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

南塞拉大陆动力学项目（SSCD）的第一阶段得出了一个令人惊讶的结果：根据被动和主动地震成像，一个比周围低地高2800米的山脉，其地壳厚度与低地（30-40公里）几乎相等。邻近盆地和山脉省的三维构造重建表明，新近纪喜马拉雅东部、盆地和山脉地壳都有两倍的减薄作用。这些结果证实了山脉下浮力的上地幔起源，并且可能是对科迪勒拉岩石圈动力学中一个尚未解决的主要问题的最明显的说明：新近纪地壳变薄导致的浮力的严重丧失，如何与长期存在的古植物学、地貌学和地层学的争论相协调，这些争论表明，晚新生代科迪勒拉范围内的1-2公里或更多的隆起？明显的端元解包括：(1)东喜马拉雅地壳很少或没有变薄；(2)上地幔密度异常大的下降；(3)安第斯型高原的区域沉降，而不是隆升。该奖项是SSCD第二阶段的一个组成部分，其目标是通过集中的多学科方法评估上述假设，包括平衡横截面，地震层析成像，热时计和同位素示踪研究，长周期MT和Sierran花岗岩类的低温热时计。* * *

9526864 Glazner 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 include: (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. ***