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Archean greenstone-tonalite duality: Thermochemical mantle convection models or plate tectonics in the early Earth global dynamics? 总被引：2，自引：0，他引：2
Mantle convection and plate tectonics are one system, because oceanic plates are cold upper thermal boundary layers of the convection cells. As a corollary, Phanerozoic-style of plate tectonics or more likely a different version of it (i.e. a larger number of slowly moving plates, or similar number of faster plates) is expected to have operated in the hotter, vigorously convecting early Earth. Despite the recent advances in understanding the origin of Archean greenstone–granitoid terranes, the question regarding the operation of plate tectonics in the early Earth remains still controversial. Numerical model outputs for the Archean Earth range from predominantly shallow to flat subduction between 4.0 and 2.5 Ga and well-established steep subduction since 2.5 Ga [Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937–940], to no plate tectonics but rather foundering of 1000 km sectors of basaltic crust, then “resurfaced” by upper asthenospheric mantle basaltic melts that generate the observed duality of basalts and tonalities [van Thienen, P., van den Berg, A.P., Vlaar, N.J., 2004a. Production and recycling of oceanic crust in the early earth. Tectonophysics 386, 41–65; van Thienen, P., Van den Berg, A.P., Vlaar, N.J., 2004b. On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth. Tectonophysics 394, 111–124]. These model outputs can be tested against the geological record. Greenstone belt volcanics are composites of komatiite–basalt plateau sequences erupted from deep mantle plumes and bimodal basalt–dacite sequences having the geochemical signatures of convergent margins; i.e. horizontally imbricated plateau and island arc crust. Greenstone belts from 3.8 to 2.5 Ga include volcanic types reported from Cenozoic convergent margins including: boninites; arc picrites; and the association of adakites–Mg andesites- and Nb-enriched basalts.Archean cratons were intruded by voluminous norites from the Neoarchean through Proterozoic; norites are accounted for by melting of subduction metasomatized Archean continental lithospheric mantle (CLM). Deep CLM defines Archean cratons; it extends to 350 km, includes the diamond facies, and xenoliths signify a composition of the buoyant, refractory, residue of plume melting, a natural consequence of imbricated plateau-arc crust. Voluminous tonalites of Archean greenstone–granitoid terranes show a secular trend of increasing Mg#, Cr, Ni consistent with slab melts hybridizing with thicker mantle wedge as subduction angle steepens. Strike-slip faults of 1000 km scale; diachronous accretion of distinct tectonostratigraphic terranes; and broad Cordilleran-type orogens featuring multiple sutures, and oceanward migration of arcs, in the Archean Superior and Yilgarn cratons, are in common with the Altaid and Phanerozoic Cordilleran orogens. There is increasing geological evidence of the supercontinent cycle operating back to 2.7 Ga: Kenorland or Ur 2.7–2.4 Ga; Columbia 1.6–1.4 Ga; Rodinia 1100–750 Ma; and Pangea 230 Ma. High-resolution seismic reflection profiling of Archean terranes reveals a prevalence of low angle structures, and evidence for paleo-subduction zones. Collectively, the geological–geochemical–seismic records endorse the operation of plate tectonics since the early Archean. 相似文献
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LITHOPROBE是加拿大的国家级地球科学研究计划。选择10个典型剖面,每个都不同程度地代表了加拿大典型的地质特征或具全球意义的重要构造过程。时间上其地质演化跨越了40多亿年漫长的地质年代。通过地震深反射技术为先锋的以及多种不同学科的综合研究,取得一系列成果,如证实3.0Ga前即发生与板块构造有关的作用,对古老岩石圈板块碰撞和新地壳形成过程进行了重大修正,揭示了若干大型矿集区的深部控矿构造的反射影像,使加拿大的地球科学研究走到世界的前列,本文拟通过较系统介绍LITHOPROBE,为我国深部探测技术与实验研究提供参考。 相似文献
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加拿大岩石圈探测计划(LITHOPROBE), 是加拿大政府为了全面了解北美大陆演化过程而设立的一个国家级地球科学研究合作项目, 主要科学目标和组织机构都是围绕对10个断面或者研究区进行研究的基础上而建立, LITHOPROBE被认为是国际上目前为止最成功的国家地学项目之一, 运用了地球物理(地震多道反射、地震折射和电磁等)、地球化学、地质年代学等各种地质方法。该计划在深部基础地质研究、矿产资源勘探、地质灾害预警、人才培养、深部探测仪器研制、重大科技专项的管理等方面均取得了很好的成果。LITHOPROBE也为世界其他国家的类似科研项目树立了模范。本文通过对LITHOPROBE项目立项过程、取得的成果、产生的社会效益和存在的问题等进行分析和研究, 希望对我国的深部探测起到借鉴作用。 相似文献
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加拿大岩石圈探测计划LITHOPROBE通过地质、地球物理、地球化学多种探测方法, 综合研究了加拿大地表至岩石圈地幔的地质结构和演化过程, 对北美最大太古代Superior Province克拉通的形成及增生研究堪称经典。2 720—2 680 Ma, Superior Province西部、中部和南部各原始地体及介于其间的晚太古代洋壳通过连续增生和碰撞拼贴为一体, 使得各地体原始排列方向及边界平移断层原始走向皆为近东西向。以3.0 Ga North Caribou地体为核心, 北侧Hudson Bay地体于2 720 Ma与其发生碰撞, 南部Winnipeg River地体于2 720—2 700 Ma与其碰撞并在English River盆地形成同造山期浊积岩; 往南, 相对年轻的Wabigoon 地体于2 710—2 700 Ma与Winnipeg River地体拼接, 更南侧的Wawa-Abitibi地体又拼贴于Wabigoon地体之上, 并在Quetico盆地形成同造山浊积岩和杂砂岩; 最南侧的Minnesota River Valley地体于2 680 Ma与其北侧地体拼接为一体, 先前洋壳俯冲于碰撞边界之下; 2 730—2 680 Ma, 在Superior Province东北部部发生了多期变形变质和增生活动, 形成该区北西走向造山带, 在Quebec中部地区形成巨大的马蹄形山系。Superior Province西部CWS和中部AG岩石圈地震剖面显示, 主要的地壳和地幔岩石圈俯冲带都向北缓倾; 以Timiskaming型砾岩沉积, 碱性岩浆岩发育, 壳源花岗岩侵位, 区域变质作用, 热液循环, 金矿脉定位以及造山后冷却诸多地质活动为特征, 2 680—2 600 Ma Superior Province发生克拉通化, 表明该时期Superior Province存在一个稳定的热扩散地幔隆起带。2 000 km规模原始地块和洋壳的增生及与之相伴的地块推覆和叠置, 揭示Superior Province各地体新太古代的拼合是一个似板块活动过程。 相似文献
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