南秦岭柞水—山阳地区中酸性岩体成因机制及构造背景

发布时间：2018-05-21 08:04

本文选题：南秦岭 + 花岗(斑)岩　；参考：《西北大学》2015年硕士论文

【摘要】：在南秦岭柞水-山阳地区广泛分布着一系列的小型中酸性花岗(斑)岩体,这些花岗(斑)岩体通常伴随着普遍的矿化作用。本文通过对这些中酸性的成矿小花岗(斑)岩体进行野外地质、岩相学、LA-ICP-MS锆石U-Pb年代学、地球化学等方面的综合研究,分析探讨岩石的成因类型、矿物组成、形成时代、岩浆源区、构造演化及地球动力学背景,得到了如下认识与成果：中酸性花岗(斑)岩体类型主要包括花岗闪长(斑)岩、二长花岗(斑)岩、石英闪长岩和闪长(玢)岩等。岩石中矿物组成主要为钾长石、斜长石、石英和暗色矿物角闪石、黑云母等,副矿物包括锆石、磷灰石、榍石和磁铁矿等。LA-ICP-MS锆石U-Pb定年显示,它们的加权平均年龄分别为：下官坊花岗闪长(斑)岩(146.78±0.91Ma)；园子街二长花岗(斑)岩(145.56±0.95Ma)；袁家沟二长花岗岩(143.67±0.90Ma)；小河口二长花岗岩(142.34±0.92Ma)；白沙沟石英闪长岩(141.09±0.72Ma)；池沟石英闪长岩(141.5±1.0Ma)；土地沟二长花岗(斑)岩(139.29±0.90Ma),这些年龄代表了岩体形成于晚侏罗-早白垩世。地球化学特征显示,此地区岩体具有高硅(SiO2=60.19～69.20 wt.%)、富碱(K2O+Na2O=7.00-10.21 wt.%)、高铝(Al2O3=15.03～15.91 wt.%)、低钙(CaO=1.34～4.54 wt.%)的特征,A/CNK=0.82-1.12(平均为0.92),反应岩石以具准铝质到过铝质特征的高钾钙碱性岩为主。岩石稀土元素具有轻稀土富集(LREE=103.80～191.95ppm)、重稀土亏损(HREE=8.05～15.04 ppm),稀土元素分异明显(LREE/HREE=10.83～14.89、 (La/Yb)N=12.35～21.06),铕异常不明显(δEu=0.89-1.10)的特点。微量元素蛛网图显示岩石总体具有亏损Nb、Ta、Ti、P等高场强元素(HFSE),富集K、Rb、Sr、Ba、 Pb等大离子亲石元素(LILE)的特点。结合岩体的野外地质、岩相学、年代学和地球化学特征,可以得出本区岩体属于Ⅰ型花岗岩,并具有相似的岩浆源区,岩浆可能主要来自古老地壳的重熔以及少量壳幔混合。岩体应形成于挤压背景之下,挤压使得地壳加厚,加厚地壳发生熔融,进而产生了这些小型的花岗质岩体。
[Abstract]:A series of small intermediate-acid granitic (porphyry) bodies are widely distributed in the area of tussah-Shanyang, South Qinling. These granitic (macular) rocks are usually accompanied by widespread mineralization. In this paper, through the comprehensive study of field geology, lithofacies, U-Pb geochronology and geochemistry of these intermediate-acid ore-forming Xiaohuagang (porphyry) intrusions, the genetic types, mineral composition and forming age of the rocks are analyzed and discussed. In the magmatic source area, tectonic evolution and geodynamic background, the following results have been obtained: the types of intermediate-acid granodiorite (porphyry) include granodiorite (porphyry), erchang granodiorite (porphyry), quartz diorite and diorite (porphyry). The mineral composition of the rocks is mainly composed of potash feldspar, plagioclase, quartz and dark mineral hornblende, biotite, etc. The secondary minerals include zircon, apatite, sphene and magnetite, etc. The zircon U-Pb dating shows that Their weighted average ages are: Xiaguanfang granodiorite (porphyry) 146.78 卤0.91MaA; Yuanzijie Erchang granodiorite (porphyry) 145.56 卤0.95MaA; Yuanjiagou monzogranite 143.67 卤0.90 Mai; Xiaohekou Erchangite 142.34 卤0.92MaMa; Baishagou quartz diorite 141.09 卤0.72MaA; Zigou quartz diorite 141.09 卤0.72MaA; Yuanjiagou monzogranite 143.67 卤0.90 Mai; Xiaoguanfang granite 142.34 卤0.92MaA; Baishagou quartz diorite 141.09 卤0.72MaA These ages represent the late Jurassic-early Cretaceous formation of the rock mass, 141.5 卤1.0 Ma ~ (-1) and 139.29 卤0.90 Ma ~ (-1) of the earlong granitic (porphyry) rocks. The geochemical characteristics show that the rock bodies in this area have the characteristics of high SiO2 + 60.19 ~ 69.20 wt., alkali-rich K _ 2O Na2O=7.00-10.21 wt., high Al _ 2O _ 3O _ 3 15.03 ~ 15.91 wt.T, low Ca _ 2O _ (1.34) ~ 4.54 wt.12 (average = 0.92), and the reactive rocks are mainly high-potassium calc-alkaline rocks with the characteristics of quasi-aluminous to peraluminous. The rare earth elements in rocks are characterized by LREE _ (103.80) ~ (191.95) ppm ~ (-1), HREE ~ (8.05) ~ 15.04 ppm ~ (-1), LREE / HREE ~ (10.83) ~ 14.89, La / Y _ (B) N _ (12.3521.06), EU ~ (3 +) anomaly (未 EU ~ (0.89-1.10). The trace element cobweb diagram shows that the rocks are characterized by depletion of high field strength elements such as NbTa-TIAP and enrichment of large ion lithophile elements such as K ~ (B) ~ (b) ~ (2 +) Sr ~ (2 +) Ba, Pb (LILE). Combined with the field geology, petrography, geochronology and geochemistry of the rock mass, it can be concluded that the rock body in this area belongs to type I granite and has similar magmatic source. The magma may mainly come from the remelting of the ancient crust and a small amount of crust-mantle mixing. The rock mass should be formed in a compressional background, which makes the crust thicker and thickens the crust to melt, thus producing these small granitic rocks.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121

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