Middle Permian palaeobiogeography study in East Kunlun,A''''nyêmaqên and Bayan Har

Origin, geographic distribution and evolutionhistory of the ancient organisms are the main contentsof the study of palaeobiogeography. Besides the studyof lineage distribution, ecological geographic distribu-tion is also an interesting subject in palaeobiogeogra-phy. Palaeobiogeographic research is important in thestudy of ancient ocean and the opening and closinghistory of ancient plate. The study of palaeobio-geography in the orogenic belt is especially valuablein the division of terrences a…     

Crustal structure using receiver function in the east part of A’nyêmaqên suture belt

Twenty broadband seismographs were deployed along Hongyuan, Sichuan to Wuwei, Gansu. 81 teleseismic events were recorded in one year. We computed receiver functions from teleseismic waveform data and obtained S wave velocity structure beneath each station along the profile by using receiver function inversion method. The results revealed that the crustal structure is very complex and crustal average S wave velocity is to be on the low side. Low velocity structure generally exists in the depth range of 10~40 km in the crust between Aba arc fault and northern edge fault of Qinling earth’s axis and it is a tectonic feature of complex geological process such as ancient A’nyêmaqên Tethys ocean from closing and side colliding to subducted plate exhumed or thrust rock slice lifted. The Moho is about 50 km depth along the profile and is slightly deeper in the south than in the north.     

L'activité solaire et les hivers extrêmes

Résumé Des intervalles de grande variabilité dans les températures des hivers en Europe occidentale coincident avec une période de l'activité solaire d'environ 80 ou 90 années. Le coefficient de corrélation pour la serie 1831–1937 est +0.74 à Prague, +0.82 à De Bilt.

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Summary Intervals of large variability in the winter temperatures of Western Europe coincide with a period of solar activity of about 80 or 90 years. The correlation coefficient for the year 1831–1937 amounts to +0.74 at Prague, +82 at De Bilt.

     

Application of radiolarians and other fossils in non-Smith strata--Exemplified by the A'nyêmaqên melange belt in East Kunlun Mts

The main character of melange strata in an orogenic belt is the integration of mixed materials due to the superposition, displacement or loss of various tectonic slices (blocks) of different origins and environments, different scales, different grades of deformation and metamorphism, and different stages of tectonic evolution. The approach to non-Smith strata in an orogenic belt is to focus on the understanding of the age, facies, tectonic setting of the original formation and the process of deformation-metamorphism of each tectonic slice, reconstruct the history of dispersal and integration of these tectonic slices in time and space, i.e. 4-dimensional. This paper studies the age and facies of the original formation of tectonic slices in the A'nyêmaqên melange belt based on new data of radiolarians, sporo-pollen and trace fossils, and cast new lights on the research of the evolution process of that belt.     

The Relationship Between Strong Earthquake Activity of M_S≥7.0 on the Chinese Mainland and the West Kunlun-A'nyêmaqên Secondary Arcuate Tectonic Zone

1 THESPATIALDISTRIBUTIONCHARACTERISTICSOFMODERATE STRONGEARTHQUAKESBEFORESTRONGEARTHQUAKESWITHMS≥ 7 0　　From 1 90 0to 2 0 0 2 ,6 5largeearthquakeswithMS≥ 7 0tookplaceontheChineseContinent,ofwhich 1 0weretwin quakesorstrongaftershocks.55earthquakecaseshavebeenstudiedinthispaper.ThecharacteristicsofmoderatelystrongearthquakeactivitybeforestrongearthquakeswithMS≥ 7 0wereanalyzed ,andthenotablecharacteristicswerefoundtobetheactiveandquietphenomenaayeefore…     

The Relationship Between Strong Earthquake Activity of Ms ≥ 7.0 on the Chinese Mainland and the West Kunlun- A''nyêmaqên Secondary Arcuate Tectonic Zone

The active and quiet phenomenon of moderate strong earthquakes one year before the earthquakes with M S≥7.0, the spatial distribution characteristics of the solid tide modulating and triggering earthquakes and the strong earthquake mechanisms on the Chinese continent have been studied. The secondary arcuate tectonic zone composed of the west Kunlun-Anyêmaqên faults is believed to be a very important boundary to characterize strong earthquake activity of M S≥7.0 on the Chinese continent, that is, a boundary between the seismically active region and the quiet region of moderately strong earthquakes one year before earthquakes with M S≥7.0, and a boundary of the spatial distributions between the solid tide modulating strong earthquakes (M S≥7.0) and the non-modulating ones. It might be related with the characteristics of spatial distribution of focal mechanism solutions of strong earthquakes on the Chinese Continent.     

SHRIMP zircon U-Pb age and Nd isotopic study on the Nyainqêntanglha Group in Tibet

The Nyainqêntanglha Group is traditionally viewed as the oldest metamorphic basement in the Lhasa block, but its formation age and tectonic setting remain debate. Zircons extracted from the metamorphic sequence of volcanics and intrusions of the Nyainqêntanglha Group, 10 km west of Nam Co in northern Lhasa block, have been investigated by cathodoluminescence (CL), backscattered (BSE) and dated by ion microprobe (SHRIMP). We conclude that the U-Pb age of 787 ê9 Ma of zircons from the trondhjemite imposes a constraint on maxi-mum protolith age, and minimum formation age of the Nyainqêntanglha Group is constrained by U-Pb age of 748 ê8 Ma of zircons from the granite. The formation age of the Nyainqêntanglha Group is consistent with sedimentary age of Greater Himalayan rocks, showing that they devel-oped coevally in an arc-basin tectonic setting of Neoproterozoic active continental margin along the northern margin of the India shield. The inherited zircons from the tholetiite and granite give older 207 Pb/206 Pb ages from 947 to 1766 Ma. The positive å Nd(t) value indicates that the mafic rocks were derived from the depleted mantle, but contaminated by the older continental crustal material. Integrated Nd model age and U-Pb age data provide excellent evidence for the existence of Mesoproterozoic basement in the Lhasa block during Neoproterozoic time.     

Field experiment in Soultz-sous-Forêts, 1993: Changes of the pattern of induced seismicity

The data of the known field experiment on water injection in the borehole were analyzed. Parameters of self-similarity of seismicity were estimated in comparison with the changes of water pressure. Changes of seismicity parameters that indicate the redistribution of the failure from lower scales to upper are revealed. The total number of earthquakes per series of the water initiation found to be depended exponentially on the water pressure and seismic activity maximum is delayed gradually relative to beginning of initiation. The growth of induced seismicity zone in time differs from diffusion model for water flow in the porous medium. Analysis carried out from laboratory data indicates that diffusion growth of the failure area may be realized in the dry specimen, without fluid. It could be assumed that both kinetic processes — water and the failure diffusion — can be significant for the development of seismicity induced by the water injection.     

SHRIMP zircon U-Pb age and Nd isotopic study on the Nyainqêntanglha Group in Tibet

The Nyainqêntanglha Group, called Nyainqêntan- glha orthogneisses and schist sequence by Li et al.[1], is traditionally viewed as the oldest metamorphic basement in the Lhasa block[1―4]. The uplifted blocks of basement have exposed in two regions, middle segment of Nyainqêntanglha Mountain Range and west of Nam Co. The Nyainqêntanglha Group is sparsely dated, for its protolith age, the previous ideas were very different, such as Proterozoic, Pre-Sinian, Precambrian, or early Paleozo…     

Evidence for glaciation predating MIS-6 in the eastern Nyainqêntanglha Range,southeastern Tibet

Southeastern Tibet is one of the most glaciated regions on the Tibetan Plateau both at present and during the Quaternary. Numerical dating of glacial deposits has allowed the establishment of a provisional chronology of Quaternary glacial fluctuations in this region, with the oldest glaciation(Guxiang Glaciation) occurring in marine oxygen isotope stage 6(MIS-6).During our recent field investigations, a morphostratigraphically older lateral moraine than that of the Guxiang Glaciation has been first identified, which is ~500–600 m above the Guxiang Glaciation moraine and discontinuously preserved on valley shoulders in the Bodui Zangbo River valley, eastern Nyainqêntanglha Range in southeastern Tibet. Considering the moraine is best preserved at Nitong Village, here we name the glacier advance which deposited the moraine as "Nitong Glaciation". Using electron spin resonance(ESR) technique, we dated the Nitong Glaciation moraine to 506.3±60.4 ka. Taking into account the age error and climatic conditions, we consider it most likely that the Nitong Glaciation occurred during MIS-12, although it might had happened sometime earlier.     

Geochemistry and Sr-Nd isotope characteristics of tonalites in Zêtang, Tibet: New evidence for intra-Tethyan subduction

Tonalites from the island arc rock assemblage in the Zêtang segment of the Yarlung Zangbo suture zone were analyzed for major, trace elements (including REE) and Sr-Nd isotope. The experimental datademonstrate that the tonalites have the adakite-like characteristics, including high SiO2 (58%-63%),Al2O3 (18.4%-22.4%), Sr (810×10-6-940×10-6), Sr/Y (77-106), low HREE (Y=9×10-6-11×10-6, Yb=1×10-6-1.3×10-6), with LREE enrichment and faint Eu positive anomaly. Isr (0.70421-0.70487) is relatively low whereas 143Nd/144Nd (0.512896-0.512929) and εNd(t) values ( 6.7- 7.3) are high. These feainvolvement of a small amount of oceanic sediments. The identification of Z(e)tang adakites, derived from slab melting, presents new evidence for the intra-Tethyan subduction and the previous suggestion about the existence of intra-oceanic island arc within Tethys.