SEDIMENTARY SUITES (SDS) OF EARLY SINIAN PERIOD IN CHINA
Meng Xianghua Ge Ming He Zhengjun(China university of Geosciences 562 Geological Team, Chinese Academy of Geological Sciences)
Sedimentary suite (SDS) is defined as an association of rocks and facies formed in large scale environment (sedimentary basin) of plate梩ectonic during a long period(107a). Based on the authors' proposal the criteria for clssifying sedimentary suites according to their material source, environment and energy rate equilibrium. The classification of sedimentary suites and the basinal types of Sinian is as table 1. Stable sedimentary suites are formed in craton basins. Substable sedimentary suites are widely distributed in the fault basin of continental crust, rifts and creack marginal basin(i. e.passive margin). Unstable sedimentary suites occur in the basins in respect of the spreading and accretion of ocean ridge on the active margin.The main criteria for recognition of sedimentary suites and their tectonic backgrounds include consanguineous association of rock, Q-value, matrix content, distribution of trace elements, deposition rate, shape of suite body and sedimentary rhythm. The characteristics of stable suite are as follows: association of CQ + SQ+MQ+OQ, Q90%, low matrix content, regular ME distribution, definite shape and lower deposition rate. Substable sedimentary suites show different characteristics as CF + SF + MF + OF association,Q = 90-65% , higher matrix content, gradual ME distribution, banded and shift suite body and higher deposition rate. Unstable sedimentary suites may be recognized with CR + SR + MR + OR association, Q65-15%, high matrix, irregular ME distribution, shift and indefinite shape and variable deposition rate. The characteristic stability of sedimentary suites may be recognized as sub-stable SDS and unstable SDS with different rock associations, which reflect variable deposition rate. The extension fracture and the fault subsidence of continental plate margin are generally developed in the various margins around upper Yangtze old land, and different types of substable sedimentary suite (SDS) are formed, includingcontinental volcanic-SDS and volcanic biterrigenous SDS in Early Sinian (700?800Ma). Among the boundary of Guangxi, Guangdong and Hunan provinces, the terrigenous flysch SDS and spilite-keratophyre developed in Early Sinian. they show the character of active margin of island arc basin. The formed history of volcanic SDS of Precambrian accreting ocean-rust in Guangxi can be traced back to Sibao Period in Middle Proterozoic before lOOOMa. The spilite-kerratophyre SDS of initial stage of Early Sinian is the result of the removing of accreting oceanrust towards south with the passage of time in Yengyangguan region, Eastern Guangxi, potassium value of spilite-keratophyre SDS of Early Sinian is more of the character of transitional crust. There is a mangnifirous silic-hale SDS of static-imited sea type in back-arc spreading basin. It is developed between the volcanic biterrigenous SDS formed in the fault marginal basin of southeastern Yangtze massif and the neutral spilite-uartze-eratophyre of transitional crust in Guangdong-unan island arc. Far apart from back-rc spreading centre in western Zhejiang and southern Anhui the SDS change gradually to volcanic polyterrigenous SDS (Zhejing, Early Sinian) and till glaciofluvial SDS with interlace of manganiferous silic-hales and iron-manganiferous carbonates. The belt of the silic-hale SDS is polymetalHc-ineroenetic prospect province in Ba, V, Mo, Mn, according to the analysis of the SDS and its paleotectonic background, the belt belongs to the member of series of volcanic-siliceous SDS in volcanic arc system of active margin.