Discovery And Characteristics Study Of Precambrian Stratigraphy Along The South Beach Of Yantan Fracture Of Beishan, Xinjiang

To date, a lot of work have been done in the research area, but because of the constraint of research extent and study conditions, almost all investigations are not as old Precambrian metamorphic stratigraphy distinguished it from the study area, and relatively basic research is weak. The study area lie the western part of the Beishan tectonic belt, locate in the northeastern margin of Tarim block ,is Rift Valley to the NEE of the Paleozoic tectonic belt between Kuruktag and Dunhuang plate. According to the three years' hard work of regional geological survey of 1:5 million in the southeast of Heishan area, this paper study more comprehensively the sets of the basic characteristics of metamorphic strata properties on the basis of a large number of field and indoor collection of geological information and data, combined with the adjacent areas Comparative Precambrian stratigraphy fully, this strata is distinguished from the sets of stratigraphic and initial as Paleoproterozoic - stratigraphy Neoarchaean.From the rock composition, it is mainly migmatite, biotite plagioclase gneiss, amphibolite, and a small amount of granulite which is composed of residues. Metamorphic facies reach amphibolite - granulite facies. Granulite and granulite are with the latter part of the general degradation of retrograde metamorphic reaction side, the mineral assemblage is hornblende and plagioclase mafic composition with metamorphic minerals and lithofacies characteristics. Mostly fine-grained mineral crystals set granular column shows that the stratigraphic units experienced at least two major tectonic events, is a metamorphic granulite facies retrograde metamorphism to amphibolite facies product, in which a small amount of granulite retrograde metamorphism is the residual body. As a clue, this paper studies fullly the rocks portfolio and metamorphism and deformation (deformation expressed as rootless folds, development of intestinal-like folds, the complete structure replacement), discusses the thermodynamic characteristics of the two-stage deterioration from the thermodynamic point of view, founds that granulite facies metamorphism stage should be below about the formation of 1.25GPa (42Km depth), the formation temperature is in about 841℃±'s high-pressure - high-pressure environment; amphibolite facies stages formed in the temperature range should be 650-657℃±; pressure 0.460-0.495GPa, on behalf of the corresponding depth of about 16.5Km, should represent the type of low pressure amphibolite facies metamorphic conditions. Through the Sm-Nd isochron dating, the amphibolite facies metamorphism of the metamorphic stages of age should be 1349±160 Ma. Fullly contrasted with the characteristics of Precambrian strata in adjacent areas, from the view of the metamorphic rock, metamorphic facies, deformation and representation of isotope and fossil age, this paper discovered the set strata is similar with the strata of the Paleoproterozoic and the new too Ancient lithology in adjacent areas, mainly for the main rock types of gray gneiss, mixed rocks, granulite category Amphibolites categories, marble etc. The rock deformation shows the characteristics of ductile deformation mobile, rootless folds, development of intestinal-like fold. Mostly metamorphic facies is amphibolite facies, partial up to granulite facies. All explain the set strata is consistent and similar with the strata of Paleoproterozoic - stratigraphy Neoarchean in adjacent areas, should be formed in the same or similar background dynamics of the structure. Therefore, it is initial Paleoproterozoic -Neoarchaean stratigraphy.