Collaborative Research: Continental Mountains in Extensional Environments: The Sierran Paradox

9526455菲尼南塞拉利昂大陆动力学项目的第一阶段产生了一个令人惊讶的结果：根据被动和主动地震成像，比周围低地高出2800m的山脉具有几乎与低地(30-40公里)相同的厚度。毗邻的盆地和山脉省的三维构造重建表明，新近纪西尔兰东部和盆地和山脉地壳都变薄了两倍。这些结果证实了山脉下方浮力的上地幔起源，并可能是科迪勒岩石圈动力学中一个重大未解决问题的最鲜明的例证：新近纪地壳减薄造成的浮力严重损失如何与长期存在的古植物学、地貌学和地层学论点相一致，这些论点表明科迪勒拉范围内晚新生代抬升了1-2公里或更多？明显的端元解决方案暗示：(1)东部锡尔兰地壳很少变薄或没有减薄(2)上地幔密度异常大幅下降(3)安第斯高地台区的区域下沉，而不是隆起。该奖项是SSCD第二阶段的一个组成部分，该阶段的目标是用一种集中的、多学科的方法评估上述假设，涉及平衡截面、地震层析成像、热计时和同位素示踪研究、长周期MT和Sierran花岗岩的低温热计时研究。***

9526455 Phinney The first phase of the Southern Sierra Continental Dynamics Project (SSCD) yielded the surprising result that a mountain range standing up to 2800 m higher than surrounding lowlands has a sialic crust of thickness nearly equal to that of the lowlands (30-40km), based on both passive and active seismic imaging. Three-dimensional tectonic reconstruction of the adjacent Basin and Range province suggests Neogene thinning of both eastern Sierran and Basin and Range crust by a factor of two. These results confirm an upper mantle origin for buoyancy beneath the range, and present perhaps the starkest illustration of a major unsolved problem in the dynamics of the cordilleran lithosphere: How can the profound loss of buoyancy from Neogene crustal thinning be reconciled with long-standing paleobotanical, geomorphological, and stratigraphic arguments indicating 1-2 km or more of Cordillera-wide late Cenozoic uplift? Obvious end member solutions inalude: (1) little or no thinning of eastern sierran crust (2) an unusually large decrease in density in the upper mantle (3) regional subsidence of a high, Andean-type plateau, rather than uplift. This award is one component of the second phase of the SSCD that has as it's goal the evaluation of the above hypotheses with a focused, multidisciplinary approach involving balanced cross-sections, seismic tomography, thermochronometry and isotope tracer studies, long-period MT, and low-temperature thermochronometry of Sierran granitoids. ***