西准噶尔希贝库拉斯组凝灰质砂砾岩岩石学和锆石U- Pb年代学及对沉积层序的指示意义
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本文为国家自然科学基金项目(批准号41203032)、陕西省教育厅科技计划项目(批准号14KJ1761)和西北大学地质学系本科生创新基金项目(XDCX2016- 01)资助的成果。


Petrology and zircon U- Pb geochronology of tuffaceous conglomerate in the Xibeikulasi Formation, West Junggar, and its implication for sedimentary sequence
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    摘要:

    新疆西准噶尔包古图地区主要出露下石炭统火山-沉积地层,由希贝库拉斯组、包古图组和太勒古拉组组成,对于三套地层的时代归属以及地层层序长期存在争议。本文对希贝库拉斯组凝灰质砂砾岩进行了岩相学和锆石U- Pb年代学研究,为探讨以上争议提供资料。岩相学研究发现凝灰质砂砾岩中的砾石为硅质岩、晶屑凝灰岩、凝灰质砂岩、安山岩和少量灰岩,中等磨圆-次棱角状,粒径变化大(2~15mm),含量为~45%;细碎屑主要为岩屑、长石和少量石英,呈棱角状-次棱角状,粒径0. 05~0. 5mm;填隙物主要为火山灰;锆石U- Pb年代学分析结果显示,锆石的Pb206/U238表观年龄集中在327~382Ma,最年轻的峰值为330~335Ma,代表了凝灰质砂砾岩沉积同期火山活动的年龄;最大峰值为345~360Ma,指示了凝灰质砂砾岩中大部分火山岩砾石对应火山活动的时限;另有几组年龄集中在411~428Ma、~455Ma和482~504Ma,对应克拉玛依、达拉布特和唐巴勒蛇绿岩的年龄。综合以上研究,认为希贝库拉斯组的沉积时代为早石炭世维宪期,并结合前人研究成果推断本区三套地层的沉积层序自下而上依次为希贝库拉斯组、包古图组、太勒古拉组。

    Abstract:

    The Lower Carboniferous strata consisting of the Xibeikulasi, Baogutu and Tailegula formations are widely distributed in the Baogutu area in West Junggar. But their geological age and stratigraphic sequence have long been controversial. This study carried out the petrology and zircon U- Pb geochronology investigation on tuffaceous conglomerate in the Xibeikulasi Formation were studied in order to provide some basis for the age and sequence of Lower Carboniferous strata. Petrographical analysis shows that the conglomerate in tuffaceous conglomerate accounts for 45% and is composed of sub- angular siliceous rock(2~15 mm), crystal tuff, and tuff sandstone, and a small amount of limestone, cemented by crystal- bearing volcanic ash; fine- grained detrital rock is mainly fragments, feldspar and minor quartz and occurs in angular and sub- angular shapes, with grain size of 0. 05~0. 5 mm; and filling material is mainly volcanic ash. Zircon U- Pb dating reveals that the 206Pb/238U ages of the zircons vary mainly in the range of 327~382 Ma. The youngest peak at 330~335 Ma may represent the age of volcanic activity coincidence with the deposition of tuffaceous conglomerate, and the obvious peak at 345~360 Ma may represent the crystallization ages of most volcanic rock gravels in tuffaceous conglomerate. Several sets of ages are around 411~428 Ma, ~455 Ma and 482~504 Ma, which correspond to the ages of the Keramay, Darbut and Tangbale ophiolite mélanges, respectively. Our study shows that the deposition age of the Xibeikulasi Formation is Early Carboniferous Visean. Combined with previous researches, it can concluded that the probable sequences of these three strata is Xibeikulasi, Baogutu, and Tailegula Formation from bottom to top.

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安芳,魏少妮,方正坤,郑波,邓杨.2019.西准噶尔希贝库拉斯组凝灰质砂砾岩岩石学和锆石U- Pb年代学及对沉积层序的指示意义[J].地质学报,93(8):1954-1967.
AN Fang, WEI Shaoni, FANG Zhengkun, ZHENG Bo, DENG Yang.2019. Petrology and zircon U- Pb geochronology of tuffaceous conglomerate in the Xibeikulasi Formation, West Junggar, and its implication for sedimentary sequence[J]. Acta Geologica Sinica,93(8):1954-1967.

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  • 收稿日期:2018-07-13
  • 最后修改日期:2018-09-30
  • 录用日期:2018-12-05
  • 在线发布日期: 2018-12-05
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