Collaborative Research: In Pursuit of Missing Andean Lithosphere: Constraining Late Cenozoic Crust-mantle Processes in the Puna Plateau, Central Andes

该奖项是根据2009年美国复苏和再投资法案(公法111-5)资助的。阿根廷西北部的普纳高原和玻利维亚的高原是地球上第二大高原。一个经常被引用来解释安第斯高原中部，包括阿根廷的普纳和玻利维亚的高原的现今地壳结构和海拔的流行模型是岩石圈拆沉。玻利维亚高原榴辉岩化的下地壳和岩石圈根部的完全对流移位和随后的反弹被提出，以解释高震级(大于2公里)地表抬升的古海拔证据。然而，最初被认为是岩石圈清除地点的薄壳和岩石圈以及玄武岩火山活动的地区位于阿根廷普纳高原的南部。此外，地球化学数据表明普纳之下存在奥陶系岩石圈，这反对完全消除岩石圈。这项研究的目的是使普纳高原薄壳地幔岩石圈地区的地质观测与地球物理资料相吻合。由怀俄明大学和亚利桑那大学的研究人员领导的这项国际努力是一项多学科的调查，利用构造地质学、沉积学和地层学、地质年代学、热年代学、地球化学和古生物学，以减薄的地区为目标，以限制：1)水平缩短和伸展的历史；2)盆地的演化和切割；3)岩浆地球化学；以及4)中晚新生代的古环境。这些综合的新数据被用作一个综合的数值模拟模式的输入参数，该模式将检验一组假设，以解释目前高原的地壳结构，包括：1)通过粘性瑞利-泰勒型对流不稳定完全移除地幔岩石圈和可能的下地壳；2)在整个高原范围内部分移除地幔岩石圈和可能的下地壳，在粘性对流不稳定之后保留最上层的地幔岩石圈；3)通过小范围的粘性对流不稳定，部分移除地幔岩石圈和可能的下地壳；4)通过粘性对流不稳定完全移除地幔岩石圈和可能的下地壳；5)大陆弧后型环境中的岩石圈伸展作用。安第斯高原、青藏高原等造山带大高原隆升的构造解释很多，也有争议。该项目的目标是通过使用地质观测作为对过程的数值和物理模型的约束来测试这些模型。这项研究将最终限制普纳高原内地幔作用与变形、隆升、下沉和岩浆作用之间的联系，这一天然实验室将为地球上其他地球动力学相似的地区提供范例。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The Puna Plateau, northwestern Argentina, together with the Altiplano of Bolivia, is the second largest plateau on Earth. One popular model often invoked to explain the present day crustal structure and elevation of the Central Andean Plateau, including the Argentinean Puna and the Bolivian Altiplano, is lithospheric delamination. Full, convective removal of eclogitized lower crust and lithospheric root and subsequent rebound in the Altiplano of Bolivia is proposed to explain paleoaltimetric evidence for high magnitude (greater than 2 kilometers) surface uplift. However, the region of thin crust and lithosphere and of basaltic volcanism originally argued to be the site of lithospheric removal is located to the south in the Puna Plateau of Argentina. Moreover, geochemical data suggest the presence of Ordovician lithosphere beneath the Puna, arguing against complete lithospheric removal. The objective of this research project is to reconcile the geological observations with geophysical data in the area of thin crust and mantle lithosphere in the Puna Plateau. This international effort, lead by researchers at the University of Wyoming and University of Arizona, is a multidisciplinary investigation utilizing structural geology, sedimentology and stratigraphy, geochronology, thermochronology, geochemistry and paleontology, targeting the thinned region in order to constrain: 1) the history of horizontal shortening and extension; 2) basin evolution and incision; 3) magma geochemistry; and 4) paleo-environment in the mid-late Cenozoic. These comprehensive new data are being used as input parameters to a combined numerical-analog model that will test a set of hypotheses to explain the present crustal configuration of the Plateau including: 1) full removal of mantle lithosphere and possibly lower crust through viscous Rayleigh-Taylor type convective instability; 2) partial removal of mantle lithosphere and possibly lower crust plateau-wide, leaving a horizon of uppermost mantle lithosphere intact following viscous convective instability; 3) partial removal of mantle lithosphere and possibly lower crust via small-scale viscous convective instability; 4) full removal of mantle lithosphere through; 5) lithospheric extension in a continental back-arc type environment.The tectonic explanations for the uplift of large plateaus in orogenic belts, such as the Altiplano in the Andes and the Tibet plateau, are numerous and controversial. The objective of this project is to test these models by using geological observations as constraints on numerical and physical models of the processes. This research will ultimately constrain the connection between mantle processes on deformation, uplift, subsidence and magmatism within the Puna Plateau, a natural laboratory that will serve as an example for other geodynamically similar regions on Earth.