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首页> 外文期刊>Tectonophysics: International Journal of Geotectonics and the Geology and Physics of the Interior of the Earth >Low-temperature thermochronological record of exhumation of the Bitterroot metamorphic core complex, northern Cordilleran Orogen
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Low-temperature thermochronological record of exhumation of the Bitterroot metamorphic core complex, northern Cordilleran Orogen

机译：北部科迪勒山造山带苦根变质核心复合物掘出的低温热年代学记录

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摘要

The Bitterroot metamorphic core complex is an exhumed, mid-crustal, plutonic-metamorphic complex that formed during crustal thickening and subsequent extension in the hinterland of the North American Cordilleran Orogen, in the northern Idaho batholith region. Extension was accommodated mainly on the Bitterroot mylonite zone, a 500-1500-m-thick shear zone that deforms granitic intrusive rocks as young as 53-52 Ma, as well as older high-grade metamorphic rocks and plutons. Exhumation of the core complex, in Eocene time, is marked in the shear zone by the transition from amphibolite-facies mylonitization, to greenschist-facies mylonitization, chloritic brecciation, to brittle faulting that progressed from shallower crustal levels in the west to deeper crustal levels in the east from ca. 53 - 30 Ma based on U-Pb, Ar-Ar, and fission-track data. Apatite and zircon fission-track data record the lower-temperature part of the exhumation history and help define when the shear zone became inactive, as well as the transition from rapid, core complex-style extension to slower basin-and-range-style extension. They indicate that the western pail of the complex was exhumed to within 1-2 km of the surface by similar to 48-45 Ma, while the eastern pail of the complex was still at amphibolite-facies conditions and that the eastern pail of the complex was not exhumed below - 60 degreesC until after 30 Ma. Younger apatite Fission-track ages (:! 26 Ma) on the eastern range front of the Bitterroot Mountains suggest that the present topographic expression of the mylonite front was due to Miocene high-angle faulting and widening of the Bitterroot Valley. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 44]
机译：Bitterroot变质岩心复合体是在北爱达荷州岩基岩地区北美洲山脉山脉造山带腹地增厚和随后扩展过程中形成的发掘，中地壳、,状变质的复合体。延伸主要集中在苦涩根部的镁铁矿带上，这是一个500-1500-m厚的剪切带，可使年龄在53-52Ma的花岗岩侵入性岩石以及较老的高级变质岩和岩体变形。在始新世时期，岩心复合物的发掘在剪切带中表现为从闪石岩相的长粒化到绿片岩相的长粒化，绿泥石化作用，再到从西部浅层地壳到深层地壳的脆性断层的过渡。大约在东方基于U-Pb，Ar-Ar和裂变径迹数据得出的53-30 Ma。磷灰石和锆石裂变径迹数据记录了发掘历史中的较低温度部分，并有助于定义何时剪切带变为非活动状态，以及从快速，岩心复杂型扩展到较慢的盆地和范围型扩展的过渡。他们表明，该复合物的西桶被挖出到地表1-2公里以内，类似于48-45 Ma，而该复合物的东桶仍处于闪石岩相条件下，并且该复合物的东桶处于直到30 Ma之后才在60°C以下发掘出来。 Bitterroot山东部山脉前缘的年轻磷灰石裂变径迹年龄（：！26 Ma）表明，该Mylonite锋面目前的地形表现是由于中新世高角度断层和Bitterroot谷地拓宽。 （C）2002 Elsevier Science B.V.保留所有权利。 [参考：44]

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