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引用本文:邹光富1 毛 英2 邹 鑫3 毛 琼4 罗 滨4 林仕良1 丛 峰1 李再会1 谢 韬1. 滇西芒市地区钾长花岗岩的成因及构造背景: 岩石地球化学和锆石U-Pb同位素年代学证据[J]. 中国地质, 2013, 40(5): 1421-1432.
ZOU Guang-fu1, MAO Ying2, ZOU Xin3, MAO Qiong4, LUO Bin4, LIN Shi-liang1, CONG Feng1, LI Zai-hui1, XIE Tao1. Petrogenesis and tectonic setting of the K-feldspar granites in Mangshi area, western Yunnan: Evidence from petro-geochemistry and zircon U-Pb isotope chronology[J]. Geology in China, 2013, 40(5): 1421-1432(in Chinese with English abstract).
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滇西芒市地区钾长花岗岩的成因及构造背景: 岩石地球化学和锆石U-Pb同位素年代学证据
邹光富1 毛 英2 邹 鑫3 毛 琼4 罗 滨4 林仕良1 丛 峰1 李再会1 谢 韬11,2,3,4
1.成都地质矿产研究所,四川 成都 610082;2.成都岩矿分析测试中心,四川 成都 610081;3.北京大学 心理学系,北京 100871;4.华北油田勘探开发研究院,河北 任丘062552
摘要:
提要:腾冲地块芒市地区钾长花岗岩分布于芒市北部五叉路乡核桃洼、江东乡杨家寨和轩岗乡南约村一带,主要由钾长花岗岩组成。芒市地区钾长花岗岩大部分是作者通过1∶5万区域地质填图,从原高黎贡山群中解体出来的。为了限定该地区岩浆事件的准确时间,本文对该区钾长花岗岩进行了LA-ICP-MS锆石U-Pb定年和地球化学研究。测得芒市地区钾长花岗岩中锆石的206Pb/238U年龄加权平均值为(60.8±0.8) Ma,其形成时代属于古近纪。该区钾长花岗岩具有高SiO2(67.97%~80.62%)、高碱(K2O+Na2O=5.08%~8.79%)、中-高钾(K2O/Na2O=1.11~17.80)、低P2O5含量(0.01%~0.15%)的特征。铝饱和指数(A/CNK)介于1.03~2.31之间,岩石属钾玄岩-高钾钙碱性过铝质-强过铝质S型花岗岩。岩石总体上富集大离子亲石元素Rb、Th、U、Ta、La、Pb、Nd、Sm、Gd等,明显亏损高场强元素Ba、Nb、Ce、Sr、Zr、Hf、Eu等。稀土元素总量(ΣREE)为56×10-6~323×10-6,平均为183×10-6,稀土元素配分曲线呈右倾型, LaN/YbN为1.58~41.60,δEu=0.18~0.71, 显示弱到中等程度的负铕异常,具有明显的轻稀土富集,重稀土亏损的特征。地球化学研究表明,该花岗岩是以含粘土的变质杂砂岩和粘土岩部分熔融形成的,岩浆可能来源于本区中晚元古代高黎贡山群为代表的地壳物质的部分熔融。是典型壳源成因类型,具岛弧型同碰撞花岗岩特征。该区古近纪钾长花岗岩的形成表明,在60.8 Ma以前,雅鲁藏布江—密支那洋已关闭,印度板块与冈底斯—腾冲板块之间的俯冲、碰撞作用已经发生,并处于岩浆弧形成阶段,为印度板块与冈底斯—腾冲板块之间俯冲、碰撞、成弧造山构造岩浆活动的响应。古近纪钾长花岗岩形成时代及其构造环境的厘定,为进一步探讨腾冲地块构造演化提供了新证据。
关键词:  古近纪钾长花岗岩;锆石U-Pb定年  地球化学  构造意义;腾冲地块;滇西
DOI:
分类号:
基金项目:中国地质调查局项目“云南1︰5万梁河县、江东、帕底幅区域地质调查项目”(1212010784007)资助。
Petrogenesis and tectonic setting of the K-feldspar granites in Mangshi area, western Yunnan: Evidence from petro-geochemistry and zircon U-Pb isotope chronology
ZOU Guang-fu1, MAO Ying2, ZOU Xin3, MAO Qiong4, LUO Bin4, LIN Shi-liang1, CONG Feng1, LI Zai-hui1, XIE Tao11,2,3,4
1. Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, Sichuan, China;2. Chengdu Comprehensive Rock and Mineral Testing Center, Chengdu 610081, Sichuan, China;3.Department of Psychology, Peking University, Beijing 100871;4. Research Institute of Petroleum Exploration and Development, North China Oil Field Company, PetroChina, Renqiu 062552, Hebei, China
Abstract:
Abstract:Located in Tengchong block of western Yunnan, the Paleocene K-feldspar granites in northern Mangshi are mainly composed of K-feldspar granites. Most of the Mangshi K-feldspar granites resulted from the disintegration of original Gaoligong Group, as evidenced by 1∶50000 regional geological mapping. To precisely limit the age of the K-feldspar magmatic mineralization in Mangshi area, the authors analyzed the granites by using LA-ICP-MS zircon U-Pb technique and geochemical methods. The zircon LA-ICP-MS dating indicates that the K-feldspar granites was emplaced at (60.8±0.8) Ma. The granite mass was formed in the Paleocene period. Geochemical data show that the Lianghe granites are K basaltic, high-K calc-alkaline and peraluminous to strongly peraluminous series, characterized by high content of SiO2 (67.97%~80.62%), high content of K2O+Na2O (5.08%~8.79%), medium to high K(K2O/Na2O=1.11~17.80), and lower content of P2O5 (0.01%~0.15%) with peraluminous ratio (A/CNK) being 1.03~2.31. ACF plot indicates that the granites are S type granites. Mangshi granites are also enriched in Rb, Th, U, Ta, La, Pb, Nd, Sm and Gd,but strongly depleted in Ba, Nb, Ce, Sr, Zr, Eu and Hf. The REE content is between 56.42×10-6 and 322.91×10-6, 183.15×10-6 on average, with (La/Yb)N ratios being 1.58~41.60 and δEu being 0.18~0.71. REE diagram shows right inclination and obvious negative Eu anomalies. The intrusion is remarkably characterized by enriched LREE and depleted HREE. The chondrite-normalized REE patterns show negative Eu anomalies. Magma source was probably derived from the emplacement of partially melted granitic magma dominated by greywacke and claystone, which is typical of crustal genesis. The K-feldspar granite was derived from partial melting of the Mid-Proterozoic metamorphosed basement (Gaoligong Group). According to geochemistry and the trace element discrimination diagrams for tectonic interpretation, the Paleocene K-feldspar granites are considered to be of the island arc and syn-collision type formed in a transitional tectonic setting from the compressional system to the island arc system. The Paleocene K-feldspar granite was formed in the syn-collision and island arc tectonic setting. The Paleocene K-feldspar granites in northern Mangshi area indicate that the Yaluzangbu-Mizhila Ocean had been closed and the subduction and collidion between the Indian plate and the Gangdise-Tengchong massif had occurred before 60.80Ma. Tengchong block was formed in magmatic arc tectonic setting at that time. The Gangdise-Tengchong block tectono-magmatic orogenesis was intimately related to the closure and subduction and collidion orogenesis between the Indian plate and the Gangdise-Tengchong massif. The determination of the crystallization and origin of Mangshi K-feldspar granites provides new evidence for the Paleocene tectonic evolution of the Tengchong massif.
Key words:  Paleocene K-feldspar granite  zircon U-Pb dating  geochemistry  tectonic implications  Tengchong block  western Yunnan