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现代地质 ›› 2020, Vol. 34 ›› Issue (05): 1067-1076.DOI: 10.19657/j.geoscience.1000-8527.2020.038

• 岩石学 • 上一篇    下一篇

黑龙江张家湾地区中侏罗世A型花岗岩地球化学特征及构造环境分析

任永健1(), 程烁1(), 张明明1, 曹光远2, 于汪1, 赵寒1, 梁恒1, 王富强1, 祁才吉1   

  1. 1.中化地质矿山总局 地质研究院, 北京 100013
    2.中化地质矿山总局, 北京 100013
  • 收稿日期:2018-10-18 修回日期:2020-05-06 出版日期:2020-10-28 发布日期:2020-10-29
  • 通讯作者: 程烁
  • 作者简介:程 烁,女,工程师,1988年出生,机电与维修专业,主要从事地质图件编制、期刊编辑工作。Email: 641318804@qq.com
    任永健,男,高级工程师,1986年出生,矿产普查与勘探专业,主要从事区域地质矿产调查工作。Email: mysky0315@126.com
  • 基金资助:
    中国地质调查局项目“黑龙江1∶5万南蛤拉河子等四幅区域地质矿产调查”(1212011220474)

Geochemistry Characteristics and Tectonic Environment Analysis of Middle Jurassic A-type Granites in Zhangjiawan Area, Heilongjiang Province

REN Yongjian1(), CHENG Shuo1(), ZHANG Mingming1, CAO Guangyuan2, YU Wang1, ZHAO Han1, LIANG Heng1, WANG Fuqiang1, QI Caiji1   

  1. 1. Geological Institute of China Chemical Geology and Mine Bureau,Beijing 100013,China
    2. China Chemical Geology and Mine Bureau,Beijing 100013,China
  • Received:2018-10-18 Revised:2020-05-06 Online:2020-10-28 Published:2020-10-29
  • Contact: CHENG Shuo

摘要:

通过对黑龙江张家湾地区中侏罗世正长花岗岩和碱长花岗岩进行岩石地球化学分析,探讨该区域花岗质岩浆作用、成因类型及其构造环境。研究结果表明,正长花岗岩和碱长花岗岩具有高SiO2(73.12%~77.82%)、富碱(K2O+Na2O=6.36%~8.56%)、富铁贫镁(TFeO/MgO=6.67~25.43)的特点,铝饱和指数A/CNK值大多大于1.1,Eu负异常明显(δEu=0.01~0.74),富集Th、U、K和Rb,亏损Ba、Sr、P和Ti;锆石饱和温度变化范围为757~900 ℃,平均为816 ℃,具有A型花岗岩的特征;岩石由高分异花岗岩向过铝质A型花岗岩演化。稀土元素特征指示,岩浆物源由幔源和下地壳物质混合而成,中侏罗世正长花岗岩和碱长花岗岩构造类型为A2型花岗岩,形成于造山后岩石圈伸展环境作用阶段。上述岩石地球化学特征表明,受古太平洋板块向西俯冲-碰撞后造山作用的影响,中侏罗世张家湾地区处于造山后伸展拉张的环境,岩石圈由挤压向伸展构造背景转变,地幔物质上涌并伴随岩浆的底侵作用,引发地壳物质的熔融,最终形成了该区域的正长花岗岩和碱长花岗岩。

关键词: 张家湾, 中侏罗世, A型花岗岩, 地球化学, 构造环境

Abstract:

Through comprehensive petrographic and geochemical analyses of the Middle Jurassic syenite and alkali feldspar granite in Zhangjiawan area (Heilongjiang Province), we explore the regional granitic magmatism, genetic type and tectonic environment. The results show that the syenite granite and alkali feldspar granite have high SiO2(73.12%-77.82%), and are alkali-rich (K2O+Na2O = 6.36%-8.56%), Fe-rich and Mg-poor (FeO T/MgO = 6.67-25.43). The rocks have aluminum saturation index (A/CNK value) mostly above 1.1, distinct negative Eu anomalies (δEu = 0.01-0.74), enrichments in Th, U, K and Rb, and depletions in Ba, Sr, P and Ti. Zircon saturation temperatures are calculated to be 757-900 ℃, with an average of 816 ℃. The granites are A-type, and likely evolved from highly-fractionated granite to peraluminous A-type granite. REE features indicate that the magma was sourced from a mixture of mantle and lower crustal materials. The mid-Jurassic syenite granite-alkaline granite is A2-type, and was likely formed in a post-orogenic lithospheric extension setting. The above-mentioned lithogeochemical characteristics indicate that the Middle Jurassic regional tectonics was influenced by the west-dipping Paleo-Pacific subduction and post-collisional orogeny. The Zhangjiawan area was in a post-orogenic extension environment, and the lithosphere tectonic regime changed from compressive to extensional. The mantle upwelling accompanied by magma intrusion may have triggered the melting of crustal materials, which formed the syenite and alkali feldspar granite in the area.

Key words: Zhangjiawan area, Middle Jurassic, A-type granite, geochemistry, tectonic environment

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