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Structural pattern of eastern Himalayan syntaxis in Namjagbarwa and its formation process

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Science china Earth sciences 2004年第2期47卷 138-150页

作者： zhang jinjiang, Jl Jianqing, ZHONG Dalai, DING Lin & HE Shundong1. Department of {2., Peking University, beijing 100871, china 2. institute of geology and geophysics, chinese academy of sciences, beijing 10002., china correspondence should be addressed to zhang jinjiang (email: zhjj@***) 1. Department of geology Peking University 100871 Beijing China 2. institute of geology and geophysics Chinese Academy of Sciences 100029 Beijing China

The structural pattern of the eastern Himalayan syntaxis in Namjagbarwa consists of two series of structures with different styles. One series compiles the earlier ductile contractional and lateral-slip deformation system, formed by nearly north-south shortening within the syntaxis, left-lateral and right-lateral slipping along its western and eastern boundaries respectively. They were possibly produced by the indentation of the Indian continent into Asian continent after India-Asia collision. The peak deformation-metamorphic ages in these structures are 62.60 Ma, ~2. Ma and ~13 Ma. The other series is composed of ductile-brittle normal faults distributing concentrically and dipping toward the outsides of Namjagbarwa Peak. They were probably the collapse structures caused by rapid uplift in a later time and the beginning ages for the normal faulting are about 7.3-6.3 Ma. Keywords Namjagbarwa - eastern Himalayan syntaxis (EHS) - structural pattern - formation process - structural chronology

关键词： Namjagbarwa, eastern Himalayan syntaxis (EHS), structural pattern, formation process, structural chronology.

Geochemical research on C-O and Sr-Nd isotopes of mantle-derived rocks from Shandong Province, china

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Science china Earth sciences 2004年第2期47卷 171-180页

作者： LIU Jianming, zhang Hongfu, SUN Jinggui & YE Jie1. institute of {2. and geophysics, chinese academy of sciences, beijing 10002., china 2. School of Earth Science, Jilin University, Changchun 130061, china correspondence should be addressed to Liu Jianming (email: jmliu@***) 1. institute of geology and {2. Chinese Academy of Sciences 100029 Beijing China 2. School of Earth Science Jilin University 130061 Changchun China

This paper presents systematic studies on the C-O and Sr-Nd isotopic compositions for Cretaceous Badou carbonatites, Fangcheng basalts, and Jiaodong lamprophyres and Paleozoic Mengyin kimberlites in Shandong Province, china. Paleozoic kimberlites have normal and uniform C-O isotopic compositions with δ13C and δ18O in the range of -4.8‰--7.6‰ and +9.9‰-+13.2., respectively. However, Cretaceous three different types of mantle-derived rocks have quite different C-O isotopic compositions, indicating that the mantle sources are probably partially contaminated with organic carbon-bearing crustal materials. These Cretaceous rocks show uniform and EMII-like Sr-Nd isotopic compositions and also indicate that the mantle sources were affected by recycled crustal materials. Comparative studies of C-O and Sr-Nd isotopes reveal that the lithospheric mantle beneath the eastern North china Craton had different isotope characteristics in the Paleozoic, the early Cretaceous, and the Tertiary time. This demonstrates that the lithospheric mantle beneath the region underwent at least twice reconstructions since the Paleozoic. Available data imply that the first reconstruction mainly happened during the Triassic-Jurassic time with gradual changes and the second in the Cretaceous with abrupt changes. Results also show that the early Cretaceous (especially at 12.-130 Ma) was perhaps the key period leading to the dramatic change of the Mesozoic geodynamics on the eastern North china Craton.

关键词： mantle-derived rocks, carbonate minerals, C-O isotope, Sr-Nd isotope, lithospheric mantle, Shandong.

SHRIMP ages of detrital zircons from the Changcheng System in the Ming Tombs area,beijing:Constraints on the protolith nature and maximum depositional age of the Mesoproterozoic cover of the North china Craton

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chinese Science Bulletin 2003年第22期48卷 2500-2506页

作者： WAN Yusheng1,2. zhang Qiaoda1 & SONG Tianrui1 1. institute of {2., chinese academy of Geological sciences, beijing 100037, china 2. beijing SHRIMP Laboratory, beijing 100037, china correspondence {12. be addressed to Wan Yusheng (e-mail: wanyusheng@***) institute of geology Chinese Academy of Geological Sciences Beijing 100037 China

The Mesoproterozoic Changcheng System is widely distributed in the North china Craton. Determining its time of deposition and sources is important to understand the Precambrian crustal evolution of the North china Craton. This paper suggests age distribution patterns for detrital zircons from clastic sediments of the Changcheng System in the Ming Tombs area, {2.. Samples of feldspar-bearing sandstone (CHc-2. and pure sandstone (CHc-9) were collected from the Changzhougou Formation, which constitutes the basal part of the Changcheng System. Detrital zircons show an age range from 2.35 to 2.60 Ga. However, sample CHc-9 in the upper Changzhougou Formation also contains some zircons with ages of 1.9-1.8 Ga and 2.3-2.1 Ga. The age patterns lead to the following conclusions: (1) Most of the detrital material came from a source area composed predominantly of ~2.5 Ga continental crust of the North china Craton; (2. 1.9-1.8 Ga reflects the age record of Palaeoproterozoic continent-continent collisional event in the North china Craton; and (3) the oldest age for deposition of the Changcheng System is 1.8 Ga.

关键词：锆石原岩中国北部地区地壳演变

Ultramafic xenoliths in Mesozoic diorite in west Shandong Province

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Science china Earth sciences 2004年第6期47卷 489-499页

作者： CHEN Lihui1,2.& ZHOU Xinhua2.1.The Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education,china and School of Earth and Space sciences,Peking University,{2. 100871,china 2.institute of geology and geophysics,chinese academy of sciences,{2. 10002.,china correspondence should be addressed to Chen Lihui(email: lihui_chen@***) 1. The Key Laboratory of Orogenic Belts and Crustal Evolution Ministry of Education China and School of Earth and Space Science Peking University 100871 Beijing China 2. institute of geology and geophysics Chinese Academy of Sciences 100029 Beijing China

Ultramafic xenoliths are common in Tietonggou intrusion, Laiwu, Shandong Prov-ince. Peridotite xenoliths develop two-stage metasomatism popularly: (i) The early metasoma-tism is characterized by intergranular clinopyroxene and phlogopite; (ii) The later metasomatism is characterized by orthopyroxene veins with a few plagioclases and amphiboles. These ul-tramafic xenoliths are thought to be mostly from the crust-mantle transitional zone on the basis of their combination, mineral chemistry, equilibrium temperature, and metasomatic characteristics. Major elements, rare earth elements, and Sr-Nd isotopic composition of the ultramafic xenoliths indicate that there is a petrogenetic relationship between the silica-enriched xenoliths and their host diorites. We propose that such silica enrichment might be an indicator of melt-rock interac-tions in the Mesozoic lithosphere beneath western Shandong.

关键词： ultramafic xenoliths, crust-mantle transitional zone,metasomatism, Tietonggou intrusion, Laiwu.

Development of joints and Shear fractures in the Kuqa depression and its implication to regional stress field switching

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Development of joints and Shear fractures in the Kuqa depres...