Magmatic and tectonic development of the western Aleutians: An oceanic arc in a strike‐slip setting
Magmatic and tectonic development of the western Aleutians: An oceanic arc in a strike‐slip setting
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西阿留申群岛的岩浆和构造发育：走滑环境中的大洋弧
DOI：
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
R. Kay
中科院分区：
文献类型：
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作者：
G. Yogodzinski;J. Rubenstone;S. Kay;R. Kay
阿留申群岛西部阿图岛古近纪基底系列以拉斑玄武岩为主，其化学成分与洋中脊玄武岩相似（MORB; La/Yb> 2，Nd >+10.0，206Pb/204 Pb < 18.4）。这些玄武岩在“开放”岩浆系统中演化。同生流纹花岗岩和钠长花岗岩在化学上类似于现代洋脊的火山岩（例如，冰岛，加拉帕戈斯传播中心）。化学弧型拉斑玄武岩的出现，与高的Th/La和La/Ta相对MORB，表明一个亏损的MORB样地幔源是由俯冲组件的改造。阿图岛地下室系列不是异地的。地质和构造的限制意味着形成在弧相邻，transtensional裂谷，在一个走滑制度，建立了1.43亿年。前这种裂谷作用可能在1043 Ma至15 Ma之间产生了大部分阿留申西部地壳。随后，阿图岛和整个阿留申群岛西部爆发了少量富含晶体的安山岩和英安岩。这些强烈的钙碱性岩石（FeO*/MgO = 1.1，CaO/Al 2 O3 = 0.35，SiO2为65%）在化学性质上类似于皮普火山的镁质安山岩，皮普火山是一座热液活动海山，位于现代西部弧的广泛压扭体制内的小型扩张结构之上。据推测，这种挤压转换的背景已经在大约1500万年前的整个阿留申群岛西部建立起来。前从拉斑玄武岩岩浆活动在transstensional政权强烈calcalcalkaline岩浆活动在压扭政权的开关可能是由于堵塞的阿留申-堪察加交界处与浮力，俯冲相关的岩石。这些断层可能起源于东部，并沿西弧沿着走滑运动搬运。
The Paleogene Basement Series on Attu Island in the Western Aleutians is dominated by tholeiitic basalts chemically similar to mid-ocean ridge basalts (MORB; La/Yb ∼ 2, ϵNd > +10.0, 206Pb/204Pb < 18.4). These basalts evolved in “open” magma systems. Contemporaneous rhyolites and albite granites are chemically analogous to silicic volcanic rocks of modern ocean ridges (e.g., Iceland, Galapagos Spreading Center). The occurrence of chemically arc-type tholeiitic basalts, with high Th/La and La/Ta relative to MORB, suggests that a depleted MORB-like mantle source was variably modified by a subduction component. The Attu Basement Series is not allochthonous. Geological and tectonic constraints imply formation in arc-adjacent, transtensional rifts that developed in a strike-slip regime that was established ∼43 m.y. ago. Rifting of this kind may have produced much of the Western Aleutian crust between ∼43 and 15 Ma. Subsequently, small volumes of crystal-rich andesite and dacite were erupted on Attu Island as well as throughout the Western Aleutians. These strongly calcalkaline rocks (FeO*/MgO∼1.1, CaO/Al2O3 ∼0.35 at 65% SiO2) are chemically akin to magnesian andesites of Piip Volcano, a hydrothermally active seamount that overlies small dilational structures within the broadly transpressional regime of the modern western arc. This transpressional setting is inferred to have been established throughout the Western Aleutians approximately 15 m.y. ago. The switch from tholeiitic magmatism in a transtensional regime to strongly calcalkaline magmatism in a transpressional regime may have resulted from clogging of the Aleutian-Kamchatka junction with buoyant, subduction-related terranes. These terranes probably originated to the east and were transported by strike-slip motion along the western arc.