Paleogene evolution of the Kodiak Islands, Alaska: Consequences of ridge‐trench interaction in a more southerly latitude
Paleogene evolution of the Kodiak Islands, Alaska: Consequences of ridge‐trench interaction in a more southerly latitude
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DOI：
10.1029/tc002i003p00265
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发表时间：
1983-06
期刊：
影响因子：
4.2
通讯作者：
J. Moore;T. Byrne;P. W. Plumley;M. Reid;H. Gibbons;R. Coe
中科院分区：
文献类型：
--
作者：
J. Moore;T. Byrne;P. W. Plumley;M. Reid;H. Gibbons;R. Coe
阿拉斯加的科迪亚克群岛主要由晚白垩世和古近纪增生的深海岩石复合体组成。早古新世岩浆事件侵入了含有洋中脊玄武岩（MORB）、安山岩和花岗闪长岩的增生杂岩。地球化学证据表明安山岩和花岗闪长岩都是 MORB 和沉积物的混合物。火山岩与粗碎屑沉积物互层，并随粗碎屑沉积物变形；花岗闪长岩侵入体，其 K-Ar 年龄可追溯到古新世早期沉积岩和火山岩侵位后的 62 Ma。俯冲复合体与库拉-法拉隆山脊的相互作用最简单地解释了这一早期古新世岩浆事件。对火山岩的古地磁研究表明，这种相互作用发生在北纬 40.3±6°，即科迪亚克群岛相对于北美的预期位置以南 25.3±9°。目前科迪亚克增生杂岩西北部的岩浆弧在白垩纪晚期和古新世早期很活跃，在山脊-海沟相互作用后减弱，并从始新世晚期到中新世时期复活。岩浆复苏与科迪亚克群岛始新世到渐新世海底扇沉积物的仰冲剥离同时发生。这些扇沉积物的岩石学表明它们最有可能是黄道带扇的最接近的等同物，从而限制了它相对于科迪亚克群岛的相对运动。解释科迪亚克增生杂岩向北运动的可能模型包括（1）将增生杂岩和可能相关的弧与向北移动的库拉板块耦合，并在古近纪时期闭合弧以北的洋盆，（2）将科迪亚克增生杂岩置于古地磁数据的北限处，随后的向北运动通过小型弧后盆地的闭合和/或陆内缩短来完成，以及（3）横流科迪亚克增生杂岩的断层和向北运动，目前没有邻近的弧。
The Kodiak Islands of Alaska are principally composed of a Late Cretaceous and Paleogene complex of accreted deep-sea rocks. An early Paleocene magmatic event invaded the accretionary complex with mid-ocean ridge basalt (MORB), andesite, and granodiorite. Geochemical evidence suggests both the andesite and granodiorite are mixtures of MORB and sediment. The volcanic rocks are interlayered with coarse clastic sediments and deformed with the latter; the granodioritic intrusions, with K-Ar ages as old as 62 Ma postdate emplacement of the early Paleocene sedimentary and volcanic rocks. Interaction of the subduction complex with the Kula-Farallon ridge most simply explains this early Paleocene magmatic episode. Paleomagnetic studies of the volcanic rocks indicate this interaction occurred at 40.3±6° north latitude, which is 25.3±9° south of the expected position of the Kodiak Islands relative to North America. The magmatic arc presently northwest of the Kodiak accretionary complex was active during the Late Cretaceous and early Paleocene, diminished after the ridge-trench interaction, and resurged from late Eocene into Miocene time. The magmatic resurgence is coeval with the obductive offscraping of Eocene to Oligocene(?) submarine fan deposits in the Kodiak Islands. The petrology of these fan deposits indicates they are the most likely proximal equivalent for the Zodiac fan, thereby limiting its relative motion with respect to the Kodiak Islands. Possible models accounting for the northward motion of the Kodiak accretionary complex include (1) coupling the accretionary complex and possibly related arc to the northward-moving Kula Plate and closing an ocean basin north of the arc in Paleogene time, (2) emplacing the Kodiak accretionary complex at the northward limit of the paleomagnetic data, with subsequent northward motion accomplished by closure of a small back arc basin and/or intracontinental shortening, and (3) transcurrent faulting and northward motion of the Kodiak accretionary complex without the presently adjacent arc.