新疆卡鲁安硬岩型锂矿床花岗岩与伟晶岩成因关系:锆石U- Pb定年、Hf- O同位素和全岩地球化学证据
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本文为国家重点研发计划“深地资源勘查开采”专项“锂能源金属矿产基地深部探测技术示范”项目(编号2017YFC0602700)“同位素地球化学与配套深部探测技术研究”课题(编号2017YFC0602705)和东华理工大学高层次人才引进配套经费(编号1410000425)联合资助的成果。


Genetic relationship between granite and pegmatite in Kaluan hard- rock- type lithium deposit in Xinjiang: results from zircon U- Pb dating, Hf- O isotopes and whole- rock geochemistry
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    摘要:

    卡鲁安锂矿床位于新疆阿尔泰造山带,是中国主要的稀有金属矿床产地之一,但前人工作程度较低、研究工作较少,其岩石成因和成矿机制有待于深入系统研究。文章系统研究了新疆卡鲁安含矿伟晶岩、无矿伟晶岩、外围花岗岩、外围伟晶岩、角岩、片岩、板岩等全岩样品的主量元素、稀土微量元素、Pb- Sr- Nd同位素以及锆石U- Pb定年和Hf- O同位素,旨在揭示卡鲁安矿区花岗岩与伟晶岩形成时代、岩浆起源及其演化过程,进而探讨两者之间的成因联系。年代学数据显示,卡鲁安矿区外围黑云母花岗岩、含矿伟晶岩和外围伟晶岩锆石SIMS U- Pb年龄分别为407. 9±2. 3Ma( n =25,MSWD=1. 4)、205. 0±12. 0Ma( n =6,MSWD=2. 2)和205. 0 Ma。外围黑云母花岗岩以高SiO2(71. 16%~75. 39%)、高CaO(1. 15%~1. 85%)、低Fe2O3/FeO (<0. 4)、过铝质(A/CNK=1. 04~1. 09) 和富碱性暗色矿物(>8%)等为特征。在稀土微量元素组成方面,具有弱分异的Zr/Hf(25~55)和Nb/Ta(5. 4~8. 8)比值,相对富集Rb、Th、U、Pb、Hf和LREEs,亏损Ba、Nb、Sr、P、Ti等元素,为典型的弱分异S型花岗岩,其源岩可能为一套变质沉积岩。在Hf- O同位素组成方面,含矿伟晶岩( ε Hf( t )=-0. 2~2. 0, δ 18O=7. 88‰~10. 87‰)和外围伟晶岩( ε Hf( t )=-0. 7~8. 1, δ 18O=6. 87‰~9. 48‰)与外围黑云母花岗岩( ε Hf( t )=1. 3~7. 4, δ 18O=8. 62‰~10. 08‰)具有一致性,指示含矿伟晶岩和外围伟晶岩与外围黑云母花岗岩可能具有相同的物质源区。黑云母花岗岩与片岩、板岩具有类似的稀土微量元素配分模式、类似的Pb- Sr- Nd同位素组成和Nd同位素模式年龄,指示由片岩、板岩部分熔融产生的;同时,含矿伟晶岩和无矿伟晶岩也展现出类似的稀土元素和微量元素配分模式,但其∑REE含量明显低于外围黑云母花岗岩,表明这些伟晶岩可能与外围黑云母花岗岩具有成因关系。但黑云母花岗岩比伟晶岩成岩时代早近200 Ma,所以伟晶岩不是外围黑云母花岗岩结晶分异的产物。值得关注的是2件含矿伟晶岩与片岩、板岩具有类似的稀土微量元素配分模式、类似的Pb- Sr- Nd同位素组成和Nd同位素模式年龄,表明伟晶岩也与片岩、板岩部分熔融有关。外围伟晶岩、含矿伟晶岩和无矿伟晶岩的CaO/Na2O比值(0. 01~0. 19)指示其物源是以泥质岩为主;而黑云母花岗岩CaO/Na2O比值(0. 36~0. 51)指示源区以砂屑岩为主。综上所述,本文认为黑云母花岗岩与伟晶岩是由相同源岩的不同岩性(贫黏土的碎屑岩与富黏土的泥质岩)经不同时代构造演化的产物,其源岩均来自库鲁木提群(S2- 3 KL )的片岩和板岩,具有密切的亲缘关系。

    Abstract:

    The Kalu’an lithium deposit is located in the Altay orogenic belt in Xinjiang, which is one of the main rare metal deposits in China. Due to less research work in the Kalu’an lithium deposit, its petrogenesis and metallogenic mechanisms need to be systematically studied. In this paper, results of major elements, trace elements, rare earth elements (REEs) and Pb- Sr- Nd isotopes analyses of spodumene- bearing pegmatites, spodumene- barren pegmatites, outer granites, outer pegmatites, hornstones, schists and slates, and zircon U- Pb and Hf- O isotopic data of outer granites, spodumene- bearing pegmatites and outer pegmatites from the hard- rock- typelithium deposit in Kalu’an, Xinjiang are used to determine the formation age, magmatic origin and evolutionary process of granite and pegmatite, and to further investigate their genetic relationship. Geochronological data indicate that the SIMS U- Pb ages of zircons from the outer biotite granites, spodumene- bearing pegmatites and outer pegmatites are 407. 9±2. 3 Ma ( n =25, MSWD=1. 4), 205. 0±12. 0 Ma ( n =6, MSWD=2. 2), and 205. 0 Ma respectively. The outer biotite granites from Kalu’an are characterized by high SiO2 (71. 16%~75. 39%), CaO (1. 15%~1. 85%), low Fe2O3/FeO (<0. 4). They are also peraluminous (A/CNK=1. 04~1. 09) and contain alkaline dark minerals (>8%). In terms of trace and REE compositions, outer biotite granites have weakly differentiated Zr/Hf (25~55) and Nb/Ta (5. 4~8. 8) values, are relatively enriched in Rb, Th, U, Pb, Hf and LREEs, and depleted in Ba, Nb, Sr, P and Ti. These geochemical features indicate that Kalu’an biotite granites belong to typical weakly differentiated S- type granites, whose source rocks may be a set of metamorphic sedimentary rocks. Spodumene- bearing pegmatites and outer pegmatites have consistent Hf- O isotopic compositions with outer biotite granites: ε Hf( t )=-0. 2~2. 0 and δ 18O=7. 88‰~10. 87‰ for spodumene- bearing pegmatites, ε Hf( t )=-0. 7~8. 1 and δ 18O=6. 87‰~9. 48‰ for outer pegmatites, and ε Hf( t )=1. 3~7. 4 and δ 18O=8. 62‰~10. 08‰ for biotite granites, suggesting that they may have the same source region. Outer granites from Kalu’an have similar REE and trace element patterns, Pb- Sr- Nd isotope composition, and Nd isotope pattern age with those of schists and slates, implying that they were generated by partial melting of schists and slates.Meanwhile, spodumene- bearing pegmatites and spodumene- barren pegmatites also show similar REE and trace element patterns, but their ΣREE contents are significantly lower than those of outer biotite granites, indicating that these pegmatites may have a genetic relationship with outer biotite granites. However, the formation ages of outer biotite granites are nearly 200 Ma earlier than those of pegmatites, suggesting that the pegmatites are not the products of crystalline differentiation of outer biotite granites.It is noteworthy that the two spodumene- bearing pegmatites have similar REE and trace element patterns, Pb- Sr- Nd isotope composition, and Nd isotope pattern age with those of schists and slates, implying that pegmatites are related to partial melting of schists and slates. The CaO/Na2O ratio values (0. 01~0. 19) of outer pegmatites, spodumene- bearing pegmatites and spodumene- barren pegmatites indicate that their source region is dominated by argillaceous rock; while the CaO/Na2O ratio values (0. 36~0. 51) of biotite granites indicate that their source region is dominated by arenite. Based on the above- mentioned research results, we suggest that biotite granites and pegmatitesare the products of different lithologies (clay- poor clastic rocks versus clay- rich argillaceous rocks) of the same source rock through different tectonic evolution in different ages, and their source rocks could be S2- 3 KL schists and slates with close genetic relationship.

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刘涛,田世洪,王登红,张玉洁,李贤芳,侯可军,杰肯·卡里木汗,张忠利,王永强,赵悦,秦燕.2020.新疆卡鲁安硬岩型锂矿床花岗岩与伟晶岩成因关系:锆石U- Pb定年、Hf- O同位素和全岩地球化学证据[J].地质学报,94(11):3293-3320.
LIU Tao, TIAN Shihong, WANG Denghong, ZHANG Yujie, LI Xianfang, HOU Kejun, JIEKEN·Kalimuhan, ZHANG Zhongli, WANG Yongqiang, ZHAO Yue, QIN Yan.2020. Genetic relationship between granite and pegmatite in Kaluan hard- rock- type lithium deposit in Xinjiang: results from zircon U- Pb dating, Hf- O isotopes and whole- rock geochemistry[J]. Acta Geologica Sinica,94(11):3293-3320.

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  • 收稿日期:2020-05-20
  • 最后修改日期:2020-08-27
  • 录用日期:2020-08-30
  • 在线发布日期: 2020-10-14
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