Radical change in tectonic regime and paleo-environment at the end of Neoarchean evidenced by a unique metal co-existing deposit  

新太古代末构造体制和古环境的关键转变——独特的共生金属矿床证据

作　　者：Mingguo Zhai 翟明国(State Key Laboratory of Continent Dynamics,Northwest University,Xi'an 710075,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Planetary and Earth Science,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]State Key Laboratory of Continent Dynamics,Northwest University,Xi'an 710075,China [2]State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [3]College of Planetary and Earth Science,University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Science Bulletin》2022年第23期2438-2448,M0004,共12页科学通报（英文版）

基　　金：supported by the Major Project of the National Natural Science Foundation of China (41890834 and 92162323);the Strategic Pilot Technology (B-type) Project of Chinese Academy of Sciences (CAS) (XDB18030205);the Key International Program of CAS (132A11KYSB20180042);the Key Research Program of Frontier Science, CAS (QYZDY-SSW-DQC017)。

摘　　要：Banded iron formation and Cu-Zn sulfide deposits within volcanic-argillaceous sequences(as volcanogenic massive sulphide deposits(VMS)-like type) occur together in the Qingyuan greenstone belt of the North China Craton,recording the first appearance of oxidized ores and sulfide ores co-existing in the early Earth.The unique metal co-existing deposits should meet two requirements:tectonic setting and sedimentary environment.As regards to tectonic setting,plate-like tectonics might have started since the end of the Neoarchean because continents had grown large enough and there occurred volcanic arcs and backarc basins similar to modern ones in a way.Partial melting of subducted continental crust is conductive to providing ore-forming elements.As for sedimentary environment,late Neoarchean seawater was rich in Fe^(2+) and anoxic.Instantaneous oxidation of the seawater resulted possibly from frequent submarine volcanic eruptions and facilitated precipitation of the banded iron formation.At this point,it is also favorable for the enrichment of Cu and Zn ions in seawater.The VMS-like deposits tended to form when the seawater was reduced again.Studies of isotopic elements like sulfur,oxygen,iron and silicon support the above geological processes.It is shown that the geologic conditions only existed in the late Neoarchean and Paleoproterozoic for a short period of time.The banded iron formations disappeared around 1.85 Ga,and the associated sulfide metal deposits also became dominant sedimentary exhalative deposits in the meso-Neoproterozoic Boring Billion,as a result of increasing oxidation of the oceans and the increasing maturity of the continental crust.This study is significant not only for decoding metallogenic genesis but also helping understand rapid change in Precambrian tectonic regimes and Earth’s environments.在地球特别是大陆演化的历史上,物质的演化是关键证据.岩石是最有效载体和研究对象.我国东北的新太古代条带状铁建造(BIF)和产于火山-泥质岩中的块状Cu-Zn硫化物矿床(VMS-like),提供了氧化矿床和硫化矿床共生的实例.这种独特共生矿床的形成需要构造机制和地球环境条件的双重控制:类似现代板块构造的壳内俯冲和陆壳部分熔融,可以提供成矿元素;频繁的火山喷发导致的光化学等复杂作用使得海水氧化程度发生变化,能够提供成矿的条件.上述构造和古环境的耦合只出现在新太古代末-古元古代初有限的时间段内,延续到大氧化事件的结束(~1.85 Ga).它们的时代~2.5 Ga,正是太古宙与元古宙的分界年龄,指示了地球历史上绝无仅有的巨大变革.

关 键 词：Co-existing metal deposits Late Neoarchean Indicator of transition Tectonic regimes Earth’s environments 

分 类 号：P534.2[天文地球—古生物学与地层学]