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南天山盲起苏花岗岩体的成因及构造意义:来自年代学、地球化学及Nd-Hf同位素证据
投稿时间:2019-08-21  修订日期:2020-02-06  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2020066
摘要点击次数: 52
全文下载次数: 52
作者单位E-mail
于新慧 中国地质大学北京 地球科学与资源学院
中国地质大学北京 地球科学与资源学院 
yxhcugb@163.com 
秦切) 中国地质科学院地质研究所 qieqin@foxmail.com 
黄河 中国地质科学院地质研究所  
王涛 中国地质科学院地质研究所  
张招崇) 中国地质大学北京 地球科学与资源学院  
童英) 中国地质科学院地质研究所  
郭磊) 中国地质科学院地质研究所  
宋鹏) 中国地质科学院地质研究所  
基金项目:NSFC新疆联合基金重点支持项目(项目编号:U1403291)和中国地质调查局二级项目(DD20190001)
中文摘要:出露于南天山造山带额尔宾山中部的盲起苏岩体由东部黑云母花岗闪长岩、西部黑云母花岗岩和中部二云母花岗岩组成。通过对该岩体进行锆石U-Pb定年,厘定东部、西部和中部不同岩相花岗岩的形成年龄分别为302±4 Ma、299±3 Ma和292±2 Ma。该岩体的SiO2含量为65.34 %~72.84%,其中东部和西部花岗岩的Al2O3的含量为14.40%~16.51%,A/CNK为1.00~1.11(平均1.05),Na2O+K2O的含量为7.26 %~8.52 %,K2O/Na2O为0.97~1.44(平均1.21),属过铝质高钾钙碱性系列岩石;中部花岗岩的Al2O3的含量为14.17%~14.92%,A/CNK为1.09~1.14(平均1.12),Na2O+K2O的含量为8.36%~8.80%,K2O/Na2O为1.61~1.80(平均1.72),属强过铝质钾玄岩钙碱性系列岩石。岩石的稀土元素具有富集轻稀土元素((La/Yb)N =9.58~44.94,其均值为28.63)和亏损重稀土元素(HREE、LREE/HREE=8.00~22.97,其均值为16.00)的特征,各部分岩体均具一定程度的Eu负异常(东部δEu=0.67~0.81;西部δEu=0.48~0.78;中部δEu=0.44~0.48)。岩石富集大离子亲石元素(K、Rb、Ba)、富集高场强元素(Th、U、Hf、Zr、Ce),亏损高场强元素(Nb、Ta、Ti)和具高Sr/Y比值的特征。盲起苏岩体东部、西部和中部的εHf(t)的值分别为-11.12至-1.53、-5.31至-0.35和-14.43至-2.51,二阶段Hf模式年龄(tDM2)在1.30 ~2.20 Ga之间;该岩体东部的εNd(t)的值为-6.89至-10.07,(143Nd/144Nd)i的值为0.5117至0.5119。结合区域地质背景和前人研究资料,本文认为盲起苏花岗岩体可能是由加厚的变质火成岩地壳发生部分熔融,经不同程度结晶分异形成的同碰撞或者后碰撞早期阶段的花岗岩。
中文关键词:南天山  晚古生代  花岗岩  同碰撞  结晶分异
 
Genesis and Tectonic Significance of the Mangqisu pluton in the South Tianshan:Evidence from geochronology, geochemistry and Nd-Hf isotopes
Author NameAffiliationE-mail
yuxinhui CHINA UNIVERSITY OF GEOSCIENCES :School of Geosciences and Resources yxhcugb@163.com 
qinqie Institute of Geology, Chinese Academy of Sciences qieqin@foxmail.com 
huanghe Institute of Geology, Chinese Academy of Sciences  
wangtao Institute of Geology, Chinese Academy of Sciences  
zhangzhaochong CHINA UNIVERSITY OF GEOSCIENCES  
tongying Institute of Geology, Chinese Academy of Sciences  
guolei Institute of Geology, Chinese Academy of Sciences  
宋鹏 Institute of Geology, Chinese Academy of Sciences  
Abstract:The Mangqisu pluton in the central part of the Erbeng Mountain tectonically belong to the South Tianshan Orogenic Belt, and consists mainly of biotite granodiorite unit in the east, biotite granite unit in the west and two-mica granite unit in the central. Our new zircon U-Pb results assign emplacement ages of the eastern, western and central units of 302±4 Ma, 299±3 Ma and 292±2 Ma, respectively. Geochemically, the Mangqisu pluton has SiO2 ranging from 65.34%-72.84%. Samples from eastern and western parts of the pluton show high Al2O3 (14.40%-16.51%), A/CNK (1.00-1.11, the average is 1.05), moderate Na2O+K2O (7.26%-8.52%), and K2O/Na2O ratios ranging from 0.97-1.44 (with an average of 1.21), and are of weakly peraluminous and high-K calc-alkaline series. The central granite unit displays 14.17%-14.92% Al2O3, Na2O+K2O (8.36%-8.80%), and K2O/Na2O ratios (1.61-1.80, the average is 1.72), suggesting that they are of strong peraluminous (A/CNK=1.09-1.14, with an average of 1.12) and shoshonite series. They are enriched in LREE ((La/Yb)N =9.58-44.94, with an average of 28.63 ) and depleted in HREE (LREE/HREE=8.00-22.97, with an average of 16.00), and exhibit negative Eu anomalies, with δEu ranging from 0.67 to 0.81 in the eastern unit, from 0.48 to 0.78 in the western unit and from 0.44 to 0.48 in the central unit. According to primitive mantle-normalized trace element patterns, the studied rocks are enriched in large ion lithophile elements (K, Rb, Ba) and high field-strength elements (Th, U, Hf, Zr, Ce), and depleted in high field-strength element (Nb, Ta, Ti), and have the characteristic of high Sr/Y ratio. In-situ zircon Hf isotopic data of the Mangqisu pluton shows εHf(t) values of the eastern, western and central units ranging from -11.12 to -1.53, -5.31 to -0.35 and -14.43 to -2.51, respectively. And two-stage model age (tDM2) varies from 1.30 Ga to 2.20 Ga. According to Sr-Nd isotope data, εNd(t) value of the eastern ranges from -6.89 to -10.07, the (143Nd/144Nd)i varies from 0.5117 to 0.5119. Combined with regional geological background and previous research datas, we suggest that the Mangqisu pluton can be regarded as syn-collision or early stage of post-collision granitoids and was derived from partial melting of the thickened metamorphic igneous crust, and Experienced different degrees of fractional crystallization.
keywords:South Tianshan  Late Paleozoic  Granite  Syn-collision  Fractional crystallization
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