宁武—静乐盆地侏罗系碎屑岩地球化学特征及地质意义
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本文为中国地质科学院地质力学研究所基本科研业务费项目(编号 DZLXJK201208)、国家深部探测技术与实验研究专项(Sinoprobe 08 01)的成果。


Geochemistry of Jurassic Detrital Rocks and Geological Significance in Ningwu—Jingle Basin
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    摘要:

    宁武—静乐盆地侏罗系地层包括下侏罗统永定庄组,中侏罗统大同组、云岗组和天池河组,主要由粉砂岩夹泥岩组成。前侏罗纪古地貌背景和古流向相结合研究表明,物源区主要来自于北东方向的阴山—燕山造山带中段,对盆地内陈家半沟剖面24件碎屑岩样品的主量、稀土和微量元素进行了分析,可以为演绎源区早—中侏罗世的物源属性和构造背景提供一定的依据。通过研究主要得出以下结论:① 碎屑岩样品中CO2与CaO具有较好的相关性,δCe与δEu、δCe与∑REE、化学蚀变指数(CIA)与Th/U、CIA与Th/Sc不具有相关性,说明研究区侏罗系碎屑成分主要受控于源岩特征,不受化学风化作用及氧化—还原条件的影响;②稀土元素的配分模式基本相同,LREE/HREE 值高和明显的负Eu 异常,表明早中侏罗世具有相同的物源,岩石以亲花岗岩、长英质为主,母岩碎屑主要来自于上地壳,尚没有地幔物质的参与,REE—La/Yb、La/Th—Hf、Co/Th—La/Sc、Th—Hf—Co、SiO2/Al2O3—∑REE、K2O/Na2O—∑REE判别图解,也反映了相似的物源特征;③中侏罗世云岗期至天池河期,碎屑物质中CaO、CO2、Gd、成分变异指数(ICV)值以及(Gd/Yb)N值突然增加,表明源区处于快速隆升、剥蚀阶段,大量的古老沉积物质不断加入,这一变化可能与燕山运动的起始时限及造山过程存在紧密的联系。

    Abstract:

    The Jurassic strata of the Ningwu—Jingle Basin, the Yongdingzhuang Formation of Lower Jurassic, the Datong, Yungang and Tianchihe Formation of Middle Jurassic, are primarily composed of siltstone and mudstone Provenance area is mainly point to the central Yinshan—Yanshan Orogen according to former Jurassic Palaeogeomorphology and Paleocurrent Based on the geochemical signatures of major elements, trace elements, and rare earth elements from 24 samples, which picked from Chenjiabangou profile on the Ningwu—Jingle Basin, three conclusions have been obtained Firstly, in these samples, CO2 vs. CaO have a good correlation, δCe vs. δEu , δCe vs. ∑REE、CIA vs. Th/U、CIA vs. Th/Sc have no correlation, those imply that the Jurassic detrital rocks are mainly controlled by source characteristics, were not impacted by chemical weathering and oxidation — reduction conditions Secondly, the distribution patterns of rare earth elements are basically the same, LREE/HREE ratios are high, Eu negative anomalies are evident, which show that provenance are the same during the Early—Middle Jurassic, and the rocks are the main pro granite and felsic, and the parent rock debris come mainly from the upper crust,have no mantle material, those discrimination diagrams about REE—La/Yb,La/Th—Hf,Co/Th—La/Sc,Th—Hf—Co,SiO2/Al2O3—∑REE,K2O/Na2O—∑REE prove the same viewpoint Thirdly, during Yungang and Tianchihe of Middle Jurassic, a sudden rise on CaO content, CO2 content, Gd content, ICV,(Gd/Yb)n ratio, which show that the Provenance area is in rapid uplift and erosion stage, with a large number of ancient sedimentary material being added, the starting time of the Yanshan movement may be the early Yungang term of Middle Jurassic

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李振宏,董树文,渠洪杰,胡健民.2013.宁武—静乐盆地侏罗系碎屑岩地球化学特征及地质意义[J].地质论评,59(4):637-655,[DOI].
.2013. Geochemistry of Jurassic Detrital Rocks and Geological Significance in Ningwu—Jingle Basin[J]. Geological Review,59(4):637-655.

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