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与玻利维亚的高原一起，是地球上第二大高原。一个流行的模型经常被用来解释现今安第斯高原中部的地壳结构和海拔，包括阿根廷的普纳和玻利维亚的高原，是岩石圈分层。充分，对流去除榴辉岩化下地壳和岩石圈根和随后的反弹，在玻利维亚高原提出解释古高度证据高幅度（大于2公里）的表面隆起。然而，薄地壳和岩石圈以及玄武质火山活动的区域最初被认为是岩石圈移动的地点，位于阿根廷的普纳高原南部。此外，地球化学数据表明，存在奥陶纪岩石圈下的普纳，反对完整的岩石圈删除。本研究项目的目的是在普纳高原薄壳-地幔岩石圈区将地质观测与地球物理资料相结合。这项国际努力由怀俄明州大学和亚利桑那大学的研究人员领导，是一项多学科调查，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，以变薄地区为目标，以限制：1）水平缩短和延伸的历史; 2）盆地演化和切割; 3）岩浆地球化学;（4）中晚新生代古环境。这些综合性的新数据正被用作一个联合数值模拟模型的输入参数，该模型将检验一组解释高原现今地壳结构的假设，包括：1）通过粘性Rayleigh-Taylor型对流不稳定性，地幔岩石圈和可能的下地壳被完全去除;（2）地幔岩石圈的部分移动和下地壳高原的可能性，留下一个完整的地幔岩石圈层位后，粘性对流不稳定;（3）通过小尺度粘性对流不稳定性，地幔岩石圈和下地壳可能被部分去除：（4）地幔岩石圈被完全去除; 5）大陆弧后岩石圈拉张作用。造山带大型高原隆升的构造解释，如安第斯山脉的高原和青藏高原，数量众多且有争议。本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地幔过程之间的联系，变形，隆起，沉降和岩浆活动在普纳高原，一个天然的实验室，将作为一个例子，地球上其他地球动力学类似的地区。

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.