Late Paleozoic tectonothermal evolution of the western Piedmont and eastern Blue Ridge, Georgia: Controls on the chronology of terrane accretion and transport in the southern Appalachian orogen
Late Paleozoic tectonothermal evolution of the western Piedmont and eastern Blue Ridge, Georgia: Controls on the chronology of terrane accretion and transport in the southern Appalachian orogen
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佐治亚州皮埃蒙特西部和蓝岭东部的晚古生代构造热演化：对阿巴拉契亚造山带南部地体增生和运输年代的控制
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发表时间：
1988
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通讯作者：
R. D. Dallmeyer
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作者：
R. D. Dallmeyer
东部蓝岭的海伦和塔卢拉福尔斯推覆体以及部分西部皮埃蒙特（乔加-瓦尔哈拉杂岩的较高等级层序和六英里推覆体的东部）的角砾岩记录为3.22 - 3.33亿年。40 Ar/ 39 Ar平台年龄，其日期为变质冷却后，通过晶内保留氩所需的温度。Chauga-Walhalla杂岩的低等级部分和六英里推覆体（Alto allochthon）西部的角石记录了更古老的高原年龄（3.22 - 3.62亿年）。这些释放光谱表明，没有一个叠加的变质历史，高原年龄的解释日期区域穿时冷却的外来岩晚泥盆世或更早的高级变质作用。东部蓝岭和西部皮埃蒙特所有结构单元内的白云母记录为3.02 - 3.18亿年。4 O Ar/ 39 Ar坪年龄是通过较低的闭合温度（~ 350 °C？）进行变质冷却后的年龄。这些结构单元的黑云母产量为312-348百万年。40 Ar/ 39 Ar坪年龄。黑云母年龄的地质意义是不确定的，因为变量与外来氩污染。Alto外来岩似乎起源于西皮埃蒙特，在晚泥盆世或更早的高级变质作用之后，可能在最初的古陆增生到北美期间发展起来。穿时变质后冷却的外来岩可能发生在其运动到更高的地壳水平与侵位在较低级别的岩石Chauga-Walhalla复杂。侵位发生在当地发展的退行性糜棱岩面料有关的构造活动在布里瓦德断层带和区域冷却之前，通过白云母关闭温度。
Hornblende within the Helen and Tallulah Falls nappes of the eastern Blue Ridge and portions of the western Piedmont (higher grade sequences of the Chauga- Walhalla complex and eastern portions of the Six-Mile nappe) record 322-333-m.y. 40 Ar/ 39 Ar plateau ages which date post metamorphic cooling through temperatures required for intracrystalline retention of argon. Hornblende within lower-grade portions of the Chauga-Walhalla complex and western portions of the Six-Mile nappe (Alto allochthon) records older plateau ages (322-362 m.y.). None of these release spectra suggests a super-posed metamorphic history, and the plateau ages are interpreted to date regionally diachronous cooling of the allochthon following a Late Devonian or earlier high-grade metamorphism. Muscovite within all structural units of the eastern Blue Ridge and western Piedmont records 302-318-m.y. 4O Ar/ 39 Ar plateau ages which date post meta-morphic cooling through lower closure temperatures (∼350 °C?). Biotite from these structural units yields 312-348-m.y. 40 Ar/ 39 Ar plateau ages. The geologic significance of the biotite ages is uncertain because of variable contamination with extraneous argon. The Alto allochthon appears to have originated within the western Piedmont following a Late Devonian or earlier high-grade metamorphism which may have developed during initial terrane accretion to North America. Diachronous postmetamorphic cooling of the allochthon likely occurred during its movement to higher crustal levels associated with emplacement over lower-grade rocks of the Chauga-Walhalla complex. Emplacement occurred prior to local development of retrogressive mylonitic fabrics related to tectonic activity within the Brevard fault zone and prior to regional cooling through muscovite closure temperatures.