地学前缘 ›› 2022, Vol. 29 ›› Issue (2): 234-240.DOI: 10.13745/j.esf.sf.2021.10.40

• 洋板块地质与造山带地质 • 上一篇    下一篇

长乐—南澳构造带泉港临头片麻状英云闪长岩中岩浆绿帘石的发现及其地质意义

崔显岳1(), 陈柏林1, 司晓博2, 邓晋福2, 冯艳芳3,*(), 肖庆辉2   

  1. 1.中国地质科学院 地质力学研究所, 北京 100081
    2.中国地质大学(北京), 北京 100083
    3.中国地质调查局 发展研究中心, 北京 100037
  • 收稿日期:2021-08-12 修回日期:2021-10-27 出版日期:2022-03-25 发布日期:2022-03-31
  • 通讯作者: 冯艳芳
  • 作者简介:崔显岳(1973—),男,博士,高级工程师,主要从事区域地质调查和研究。E-mail: 940911816@qq.com
  • 基金资助:
    中国地质科学院所长基金项目“构造体系与成矿作用的耦合与衍生:以中国东部矿集区为例”(JYYWF20180602);中国地质调查局“地质矿产调查数据集成与处理应用”(DD20190429);中国地质调查局“地质调查标准化与标准制修订(2022—2025)”二级项目(DD20221826)

Magmatic epidote in Quanganglintou gneissic dacodiorite from the Changle-Nan’ao structural zone: Discovery and geological significance

CUI Xianyue1(), CHEN Bolin1, SI Xiaobo2, DENG Jinfu2, FENG Yanfang3,*(), XIAO Qinghui2   

  1. 1. Institute of geomechanics, Chinese academy of geological sciences, Beijing 100081, China
    2. China university of geosciences, Beijing 100083, China
    3. Development research center of China geological survey, Beijing 100037, China
  • Received:2021-08-12 Revised:2021-10-27 Online:2022-03-25 Published:2022-03-31
  • Contact: FENG Yanfang

摘要:

岩浆绿帘石能够作为压力计反映岩体侵位深度,进而可估算地壳抬升剥蚀速率及地壳演化历史,因而引起了人们的研究关注。在长乐—南澳构造带泉港临头地段发现了片麻状英云闪长岩中的岩浆绿帘石。该地段是我国当前报道岩浆绿帘石的第5处产出地,但在东南沿海地区尚属首次发现。含岩浆绿帘石的片麻状英云闪长岩形成于早白垩世(K1),以钙性(C,Peacock碱钙指数)、中钾钙碱性系列(MKCA)、准铝质和弱过铝质、钙碱性系列(CA,Miyashiro SiO2-FeO*/MgO)为主,具镁安山岩系列(MA)性质,呈奥长花岗岩演化趋势(Tdj);轻稀土(LREE)较富集,铕负异常不明显;微量元素呈现较大的钽(Ta)、磷(P)和钛(Ti)负异常,显示出造山带火山弧花岗岩的特征。片麻状英云闪长岩中绿帘石岩相学特征显示,黑云母和自形的绿帘石分布于斜长石的隙间,为典型的填间结构;绿帘石与黑云母相互接触、相互包裹,是一起从富水的晚期岩浆中结晶出来的原生矿物,不是交代斜长石的岩浆期后的次生矿物。绿帘石电子探针分析结果显示Ps值为24~29,TiO2含量均小于0.1%。综合绿帘石岩相学与化学特征知悉,泉港临头片麻状英云闪长岩中的绿帘石为岩浆绿帘石。岩浆绿帘石形成压力约870 MPa,深度为25~32 km,而现今东南沿海陆壳厚度约30 km,据此推测,早白垩世(K1)时东南沿海陆壳厚度为55~62 km;早白垩世(K1)之后,地壳可能经历了多次抬升。

关键词: 岩浆绿帘石, 发现, 地质意义, 片麻状英云闪长岩, 长乐—南澳构造带

Abstract:

Magmatic epidote can be used as a pressure gauge to reflect the emplacement depth of the rock mass, from which the rate of crustal uplift and denudation and the history of crustal evolution can be assessed. Magmatic epidote in Quangangintou gneissic tonalite from the Changle-Nan’ao structural belt is the fifth epidote occurrence reported in China and the first discovered in the southeast coastal area. The gneissic tonalite, formed in the Early Cretaceous (K1), is dominated by calcic, medium-potassium, calc-alkaline series and metaluminous, weak peraluminous, calc-alkaline series, possessing the properties of magnesium andesite and showing the trondhjemite evolutionary trend. Light rare earth elements are relatively enriched in the gnessic tonalite, with no obvious negative Eu anomaly. Large Ta, P and Ti negative anomalies show the characteristics of volcanic arc granites in orogenic belts. As revealed by petrographic analysis, the biotite and automorphic epidote are distributed in the gaps in plagioclase forming a typical filling structure. The two minerals, wrap around each other, appear as primary minerals co-crystallized from the late water-rich magma, not secondary ones formed after the magmatic period of metasomatic plagioclase. By EPMA analysis, the power factor Ps for the epidote is between 24-29, and TiO2 content is less than 0.1%. Petrographic and chemical analyses further reveal the epidote in gneissic tonalite is magmatic epidote, formed underground at a pressure of ~8.7 kbar and a depth of 25-32 km. Combining the above results with the crustal thickness of ~30 km for the present southeast coast continent, the corresponding Early Cretaceous (K1) crustal thickness is estimated at about 55-62 km. After the Early Cretaceous (K1), the crust might have experienced multiple uplifts.

Key words: magmatic epidote, discovery, geological significance, gneissic tonalite, Changle-Nan’ao structural belt

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