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

9526974农民南部山脉大陆动力学项目（SSCD）的第一阶段产生了令人惊讶的结果，一个比周围低地高出2800米的山脉，其厚度几乎与低地相等（30- 40公里），基于被动和主动地震成像。 三维构造重建相邻的盆地和山脉省建议东部Sierran和盆地和山脉地壳的两个因素的新近纪减薄。 这些结果证实了上地幔的浮力范围内的起源，并提出了一个主要的未解决的问题，在动力学的科迪勒拉岩石圈：如何才能深刻的浮力损失从新近纪地壳减薄与长期存在的古植物，地貌和地层参数表明1-2公里或更多的科迪勒拉宽晚新生代隆起调和？ 明显的端元解包括：（1）东锡尔兰地壳的减薄很少或没有减薄;（2）上地幔密度异常大幅度降低;（3）安第斯型高原的区域沉降，而不是隆起。 该奖项是SSCD第二阶段的一个组成部分，其目标是通过重点突出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，热年代学和同位素示踪研究，长周期MT以及Sierran花岗岩类的低温热年代学。 ***

9526974 Farmer 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. ***