摘要
准噶尔盆地基底的属性和时代,长期以来一直是地质界激烈争论的问题。根据区域地质背景分析,准噶尔盆地东北缘卡拉麦里蛇绿岩带南侧出露的一套基本连续的、被置于中志留统-下石炭统的浅海相陆源碎屑沉积岩系的物源区,位于准噶尔盆地东部盆地堆积物之下。为此选择其中被1:20万区调置于中泥盆世卡拉麦里组上部层位的砂岩进行碎屑锆石SHRIMP U-Pb 定年研究,以期获得准噶尔盆地东部基底时代和属性的信息。测定的86颗碎屑锆石、89个点的年龄分布范围从(327±8)Ma 至(3073±10)Ma;其中碎屑锆石的表面年龄主要集中分布在320Ma～540Ma,显示出多峰的特征,其主峰为 365Ma,次要的峰分别为460～480Ma、510～520Ma 和530～540Ma。该样品中还含有至少22粒表面年龄大于550Ma 的碎屑锆石,其中550～690Ma 的碎屑锆石有4粒,827Ma～1083Ma 的碎屑锆石有8粒,1513Ma 和1700Ma 锆石各1粒,1942Ma～2051Ma 的锆石有2粒,2464～2490Ma 和2876Ma～3073Ma 的碎屑锆石各3粒。根据样品的岩石学特征和碎屑锆石的矿物学特征及表面年龄,结合区域岩浆活动的分析,我们获得如下初步结论:(1)所研究砂岩的沉积时代不是泥盆纪的,可能是早石炭世晚期,其源区位于准噶尔盆地东部;(2)源区地质体组成主体是奥陶纪至石炭纪活动陆缘岩浆岩,寒武纪至新元古代中期和新元古代早期至中元古代等时期的岩浆杂岩等组成,以及推测的少量早前寒武纪杂岩;表明准噶尔盆地东部的基底为奠基在前奥陶纪陆壳基底之上的古生代岛弧。
There has been a hot-debated issue on the tectonic attribute and ages of the basement of Junggar basin in geological field for a long time. On the basis of Paleozoic regional geological setting, the authors believe that the provenance of Middle Silurian to lower Carboniferous shallow-sea terrigenous clastic sequences, which are exposed in the regions south of the Kalamaili ophiolite belt in East Junggar, may be located in the east part of Junggar basin. So, SHRIMP U-Pb dating of detrital zircons from the sandstone in the Kalamaili formation of the sequences, which is classified by 1 ： 200,000 regional geological survey into the middle Devonian in geological time, can obtain the information on the features of the basement of Junggar basin. 86 detrital zircons yield 89 apparent ^206Pb/^238 U or ^206Pb/＆^207 Pb ages between （ 327 ± 8 ） Ma and （ 3073 ± 10） Ma, mainly distributed between 320 Ma and 540Ma with many peaks, a dominant peak at 365Ma and some lesser spikes at between 460 - 480Ma, 510 - 520Ma, and 530- 540Ma, respectively. In addition, 22 older zircons with ages older than 550Ma are found. Of them, four gains with apparent ages from 550Ma to 690Ma, eight grains with from 827Ma to 1083Ma, two grains with 1513Ma, and 1700Ma, two with 1994Ma and 2051Ma, three with from 2464Ma to 2490Ma, and three with from 2876Ma to 3073Ma, respectively. According to petrology of the studied sample, CL images and apparent ages of dated zircons, in combination with regional geological magmatic activities, the authors come to the following preliminary conclusions ： （ 1 ） it is possible that the deposition of the studied sandstone is in the late of the early Carboniferous not Devonian, and its debris come from the eastern Junggar basin, （2） the provenance of the sandstone is probably composed of Carboniferous to Ordovician mid-acid magmatic rocks, Cambrian to middle Neoproterozoic and early Neoproterozoic to Mesoproterozoic magmatic complexes, and supposedly minor early Precambrian rocks, indicating that the basement of Junggar basin is tectonically a Paleozoic magmatic arc imposed upon the Pre-Ordovician continental crust.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第7期1577-1590,共14页
Acta Petrologica Sinica
基金
国家自然科学基金项目(编号40672138)
国家重点基础研究发展规划项目"中国西部中亚型造山与成矿"综合研究课题"中亚型造山与成矿综合研究"(编号2001CB409810
2007CB411306)成果.
