豫西济源盆地中生代泥岩地球化学特征对物源区的指示

Geochemistry of Mudstones from Mesozoic Jiyuan Basin,West Henan:Implications for Provenance Analysis

秦岭造山带印支期造山作用控制着济源盆地的形成与演化,对盆地中沉积物物源进行研究,有利于恢复造山带造山-隆升的细节.通过对济源盆地中生代泥岩地球化学的系统分析,发现样品的CIA(化学风化指数)校正值在早-中三叠世、晚三叠世、早-中侏罗世和中侏罗世后期的平均值分别为68.5、76.4、86.0和73.7,这一演化特征可能反映其经历了古气候控制的化学风化过程.但是三叠纪样品CIA值明显过低,可能与源区活动的构造背景相关;ICV(成分变异指数)值显示沉积物具有初次沉积的特征,反映了源区早期发生过弧-陆碰撞或具备陆缘弧特征的克拉通基底隆升.而早-中侏罗世样品表现为高的CIA值,ICV值显示沉积物具有再循环特征,其初次沉积可能发生在弧后盆地中,后随造山带的隆升,被剥露再搬运而沉积下来.泥岩物源区构造环境判别结果显示,沉积物主要来自活动大陆边缘和被动大陆边缘,且含有较多大陆岛弧(陆缘弧)的信息.由此说明,中生代济源盆地盆缘构造活动经历了由克拉通基底隆升到造山带剥露的过程,这一过程与秦岭造山带印支期的造山作用密切相关.

The sedimentary development of the Jiyuan basin was controlled by the Qinling orogenic belt during the Early Mesozoic. Therefore, mountain building and uplift of the Qinling orogenic belt can be evidenced by the sediments from the Jiyuan basin. The Mesozoic mudstones geochemistry has been investigated to determine the provenance of the Jiyuan basin. The average values of corrected CIA （chemical weathering index） from the Early-Middle Triassic, Late Triassic and Early-Middle Jurassic samples increase from 68. 5 to 76. 4, then to 86 successively, but decrease to 73.7 from the late Middle Jurassic samples. The variation of CIA might correspond to the changing paleoclimate during the Mesozoic. However, the much lower values of CIA from the Triassic samples may be restricted to the active tectonic setting. The values of ICV （compositional variation index） reflect that the first cycle sediments are mainly concentrated in the Triassic samples. These sediments may come from the uplifted basement of the North China craton, which should consist of the continental marginal arc and/or arc-continent collision zone. The Early-Middle Jurassic samples showing higher CIA may be related with the recycling clastics of the uplifting orogen, whereas first deposition might occur in the back-arc basin. In the tectonic discrimination diagrams, the sediments from Jiyuan basin mainly formed under the active continental margin and the passive continental margin, but contained much more continental island arc materials. Our data support that sediments from the uplifted basement of the North China eraton to the denudation of the orogen is most likely related to the Qinling orogenesis during the Indosinian.