Formation mechanism of Archean oceanic and continental crusts

太古代洋壳和陆壳的形成机制

• 批准号: 05402022
• 负责人: MARUYAMA Shigenori
• 金额: $ 21.82万
• 依托单位: Department of Earth and Planetary Sciences, Tokyo Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (A)
• 财政年份: 1993
• 资助国家: 日本
• 起止时间: 1993 至 1995
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-05402022/
• 关键词: Archean plate tectonics; oceanic crust; continental crust; hot spot; komatiite; slab melting; potential mantle temperature; TTG; 中央海嶺玄武岩; 花崗岩; マントル組成; 地殻; 太古代テクトニクス; 海洋地殻形成過程; マントルポテンシャル温度; グリーンランドイスア; 西オーストラリアピルバラ; 太古代オフィオライト; 海洋マントル

Through the detailed field mapping in the Archean orogenic belts of the 3.8 Ga Isua supracrustal belt, West Greenland, 3.5Ga Marble Bar and North Pole regions in eastern Pilbara, 3.3Ga Cleaverville region in western Pilbara, and 2.5Ga Hamersley region in southem Pilbara in Western Australia, Archean MORB,OIB and TTG were identified and collected systematically. For the identification of tectonic setting for each igneous rock, the principle of accretionary geology was applied. Primary magma composition, its temperature, and source mantle composition for each tectonic setting in the Archean time, were estimated, and the following conclusions were led ;(1) Formation mechanism of Archean oceanic crust at spreading center is essentially same as that of modern Earth, however, the details are slightly different depending on hotter Archean mantle. For example, the thickness of oceanic crust was 2-3 times thicker (ca.20km) than today.(2) Archean hot spot magma was generated from ascending mantle plume about 400 C higher than that of modern Iceland, by which specific magma low-Al komatiite was formed only in Archean time.(3) Source mantle had already been differentiated even at 3.8Ga among mid-oceanic ridge, mantle wedge, and hot spot.(4) Archean mantle was richer in crustal component than today, e.g., Mg value of olivine was 85 in the Archean (cf.89 in the modern Earth).(5) Archean continental crust was formed through the slab-melting. REE abundance and concentration of Archean TTG zoned plutons suggest that the Phanerozoic TTG was also formed by slab-melting by subduction of young oceanic lithosphere.

通过对西澳大利亚3.8Ga Isua表壳带、西格陵兰、皮尔巴拉东部3.5Ga Marble Bar和North Pole地区、皮尔巴拉西部3.3Ga Cleaverville地区和皮尔巴拉南部2.5Ga哈默斯利地区太古宙造山带的详细野外填图，系统识别和采集了太古宙MORB、OIB和TTG。为了确定每种火成岩的构造环境，应用了增生地质学原理。估算了太古代各构造背景下的原始岩浆成分、温度和源区地幔成分，得出以下结论：（1）太古代扩张中心洋壳的形成机制与现代地球基本相同，但因太古代地幔温度不同而略有不同。例如，洋壳的厚度是今天的2-3倍（约20公里）。(2)太古宙热点岩浆是由比现代冰岛高400 ℃的上升地幔柱产生的，只有在太古宙时才形成特定的低铝科马提岩。(3)洋中脊、地幔楔和热点区的源幔早在3.8Ga就已分异。(4)太古代地幔的地壳成分比现今丰富，太古代橄榄石的Mg值为85（现代地球为89）。(5)太古代陆壳是通过板片熔融作用形成的。太古代TTG分带岩体的稀土元素丰度和富集度表明，太古代TTG也是由年轻的大洋岩石圈俯冲而形成的。

项目成果

A.P.NUTMAN,H.HAGIYA and S.MARUYAMA: "SHRIMP U-Pb single zircon geochronology of a Proterozoic mafic dyke,Isukasia,southern West Greenland" Bulletin of the Geological Society of Denmark. 42. 17-22 (1995)

A.P.NUTMAN、H.HAGIYA 和 S.MARUYAMA：“西格陵兰伊苏卡西亚元古代镁铁岩脉的 SHRIMP U-Pb 单锆石地质年代学”丹麦地质学会公报。

A.Tomiya and E.Takahshi: "Reconstruction of an Evolving Magma Chamber beneath Usu Volcano since the 1663 Eruption" Journal of Petrology. 30-3. (1995)

A.Tomiya 和 E.Takahshi：“自 1663 年喷发以来乌珠火山下方不断演化的岩浆房的重建”《岩石学杂志》。

Kumazawa,M. and Maruyama,S.: "Whole earth tectonics" The Jounal of the Geological Society of Japan. 100. 81-102 (1994)

熊泽，M.

K.Shinotsuka,H.Hidaka and M.Ebihara: "Detailed abundances of rare earth elements,thorium and uranium in chondritic meteorites : An ICP-MS study" Meteoritics. 30. 694-699 (1995)

K.Shinotsuka、H.Hidaka 和 M.Ebihara：“球粒陨石中稀土元素、钍和铀的详细丰度：ICP-MS 研究”陨石学。

A. Tomiya and E. Takahashi: "Reconstruction of an Evolving Magma Chamber beneath Usu Volcano since the 1663 Eruption" JOURNAL OF PETROLOGY. vol. 30 no. 3. 617-636 (1995)

A. Tomiya 和 E. Takahashi：“自 1663 年喷发以来乌珠火山下方不断演化的岩浆房的重建”《岩石学杂志》。