地学前缘 ›› 2019, Vol. 26 ›› Issue (1): 286-299.DOI: 10.13745/j.esf.yx.2017-3-51

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河北武安坦岭多斑斜长斑岩中基质矿物特征及其研究意义

刘璐璐，苏尚国，杨睿娜，罗照华，崔晓亮   

  1. 1. 中国地质大学(北京) 地球科学与资源学院, 北京 100083
    2. 河南省地质矿产勘查开发局 第二地质矿产调查院, 河南 郑州 450001
  • 收稿日期:2017-01-05 修回日期:2017-03-20 出版日期:2019-01-30 发布日期:2019-01-30
  • 通讯作者: 苏尚国(1965—)，男，博士，教授，博士生导师，主要从事岩石学及矿床学的教学及研究工作。
  • 作者简介:刘璐璐(1987—)，女，博士，矿物学、岩石学、矿床学专业。E-mail：Liululu0409@163.com
  • 基金资助:
    中国地质调查局项目(12120115069701)；国家自然科学基金项目(41272105)；教育部博士学科点基金项目

Characteristics and research significance of matrix minerals in Tanling poly-phenocryst plagioporphyry, Wu'an, Hebei Province

LIU Lulu,SU Shangguo,YANG Ruina,LUO Zhaohua1,CUI Xiaoliang   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
    2. No.2 Institute of Geological and Mineral Resources Survey, Henan Bureau of Geo-exploration and Mineral Development, Zhengzhou 450001, China
  • Received:2017-01-05 Revised:2017-03-20 Online:2019-01-30 Published:2019-01-30
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摘要： 河北武安坦岭斜长斑岩具有多斑斑状结构，基质为显微晶质结构。岩相学观察表明，斜长石斑晶有一个宽广的核部和一个宽度可变的条纹长石反应边，个别核部包含有角闪石、黑云母等矿物。基质矿物主要由蓝透闪石、条纹长石(An0Ab8.4Or91.5～An0.1Ab57.3Or42.6)、石英、钾长石(An0.3Ab5.9Or93.7～An0.3Ab4.7Or95.2)、钠长石(An0.2Ab98.3Or1.5～An0.1Ab99.2Or0.7)、磁铁矿、赤铁矿、钛铁矿、磷灰石、榍石和锆石等11种矿物组成。角闪石温压计计算结果得出，基质角闪石核部的结晶压力高于边部，核部为34.05 MPa，对应的结晶温度为660.35 ℃，结晶深度为1.29 km；边部的结晶压力为24.32 MPa，结晶温度为598.32 ℃，结晶深度为0.92 km；而斜长石斑晶中的角闪石形成时压力为159.51～178.19 MPa，温度为817.68～819.79 ℃，对应的形成深度为6.03～6.73 km。基质角闪石在Al2O3TiO2图上落在壳源区，而斑晶中的角闪石和黑云母都落在壳幔混合区。斜长石、条纹长石、磁铁矿和磷灰石的微量和稀土元素测试数据显示，其都具有相对富集LILE、亏损HFSE的特点，暗示了基质矿物的形成有流体参与。ICT三维扫描结果显示，斜长斑岩基质中的孔隙体积含量约为3.428%，铁质体积含量为4.371%，且铁氧化物和孔隙具弱连通性。通过讨论分析，笔者得出：(1)坦岭斜长斑岩中斜长石斑晶具有明显的交代结构，且晶体本身没有明显熔蚀现象，这些特征表明大量的斜长石斑晶快速上升，即“冻结岩浆房”的活化机制与流体密切相关；(2)斜长斑岩中基质矿物有十一种，且矿物类型复杂，不符合平衡系统矿物相律，应属于流体晶矿物组合；(3)坦岭斜长斑岩的基质“岩浆”可能是一种富Fe、K、P、Si、Na等元素的熔体流体流；(4)多斑斜长斑岩的形成经历了①深度6~7 km的深部岩浆房形成斜长石堆晶→②富Fe、K、P、Si、Na等元素的熔体流体流加入深部岩浆房，冻结岩浆房活化→③由于流体超压，含大量斜长石斑晶的熔体流体在地壳浅部(0.9～1.2 km)呈小岩株状或岩脉状就位。多斑斜长斑岩为深部找矿提供了有力的线索。

 

关键词: 多斑斜长斑岩, 基质矿物, 角闪石, 矿物温压计, 冻结岩浆活化

Abstract: The poly-phenocryst plagioporphyry in Tanling, Wu'an (Hebei) was found with poly-phenocryst porphyrotopic texture and microcrystalline matrix. The rim of plagioclase phenocrysts consists of variable-width perthite, while oligoclase-albite made up the broad core where trace of amphibole and biotite were found in isolated phenocrysts. The matrix comprises 11 minerals mainly: winchite, perthite (An0Ab8.4Or91.5An0.1Ab57.3Or42.6), quartz, potassium feldspar (An0.3Ab5.9Or93.7An0.3Ab4.7Or95.2), albite(An0.2Ab98.3Or1.5An0.1Ab99.2Or0.7), magnetite, hematite, ilmenite, apatite, sphene, and zircon. T-P calculation of amphiboles using amphibole barometer showed that the average crystal pressure decreased from 34.05 to 24.32 MPa, corresponding temperature dropped from 660.35 to 598.49 ℃, and crystal depth changed from 1.29 to 0.93 km in the matrix amphibole core. In contrast, crystal pressure (159.51178.19 MPa), temperature (817.68819.79 ℃) and depth (6.036.73 km) were all higher in the plagioclase phenocryst amphiboles. Al2O3-TiO2 diagram showed that the plagioclase phenocryst amphibole and biotite in plagioclase phenocryst was crust-mantle mixed origin, and the matrix amphibole was crust origin. LA-ICP-MS analysis of matrix minerals revealed that Al2O3-TiO2 most of them were enriched in LILE and depleted in LREE, indicating fluid was involved during the formation of matrix minerals. ICT scannogram demonstrated that pore and iron oxides volume in the matix was about 3.428% and 4.371% respectively, and they each had weak-connectivity. Above all, we suggest that: (1) A large amount of plagioclase phenocrysts ascended rapidly to near surface with no sign of corrosion or resorption, suggesting the remobilizing mechanism of frozen magma chambers is closely related to fluid; (2) the matrix magma of plagioporphyry was probably a melt-fluid flow rich in Fe, K, P, Si, Na, etc., and (3) the plagioporphyry in Tanling, Wu'an may provide physical boundary conditions for migration or unloading of ore-forming material as well as clues for deep prospecting.

Key words: Poly-phenocryst plagioporphy, amphibole, geothermobarometer, remobilizing mechanism of frozen magma chambers

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