The Research Of Zircon Chronology In Orogenic Belts--A Case Study In Jinshuikou Zone

This study bases on the subjection of The China Geological Survey: ThePrecambrian Important Geological Events Sequence of Kunlun Mountain and TheContrasting between West Kunlun and East Kunlun, which belongs to thesubjection: The Group of Precambrian Important Events in Midwest in China andits Globle Tectonic Significances. There are several hundrends Samples of rocksand more than 20 samples of zircon grains collected in Jinshuikou and its adjacentzone, East Kunlun Orogenic Belt, during the field route section and the localgeologic mapping. By the researches of system mineralogy and interior structureand chronology of zircon in these zones, the characteristics of magmatic zircons andmetamorphic zircons have been summarized. According to these characteristics, therestricted relationships between the characteristics of zircon and the geologicalinterpretions of the U-Pb dating datum of zircon are discussed. Based on thegeological interpretations of the U-Pb dating datum of zircon, the formation timeand the metamorphic age of some important geologic bodies have been obtained inJinshuikou and its adjacent zone, East Kunlun. These studies have offered somevery credible datum for the chronologic research of East Kunlun Orogene Belt andestablished the geological events sequence of Jinshuikou zone before Devonian.According to which, the geologic evolvement in this area can be divided into threemajor stages. Moreover, based on the research of geochemistry, the source rockassemblages of the important metamorphic rocks, the genesis and tectonic settingsof key magmatic bodies in Jinshuikou zone have been discussed. There are veryimportant significances not only in the researches of basic geology, but in thediscussions of geologic evolvement in East Kunlun. 第 IV 页 共 7 页吉 林 大 学 硕士学位论文 Therefore, some basic cognitions can be achieved: 1. Taken the past research fruits into account, the source rocks of BaishaheFormation of Jinshuikou Group, bedded formation in Jinshuikou Zone, areargillaceous sedimentary rock, magnesian carbonate and basic volcanic rock, whichbelong to amphibolite-granulite faces. It is shown that this formation has formed inrelatively stable continental edge. 2. U-Pb isotopic dating of zircon is a common and comparatively crediblechronological method in orogenic belt. The interpretations of its analyzed resultsdepend on the studies of the interior structure and micro genesis of zircon. Thestudies of the interior structures of zircon shown that there are two geneticclassifications of zircon in orogenic belt: magmatic zircon and metamorphic zircon,whose differences are obvious. The magmatic zircon always has oscillatory zoneand rather high background of Raman spectrum. In this kind of zircons, the microcathode luminescence is rather bright and the ratio of Th/U is less than 0.1. On theother hand, the metamorphic zircon has rather low background of Raman spectrum.In the kind of zircons, the micro cathode luminescence is rather dark and the ratioof Th/U is more than 0.1. The studies of the interior structures of zircon indicatethat Raman spectrum and cathode luminescence are an efficient method todistinguish the two genetic classifications of zircon. Furthmore, there are inheritedzircon, metamorphic zircon, anatectic zircon and metamorphic overgrowth zircon inJinshuikou Zone, whose characteristics are different. 3. The research of geochemical shows that biotite granodiorite in Jinshuikou isI-type granite, but garnet cordierite biotite granite, geneissic biotite granite andgarnet biotite monzonitic granite show the characteristics of S-type granite. TheI-type granites may be the result of assimilating and contaminating alliticsupracrustal material by diorite-magma. But the S-type granites are the result ofanatexis of allitic supracrustal material in high regional heat flux. These two typesof granites may have...