中国早震旦世沉积建造及盆地格局

SEDIMENTARY SUITES (SDS) OF EARLY SINIAN PERIOD IN CHINA

本文根据作者提出的沉积建造(sediment-suite)新概念和分析原理,对我国早震旦世沉积建造类型进行了划分;讨论了各类沉积建造形成的板块构造背景条件;并且首次编制了中国早震旦世沉积建造图和盆地类型图。 建造分析表明,早震旦世南方和北方两大古板块具有明显不同的发育特点:上扬子古陆及四周边缘处于断裂活动发育期,形成典型复陆屑建造和火山复陆屑建造;其东南缘(华东南地区)发育有岛弧系活动边缘盆地的建造类型:细碧角斑岩建造、硅质页岩建造、杂陆屑建造、火山复理石建造;其北缘(秦岭地区)有一个活动边缘——原始大洋的发展过程,形成陆源复理石建造、碳酸盐复理石建造以及类似于洋中脊的微晶碳酸盐建造。 早震旦世的北方大陆板块显示完全不同的沉积建造发育进程。除了新疆、祁连、内蒙地区有活动型沉积违造类型外,在广阔的东部、东南及南部边缘均深持稳定克拉通盆地的沉积建造发育特征。

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, Q>90%, 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, Q<65-15%, 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.