滇西凤庆“王雅岩组”特征及变质矿物研究

发布时间：2018-06-07 03:04

  本文选题：昌宁-孟连带 + 变质作用　； 参考：《成都理工大学》2015年硕士论文

【摘要】：昌宁-孟连带的演化历史一直是中外地质学者和专家研究的热点。“王雅岩组”位于昌宁-孟连带南段的西缘,其地层划分、岩石特征及变质特征,以及地质演化等方面,仍有诸多存疑。通过对滇西凤庆地区“王雅岩组”野外剖面及路线地质调查,室内岩石薄片研究及成分测试,经综合对比认为:该套岩石的主要岩性为蓝晶石石榴石十字石黑云母片岩、黑云母石英片岩,其内部夹少量长英质(花岗质)片岩、千糜岩,有2期花岗岩脉侵入(其中有一期与区域上印支期花岗岩同期)。岩石经过后期变质变形改造后发育成同质构造片岩、糜棱岩等,代表性矿物共生组合(泥质岩类)为:M1:十字石(St)+铁铝榴石(Alm)+黑云母1(Bi)+斜长石(Pl)+石英(Q);M2:蓝晶石(Ky)+铁铝榴石(Alm)+黑云母2(Bi)+钾长石(K)+白云母(Mus)+石英(Q);M3:铁铝榴石(Alm)+黑云母3(Bi)+石英(Q),糜棱岩化出现:石英(Q)+绢云母(Ser),总体显示造山变质特征。岩石化学特征表明其原岩为长英质岩类和泥质岩类的沉积岩。根据变质矿物成分分析数据及其结晶化学研究:该套岩石中的蓝晶石晶体化学式为(Fe0.0049-0.0189Al1.9311-1.9933)1.9453-1.9929[(Si0.95-0.9956 Al0.0046-0.05)1O4]O,AlⅣ/AlⅥ约为0.0251;十字石为(Fe0.6503-0.7006Al0.024-0.5016)0.8-1.3Al4[(Al0.1136Si1.8864)O4]2O2(OH)2,AlⅣ/AlⅥ约为0.0252,其XMg值较低,属铁十字石;石榴石以铁铝榴石为主,镁铝榴石(2.75%~9.29%);钙铝榴石(6.64%~19.63%),其晶体化学为:Ca0.2553-0.6032,Mg0.0851-0.2816,Fe1.8667-2.2495,Mn0.1370-0.4168)2.9334-2.9698Al1.869-1.997[(Al0.0008-0.0182Si0.9818-0.9992)1O4]3,AlⅣ/AlⅥ约为0.0091,其F总变化于88.87~95.97之间,显示石榴石形成于不同压力条件。黑云母为富铁黑云母,成分表现为高Al2O3(平均为20.72%)和Fe OT(20.16%)而低Mg O(平均为9.16%),MF值介于0.408~0.540之间(较高),Ti O2质量分数在1.16%~2.32%之间;按其矿物特征及成因可分为三期:M1黑云母与十字石同期,被后期变形改造而呈旋斑状;M2黑云母为长鳞片状黑云母;M3黑云母呈单片、无定向排列。综合研究认为:“王雅岩组”变质岩共经历了三期变质作用:第一次变质变形(M1-D1),也是本套岩石的初始变质期,即十字石、石榴石的形成阶段,变质温压达511℃~513℃,变质压力达0.439GPa;为低压相系绿帘角闪岩相;第二次变质变形(M2-D2),即蓝晶石、白云母的形成阶段,变质温压达553℃,变质压力达0.551Gpa;为中压相系角闪岩相。第三次变质作用(M3-D3),形成黑云母+石榴石变质矿物组合,变质温压达303℃~310℃,变质压力达0.09Gpa,属低压相系绿片岩相;其后发生变形(D4),和变形(D5),主要形成片理褶皱,伴随有局部糜棱岩化,形成绢云母+石英组合。综上,结合区域构造背景可知,主变质期(晋宁期)要早于主变形期(燕山-喜马拉雅期)。该套岩石首先经历了低压型绿帘角闪岩相到升温升压至中压角闪岩相的进变质,然后再经历了降温降压至低压型绿片岩相的退变质过程。
[Abstract]:The evolutionary history of the Changning-Menglian belt has been a hot spot for geologists and experts both at home and abroad. "Wangya Yan formation" is located in the western margin of the southern section of Changning-Menglian belt. Its stratigraphic division, rock characteristics and metamorphic characteristics, as well as geological evolution are still doubtful. Based on the field profile and route geological investigation of "Wangya formation" in Fengqing area, western Yunnan Province, and the laboratory study of thin rock slice and composition test, it is concluded that the main lithology of this set of rocks is the bluestone garnet cross biotite schist. Biotite quartz schist with a small amount of felsic (granitic) schist and mylonite intercalated in its interior, with two stages of granite vein intrusion (one of which coincides with the regional upper Indosinian granite). After the later metamorphic transformation, the rocks developed into homogeneous structural schist, mylonite, etc. Representative mineral symbiotic assemblages (=: M1: Stectite) Almite (Alm) biotite (1) plagioclase) Quartz (QN) M2: Kyydite) Almite (Almite) biotite (K) Musmica) Quartz QP3: Alm (Alm) biotite 3Bi) The occurrence of quartz and mylonitization: quartz Q) serine, which shows the characteristics of orogenic metamorphism in general. The petrochemical characteristics indicate that the source rocks are feldspar and argillaceous sedimentary rocks. According to the analysis data of metamorphic mineral composition and its crystallization chemistry, the crystal chemical formula of bluestone in this set of rocks is: Fe0.0049-0.0189Al1.9311-1.9933A1.9453-1.9929 [Si0.95-0.9956 Al0.0046-0.05)1O4] Ochal 鈪，

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