江苏徐州白露山岩管地质特征及与金刚石成因关系探讨  

Geological characteristics of the Bailushan rock mass and its relationship with diamond genesis in Xuzhou, Jiangsu Province

作　　者：周琦忠 张琪[1] 冯学知[1] 王博 邱磊 王国强[1] 黄友波[1] ZHOU Qizhong;ZHANG Qi;FENG Xuezhi;WANG Bo;QIU Lei;WANG Guoqiang;HUANG Youbo(NO.5 Geological Team of Jiangsu Geology and Mineral Bureau,Xuzhou,Jiangsu,221004)

机构地区：[1]江苏省地质矿产局第五地质大队,江苏徐州221004

出　　处：《地质学报》2020年第9期2748-2762,共15页Acta Geologica Sinica

基　　金：江苏省地质矿产勘查局地质勘查基金项目“江苏省徐州市吴桥-石匣地区原生矿普查”(编号苏地矿发[2016]86号、苏地矿发[2017]96号);江苏省地质矿产勘查局科研项目“苏北岩石圈地幔及金刚石找矿研究”(编号苏地矿发[2018]82号文)资助成果。

摘　　要：近年来,在开展苏北原生金刚石找矿时,从白露山岩管中选获了2颗大颗粒金刚石,粒径均大于1mm,分别属ⅠaB型和ⅠaA型,这是苏北地区首次发现的大颗粒原生金刚石。本文在对白露山岩管的岩石学、岩石地球化学、锆石U-Pb同位素年龄以及金刚石特征等描述基础上,对岩管成因进行了分析,并探讨了该岩管与金刚石的关系。结果表明:白露山岩管的形态反映了裂隙-中心式喷发的隐爆火山岩岩管的特征,其主体岩性为橄榄玄武岩,角砾成分包括橄榄玄武岩、灰岩、凝灰质、闪斜煌岩和片麻岩等。橄榄玄武岩总体具有高镁、低铝、低钛的特点,整体富集大离子亲石元素和LREE,高场强元素和HREE略亏损,与洋岛玄武岩(OIB)较为接近,但存在与岛弧玄武岩(IAB)相似的强烈Nb负异常特征。其形成于中新生代太平洋板块俯冲、华北克拉通岩石圈减薄背景下,起源于深约75~100 km的受俯冲流体交代的岩石圈地幔,在石榴子石稳定域由角闪石石榴子石二辉橄榄岩经2%~5%的部分熔融而来。在岩浆演化过程中遭受了一定程度的地壳混染和分离结晶作用,然后在板内快速拉张的环境下,橄榄玄武岩浆沿构造薄弱地带侵入至地壳浅部隐爆形成,且在上升过程中捕获了大量的围岩角砾。金刚石不是白露山橄榄玄武岩的结晶产物,而可能是来自捕获的被徐宿弧形构造推覆掩盖的古生代含金刚石母岩。Two large particle diamonds were selected from the Bailushan rock pipe during recent primary diamond prospecting in northern Jiangsu. The diamonds are of type ⅠaB and ⅠaA respectively and their particle sizes are greater than 1 mm. They are the first large particle primary diamonds discovered in the northern Jiangsu. In this paper, based on petrology, rock geochemistry, zircon U-Pb isotope age, and diamond characteristics of the Bailushan rock pipe, the genesis of the rock pipe is inferred and its relationship with diamonds is discussed. The result shows that the morphology of the Bailushan rock pipe reflects the characteristics of the fissure-central eruption of the hidden explosion volcanic rock pipe. Its main lithology is olivine basalt and its breccia composition includes olivine basalt, limestone, tuff, lamprophyre and breccia. Olivine basalt has the characteristics of high magnesium, low aluminum and low titanium. These characteristics are similar to the Ocean Island Basalt as the lithophile elements and light rare earth are enriched, but high field strength elements and heavy rare earth are slightly less. However, there is a strong Nb negative anomaly feature that is similar to the Island Arc Basalt. It was formed against the background of Meso-Cenozoic Pacific plate subduction and the lithospheric thinning of the North China Craton. The lithospheric mantle originated from a depth of about 75~100 km and was replaced by subduction fluid. It was partially melted from 2%~5% hornblende garnet diorite in the spinel stability zone and has suffered a certain degree of crustal contamination, separation and crystallization during magma evolution. Subsequently, olive basalt magma intruded into the shallow crustal formation along the weak structural zone under the environment of rapid tension in the plate. A large amount of surrounding rock breccia was captured during the ascent. Diamonds are not a crystalline product of olivine basalt in Bailushan. They may be from the captured Paleozoic diamond-bearing parent r

关 键 词：江苏徐州 白露山岩管 橄榄玄武岩 岩石地球化学 岩石成因 金刚石 

分 类 号：P619.241[天文地球—矿床学]