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Huang J.,Hefei University of Technology | Xiao Y.,Hefei University of Technology | Gao Y.,University of Houston | Hou Z.,Hefei University of Technology | Wu W.,Geological Survey of Hubei Province
Journal of Metamorphic Geology

Niobium and Ta concentrations in ultrahigh-pressure (UHP) eclogites and rutile from these eclogites and associated high pressure (HP) veins were used to study the behaviour of Nb-Ta during dehydration and fluid-rock interaction. Samples were collected through a ~2km profile at the Bixiling complex in the Dabie orogenic belt, Central-Eastern China. All but one eclogite away from veins (EAVs) display nearly constant Nb/Ta ratios ranging from 16.1 to 19.2, with an average of 16.9±0.8 (2 SE), similar to that of their gabbroic protolith from the Yangtze Block. Nb/Ta ratios of rutile from the EAVs range from 12.7 to 25.3 among different individual grains, with the average values close to those of the corresponding bulk rocks. These observations show that Nb and Ta were not significantly fractionated by prograde metamorphism up to eclogite facies when no significant fluid-rock interaction occurs. In contrast, Nb/Ta ratios of rutile from eclogites close to veins (ECVs) are highly variable from 17.8 to 49.8, which are systematically higher (by up to 17) than those of rutile from the veins. These observations demonstrate that Nb and Ta were mobilized and fractionated during localized fluid flow and intensive fluid-rock interaction. This is strongly supported by Nb/Ta zoning patterns in single rutile grains revealed by in situ LA-ICP-MS analysis. Ratios of Nb/Ta in the ECV-hosted rutile decrease gradually from cores towards rims, whereas those in the EAV-hosted rutile are nearly invariable. Furthermore, the vein rutile shows Nb/Ta zoning patterns that are complementary to those in rutile from their immediate hosts (ECVs), suggesting an internal origin for the vein-forming fluids. The Nb/Ta ratios of such fluids evolved from low values at the early stage of subduction to higher values at later supercritical conditions with increased temperature and pressure. Quantitative modelling was conducted to constrain the compositional evolution of metamorphic fluids during dehydration and fluid-rock interaction focusing on Nb-Ta distribution. The modelling results based on our proposed multistage fluid phase evolution path can essentially reproduce the natural observations reported in the present study. © 2012 Blackwell Publishing Ltd. Source

Zhou L.,Zhejiang University | Zhang D.,Hangzhou Normal University | Wang J.,Hangzhou Normal University | Huang Z.,Geological Survey of Hubei Province | Pan D.,State Oceanic Administration
Remote Sensing

Coal fires have been found to be a serious problem worldwide in coal mining reserves. Coal fires burn valuable coal reserves and lead to severe environmental degradation of the region. Moreover, coal fires can result in massive surface displacements due to the reduction in volume of the burning coal and can cause thermal effects in the adjacent rock mass particularly cracks and fissures. The Wuda coalfield in Northern China is known for being an exclusive storehouse of prime coking coal as well as for being the site of occurrence of the maximum number of known coal fires among all the coalfields in China and worldwide, and is chosen as our study area. In this study, we have investigated the capabilities and limitations of ALOS PALSAR data for monitoring the land subsidence that accompanies coal fires by means of satellite differential interferometric synthetic aperture radar (DInSAR) observations. An approach to map the large and highly non-linear subsidence based on a small number of SAR images was applied to the Wuda coalfield to reveal the spatial and temporal signals of land subsidence in areas affected by coal fires. The DInSAR results agree well with coal fire data obtained from field investigations and thermal anomaly information, which demonstrates that the capability of ALOS PALSAR data and the proposed approach have remarkable potential to detect this land subsidence of interest. In addition, our results also provide a spatial extent and temporal evolution of the land subsidence behavior accompanying the coal fires, which indicated that several coal fire zones suffer accelerated ongoing land subsidence, whilst other coal fire zones are newly subsiding areas arising from coal fires in the period of development. © 2013 by the authors; licensee MDPI, Basel, Switzerland. Source

Li C.,CAS Institute of Vertebrate Paleontology and Paleoanthropology | Rieppel O.,Field Museum | Wu X.-C.,Canadian Museum of Nature | Zhao L.-J.,Zhejiang Museum of Nature History | Wang L.-T.,Geological Survey of Hubei Province
Journal of Vertebrate Paleontology

A new genus and species of marine reptile is described from the Pelsonian (Anisian, Middle Triassic) of Luoping County, Yunnan Province, southwestern China. This diapsid reptile with a secondarily closed upper temporal fossa is the sister taxon to Saurosphargis from the lower Muschelkalk (Anisian, Middle Triassic) of central Europe. It further emphasizes the close faunal affinities between the Eastern and Western Tethyan realm. The new taxon is convergent on cyamodontoid placodonts in having developed a dorsal body armor composed of small osteoderms. The underlying ribs are transversely broadened so as to establish contact along their length, thus forming a closed dorsal 'rib basket,' a unique morphology shared with Saurosphargis. © 2011 by the Society of Vertebrate Paleontology. Source

Xie G.,Chinese Academy of Geological Sciences | Mao J.,Chinese Academy of Geological Sciences | Xiongwei L.,Geological Survey of Hubei Province | Duan C.,China University of Geosciences | Yao L.,China University of Geosciences

Late Mesozoic intrusive and volcanic rocks are widespread in the southeast Hubei Province, Middle-Lower Yangtze River Belt (YRB), East China. Detailed in situ zircon U-Pb and Hf isotope, elemental and Sr-Nd-Pb isotopic data are presented in this paper for Late Mesozoic volcanic rocks from the Jinniu Basin, YRB, aiming to constrain their age, petrogenesis, and tectonic implications. The Jinniu volcanic rocks show a bimodal distribution in composition, with dominant rhyolite and dacite, and subordinate basalt and basaltic andesite. New SHRIMP and LA-ICPMS zircon U-Pb ages indicate that the volcanic rocks of three Formations in the Jinniu basin were erupted at quite a short age range of about 5Ma during the Early Cretaceous (130-125Ma). The mafic rocks are moderately enriched in large-ion-lithophile-elements (LILE) (e.g., Ba, Th, U, and Pb) and light rare-earth-elements (LREE), and are characterized by negative Nb, Ta, and Ti anomalies, and relatively high TiO2 (0.72-2.06%) and Nb (9.20-26.5ppm) contents. These analyses indicate that the geochemical characteristics of the mafic rocks in the Jinniu basin are similar to worldwide Phanerozoic Nb-enriched basalt and andesites (NEBA). New in situ zircon U-Pb ages and field geological relationships demonstrate that NEBA in the southeast Hubei Province are not spatially or temporally associated with high-silica adakitic rocks, but were most likely derived from an enriched lithospheric mantle with assimilation of minor crustal materials, and then fractional crystallization during the evolution of the magma. Overall, the felsic rocks in the Jinniu basin have geochemical characteristics, and Sr-Nd-Pb signatures, and in situ zircon Hf isotopic compositions similar to those of the mafic rocks. Compared with the mafic rocks, the felsic rocks are characterized by enriched and variable concentrations of LILE and REE (e.g., Ba=33.3-1372ppm, Y=11.4-33.6ppm, YbC=5.07-18.7), and negative Eu anomalies (δEu=0.22-0.98), as well as a wide range of radiogenic Nd-Pb isotopic values with εNd (t)=-10.2 to -2.4, (206Pb/204Pb)i=17.659-18.705, (207Pb/204Pb)i=15.478-15.663, and (208Pb/204Pb)i=37.654-38.935, and in situ zircon Hf compositions of εHf (t)=-12.7 to -1.8. These features indicate that the genesis of felsic magma in the Jinniu basin is consistent with extensive fractional crystallization and large amounts of crustal contamination from an evolved mafic magma (SiO2=~55%). The bimodal volcanic rocks in this study provide convincing evidence that Early Cretaceous volcanic rocks in the YRB developed in a back-arc extensional tectonic regime. © 2011 Elsevier B.V. Source

Shi D.,Chinese Academy of Geological Sciences | Lu Q.,Chinese Academy of Geological Sciences | Xu W.,Chinese Academy of Geological Sciences | Yan J.,Chinese Academy of Geological Sciences | And 3 more authors.

To understand the formation and the tectonic process of the Mesozoic middle-lower Yangtze metallogenic belt (YMB), the SinoProbe program deployed a quasi-linear passive source seismic array across the belt. We performed receiver function profiling and measurement of shear-wave splitting parameters with the collected data. Our results show that the Moho depth varies significantly along the profile and that a "mantle uplift" exists right beneath the YMB. We also found that the lower crust of the YMB is different from that of its adjacent areas in structure on the receiver function profile. It possesses seismic anisotropy with direction roughly parallel to the belt. Our SKS/SKKS shear-wave splitting results also show similar belt-parallel azimuthal anisotropy right beneath the YMB. We interpret the seismic anisotropy in the lower crust of the YMB as the result of mineral crystal alignment caused by melting and belt-parallel flow in the Mesozoic ore-forming process. Besides, we observed a nearly south-dipping converter extending from shallow to lower crust beneath the Hefei Basin, which most possibly resulted from the Mesozoic crustal extension. We interpret the "mantle uplift" and the crustal extensional structures to be consequences of asthenospheric upwelling during the Mesozoic ore-forming process. Our results suggest that the lower crust of the YMB was most likely one part of the multi-level metallogenic magma system in the Mesozoic magmatism and mineralization processes, and the formation of the metallogenic belt to be a result much similar to the MASH (Melting, Assimilation, Storage and Homogenization; cf. Hildreth and Moorbath, 1988; Richards, 2003) process. First, the asthenospheric upwelling resulted in a crustal extensional environment; then the melts from the upwelling asthenosphere intruded into the lower crust of the YMB, and assimilation occurred when they mixed with in situ lower crustal materials, which led to the formation of adakitic-like magma; the adakitic-like magma rose up along extensional structures, and reacted with country rocks to form mineral deposits. © 2013 Elsevier B.V. Source

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