Extreme ductile thinning of Cambrian marbles in the Northern Snake Range metamorphic core complex, Nevada, USA: Implications for extension magnitude and structural evolution
Extreme ductile thinning of Cambrian marbles in the Northern Snake Range metamorphic core complex, Nevada, USA: Implications for extension magnitude and structural evolution
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DOI：
10.1016/j.jsg.2023.104912
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发表时间：
2023-07
影响因子：
3.1
通讯作者：
S. Long;Jeffrey Lee;N. Blackford
中科院分区：
文献类型：
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作者：
S. Long;Jeffrey Lee;N. Blackford
北方蛇岭变质核杂岩内岩石的详细地层学为研究高强度大陆伸展期间韧性应变的几何形状和大小提供了一个难得的机会。在该山脉的北方部分，北方蛇岭滑脱层（NSRD）下盘的中-晚寒武世大理石在晚始新世-晚渐新世韧性伸展期间变薄，在相邻山脉中的地层厚度为1107 ± 107 m。从西到东，这些岩石在12公里的线性平行距离上从869-935米厚（15-21%的结构减薄）减薄到54-88米厚（92-95%的结构减薄）。韧性伸展应变伴随着普遍的线性平面组构的发展，并产生了100-500米长，15-25米厚，相隔1公里的钙质片岩单元。平行于线状构造的韧性伸展幅度从24 ± 21%向东增加到1226 ± 256%，整个范围内的韧性伸展总量为12.1 ± 2.2 km（167 ± 31%）。石英重结晶显微结构和已发表的方解石-白云石温度测量表明，在始新世晚期-渐新世晚期韧性拉伸剪切作用初期，变形温度为400-550 °C。从西到东的范围内，岩石在NSRD下盘经历了一个渐进的更长的韧性拉伸应变历史和延长的停留时间在较高的温度下，这是由剥蚀相关的冷却的东迁移的帮助，并可能增强应变加热和/或前伸展的下盘岩石向东倾斜。这些因素促进了极端应变梯度的发展。
The detailed stratigraphy of rocks within the Northern Snake Range metamorphic core complex provides an exceptional opportunity to investigate the geometry and magnitude of ductile strain during high-magnitude continental extension. In the northern part of the range, Middle-Late Cambrian marbles in the footwall of the Northern Snake Range dècollement (NSRD), which have a stratigraphic thickness of 1107 ± 107 m in adjacent ranges, were thinned during Late Eocene-Late Oligocene ductile extension. From west to east across the range, these rocks have been thinned from 869-935-m-thick (15–21% structural thinning) to 54-88-m-thick (92–95% structural thinning) across a 12 km lineation-parallel distance. Ductile extensional strain was accompanied by the development of pervasive linear-planar fabrics and produced megaboudins of calcareous schist units that are 100-500-m-long, 15-25-m-thick, and separated by as much as 1 km. The magnitude of lineation-parallel ductile extension increases eastward across the range from 24 ± 21% to 1226 ± 256%, and total ductile extension across the range is 12.1 ± 2.2 km (167 ± 31%). Quartz recrystallization microstructures and published calcite-dolomite thermometry indicate deformation temperatures of ∼400–550 °C during initial Late Eocene-Late Oligocene ductile extensional shearing. West to east across the range, rocks in the NSRD footwall experienced a progressively longer ductile extensional strain history and a prolonged residence time at higher temperatures, which was aided by the eastward migration of denudation-related cooling and was likely enhanced by strain heating and/or a pre-extensional eastward dip of footwall rocks. These factors promoted the development of the extreme strain gradient.