Chronology and tectonic implications of Neoproterozoic blocks in the South Qinling Orogenic Belt, Central China
Chronology and tectonic implications of Neoproterozoic blocks in the South Qinling Orogenic Belt, Central China
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DOI：
10.1016/j.gr.2015.01.006
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发表时间：
2016-02
影响因子：
6.1
通讯作者：
F. Hu;Shuwen Liu;M. Santosh;Z. Deng;Wei Wang;Wanyi Zhang;Ming Yan
中科院分区：
文献类型：
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作者：
F. Hu;Shuwen Liu;M. Santosh;Z. Deng;Wei Wang;Wanyi Zhang;Ming Yan
秦岭造山带位于华北板块和扬子板块之间，由北秦岭造山带、南秦岭造山带和扬子板块北方边缘组成。详细的地质和年代学研究揭示了SQB中、西段不同规模的新元古代地块，包括马道地块（MDB）、糜浑镇岩体（MHI）、郑沟地块（ZGB）和冷水沟地块（LSB），它们构成了基底陆块的一个东西向新元古代隆起带。这些区块主要由四个岩性组组成。第1组主要由LSB中的闪长岩组成，其中锆石的加权平均206 Pb/238 U年龄约为1.25 μ m。941年。第2组主要由MHI和LSB中的角闪辉长岩和闪长岩组成，形成于约1000年。公元885年第3组包括MDB、MHI、ZGB和LSB中的块状闪长岩、石英闪长岩、英云闪长岩、花岗闪长岩和二长花岗岩，它们侵位于约2000年。785-740 Ma。第4组为角闪石辉长岩，侵位年龄约为2000年。详细的全岩地球化学和锆石Hf同位素研究表明：（1）第1群闪长岩是亏损地幔部分熔融的产物，亏损地幔被板片熔体富集，其母岩浆受到地壳物质的混染。(2)第2群辉长岩是由亏损地幔部分熔融形成的，而闪长岩则是辉长岩岩浆分离结晶的产物。(3)根据岩石组合和锆石Hf同位素特征，可进一步将第3群划分为块状闪长岩、石英闪长岩、英云闪长岩、花岗闪长岩和二长花岗岩（DTGM）两个亚群，另一个亚群由片麻状石英闪长岩和花岗闪长岩组成。其中，DTGM是通过来自亏损地幔楔的熔融物之间的岩浆混合的板片衍生的流体和熔融物从年轻的来源，随后经历了角闪石为主的分馏，而片麻状花岗岩类通过部分熔融增厚的下地壳贫化地幔熔融物的污染。(4)第4群辉长岩起源于亏损的岩石圈地幔，该地幔被软流圈幔源物质贡献的板状熔体和流体富集。结合前人对SQB中新元古代地块和YZC北方边缘基底地块的研究资料，我们新的地质、年代学和地球化学数据表明SQB中存在一个大型新元古代隆起带，该隆起带被古生代-中生代岩浆活动和变形破坏。新元古代SQB隆起带可能在勉略洋形成时与扬子大陆北方边缘分离，并可能在活动大陆边缘背景和随后的大陆裂谷背景下演化，伴随着显著的地壳生长。岩浆活动还形成了重要的新元古代矿床，并为中生代一些主要矿床提供了物质来源。
The Qinling Orogenic Belt (QOB) located between the North China Craton (NCC) and the Yangtze Craton (YZC) is composed of the North Qinling Belt (NQB), the South Qinling Belt (SQB) and the northern margin of the YZC. Detailed geological and geochronological investigations have revealed distinct Neoproterozoic blocks of various scales in the middle and western segments of the SQB, including the Madao block (MDB), Mihunzhen intrusion (MHI), Zhenggou block (ZGB), and Lengshuigou block (LSB) which constitute an east-west trending Neoproterozoic uplift zone of the basement continental blocks. These blocks are mainly composed of four lithological groups. Group #1 consists mainly of diorites in the LSB, the zircons from which yield a weighted mean206Pb/238U age of ca. 941 Ma. Group #2 is chiefly composed of hornblende gabbros and diorites in the MHI and LSB, which were formed at ca. 885 Ma. Group #3 comprises massive diorites, quartz diorite, tonalites, granodiorites, and monzogranites in the MDB, MHI, ZGB and LSB, which were emplaced during ca. 785–740 Ma. Group #4 is composed of hornblende gabbros with an emplacement age of ca. 667 Ma in the ZGB.Detailed whole-rock geochemical and zircon Hf isotopic studies reveal the following: (1) The diorites of Group #1 were produced by partial melting of depleted mantle which was enriched by slab-derived melts, with the parental magmas contaminated by crustal materials. (2) The gabbros of Group #2 were derived from the partial melting of depleted mantle enriched by slab-derived melts and the diorites are the fractional crystallization products of the gabbroic magmas. (3) Group #3 which can be further sub-divided based on lithological assemblages and zircon Hf isotopic features into two subgroups, one representing massive diorites, quartz diorite, tonalites, granodiorites, and monzogranites (DTGMs) and the other composed of gneissic quartz diorites and granodiorites. Among these, the DTGMs were derived through magma mixing between melts derived from the depleted mantle wedge altered by slab-derived fluids and melts from juvenile sources, which subsequently underwent amphibole-dominated fractionation, whereas the gneissic granitoids formed through partial melting of thickened lower crust contaminated by depleted mantle melts. (4) The gabbros of Group #4 originated from a depleted lithospheric mantle that was enriched by slab-derived melts and fluids with contribution of asthenospheric mantle-derived materials. In conjunction with data from previous studies on the Neoproterozoic blocks in the SQB and basement blocks in the northern margin of the YZC, our new geological, geochronological and geochemical data suggest a large Neoproterozoic uplift zone in the SQB, which was destructed by Paleozoic to Mesozoic magmatism and deformation. The Neoproterozoic uplift zone of the SQB might have been separated from the northern margin of the YZC during the formation of the Mianlue Ocean, and might have evolved under an active continental margin setting and subsequent continental rift setting accompanied by significant crustal growth. The magmatism also resulted in the formation of important Neoproterozoic ore deposits and supplied the material sources for some of the major Mesozoic ore deposits.