查看更多>>摘要：In order to decipher element mobility in UHP meta-sedimentary rocks in the continental subduction zone, major and trace element compositions are investigated for a continuous profile from a representative UHP region in the Dabie Mountains. Among the lithologic contact zone, contents of K, Ca, LREE, and LILE exhibit varying degrees of downward trends in both marble and eclogite toward the contact zone, indicating that marble and their associated eclogite can release a large amount of K, Ca, and a small number of LILEs and LREEs. Titanite is the main Ti phase in both marble and eclogite. Titanite rims around rutile can occasionally be seen in eclogite. Contents of Ti and HFSE exhibit a well-coupled relation among marble and eclogite, indicating that substantial Ti and HFSEs were migrated from eclogite to marble, in accord with the capacity of a melt medium. Rutiles and titanites in marble exhibit a relatively limited variation in Nb/Ta ratios (12.9-16.2), similar to those of titanites in eclogite (14.2-16.7), which demonstrates that rutiles and titanites in marble were sourced from eclogite because of short-distance migrations of Ti and HFSEs. According to the P-T path and the temperature and pressure conditions of the peak metamorphism reported by previous studies, the eclogite associated with marble may not form supercritical fluids in the subduction zone because of the addition of carbonate minerals.
查看更多>>摘要：The Bipindi iron ore district is located in the central section of the Nyong Complex at the northwestern margin of the Congo Craton in Southwest Cameroon. This iron district contains numerous iron mineralization hosted by the Mewongo, Bibole, Kouambo, and Zambi banded iron formations (BIFs). These BIFs contain magnetite as the main iron ore mineral associated with pyrite, and gangue minerals are quartz with minor chlorite and amphibole. The origin of iron ore from these BIFs was investigated using a combination of in-situ magnetite and whole-rock chemistry. The studied BIF ore samples have a narrow range of TFe between 30.90 wt.％ and 43.20 wt.％, indicating a low-grade ore. The geochemical signatures of magnetite such as low contents of base metals (e.g., Cu, Co, V, and Zn) and low Co/Zn ratios < 0.85 indicate a hydrothermal origin. Combined with the geochemical features of these BIFs, e.g., high Fe/Ti and Fe/Al ratios (mean > 600 and > 75, respectively), we suggest that magnetite was derived from a mixture of seawater and ～0.1％ low-temperature hydrothermal fluids in an oxidizing environment. Collectively, low-temperature hydrothermal and later metamorphic fluids were necessary for the transformation of the protolith Nyong Complex BIFs to iron ore.
查看更多>>摘要：The basalts within the greenstone belt worldwide serve as an ideal target to decipher the nature of Archean mantle sources and further to extend the understanding of the early stages of Earth's evolution. To provide important insights into the issues, we carried out a detailed investigation of whole-rock geochemistry and Sm-Nd isotopes, and zircon U-Pb-Hf isotopes for the Late Neoarchean metamorphosed basalts in eastern Hebei, North China Craton. U-Pb isotopic dating using the LA-ICP-MS on zircons reveals that the basalts in eastern Hebei erupted at ca. 2.48-2.51 Ga and subsequently experienced multiple regional metamorphic events at 2477 and 1798 Ma, respectively. The metamorphosed basalts are featured by low SiO2, MgO, K2O + Na2O, and high FeO contents, endowed with the subalkaline and high-Fe tholeiitic affinities. The radiogenic initial Nd and Hf isotope values and correlations among V, Ni and Cr contents strongly imply that the basalts experienced significant clinopyroxene and olivine fractionation and minor crustal contamination during magma evolution. They are also characterized by the relatively low total REE contents and exhibit significant depletions to moderate enrichments in the LREE contents, indicating the derivation from a deep mantle source in an Archean proto-mantle plume setting.
查看更多>>摘要：Voluminous Early Cretaceous granitoids and associated large-scale ore deposits are distributed within the southern Great Xing'an Range (SGXR), NE China. Based on previously published geochronology and zircon Hf-isotope data, Hf isotope mapping is undertaken to improve our understanding of crustal architecture and its controls on ore deposits. The ore-related Early Cretaceous granitoids were sourced predominantly from juvenile crust, with the involvement of variable proportions of ancient crustal materials. The crustal architecture, as inferred from Hf isotopic contour maps, indicates two distinct Hf isotopic domains in SGXR, including (1) a higher-εHf (+7 to +11) juvenile crust containing minor ancient crustal material, and (2) a lower-εHf (+2 to +6) juvenile crust containing a greater proportion of ancient crustal materials.The Hf isotopic maps identify links between crustal architecture and regional metallogeny. Copper deposits and other deposits with significant Cu production are restricted mainly to the higher-εHf juvenile crustal regions in the northern and eastern SGXR. Deposits dominated by other metals (e.g., Mo, Sn, W, Pb, Zn, and Ag) occur mainly in the lower-εHf juvenile crustal regions in the southern and western SGXR. Interaction between juvenile crust-derived melts and ancient crustal components played an important role on the distribution of various ore metals.
查看更多>>摘要：As an unconventional natural gas resource, coalbed methane (CBM) development releases a large amount of CBM wells co-produced water. Geochemical characteristics of the co-produced water provide an essential foundation for the production dynamics of CBM reservoirs if the impacts of fracturing fluids and other aquifers can be ignored. In the Shizhuangnan Block of the southern Qinshui Basin, constant and trace elements in CBM co-produced water from the wellheads were collected and determined, which is applied to assess water source, fracturing fluid effect, and CBM production. Based on principle component analysis and hierarchical clustering analysis, the water samples are divided into four categories. It suggests that different characteristics affected by water-rock interaction, reservoir environment, aquifer recharge, and hydraulic fracturing result in the various ratios of Na+/Cl-, alkalinity (HCO3-+ CO32-)/Cl- and other specific rules. Moreover, Cl- is selected as a dividing line for complete fracturing fluid flow back, associated with organic-bound chlorine complexes in the original coal seam water. Compared to constant elements, there is a significant correlation between Li and Sr concentrations and CBM productivity, so templates regarding trace elements can be used to distinguish various sources of the co-produced water.
查看更多>>摘要：Arroyo Verde epithermal deposit, in the North Patagonia region of Argentina, is located within the Lower Chon Aike volcanism and is developed between 192.6 ± 2.5 Ma (mineralization host rock) and 189.5 ± 2.6 Ma (overlying lava). Marifil volcanic complex is the host rock for these veins, veinlets and breccias. This particular small deposit has developed low to intermediate sulphidation characteristics, with gangue mineral textures associated with several ore minerals. Electron probe microanalysis determines electrum, silver minerals such as acanthite, and tetrahedrite, related Ag-Cu minerals like jalpaite, mckinstryite, stromeyerite, and base metals like chalcopyrite, sphalerite, galena and pyrite. Fluid inclusions in quartz of two out of five events indicate that these Low Jurassic veins were formed due to subtle boiling and dilution mechanisms and by low-salinity (3.4 wt.％ to 6.7 wt.％ NaCl Eq) magmatic-hydrothermal fluid at 225 to 310 ℃.The fluid inclusion measurements that indicate boiling (Event 3) were plotted, and based on this data, we interpret that the Arroyo Verde deposit has been eroded between 550 and 700 m. This particular character has not been previously recorded for other sectors of the eastern north Patagonian region.
查看更多>>摘要：'Single shot' laser-ablation split-stream (SS-LASS) technique analyzing unpolished zircon grains makes their thin rims tenable for determination, which thus offers great potential in deciphering the timing of multiple and short-lived episodes of anatexis and metamorphism in deeplysubducted continental crusts. Dominated granitic gneisses in the deeply subducted continental crust undergoing considerable fluid-melt activities persist multistage growth of zircon. Therefore, a comparative study of SS-LASS and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) zircon dating was conducted on the granitic gneisses from the Sulu belt in this study. Zircons mostly show a core-mantle-rim structure with CL-bright rims thinner than 5 μm. For LA-ICP-MS dating, relict magmatic zircon cores yield protolith ages of ca. 756-747 Ma; whereas the dark mantles record synexhumation anatexis at ca. 214 Ma. By contrast, according to the U-Pb dates, trace element features, zircon crystallization temperatures and geological context, SS-LASS zircon petrochronology deciphers three episodes of anatectic events, as follows: (i) the first episode of anatexis at ca. 218-217 Ma dominated by phengite-breakdown melting, likely facilitating the exhumation of the UHP slice from mantle depth; (ii) the second episode of anatexis at ca. 193-191 Ma indicating part of northern Dabie-Sulu belt was still "hot" because of buried in the thickened orogenic crust at that time; (iii) the third episode of anatexis (ca. 162-161 Ma) consistent with the intrusion ages (ca. 161-141 Ma) of the Jurassic to Cretaceous granitoids in this orogen, suggesting the initial collapse of the orogenic root of the Sulu belt occurred at Late Jurassic due to the Izanagi plate initially subducting beneath the margin of Eastern Asia. This study sheds new light upon the utilization of SS-LASS petrochronology deciphering multiple anatectic events in the deeply-subducted continental crust and supports us in better understanding the tectonic evolution of Dabie-Sulu Orogen.
查看更多>>摘要：The Daqing Shan (DQS) located in the Yinshan-Yanshan Orogenic Belt plays an important role in the Mesozoic to Cenozoic evolution of the North China Craton. However, the cooling and exhumation history since the Cretaceous is still controversial. Integrating the apatite fission track (AFT) data in both this study and previous works, a three-stage exhumation history from Cretaceous to Neogene of the DQS is proposed. (1) The first stage is composed of the early exhumation during Early Cretaceous driven by the collision between the North China and Siberia cratons (ca. 148-132 Ma) and the far-field effect of the subduction of the Pacific Plate (ca. 132-114 Ma). (2) Due to the subsidence of the Hetao Basin and the subsequent compensation between the DQS and the Hetao Basin, the DQS experienced the second rapid exhumation from Early Eocene to Early Oligocene (ca. 54-29 Ma). (3) Since the Late Miocene (ca. 13.5 Ma), the third rapid cooling and exhumation of the DQS occurred due to the far-field effect of the uplift of the Tibetan Plateau and the subduction of the Pacific Plate.
查看更多>>摘要：Various models exist to explain the formation of the Tibetan Plateau, including "tectonic escape", "pure shear thickening", "convective removal of the lithospheric mantle", and "lower crustal flow" model. The first two models are primarily constructed on pure mechanical models but are unable to reasonably explain the tension and shear phenomena inside the plateau. The latter two are rheological dynamic models based on deep geophysical observations. However, the spatial range of the lower crustal flow and its role in the plateau formation/uplift remain controversial. Five multi-terrane viscoplastic thermomechanical models were constructed to simulate the uplift and lithospheric structure change of the Tibetan Plateau during the post-collision stage (since 35 Ma) under the convergence of the Indian Plate. Results show that the plateau's formation begins with crustal thickening, blocked by strong terranes at the northern plateau, and expanded laterally to the east. The lithosphere thickens gradually and experiences delamination at its base, elevating temperature within the crust and forming partial melting layers in the central plateau. As convergence persists on the southern side, the northern plateau's lithosphere bends downward and undergoes delamination, further heating the crust and promoting the northward and eastward flow of partial melting layers, leading to secondary uplift around the plateau.
查看更多>>摘要：The Gengma-Lancang-Menghai seismic belt, the southernmost part of the North-South seismic belt, is controlled by four active faults: the Nantinghe fault (NTHF), the Sanjianshan fault (SJSF), the Hanmuba-Lancang fault (HMB-LCF), and the Heihe fault (HHF), from northwest to southeast. However, the tectonic activity of the faults in the Gengma-Lancang-Menghai seismic belt has not been fully studied yet. In the present work, we conducted tectonic geomorphic indices to analyze the relative tectonic activity along the faults in the seismic belt based on the digital elevation model. We interpreted asymmetric factor, index of drainage basin shape, hypsometric integral, normalized streamlength gradient, valley floor-to-width to height ratio, and longitudinal profiles to show that the relative tectonic activity is higher in the north and lower in the south, and is strong in the region from Shanjia to Huimin in the center of the seismic belt.
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