Primary Study On The Black Spherulitic Rock Origin Of Lucaogou Formation In Yuejingou Section,Santanghu Basin

Recent studies showed that Middle Permian of Santanghu basin in northern Xinjiang is the lacustrine sedimentation,under the background of intracontinental rift,have exhalative hydrothermal sedimentary and volcano eruption,and hydrothermal fluid may from mantle.A set of spherulite-bearing laminated black and white silidous rocks have first been discovered in of Lucaogou formation of middle Permian in Yuejingou,Santanghu Basin,Xinjiang.called:Black spherulitic strata.based on the mineralogy study,petrology study,Geochemistry study,and the limit of temperature analysed formation temperature,source of diagenetic material,Sedimentary environment and forming mechanism.Concluded as follows:(1)Carbon is in most Black spherulitic strata.raman spectrum studies of carbonaceous materials indicates high temperature of 287.3?.quarts have comparatively high content of Na?Al?Sr,may indicate high temperature 350?.Calcites show negative ?18OPDB anomaly.The limit of temperature above indicates that rock formation may correlate to mesothermal-hydrothermal.(2)Native iron,manganiferous native iron,chromium bearing native iron and brass-zinc alloy have first been discovered in Black spherulitic rocks.The formation of natural metal most correlate to mantle.Reported manganiferous native iron and chromium bearing native iron are all intermetallic compounds of mantle.Natural metals are clastic particles,or in the fissures and pore on Melting Erosion of particles,so natural metals have no In-situ crystallization characteristic.The author thinks the natural metals in Black spherulitic rocks are from mantle,and are preserved in the stratum containing charcoal.(3)Average of the content of SiO2 in the Black spherulitic rocks is 71%.The limit of temperature above indicates that Black spherulitic rocks have abnormal diagenetic temperature.So the Black spherulitic rocks are similar to siliciliths.But the mineral assemblage of Black spherulitic rocks are quarts(dominantly),feldspar,calcite.The ratio of Fe/Ti?(Fe+Mn)/Ti?Al/(Al+Fe+Mn)?U/Th and Ba/Sr aren't reach the standard of hydrothermal sedimentary silicious rock.The Black spherulitic rocks have lamellar structure and have no residual of pyroclastic,but volcanogenic silicolite has block structures.This shows that use silicolite named Black spherulitic rocks isn't appropriate.So author thinks Black spherulitic rock is a new type of hydroclastites and hydrothermal exhalites.Because of contamination of magmatic debris,the relevant parameter of Black spherulitic rocks are different from hydrothermal sedimentary silicious rock.(4)Black spherulitic strata has the characteristic of variational reservoir lithology and interbedded.the ratio of Th/U less than 2,V/(V+Ni)ratio greater than 0.7,the ratio of V/Sc larger average 6.21,?Eu strong negative anomaly.All of them reflect the formation of Black spherulitic strata in the reductive sedimentary environment.Sr/Ba greater than 1 reflects the higher salinity of sedimentary environment.The V/Ni ratio is greater than 1,indicating that the sedimentary environment of the study area is terrestrial environment.The characteristics of the present study are as follows:the Black spherulitic rocks are formed in lacustrine sedimentation under the background of intracontinental rift,and have the characteristic of multivariate,high salinity and reducing environment.(5)Based on the analysis of substance composition,formation of source region and intrusive passage of C-H-O fluid,author thinks that C-H-Ofluid meeting the requirement of diagenetic fluid of Black spherulitic rocks.