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赵冰冰,邓宇峰,周涛发,袁峰,张达玉,邓刚,李卫东,李跃. 2018. 东天山白鑫滩含铜镍矿镁铁-超镁铁岩体的岩石成因:年代学、岩石地球化学和Sr-Nd同位素证据. 岩石学报, 34(9): 2733-2753
东天山白鑫滩含铜镍矿镁铁-超镁铁岩体的岩石成因:年代学、岩石地球化学和Sr-Nd同位素证据
作者单位E-mail
赵冰冰 合肥工业大学资源与环境工程学院, 合肥 230009
浙江省地矿勘察院, 杭州 310013 
 
邓宇峰 合肥工业大学资源与环境工程学院, 合肥 230009 dyfeng_214@sina.com 
周涛发 合肥工业大学资源与环境工程学院, 合肥 230009  
袁峰 合肥工业大学资源与环境工程学院, 合肥 230009  
张达玉 合肥工业大学资源与环境工程学院, 合肥 230009  
邓刚 新疆地勘局第六地质大队, 哈密 839000  
李卫东 新疆地勘局第六地质大队, 哈密 839000  
李跃 合肥工业大学资源与环境工程学院, 合肥 230009  
基金项目:本文受国家自然科学基金项目(41303031、41672069、41630316),"十二五"国家科技支撑计划项目(2011BAB06B01)和中央高校基本科研业务费专项资金(JZ2018HGTB0246)联合资助.
摘要:
      自20世纪70年代以来,新疆东天山觉罗塔格构造带库姆塔格沙垅以东地区发现了大量的镁铁-超镁铁岩体和岩浆铜镍硫化物矿床,但是在沙垅以西地区没有大的找矿突破。白鑫滩含铜镍矿镁铁-超镁铁岩体为近几年在库姆塔格沙垅以西地区发现的岩浆铜镍硫化物矿床,研究工作薄弱,本文通过对白鑫滩岩体的岩石学、年代学、岩石地球化学和Sr-Nd同位素分析来解释其岩石成因。白鑫滩岩体不同岩相中矿物的粒径和含量的变化规律说明岩体为三期岩浆侵入作用形成,第一期为顶部的角闪辉长岩;第二期的橄榄辉长岩、斜长二辉橄榄岩和含长橄榄二辉岩,矿物种类相同,含量呈渐变关系;第三期为底部为的辉长岩,矿物粒径相对顶部的角闪辉长岩较小。白鑫滩岩体与黄山东、黄山西岩体具有相似的稀土元素和微量元素配分型式,大离子亲石元素(Rb、Ba、U、K)相对富集,而部分高场强元素(Nb、Ta、Ti)相对亏损,稀土元素呈轻稀土略微富集的右倾样式,均表现出岛弧火山岩的地球化学性质,εNdt)值(2.84~5.05)和(87Sr/86Sr)(t)值(0.704113~0.705682)介于软流圈地幔与岩石圈地幔之间。但是与黄山东、黄山西岩体相比,白鑫滩岩体不相容元素含量更高,且εNdt)值更低,(87Sr/86Sr)(t)值更高,还具有较高的La/Nb(2.00~3.33),较低的La/Ba(0.02~0.15),这些特征说明白鑫滩岩体的原始岩浆为岩石圈与软流圈物质相互作用的产物,且白鑫滩岩体的原始岩浆中软流圈物质相对于黄山东和黄山西岩体加入的比例更小。白鑫滩橄榄辉长岩年龄为287±3Ma,晚于该地区蛇绿岩(336~503Ma)、岛弧火山岩(320~322Ma)、岛弧花岗岩(316~328Ma)和含矿斑岩侵入体(326~334Ma)的年龄,与A型花岗岩和双峰式火山岩(284~294Ma)的年龄基本一致,而且白鑫滩岩体单斜辉石的化学成分与拉张裂谷环境的堆晶岩相似,因此推断白鑫滩岩体形成于后碰撞拉张环境。
英文摘要:
      There are a lot of mafic-ultramafic rocks and magmatic sulfide deposits have been found in the east of Kumutage sand ridge since the 1970s, while in the west of which there has been no prospecting breakthrough yet. The Baixintan Ni-Cu sulfide-bearing mafic-ultramafic intrusion was discovered in the west part of Kumutage sand ridge in recent years, but the studies of it are relatively weak. The objective of this paper is going to constrain the petrogenesis of Baixintan intrusion by analyzing its chronology, major elements, trace elements and Sr-Nd isotope data. The variations of the mineral grain size and content in different lithofacies indicate that the Baixintan intrusion was formed by three magmatic stages. The first stage is the hornblende gabbro at the top of the intrusion. The second stage contains the olivine gabbro, plagioclase lherzolite and Pl-bearing olivine websterite, whose mineral contents change gradually. The third stage is the gobbro at the bottom of the intrusion, with smaller mineral grain size than the hornblende gabbro. The Baixintan intrusion has the similar trace element partition pattern with the Huangshandong and Huangshanxi intrusions. They are characterized by enrichment in the large ion lithophile elements (Rb, Ba, U, K) and depletion in high field-strength elements (Nb, Ta, Ti). The REE pattern shows a slight enrichment in LREE relative to HREE. These geochemistry characteristics are similar with those of island-arc volcanic rock. The εNd(t) (2.84~5.05) and (87Sr/86Sr)(t) (0.704113~0.705682) of the Baixintan rocks ploting between the asthenosphere mantle and lithospheric mantle suggest that the primary magma of the intrusion was the product of interaction between lithosphere and asthenosphere. However, compared with Huangshandong and Huangshanxi intrusions, the Baixintan intrusion has higher incompatible elements contents, lower εNd(t) value and La/Ba (0.02~0.15) ratio, higher (87Sr/86Sr)(t) value and La/Nb (2.00~3.33) ratio indicating that there was less involvement of upwelling asthenospheric mantle in the Baixintan intrusion relative to the Huangshandong and Huangshanxi intrusions. The olivine gabbro in Baixintan intrusion has an age of 287±3Ma which is younger than age of the ophiolite (336~503Ma), island arc volcanic rocks (320~322Ma), island arc granite (316~328Ma) and porphyry intrusion (326~334Ma) in this area, but contemporary with the age of A-type granite and bimodal volcanic rocks (284~294Ma). In addition, the chemical composition of clinopyroxene of Baixintan intrusion is similar with the mafic-ultramafic cumulate formed in extensional rift environment. These features indicate that Baixintan intrusion was formed in an extensional environment after the collision.
关键词:库姆塔格沙垅以西  白鑫滩镁铁-超镁铁岩体  Sr-Nd同位素  岩石圈地幔  后碰撞拉张  东天山
投稿时间:2017-06-28  修订日期:2018-02-01
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