胶东早白垩世基性脉岩岩石成因与成矿动力学驱动

发布时间：2018-05-28 06:08

  本文选题：早白垩世 + 胶东半岛　； 参考：《中国地质大学(北京)》2017年博士论文

【摘要】：在胶东半岛,广泛发育早白垩世基性脉岩群并与金矿床密切伴生。本文选取胶东早白垩世基性脉岩进行系统研究,探究脉岩成因演化和形成动力学机制,不仅为胶东半岛深部构造演化提供重要信息,而且可初步探讨基性脉岩与大规模金成矿的关系。胶东基性脉岩受区域构造控制展布,岩石类型以煌斑岩和辉绿岩为主。最新年代学研究厘定基性脉岩主要形成于早白垩世(130~110 Ma),基性脉岩均具有岛弧型基性岩浆特征,如低SiO2、高MgO、Cr和Ni含量、富集大离子亲石元素(LILE)和轻稀土元素(LREE)、亏损高场强元素(HFSE)、高(87Sr/88Sr)i比值、低?Nd(t)和?Hf(t)值,指示其来源于华北克拉通(NCC)富集岩石圈地幔。高Dy/Yb比值反映脉岩岩浆源自含角闪石二辉橄榄岩在尖晶石-石榴石相过渡区低程度部分熔融。岩浆演化过程中,脉岩岩浆经历了橄榄石和单斜辉石的分离结晶,地壳混染作用不明显。基性脉岩具有低δ26Mg值,表明其地幔源区经历了碳酸盐交代。基性脉岩具有低Os含量和高187Os/188Os值指示地幔源区经历了以流体为主的俯冲交代作用从而形成大量的富集岩脉,该富集岩脉与橄榄岩围岩发生部分熔融,熔体混合形成基性脉岩岩浆。此外,苏鲁基性脉岩与胶北基性脉岩同位素特征存在轻微差异,指示三叠纪时期扬子克拉通(YC)向NCC俯冲交代作用的影响。中生代时期,古太平洋板块向西俯冲交代改造了上覆NCC岩石圈地幔。早白垩世时期,板片回撤以及伊邪那岐板块改变俯冲方向,导致NCC东部岩石圈地幔伸展-减薄,并伴随软流圈的上涌。岩石圈地幔底部被软流圈上升所带来的热持续侵蚀而发生部分熔融,形成岛弧型基性脉岩岩浆。上涌的软流圈地幔降压熔融产生洋岛型基性脉岩岩浆。通过典型矿区基性脉岩与金矿对比研究发现,胶东基性脉岩从成矿前、成矿期到成矿后均有产出,但是脉岩形成的高峰期在成矿期;基性脉岩与金矿脉紧密伴生产出,成矿流体与基性岩浆均具有幔源特征;但基性脉岩铂族元素特征揭示,脉岩岩浆源自地幔的低程度部分熔融,导致大量的亲硫元素(PGEs和Au)留在了地幔,基性脉岩可能没有为胶东大规模金成矿提供幔源成矿物质。
[Abstract]:In Jiaodong Peninsula, the early Cretaceous basic dike rock group is widely developed and is closely associated with the gold deposit. In this paper, the early Cretaceous basic dikes in Jiaodong were studied systematically, and the genetic evolution and dynamic mechanism of the dikes were explored, which not only provided important information for the evolution of the deep structure of the Jiaodong Peninsula. Furthermore, the relationship between basic dikes and large-scale gold mineralization can be preliminarily discussed. The basic dikes of Jiaodong are controlled by regional tectonics, and the main rock types are lamprophyre and diabase. According to the latest geochronological study, the basic dikes were mainly formed in the early Cretaceous, and the basic dikes were characterized by island arc basic magma, such as low Sio _ 2, high MgO _ (2) Cr and Ni contents. The enrichment of large ion lithophile elements LILE) and light rare earth elements (LREEN), the depletion of high field strength elements (HFSEI), the high ratio of 87 Sr / 88 Sr ~ (2 +), and the values of low ~ (87) ND ~ (8) S ~ (+) and HfT) indicate that they are derived from the enriched lithospheric mantle of the North China Craton (NCCs). The high Dy/Yb ratio indicates that the dike magma originated from amphibole-bearing pyroxenite in low degree partial melting in the spinel-garnet phase transition zone. In the process of magmatic evolution, the dike rock magma experienced the separation and crystallization of olivine and clinopyroxene, and the crustal mixing was not obvious. The low 未 26Mg value of the basic dike rocks indicates that the mantle source region experienced carbonate metasomatism. The low Os content and high 187Os/188Os value of the basic dikes indicate that the mantle source region experienced fluid dominated subduction and metasomatism, resulting in the formation of a large number of enriched veins, which partially melted with the surrounding rock of peridotite. The melt mixes to form the basic dike magma. In addition, there is a slight difference in isotopic characteristics between the basic dikes of Sulu and Jiaobei, indicating the influence of the Yangtze craton (YC) subduction and metasomatism to NCC during the Triassic. During the Mesozoic, the paleo-Pacific plate subducted westward and transformed the NCC lithospheric mantle. In the early Cretaceous period the plate retreat and the change of the subduction direction of the Ixonaki plate resulted in the extension and thinning of the lithospheric mantle in the eastern part of NCC and the upwelling of the asthenosphere. The lithospheric mantle bottom is partially melted by the continuous thermal erosion caused by the rise of the asthenosphere and the island arc type basic dike magma is formed. The upwelling asthenosphere mantle depressurizes and melts to produce the oceanic island type basic dike magma. Through the comparative study of basic dikes and gold deposits in typical ore areas, it is found that the basic dikes of Jiaodong are produced from pre-metallogenic, metallogenic to post-metallogenic, but the peak of dike formation is in metallogenic period, and the basic dikes and gold veins are produced closely together. Both the ore-forming fluid and the basic magma have mantle-derived characteristics, but the elemental characteristics of the platinum group of the basic dike rocks reveal that the dike magma originated from the low degree of partial melting of the mantle, resulting in a large number of sulphophilic elements such as PGEs and Au) remaining in the mantle. Basic dikes may not provide mantle-derived minerals for large-scale gold mineralization in Jiaodong.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P588.12;P618.51
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本文编号：1945608