Abstract Anorthosite-bearing layered intrusions are unique to the Archaean rock record and are abundant in the Archaean craton of southern West Greenland and the Superior Province of Canada. These layered intrusions consist mainly of ultramafic rocks, gabbros, leucogabbros and anorthosites, and typically contain high-Ca (>An70) megacrystic (2–30 cm in diameter) plagioclase in anorthosite and leucogabbro units. They are spatially and temporally associated with basalt-dominated greenstone belts and are intruded by syn-to post-tectonic granitoid rocks. The layered intrusions, greenstone belts and granitoids all share the geochemical characteristics of Phanerozoic subduction zone magmas, suggesting that they formed mainly in a suprasubduction zone setting. Archaean anorthosite-bearing layered intrusions and spatially associated greenstone belts are interpreted to be fragments of oceanic crust, representing dismembered subduction-related ophiolites. We suggest that large degrees of partial melting (25–35%) in the hotter (1500–1600 °C) Archaean upper mantle beneath rifting arcs and backarc basins produced shallow, kilometre-scale hydrous magma chambers. Field observations suggest that megacrystic anorthosites were generated at the top of the magma chambers, or in sills, dykes and pods in the oceanic crust. The absence of high-Ca megacrystic anorthosites in post-Archaean layered intrusions and oceanic crust reflects the decline of mantle temperatures resulting from secular cooling of the Earth.

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西格陵兰岛南部和加拿大苏必利尔省太古代克拉通含斜长岩层状侵入体的概述：对太古代构造的影响和巨晶斜长石的起源

摘要 含斜长岩的层状侵入体是太古代岩石记录所独有的，在西格陵兰岛南部和加拿大苏必利尔省的太古代克拉通中含量丰富。这些层状侵入体主要由超镁铁质岩、辉长岩、白辉长岩和斜长岩组成，通常在斜长岩和白辉长岩单元中含有高钙（>An70）巨晶（直径 2-30 cm）斜长石。它们在空间和时间上与以玄武岩为主的绿岩带有关，并被同向到后构造花岗岩侵入。层状侵入体、绿岩带和花岗岩类都具有显生宙俯冲带岩浆的地球化学特征，表明它们主要形成于超俯冲带环境。含有太古代斜长岩的层状侵入体和空间相关的绿岩带被解释为大洋地壳的碎片，代表与俯冲相关的蛇绿岩被肢解。我们认为，裂谷弧和弧后盆地下方较热（1500-1600°C）太古代上地幔中的大量部分熔化（25-35%）产生了浅的、千米级含水岩浆房。野外观察表明，巨晶斜长岩产生于岩浆房顶部，或大洋地壳的岩床、岩脉和豆荚中。后太古代层状侵入体和大洋地壳中没有高钙巨晶斜长岩反映了地球长期冷却导致地幔温度的下降。我们认为，裂谷弧和弧后盆地下方较热（1500-1600°C）太古代上地幔中的大量部分熔化（25-35%）产生了浅的、千米级含水岩浆房。野外观察表明，巨晶斜长岩产生于岩浆房顶部，或大洋地壳的岩床、岩脉和豆荚中。后太古代层状侵入体和大洋地壳中没有高钙巨晶斜长岩反映了地球长期冷却导致地幔温度的下降。我们认为，裂谷弧和弧后盆地下方较热（1500-1600°C）太古代上地幔中的大量部分熔化（25-35%）产生了浅的、千米级含水岩浆房。野外观察表明，巨晶斜长岩产生于岩浆房顶部，或大洋地壳的岩床、岩脉和豆荚中。后太古代层状侵入体和大洋地壳中没有高钙巨晶斜长岩反映了地球长期冷却导致地幔温度的下降。或在大洋地壳的窗台、堤坝和豆荚中。后太古代层状侵入体和大洋地壳中没有高钙巨晶斜长岩反映了地球长期冷却导致地幔温度的下降。或在大洋地壳的窗台、堤坝和豆荚中。后太古代层状侵入体和大洋地壳中没有高钙巨晶斜长岩反映了地球长期冷却导致地幔温度的下降。