西秦岭天水地区岛弧型基性岩浆杂岩的地球化学特征及形成时代
Geochemical characteristics and zircon U-Pb ages of island-arc basic igneous complexes in the Tianshui area, West Qinling
-
摘要: 提要：天水地区关子镇流水沟变质中基性岩浆杂岩主要由变质辉长岩—辉长闪长岩—闪长岩组成，百花变质岩浆杂岩主要由辉石岩—辉长（闪长）岩—闪长岩—石英闪长岩组成，构成较完整的同源岩浆演化序列。基性—中基性岩浆岩的地球化学特征表明其属于拉斑玄武岩系列，稀土元素分布型式呈REE近平坦型—LREE轻微富集型，微量元素原始地幔标准化的蛛网图和MORB标准化蛛网图上的分布型式总体很相似，富集大离子亲石元素（LILE）Cs、Ba、Sr、Th、U而相对亏损Rb、K和高场强元素（HFSE）Nb、P、Zr、 Sm、Ti和Y，显示同源岩浆演化成因特征。微量元素构造环境判别显示其形成于岛弧构造环境。关子镇流水沟变质中基性岩浆杂岩的TIMS法锆石U-Pb同位素年龄为（507.5±3.0）Ma，代表了杂岩体的形成时代，表明西秦岭北带岛弧型岩浆岩的形成时代为晚寒武世，同时也揭示出以关子镇蛇绿岩为代表的古洋盆的俯冲作用及产生岛弧型岩浆活动的时限可能为晚寒武世—早奥陶世。Abstract: Abstract：The Liushuigou intermediate-basic meta-igneous complex at Guanzizhen, Tianshui, is composed mainly of metagabbro-metagabbro diorite-metadiorite, and the Baihua basic meta-igneous complex consists mainly of pyroxenite-gabbro (-diorite)-diorite-quartz diorite. They form a relatively complete comagmatic evolutionary series. The geochemical characteristics of basic to intermediate-basic igneous rocks indicate that they belong to a tholeiite suite. Their chondrite-normalized REE patterns are of nearly flat and slightly LREE-enriched type, and their primitive mantle-normalized and MORB-normalized trace element spidergrams are generally similar; the LILEs Cs, Ba, Sr, Th and U are enriched, while Rb and K and the HFSEs Nb, P, Zr, Sm, Ti and Y are depleted. All these show comagmatic evolutionary and genetic characteristics. The tectonic environment discrimination by trace elements reveals that these igneous complexes formed in an island-arc setting. The TIMS single-zircon U-Pb age for the Liushuigou intermediate-basic meta-igneous rocks in the Guanzizhen area is 507.5±3.0 Ma, representing the age of these igneous complexes, which indicates that island-arc-type magmatic rocks in the north zone of the West Qinling are Late Cambrian in age and also reveals that the timing of subduction of the paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magmatic activity is probably Late Cambrian to Early Ordovician.
-
Keywords:
- basic igneous complex /
- geochemistry /
- island-arc setting /
- zircons U-Pb age /
- Early Paleozoic /
- Tianshui area /
- West Qinling
-
计量
- 文章访问数: 3940
- HTML全文浏览量: 46
- PDF下载量: 4052
下载:
