Geochronology of augen gneiss and related rocks, Yukon-Tanana terrane, east-central Alaska
Geochronology of augen gneiss and related rocks, Yukon-Tanana terrane, east-central Alaska
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阿拉斯加中东部育空-塔纳纳地体奥根片麻岩及相关岩石的地质年代学
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发表时间：
1986
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通讯作者：
H. Foster
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作者：
J. Aleinikoff;C. Dusel;H. Foster
利用多种同位素技术，我们确定了阿拉斯加中东部育空-塔纳纳地体 (YTT) 中选定变质岩的年龄。大三角洲四边形中奥根片麻岩体的 U-Pb 锆石数据表明，片麻岩的花岗岩原岩侵入了 341 ± 3 m.y。之前（较低的拦截年龄）。上部截距年龄为 2,136 ± 31 m.y。表明这些锆石中继承了早期元古代成分。该继承年龄由 2.09 ± 0.08 b.y 的 Sm-Nd 全岩模型年龄证实。来自大三角洲奥根片麻岩体。从石英岩围岩到该天体的碎屑锆石也源自早元古代（约 2.1 至 2.3 年前）地壳来源。来自其他三块奥根片麻岩的锆石出现在延伸至加拿大育空地区南部的东西向带中，具有相似的密西西比期和早元古代截距年龄。来自广泛分离的奥根片麻岩体的铷-锶全岩等时线的年龄为 333 ± 26 m.y。初始 87 Sr/ 86 Sr 比率为 0.728 ± 0.002，证实了原岩的密西西比期侵入年龄。较高的初始 87 Sr/ 86 Sr 比率进一步表明这些岩石中存在古老的地壳成分。 Rb-Sr 矿物等时线（115 ± 4 m.y.）、角闪石和云母的 K-Ar 数据（128 至 107 m.y.）以及来自奥根片麻岩和相关岩石的榍石（134. m.y.）的 U-Pb 数据与该地区的许多 K-Ar 年龄相似，证实了早白垩世热事件的发生。 YTT 中三个变火山单元的锆石 U-Pb 年龄表明，这些岩石的原岩的挤压发生于 360-380 m.y.。前。数据的分散是由普遍存在的继承和多起失联事件造成的。 YTT 中发生了重要的泥盆纪-密西西比纪火成岩活动（380-340 m.y.），随后发生了一次或可能两次变质事件（密西西比纪和白垩纪）。迄今为止，YTT 中尚未发现古生代岩浆的早元古代烃源岩，但类似早元古代年龄的岩石出现在加拿大西北地区和不列颠哥伦比亚省的东部和南部。
Using several isotopic techniques, we have determined the ages of selected metamorphic rocks in the Yukon-Tanana terrane (YTT) of east-central Alaska. U-Pb zircon data from an augen gneiss body in the Big Delta quadrangle indicate that the granitoid protolith of the gneiss was intruded 341 ± 3 m.y. ago (lower intercept age). An upper intercept age of 2,136 ± 31 m.y. indicates an inherited early Proterozoic component in these zircons. This inheritance age is substantiated by a Sm-Nd whole-rock model age of 2.09 ± 0.08 b.y. from the Big Delta augen gneiss body. Detrital zircons from quartzitic wall rocks to this body were also derived from an early Proterozoic (∼2.1 to 2.3 b.y. old) crustal source(s). Zircons from three other augen gneisses occurring in an east-west belt which extends into the southern Yukon Territory, Canada, have similar Mississippian and early Proterozoic intercept ages. A Rb-Sr whole-rock isochron from widely separated bodies of augen gneiss has an age of 333 ± 26 m.y. and an initial 87 Sr/ 86 Sr ratio of 0.728 ± 0.002, confirming the Mississippian intrusive age for the protolith. The high initial 87 Sr/ 86 Sr ratio further indicates an old crustal component in these rocks. A Rb-Sr mineral isochron (115 ± 4 m.y.), K-Ar data from hornblende and micas (128 to 107 m.y.), and U-Pb data from sphene (134. m.y.) from augen gneiss and related rocks are similar to many K-Ar ages in this region and confirm the occurrence of an early Cretaceous thermal event. U-Pb ages of zircons from three metavolcanic units in the YTT suggest that extrusion of the protoliths of these rocks occurred 360–380 m.y. ago. Scatter in the data is caused by ubiquitous inheritance and multiple lead-loss events. Significant Devonian-Mississippian igneous activity (380-340 m.y.) took place in the YTT, followed by one, or possibly two, metamorphic episodes (Mississippian? and Cretaceous). As yet, no early Proterozoic source rocks for the Paleozoic magmas have been identified in the YTT, but rocks of similar early Proterozoic ages occur to the east and south in the Northwest Territories and British Columbia, Canada.