The Petrological,Geochemical Characteristics And Tectonic Significance Of Basic And Ultrabasic Rock In Gangmari District,Notrh Qiangtang

The study area has experienced the formation, evolution, extinction of the TethysOcean, and the complex process of subduction, collision, orogenic, uplift with thenorth and south of the continent. the mafic ultramafic rock in the study area mainlyconsist of Peridotite, Gabbro, Diabase, Diabase gabbro, Tholeiitic basalt and Alkalinebasalt.This paper carried out a detailed analysis on petrogenesis, nature of the Districtsources, rock formation age, tectonic attribution of evolution and properties oflithospheric mantle, using petrography, mineralogy, elemental geochemistry, isotopegeochemistry, chronology as the research methods.The results are as follows:First,according to previous research results and research geologicalrelationships,the basic-ultrabasic rock formed in the late carboniferous, which reflectsthe Qiangtang area Pangea cracked peak time.Second, according to the characteristics of Geochemistry and tectonicdiscrimination diagrams, it is concluded that the peridotite, gabbro, basalt tectonicenvironment for the oceanic island environment,they are destructive plate marginproduct. Basalt has E-MORB and OIB features, rather than mid-ocean ridgeenvironment.Third, there are common features in mafic ultramafic rocks of the study area,meaning negative anomalies of Sr and Eu with almost no exception, which have thesimilar feature and tectonic environment with mafic ultramafic rocks in ophiolites ofJiaomuri area. The authors hypothesized that they are the old mantle pieces or piecesof source area of ophiolite in Jiaomuri area.Forth, the source region of mafic ultramafic rock has the enrichmentcharacteristics of Pb isotope, and Nd isotopic showed it had experienced theinteraction of crust-mantle. All of these indicated that magma had met thecontamination of the continental crust on its movement and evolution.Fifth, regional material of mafic ultramafic rocks comes from Source of theocean area enriched mantle EM II. Combined with the region’s tectonic background, itis believed that the enrichment and subduction are relevant, subduction making thecrustal material inject into the mantle.