Festa A.,University of Turin |
Dilek Y.,University of Turin |
Dilek Y.,Miami University Ohio |
Dilek Y.,State Key Laboratory of Geological Processes and Mineral Resources |
And 6 more authors.
Bulletin of the Geological Society of America | Year: 2013
We document in this study the internal structure of the Late Cretaceous-late Oligocene Ligurian accretionary wedge in northwestern Italy, and the occurrence in this exhumed wedge of broken formation and three different types of mélanges that formed sequentially through time. The broken formation is the oldest unit in the accretionary wedge and shows bedding-parallel boudinage structures, which developed as a result of layer-parallel extension at the toe of the internal part of the Alpine wedge front during the Late Cretaceous-middle Eocene. This broken formation experienced an overprint of tectonic, diapiric, and sedimentary processes as a result of continental collision in the late Oligo cene. The NE-vergent thrusting and asso ciated shortening produced a structurally ordered block-in-matrix fabric through mixing of both native and exotic blocks, forming the tectonic mélange. The concentration of overpressurized fluids along the thrust fault planes triggered the upward rise of shaly material, producing the diapiric mélange, which in turn provided the source material for the downslope emplacement of the youngest, late Oligocene sedimentary mélange. The sedimentary mélange units unconformably cover the collisional thrust faults, constraining the timing of both this episode of contractional deformation related to continental collision and the combination and overlap of tectonic, diapiric, and sedimentary processes. Our multiscale structural analysis of the Ligurian accretionary wedge shows that tectonic, diapiric, and sedimentary processes played a significant role in its evolution, and that the interplay between and the superposition of these different processes strongly controlled the dynamic equilibrium of the accretionary wedge in the NW Apennines-western Alps. This kind of polygenetic mélange development may be common in many modern and ancient accretionary complexes, and the processes involved in their formation are likely to be responsible for major tsunamic events in convergent margins. © 2013 Geological Society of America.
Chao D.,Chinese Academy of Geological Sciences |
Chao D.,State Key Laboratory of Geological Processes and Mineral Resources |
Yan-he L.I.,Chinese Academy of Geological Sciences |
Jing-wen M.A.O.,Chinese Academy of Geological Sciences |
And 2 more authors.
Geology in China | Year: 2012
The Washan iron deposit is a representative porphyrite iron deposit. There are two types of intrusions: One is gabbro-diorite porphyrite closely related to the iron mineralization and serves as the host rocks, and the other is granodiorite porphyry cutting across the ore body, which has been rarely studied. Detailed zircon LAICP-MS trace element measurement was performed on these two intrusions. The two intrusions have similar chondrite-normalized REE patterns of zircons and Yb, Hf and Y values, whereas zircons from the granodiorite porphyry have higher U values and U/Yb ratios. In combination with previous studies of isotope geochemistry, the authors infer that these intrusions have similar sources, and much crust material was involved in the formation of granodiorite porphyry during the ascending process. Zircon Ce(IV)/Ce(III )ratios of the granodiorite porphyry are concentrated in the range of 0-100, lower than the values of zircons (>300) from the granite related to the porphyry Cu-Au mineralization; nevertheless, they have similar characteristics of δ Eu (>0.4). Thus, it is not certain whether the granodiorite porphyry had the potential to form copper and gold deposits, and hence further researches are needed concerning the possible relationship between the granitic stocks and copper and/or gold mineralization.
She Z.,State Key Laboratory of Geological Processes and Mineral Resources |
She Z.,Wuhan University |
Strother P.,Boston College |
McMahon G.,Boston College |
And 8 more authors.
Precambrian Research | Year: 2013
In order to ascertain the origin of granular phosphorites and the roles of microorganisms in phosphogenesis, we conducted comprehensive petrographic surveys and correlated in situ micro-analyses of granular phosphorites from the Doushantuo Formation near Yichang, South China. Phosphatic granules display organically-zoned internal structures often associated with abundant cyanobacteria-like microfossils. The internal ultrastructure of the granules, as documented by Raman microspectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), is characterized by randomly-oriented apatite nano-crystals embedded with ubiquitous carbonaceous particles in the apatite groundmass. These represent primary textures formed by the rapid growth of apatite provided with abundant nucleation sites within microbial biofabrics. NanoSIMS elemental mapping revealed close correspondence of carbon and nitrogen with microfossil structures at the cellular and sub-cellular level. We propose that the Doushantuo granules themselves were formed by microbially-mediated accretionary growth followed by rapid phosphatization occurring at the sediment-water interface. Extracellular polymeric substances (EPS) produced by cyanobacteria would have played crucial roles in these processes by promoting aggregated granule growth in addition to providing nucleation sites for apatite crystallization. While previous studies have suggested a dominant role of sulfur-metabolizing microorganisms in the precipitation of phosphate in phosphorites, new observations indicate that the emplacement of most sulfur-bearing minerals in the Doushantuo phosphorites postdate phosphatization itself. Our new model of phosphorite formation thus places cyanobacterial EPS as an earlier key component of the mineralization of the Doushantuo granular phosphorites. © 2013 Elsevier B.V.
Lou D.-B.,Chinese Academy of Geological Sciences |
Xiao K.-Y.,Chinese Academy of Geological Sciences |
Zuo R.-G.,Wuhan University |
Zuo R.-G.,State Key Laboratory of Geological Processes and Mineral Resources |
Jia J.-D.,Bureau of Mineral Resources
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2012
Extracting concealed metallogenic information is a fundamental task in exploration geochemistry. The Huangshan-jing'erquan Ni-Cu metallogenic belt, in the eastern Tianshan, Xinjiang, is chosen as a study case to identify concealed local anomalies from complex geochemical background by singularity mapping technique. The results illustrate that the Ni concentration value in the geochemical map according to primary Ni contents is obviously different from that in the geochemical map by singularity mapping technique. In the former, the Ni concentration value is high in the Tuha basin and medium to low in the tectonic-magmatic belt. While in the later, there are adverse features. Due to geological analysis, high concentration value of the element Ni is resulted from intruding of mafic-ultramafic intrusions. These intrusions are of low-degree differentiation and unfavorable to form deposits in Tuha basin so that there occur large-area anomalies in the basin. However, in the tectonic-magmatic belt, though intrusions are small and with medium to low geochemical anomalies, they are differentiated well and favorable to form deposits. The concentration-aera (C-A) method is used to analyze singularity value and delineate anomalies. Because delineated anomalies fit well with known Ni-Cu deposits, they can provide geochemical evidence for delineating target regions.
Zhang J.,Wuhan University |
Yu J.,State Key Laboratory of Geological Processes and Mineral Resources |
Cheng X.,Wuhan University |
Hou S.-E.,Wuhan University
Journal of Alloys and Compounds | Year: 2012
A series of compositions with the general formula La 2(Zr 2-2xCe 2x)O 7 (0 ≤ x ≤ 0.75) were prepared by the coprecipitation-calcination method and characterized by powder XRD. The composition of prepared ceramic materials changed from single pyrochlore structure to the mixture with pyrochlore structure and fluorite structure as x increased. The lattice parameters decreased firstly and then increased while the amount of Ce 4+ at 298 K was increased. The thermal expansion coefficient of La 2Zr 2O 7 was improved by a number of Ce 4+ adoptions at high temperature. © 2011 Elsevier Ltd. All rights reserved. All rights reserved.
Lu F.-X.,Wuhan University |
Lu F.-X.,State Key Laboratory of Geological Processes and Mineral Resources
Geology in China | Year: 2010
The component evolution of ancient lithospheric mantle was constrained by three deep -seated geological processes, i.e., (1) melt extraction, (2) lithospheric mantle metasomatism of melt/fluid from different sources, and (3) interaction between lithosphere and asthenosphere/asthenospheric melt. Two stage enstatites (Py1 and Py2) were discovered in a sample of peridotite xenolith from Mengyin kimberlite. The enstatites of the early stage are residual minerals in the early peridotites with coarse-grained texture. However, the enstatites of the late stage were formed under the plastic rheological condition. A comparison of major and trace elements between the two kinds of peridotites from Mingyin, Fuxian and South Africa shows that the coarse-grained peridotites have higher Mg' (0.902-0.93) and lower Al2O3 (0.22%-2.32%) values, whereas the peridotites with shear texture have lower Mg' and higher Al2O3 (1.69%-2.75%) values, suggesting that the late stage peridotites have lower refractory degree than the early stage peridotites. This phenomenon finds expression in the mantle component evolution process not only controlled by melt extraction but also by the interaction between lithosphere and asthenosphere / asthenospheric melt. The action caused the evolution of mantle composition from refractory back to fertile, and such an evolution trend is called "inverse evolution". At least two magma extraction events and two "inverse evolution" processes occurred in ancient lithospueric mande of North China Craton approximately during the 3 Ga geological period. Compared with the action (3) in Phanerozoic, it was characterized by smaller scale, lower strength and more obvious heterogeneity.
Jin G.,Wuhan University |
Wang Z.,Wuhan University |
Hu X.,Wuhan University |
Hu S.,Wuhan University |
And 2 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2013
With the rapid development of industrialization and urbanization in China, arable land resources are still continuing to be occupied, leading to the intensification of conflicts between an increasing population and decreasing arable land resources. Thus, how to exploit and use the reserve resources of arable land in the Qinghai-Tibet Plateau has attracted much more attention under the serious situation of protecting arable land. But it is the necessary prerequisite to carry out a study on natural suitability evaluation before the exploitation and utilization of reserved arable land. This paper took the reserved arable land of 18 counties in the "Three Rivers" Area region of Tibet as an example. Eight factors of landform, climate, soil and water, that is, slope, elevation, slope direction, temperature, rainfall, soil depth, organic matter content, and distance to water area, were adopted as evaluation factors. The fuzzy weight of evidence model, which is both knowledge and data driven, was employed to get the grade of natural suitability evaluation of reserve resources of arable land, which was then compared with the result evaluated by a comprehensive index model. Evaluation results showed as follows: first, 99.38% of "reference objects" of the arable land are above the third grade on the basis of five suitability grades in total, which means that the fuzzy weight of evidence model could evaluate the natural suitability of reserved arable land effectively. Second, compared with the evaluation results of a comprehensive index model, 90.83% of the arable land resources are above the third grade, which shows the fuzzy weight of evidence model is more objective and reasonable than the comprehensive index model in this case. And it also overcomes the subjective arbitrariness in weight determination and the computation complexity by various natural conditions. Third, 11 434.1 km2 of reserved arable land had suitable natural quality, among which grade 1, 2, 3, 4, and 5 accounted for 9.6%, 5.5%, 38.6%, 22.8%, and 23.4% respectively. And we suggest that Shigatse, Konggar, Chanang, Lhazê, Nêdong, Lhasa, and Bainang counties should be the main areas for exploitation of reserved arable land in the future.
Xiong F.H.,Wuhan University |
Ma C.Q.,Wuhan University |
Ma C.Q.,State Key Laboratory of Geological Processes and Mineral Resources |
Zhang J.Y.,Wuhan University |
Liu B.,Wuhan University
Acta Petrologica Sinica | Year: 2011
The Bairiqili mafic dyke swarms in East Kunlun are principally composed of noritegabbro, with minor porphyritic diabase. The LA-ICP-MS zircon U-Pb dating indicates that the mafic dykes were emplaced with age of 251 ±2Ma. The mafic dykes are characterized by moderate Mg# (31 - 50) and high alumina ( 16. 25% - 19.49% ) , belonging to cale-alkali rocks (Na 2O + K 2O = 2.75% -3.51%; FeO T/MgO = 1.02-2.22). The rocks have lower total REE, with slightly enriched LREE and positive Eu anomalies (ΣREE =52.16 × 10 -6∼99.81 × 10 -6, (La/Yb) N=2. 08 -5.49, δEu = 1.03 -1.30) , besides, all rocks are enriched in LILE (eg. , Rb, Ba and Pb, etc. ) and depleted in HESE (eg. , Nb, Ta, P and Ti, etc ) , and have significantly different ratios of incompatible elements to that in the crust ( such as Nb/Ta ratio). Dykes have enriched Sr-Nd isotopic compositions ( ( 87Sr/ 86Sr) i= 0. 71103 - 0. 71502, ε Nd(t)= -7.4 ∼ -3. 6) , with the relative concentrated and significantly distinguished ε Hf(t) ratio ( -2. 37 ∼ 1. 07) when compared to that derived from the crust. Geochemical and isotopic studies show that the mafic dykes were derived from EM2 that have been metasomatized by fluid. Tectonic setting analysis shows that the rocks have characteristics of island arc and/or mid-ocean ridge basalts, combined with the tectonic evolution of East Kunlun, we propose that the Bairiqili mafic dykes were derived from EM2 in a subduction environment, which was metasomatized by fluid and then, triggered to partial melting to form the mafic magma, at about 250Ma, it took place back-arc extension in the north of the subduction zone, and then the mafic magma was rising to upper crust along the fissure to form the mafic dykes.
Xu Q.,CAS Institute of Tibetan Plateau Research |
Xu Q.,State Key Laboratory of Geological Processes and Mineral Resources |
Zhao J.,CAS Institute of Tibetan Plateau Research |
Pei S.,CAS Institute of Tibetan Plateau Research |
Liu H.,CAS Institute of Tibetan Plateau Research
Geophysical Journal International | Year: 2011
Detailed high-resolution images of the crust-mantle and lithosphere-asthenosphere boundaries (the Moho and the LAB, respectively) have been well observed by applying an S-receiver function technique to data collected by the Hi-CLIMB (Himalayan-Tibetan Continental Lithosphere During Mountain Building) experiment. The Moho depth variation in the range of ~50-70 km is in good agreement with that from previous P-receiver function results. The significant variation in the LAB depth indicates that the subducting Indian lithosphere drops northwards from a depth of ~80 km beneath the Himalayas to ~130 km just north of the Bangong-Nujiang suture at ~33.0°N, and undergoes a transition from low angle to flat subduction beneath the Yarlung-Zangbo suture. Our findings provide new seismic constraints on the 3-D subducting configuration of the Indian lithosphere beneath Tibet. © 2011 The Authors Geophysical Journal International © 2011 RAS.
Yang T.,Hefei University of Technology |
Leng W.,Hefei University of Technology |
Leng W.,State Key Laboratory of Geological Processes and Mineral Resources
Earth and Planetary Science Letters | Year: 2014
The presence of mantle plumes beneath old continental regions may have been underestimated due to the lack of surface expressions. New seismic results reveal a corridor-like low seismic velocity zone at the bottom of the continental lithosphere beneath the eastern United States, interpreted as the erosion of the moving continental lithosphere by a plume conduit. Here we study the dynamics of the interaction between a mantle plume conduit and a moving depleted continental lithosphere. With thermochemical numerical models in 3-D Cartesian geometry, we show that a plume conduit can erode the bottom of the continental lithosphere, generating a corridor-like low seismic velocity zone downstream the plate motion direction. This low seismic velocity corridor is typically ~300km in width and ~50km in height, with several percent of P-wave velocity reduction within it. It can survive more than 100 Myr and extend thousands of kilometers. The surface swell topography of this corridor is much smaller than those beneath the oceanic lithosphere, forming 'hidden tracks'. We propose that other 'hidden tracks', with little surface expression, may exist beneath old continental regions. Such 'hidden tracks', once found, may provide additional constraints on plate motion history. © 2014 Elsevier B.V.