青海北祁连构造带1∶5万水系沉积物元素异常对区域构造环境演化的响应

The response of element anomalies to the tectonic environment based on 1 ∶50000 stream sediment survey in North Qilian tectonic belt,Qinghai Province

北祁连构造带1∶5万水系沉积物测量元素Ag、As、Au、Ba、Bi、Co、Cr、Cu、Fe、Hg、Mo、Mn、Ni、Pb、Sn、Sb、Ti、W、Zn,其异常特征在不同地质时代随构造环境的演化而变化,与放射性同位素地球化学一样,水系沉积物元素自身在本质上包含了时间和构造背景的双重属性。通过衬值法对不同时代地层中的49 303个大数据样本元素含量原始数据进行处理,结合用以探讨地层元素地球化学特征的R型聚类分析进行分组研究。结果表明:北祁连造山带中Co、Cr、Ni的水系沉积物元素异常响应于古元古代之后造山带的裂解构造环境;Au、Bi和部分Cu异常与奥陶纪大洋的俯冲—闭合阶段构造环境对应;Pb、Zn异常可能是奥陶—志留纪北祁连弧盆体系中局部洋底火山活动中的热液喷流形成;泥盆系Hg、Sb异常尚无区域上合理的构造环境来解释;Mo含量于石炭系出现峰值,说明北祁连造山带周边处于强烈抬升剥蚀;W、Sn异常反映了奥陶纪、志留纪俯冲碰撞的构造背景。这种水系沉积物测量元素异常特征与构造带构造演化阶段同步响应的规律性表明,水系沉积物测量中幔源元素的相容(不相容)特性可很好地判别单一旋回造山带的构造环境,采用大数据样本将勘查地球化学理论拓展应用于大地构造学研究是可行的。

Elements anomalies, such as Ag, As, Au, Ba, Bi, Co, Cr, Cu, Fe, Hg, Mo, Mn, Ni, Pb, Sn, Sb, Ti, W, Zn, from 1∶50 000 stream sediment survey, North Qilian tectonic belt, vary with the tectonic evolution in different geological epochs , the elements themselves are endowed with dual properties of time and tectonic setting. According to the contrast value method, element content data of 49 303 samples from different strata were processed in combination with stratigraphic geochemical R cluster grouping. The results show that Co, Cr, Ni anomalies are in response to Paleoproterozoic postorogenic cracking, Au, Bi and part of Cu anomalies are in response to Ordovician oceanic subductionclosing stages, Pb, Zn anomalies probably corresponded to local volcanic activity in the ocean floor in OrdovicianSilurian period. Devonian Hg, Sb anomalies have no reasonable regional tectonic interpretation, and the phenomenon of Mo element content in the Carboniferous peak indicates strong uplift and erosion on the periphery of North Qilian orogenic belt. W, Sn element anomalies reflect subduction and collision setting in Ordovician and Silurian. The regularity of the stream sediment anomalies＇response to tectonic evolution suggests that the compatible （ incompatible ） features of mantlederived elements from stream sediment survey can better distinguish tectonic environments, and the combinational geochemical approach from a large data sample and tectonic study is feasible.