下寒武统黑色页岩金属富集机理与小行星撞击  

Black Shale Metal Enrichment of the Lower Cambrian and Asteroid Impact

作　　者：丁卫平[1] 代晓光[1] 邓宇飞[1] 王富强[1] DING Wei-ping;DAI Xiao-guang;DENG Yu-fei;WANG Fu-qiang(Geological Institute of China Chemical Geology and Mine Bureau,Beijing 100101,China)

机构地区：[1]中化地质矿山总局地质研究院,北京100101

出　　处：《科学技术与工程》2023年第21期8945-8958,共14页Science Technology and Engineering

基　　金：中化地质矿山总局地质研究院2021年研究项目(DYKJ202101)。

摘　　要：扬子地台寒武系下统存在富含V、Ni、Mo和铂族元素(platinum group element, PGE)等的黑色页岩,局部地区有U或者Ba、Hg、As等的富集,研究这些元素富集机理有利于寻找相关矿产或者探究地质事件。6 500万年前的小行星撞击地球产生了高PGE含量的地层或者化石,依据这一事实和陨石的特征及其他地质地球化学证据,推断下寒武统黑色页岩中Ni-Mo-PGE富集是陨石撞击结果,PGE中的Ir、Os富集最明显是因为二者最抗淋滤。U在康滇地轴东侧黑色页岩中最高可达480×10^(-6),因康滇地轴本身就存在混合型铀矿,推测黑色页岩中U来自它的风化。据V和Ba-Hg-As等的地化特性,认为V富集是受生物活动影响,但因V易于在热泉水中富集,故寒武纪早期泛非运动的构造-热事件可导致V富集成矿,Ba、Hg、As也因该事件产生构造裂隙后,它们优先随热液沿裂隙上升富集,并在海底局部成矿。此外,5.65亿年前的埃迪卡拉动物群发生地基本上就是5.8亿年前小行星撞击地点,提出此次行星撞击可能与埃迪卡拉生物群出现存在因果关系。由于在中国存在寒武纪澄江生物群大爆发事件,推测该次生物大爆发之前存在的下寒武统黑色页岩也存在陨石撞击痕迹。寒武系下统的含岩屑细砂岩夹黑色页岩甚至砾岩,反映了黑色页岩沉积时存在的突变沉积环境,加上其他地球化学特征也支持小行星撞击说。There is black shale rich in V,Ni,Mo and platinum group element(PGE)at the Lower Cambrian Formation in Yangtze Platform,and local U or Ba,Hg and As are enriched.The enrichment mechanism of these elements study is conducive to finding relevant minerals or probing geological events.The asteroid impact 65 million years ago on earth produced strata or fossils with high PGE content.Based on this fact and the characteristics of the meteorite and other geological and geochemical properties,it is inferred that Ni-Mo-PGE enrichment in the lower Cambrian black shale is the result of meteorite impact,and Ir and Os enrichment is most obvious because they are most resistant to eluviation.U reaches up to 480×10^(-6) in the black shale on the east side of Kangdian axis,there are some migmatite uranium deposit in Kangdian axis.U in the shale comes from the weathering of this deposit.Based on the geochemical characteristics of V and Ba-Sb-Hg-As,V enrichment is affected by biological activities,but V is easy to enrich in hot spring water,the tectonic-thermal events(Pan-African movement)in the early Cambrian can lead to V enrichment and mineralization.Because of this event,the geological structure broke through the seabed formation,Ba,Hg,As appear in geochemical front halo,and local mineralized in the seabed.In addition,the Ediacaran biota,which occurred 565 million years ago,was basically the site of an asteroid impact 580 million years ago,so this asteroid impact may be related to biological extinction in Ediacara,due to the Cambrian Chengjiang Fossil Site outbreak in China,speculated that the Cambrian black shale also exist meteorite impact traces.The fine sandstone with debris and black shale and even conglomerate in the Lower Cambrian reflects the black shale deposition mutation deposition environment,and other geochemical characteristics also support the asteroid impact theory.

关 键 词：小行星 撞击 下寒武统 黑色页岩 金属富集 康滇地轴 铀矿 

分 类 号：P593[天文地球—地球化学]