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Petrogenesis of opaque assemblages in the ningqiang carbonaceous chondrite

Science China Earth Sciences 2007年第6期50卷 886-896页

作者： HSU WeiBiao Laboratory for Astrochemistry and Planetary Sciences Purple Mountain ObservatoryNanjing 210008China

Numerous round to oblate opaque assemblages (OAs) are found in chondrules and matrix of the ningqiang carbonaceous chondrite. They are mainly composed of Ni-rich metal,magnetite,Fe,Ni-sulfides,with minor amounts of phosphate,phosphoran-olivine,pyroxene and trace amounts of nano-sized platinum-group metal alloys. The mineralogy of ningqiang OAs is very similar to that of OAs previously reported in Ca,Al-rich inclusions of CV chondrites. Being a rare mineral phase in nature,phosphoran-olivine is thought to form by nonequilibrium reactions between P-bearing molten metal and olivine crystals during rapid cooling. Its occurrence in ningqiang OAs indicates that the precursor of OAs was locally produced during chondrule formation,rather than directly condensed from the solar nebula as previously thought. The petrographic and mineralogical characteristics of ningqiang OAs reveal that OAs formed by low temperature alterations of pre-existing homogeneous alloys within chondrules on a planetary body.

关键词： opaque assemblages phosphoran-olivine ningqiang carbonaceous chondrite petrogenesis

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Phosphatized rare star-like mouth disc of Punctatus and its functional morphology from the earliest Cambrian of the South Shaanxi China

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Frontiers in Biology 2008年第1期3卷 106-112页

作者： Yunhuan LIU Yong LI Tiequan SHAO Zhixin ZHU Wanqian ZHANG Zhuo WANG Weixian YANG Rongxi LI Earth Science Faculty Chang’an UniversityXi’an 710054China Chinese Academy of Geological Sciences Beijing100037China

The Meishucun stage is the prelude in decipher-ing the Cambrian *** this prominent stage,rapid radioactive evolution and body-plan innovation have taken place and different associations of organism have been *** this paper we report several 3D-preserved rare star-like fossils with finely preserved soft tissues which were recovered from the Kuanchuanpu Member of the Dengying Formation in South Shaanxi,China in *** studying on functional morphology and analogy with mouthpart of Punctatus,there are evidences that this star-like organism approaches the coelenterates in systematic classification and the centre of star-like organism is its *** appearance of coelenterates marks the real beginning of metazoan ***,it has the prominent position in the origin and evolutionary history of *** the star-like organism represents the early types of coelenterate with original *** new materials provide new evidence for the origin,evolution and the functional evolution of the metazoan during the early stage of the Cambrian Explosion.

关键词： rare star-like mouth disc Punctatus coelenterat functional morphology Kuanchuanpu Member of the Dengying Formation ningqiang Shaanxi

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