中祁连拉脊山早古生代沉积岩源区和时代限定
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中国地质科学院地质研究所

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国家自然科学基金项目(面上项目,重点项目,重大项目)


Constraints of the Provenance and Deposition Time of the Early Paleozoic Sedimentary Rocks in the Lajishan Area, Central Qilian
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Institute of Geology, Chinese Academy of Geological Sciences

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    摘要:

    拉脊山混杂带之上的早古生代盆地由砾岩、砂岩和粉砂岩组成的陆相碎屑岩,在沉积时代、源区和构造属性方面缺乏研究。本文对两个杂砂岩样品进行了碎屑锆石LAICPMS UPb测年和Hf同位素分析。在两个样品中获得年轻的碎屑锆石加权平均年龄为413±5Ma,综合限定沉积时代为晚志留世-早泥盆世;碎屑锆石年龄谱明显分为4组:411~516Ma,619~ 1149Ma,1500~1621Ma和2356~2549Ma。其中411~516Ma的年龄数据约占总体的566%,所占比例最大,年龄相对集中,显示出强烈的峰值为441Ma,指示其物源可能源于中祁连加里东期俯冲增生、碰撞造山过程中产生的一系列岛弧火山岩和岩浆弧花岗岩类,这与碎屑锆石εHf(t)值(-111~+137)是一致的,同时也表明在加里东期有大量年轻的物质加入,这些物质在造山过程中遭受剥蚀成为主要的物源。碎屑锆石年龄组619~1149Ma约占总体的278%,峰值主要表现为950Ma和777Ma,与祁连造山带新元古代岩浆事件有关,反映新元古代大陆的汇聚和裂解相关的岩浆作用,与εHf(t)值是相对应的;1500~1621Ma年龄组反映碎屑物质可能来自祁连造山带;2356~2549Ma年龄组反映物源来自祁连造山带中的结晶地块,或者来自于华北板块结晶基地。综合分析表明,志留纪砂岩具有明显的多元性物源,以中祁连加里东期俯冲增生-碰撞造山过程产生的岩浆岩是主要物源区。

    Abstract:

    The early Paleozoic sedimentary basin, outcropped in the Lajishan mountain of the central Qilian orogeny, is fault contact relation with the Lajishan mélange composing of conglomerate, sandstone and siltstone. The rocks have been previously considered to represent a Silurian sequence because of lack of reliable age evidence. This study shows that the ages of detrital zircons from the sandstons are predominantly early Paleozoic, and the youngest detrital zircon grains clearly constrain that the maxium depositional age of the sedimentary sequence is ca. 413±5Ma. The ages of detrital zircons can be evidently divided into four groups:411~516Ma, 619~1149Ma,1500~1621Ma and 2356~2549Ma. Zircon with ages from 411Ma to 516Ma comprises 56.6% of the detrital zircon population, and were mainly sourced from the Qilian orogenic belt in adjacent regions. These detrital zircons in the 411~516Ma age population show approximately the same proportion of positive and negative εHf(t) values ranging from -11.1~+137, correlating with the series of igneous rocks caused by the northward subductionaccretion and collision of central Qilian in the Caledonian period. Zircon with ages from 619~1149Ma comprises 278% of the detrital zircon population, and shows the εHf(t) values ranging from -189 to+95. The age data are comparable with those zircons in the Neoproterozoic granites and volcanic rocks in the central Qilian block. The subordinate detrital zircons with ages from 1500Ma to 1621Ma and from 2356Ma to 2549Ma show mainly the negative εHf(t) values, which indicate that the material sources were probably derived from the basement of the Qilian orogenic belt and the North China plate. A comprehensive analysis shows that the material sources of late Silurian basin were characterized by obvious diversity, derived from the Qilian orogenic belt and the North China plate,and the Lajishan mélange is most significant source contribution to the sediment.

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王涛,马振慧,王宗起,张晗,王东升.2016.中祁连拉脊山早古生代沉积岩源区和时代限定[J].地质学报,90(9):2316-2333.
WANG Tao, MA Zhenhui, WANG ZongQi, ZHANG Han, WANG Dongsheng.2016. Constraints of the Provenance and Deposition Time of the Early Paleozoic Sedimentary Rocks in the Lajishan Area, Central Qilian[J]. Acta Geologica Sinica,90(9):2316-2333.

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  • 收稿日期:2016-05-10
  • 最后修改日期:2016-06-02
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  • 在线发布日期: 2016-10-09
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