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Huang Q.,Peking University | Huang Q.,The Key Laboratory of Orogenic Belts and Crustal Evolution
Journal of Asian Earth Sciences | Year: 2011

The Ms8.0 Wenchuan earthquake is one of the most catastrophic earthquakes occurred recently. Although the geophysical network around the epicentral region is not dense enough partially due to the inactivity of the Longmenshan fault, the retrospective investigation of geophysical data in and around the epicentral region would be helpful for strengthening the understanding of the seismogenic process of the Wenchuan earthquake. This paper summarized some preliminary results of the retrospective investigation, especially focusing on the seismic and electromagnetic data possibly associated with the Wenchuan earthquake and its aftershocks. The spatio-temporal investigation of the seismicity changes indicated that there is an intermediate-term seismic quiescence around the epicenter during 2006-2007. The electromagnetic data also showed some anomalous changes (including co-seismic electromagnetic changes), which may be related with the Wenchuan earthquake and its aftershocks. Although further work is definitely required to enhance the reliability of the relationship between the above geophysical changes and the seismogenic process, the above preliminary results would provide some useful information for the related study and stimulate further validation study on the precursors of the Wenchuan earthquake. © 2010 Elsevier Ltd.

Zhu Y.,The Key Laboratory of Orogenic Belts and Crustal Evolution | Zhu Y.,Peking University
Ore Geology Reviews | Year: 2011

This study focuses on zircon U-Pb and muscovite 40Ar/ 39Ar geochronology of gold-bearing mylonitized granite in the north Tianshan of China. All zircon samples have euhedral hydrothermal rims, which have replaced their igneous mantles. Igneous zircon mantles with narrow hydrothermal rims in sample TS06 give a weighted average U-Pb age of 403.7±5.6Ma (1 standard error, MSWD=1.5, n=18). Zircons in TS277 show a complex texture with core (detrital origin, 1276-2215Ma) indicating igneous mantle and a hydrothermal rim. The igneous mantles give a weighted average U-Pb age of 443.4±3.3Ma (MSWD=3.1, n=10). Two younger ages (394 and 400Ma) have been obtained on hydrothermal rims. The mantles plus rims of all zircons have positive εHf (t) values with an average of 3.99±0.86 (MSWD=2.8, n=23). The positive εHf (t) values suggest that the granite magma is derived from melting of juvenile crustal rocks. The shearing deformation post-dated granite intrusion and introduced fluid, which replaced igneous zircons via dissolution and reprecipitation. However, the age data for zircon hydrothermal rims do not represent the time of the dissolution re-precipitation. The zircons crystallized in granite in the Early Silurian (~443Ma) have been replaced on their rims during Middle Triassic deformation (248-238Ma), which was followed by brittle deformation accompanied by gold deposition at ~220Ma, based on 40Ar/ 39Ar dating of muscovite. © 2011 Elsevier B.V.

Zhang H.,The Key Laboratory of Orogenic Belts and Crustal Evolution | Zhang H.,Peking University | Zhu Y.,The Key Laboratory of Orogenic Belts and Crustal Evolution | Zhu Y.,Peking University
Ore Geology Reviews | Year: 2016

The Huilvshan gold deposit in the west Junggar (Xinjiang, China) is hosted in chloritized basalts, chlorite-siderite-altered basalts, and quartz-siderite rocks. Our study demonstrated that all these rocks were derived by alteration of basalts in a shear zone. The orebodies, consisting of quartz-sulfide veins and disseminated sulfides, formed in five stages: quartz-muscovite (I), disseminated sulfides (II), quartz-ankerite-sulfide (III), quartz-calcite-sulfide (IV), and quartz-calcite (V). Auriferous minerals are native gold in stage III and electrum in stage IV. During alteration of basalts in the shear zone, ore-forming elements were released from basalts to ore-forming fluid. Compared with fresh basalts, sulfide-bearing chloritized basalts contain much higher Sr, Ba, P, La, Ce, U, Mn, Ni, Zn, As, Ag, and Au contents. Phase analysis of the As-Cu-Fe-S-O system with the SUPCRT92 software package indicates that a decrease of the aH2S value, caused by the fluid-rock reactions and crystallization of sulfides, induced gold precipitation. © 2016 Elsevier B.V.

Shao J.A.,The Key Laboratory of Orogenic Belts and Crustal Evolution | Wei C.J.,The Key Laboratory of Orogenic Belts and Crustal Evolution
Science China Earth Sciences | Year: 2011

Granulite xenoliths are found in the early Mesozoic diorite intrusions from Chifeng and Ningcheng areas, eastern Inner Mongolia. The granulites are granoblastic and weakly gneissic with mineral assemblage of hypersthene, diopside, plagioclase and minor biotite, amphibole and ilmenite. Some samples contain the intergrowth composed of labradorite and vermicular hypersthene, and some coarse-grained plagioclases of andesine and labradorite composition occasionally develop bytownite rims with vermicular hypersthene, indicating a possible presence of garnet. Presence of blastogabbroic texture and hypersthene with diopside exsolution lamellae in some samples suggests that the protolith of the granulite is norite or gabbro. On the basis of metamorphic research and thermobaric calculation, the evolution of the granulite xenoliths is summarized into the following stages: (1) Isobaric cooling of underplated noritic or gabbroic magma in the lower crust led to the formation of probable garnet-bearing medium-high pressure granulite. (2) These higher pressure granulites were adiabatically uplifted to upper crust by dioritic magma and transformed to low pressure two-pyroxene granulite during an isothermal decompression. (3) The two-pyroxene granulite underwent retrograde metamorphism of different degrees during an isobaric cooling process as a result of crystallization and cooling of the dioritic magma. The pyroxenite-dominated cumulates and the medium-high pressure granulites may have rejuvenated the lower crust during the early Mesozoic. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.

Wang S.,The Key Laboratory of Orogenic Belts and Crustal Evolution | Wang S.,Peking University | Liu X.,The Key Laboratory of Orogenic Belts and Crustal Evolution | Liu X.,Peking University | And 7 more authors.
Physics and Chemistry of Minerals | Year: 2012

Using a conventional high-T furnace, the solid solutions between magnesiochromite and manganochromite, (Mg 1-xMn x)Cr 2O 4 with x = 0.00, 0.19, 0.44, 0.61, 0.77 and 1.00, were synthesized at 1,473 K for 48 h in open air. The ambient powder X-ray diffraction data suggest that the V-x relationship of the spinels does not show significant deviation from the Vegard's law. In situ high-T powder X-ray diffraction measurements were taken up to 1,273 K at ambient pressure. For the investigated temperature range, the unit-cell parameters of the spinels increase smoothly with temperature increment, indicating no sign of cation redistribution between the tetrahedral and octahedral sites. The V-T data were fitted with a polynomial expression for the volumetric thermal expansion coefficient (α T= a 0+a 1T+a 2T -2), which yielded insignificant a 2 values. The effect of the composition on a 0 is adequately described by the equation a 0 = [17.7(8) - 2.4(1) × x] 10 -6 K -1, whereas that on a 1 by the equation a 1 = [8.6(9) + 2.1(11) × x] 10 -9 K -2. © 2011 Springer-Verlag.

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