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。一个经常被用来解释现今地壳结构和安第斯高原中部（包括阿根廷的普纳和玻利维亚的高原）海拔高度的流行模型是岩石圈分层。玻利维亚高原（Altiplano）下地壳和岩石圈根的充分对流移除以及随后的反弹被提出，以解释高幅度（大于2公里）地表隆起的古高程证据。然而，最初被认为是岩石圈移除地点的薄壳岩石圈和玄武岩火山活动区域位于阿根廷的普纳高原以南。此外，地球化学数据表明，在普纳盆地下存在奥陶系岩石圈，反对岩石圈的完全移除。本研究项目的目的是对普纳高原薄壳幔岩石圈地区的地质观测资料与地球物理资料进行协调。这项国际研究由怀俄明大学和亚利桑那大学的研究人员领导，是一项多学科研究，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，以薄区为目标，以限制：1)水平缩短和伸展的历史；2)盆地演化与切口；3)岩浆地球化学；4)中、晚新生代古环境。这些全面的新数据被用作数值模拟组合模型的输入参数，该模型将测试一系列假设，以解释高原目前的地壳结构，包括：1)地幔岩石圈和可能通过粘性瑞利-泰勒型对流不稳定性完全移除的下地壳；2)地幔岩石圈和下地壳高原范围的部分移除，在粘性对流不稳定之后，留下一个完整的上地幔岩石圈层位；3)地幔岩石圈和可能的下地壳通过小尺度粘性对流不稳定性部分移除；4)地幔岩石圈通过完全移除；5)大陆弧后型环境下岩石圈伸展。造山带中大型高原隆起的构造解释，如安第斯山脉的Altiplano和西藏高原，数量众多且存在争议。该项目的目的是通过使用地质观测作为过程的数值和物理模型的约束来测试这些模型。这项研究将最终限定普纳高原内地幔变形、隆升、沉降和岩浆作用过程之间的联系，这是一个自然实验室，将为地球上其他地球动力学相似的地区提供一个例子。

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.