, whole-rock Sr and Nd isotopes, and in situ zircon Hf and O isotopes from the Karwar block, western peninsular India. The rocks consist predominantly of tonalite-trondhjemite-granodiorite (TTG), granite and amphibolite. The felsic rocks are grouped into three: 1. TTG-I characterised by low K2O, high Na2O and Al2O3, low Sr/Y and La/Yb ratios, slightly enriched HREEs, negative Sr, Eu and Ti anomalies, a 3.2 Ga crystallisation age, and 3.60 Ga and 3.47 Ga inherited zircons; 2. TTG-II with lower SiO2, higher Sr/Y and La/Yb ratios, stronger REE fractionation with no HREE enrichment, negative Nb and Ta anomalies, a 3.2 Ga crystallisation age, but no inheritance; 3. Granites with high SiO2 and K2O, low Na2O and Al2O3, very low Sr/Y and La/Yb ratios, weak REE fractionation with enriched REEs, negative Sr, Eu and Ti anomalies and a 2.94 Ga crystallisation age. The TTG-I formed from a mantle source, but with a significant component of older crustal material, whereas the TTG-II originated mostly from a mantle-derived juvenile magma. The granite evolved from an enriched source containing a relatively large amount of older crustal material. The precursors of TTG-I and -II are similar to mid-ocean ridge basalts (MORB), whereas the granites are similar to volcanic arc/within-plate sources and the amphibolites are remnants of gabbros/basalts. An initial 3.6 Ga crust likely formed by the underplating of an accreted oceanic plateau-like or island arc-like crust. TTG-I was produced by subduction and slab melting at a moderate depth, induced melting of mafic lower crust and older upper crust at 3.2 Ga. TTG-II formed at 3.2 Ga by subduction and with a higher degree of slab melting at a greater depth than TTG-1, together with more effective mixing with mantle peridotite, followed by intrusion and induced melting of mafic lower crust. Basaltic magmatism at 3.0 Ga and subsequent metamorphism to amphibolite resulted in extensive and thicker crust. Assimilation and melting of TTG crust at a shallow depth during the emplacement of a mantle-derived magma produced the 2.94 Ga granites. The presence of inherited zircons, combined with whole-rock major and trace elements, Nd isotopes and in situ zircon Hf and O isotopes, indicates that older crustal material was incorporated into the source magma of TTG-I and that the Karwar block originally contained 3.60 to 3.47 Ga crust that was subsequently reworked during the Paleo- and Mesoarchean.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"108 - 163"},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41368151","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Early carboniferous rifting of the Harlik arc in the Eastern Tianshan (NW China): Response to rollback in the southern Altaids?","authors":"Liangbo Li, W. Xiao, B. Windley, He Yang, Xiaoliang Jia, Miao Sang, Nijiati Abuduxun, Yin Liu","doi":"10.2475/02.2022.07","DOIUrl":"https://doi.org/10.2475/02.2022.07","url":null,"abstract":"Field, geochronological, geochemical and Sr-Nd isotopic analyses are applied to late Paleozoic gabbro-diorites and monzogranites in the Hulugou-Miaoergou regions, Harlik arc, in order to provide constraints on the tectonic evolution of the Eastern Tianshan orogen in the late Paleozoic. LA-ICP-MS zircon U-Pb ages show that the first pulse of gabbroic magmatism occurred at 348 ± 4 Ma, accompanied by simultaneous dioritic (342 ± 3 Ma) and monzogranitic (343 ± 5 Ma) magmatism, and the second pulse of gabbroic magmatism was at 334 ± 3 Ma. Most of the gabbros are medium- to high- K calc-alkaline in composition, and show enrichments in light rare earth elements (LREE) and large ion lithophile elements (LILE), but depletions in high field strength elements (HFSE, especially Nb and Ta). In combination with their juvenile isotopic signature (initial 87Sr/86Sr = 0.70345–0.70380, εNd(t) = 4.5–6), the geochemical features suggest that both pulses of gabbroic magmatism were likely derived from partial melting of asthenosphere facilitated by a flux from a subducting slab. The diorites also display the arc-related geochemical characteristics and juvenile isotopic signature (initial 87Sr/86Sr = 0.70355–0.70358, εNd(t) = 4.3–4.7), coupled with their intimate relationship with the gabbros indicate that they formed by fractional crystallization of clinopyroxene, plagioclase and amphibole from the first pulse of gabbroic magmatism. The monzogranites have relatively high A/CNK values (1.04–1.1) and are weakly to moderately peraluminous. Considering the presence of zircon xenocrysts dated at 510 to 450 Ma in the monzogranites, and their moderate molar Al2O3/(MgO+FeOT) and molar CaO/(MgO+FeOT) ratios, partial melting of supracrustal rocks of probable late Ordovician age was most likely the cause of their genesis and heterogeneity. These three different magmas (gabbroic, dioritic and monzogranitic) were probably extracted from a deep crustal hot zone. The primitive basaltic magmas continuously intruded the deep crust where they solidified, fractionated, assimilated, and heated the crust, generating in turn the peraluminous and A-type granitoids, similar to the magmas in the Lachlan orogen that intruded during progressive slab rollback. Based on all available evidence, we propose that southward slab rollback of the subducting Paleo-Asian Ocean in the early Carboniferous was responsible for the progressive emplacement of these different magmas, which eventually resulted in rifting of the Harlik arc.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"313 - 350"},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44976771","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 Neoarchean to Paleoproterozoic magmatic arc in the Trans-North China Orogen: Petrological and geochemical constraints from the Tianzhen gneisses in the Huai'an Complex","authors":"Dingyi Zhao, M. Sun","doi":"10.2475/02.2022.03","DOIUrl":"https://doi.org/10.2475/02.2022.03","url":null,"abstract":"In the past two decades, extensive investigations have been carried out on the Trans-North China Orogen (TNCO), a Himalayan-type continental collisional belt along which the Eastern Block and the Western Block amalgamated to form the basement of the North China Craton. There are now coherent outlines of the timing and tectonic processes involved in the Paleoproterozoic amalgamation of the TNCO. However, pre-collisional tectonic setting and driving mechanism of the TNCO still remain controversial. To resolve these issues, we carried out field petrological and geochemical investigations on the Tianzhen gneisses from the Huai'an Complex in the TNCO. The Tianzhen gneisses consist predominantly of tonalitic-trondhjemitic-granodioritic (TTG) series, which can be further divided into low-Yb and high-Yb types. Our results indicate that although both low-Yb and high-Yb TTG series were formed in a magmatic arc environment, their petrogenetic origins were different. The Huai'an low-Yb TTG magma was derived from the partial melting of subducted oceanic crust consisting of eclogite or 30% garnet-bearing amphibolite under 15 to 20 kbar or even higher pressure, with garnet, amphibole, and rutile as residues. In contrast, the high-Yb TTG magma was derived from the partial melting of subducted oceanic slab consisting of garnet-free or 7% garnet amphibolite under 10 to 15 kbar, leaving residual garnet and amphibole. Both magmas then interacted with the overlying mantle wedge during ascent. Thus, it can be concluded that the Tianzhen TTG magmas were derived from the partial melting of subducted oceanic crust and interaction with mantle peridotite, supporting a magmatic arc setting for the Huai'an Complex during Neoarchean to Paleoproterozoic time. Associated with other analogous gneiss complexes in the TNCO, a long-lived Neoarchean to Paleoproterozoic magmatic arc system is established in the Trans-North China Orogen.","PeriodicalId":7660,"journal":{"name":"American Journal of Science","volume":"322 1","pages":"164 - 189"},"PeriodicalIF":2.9,"publicationDate":"2022-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46466092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}