Collaborative Research: Testing Burial/Exhumation Models for the Evolution of a (U)HP Terrane in an Orogenic Upper Plate, Liverpool Land, East Greenland

Cuny Queens College, Flushing NY

Investigators

Abstract

A fundamental difficulty faced by geologists studying the evolution of large mountain ranges is the inability to directly observe the types of rock and deformation patterns that are found at deep crustal levels beneath active mountains. One way to overcome this difficulty is to study ancient mountain ranges that have since been inverted or eroded, and currently expose the deepest structural levels of a mountain range at the surface. The rocks of Liverpool Land (LL), East Greenland, expose the roots to the Caledonides, a mountain range that spanned the length of Greenland, and formed as Scandinavia collided with North America in the time span from about 440 to 360 million years ago. This collaborative effort between faculty and graduate and undergraduate students at Queens College and Cal Poly San Luis Obispo, with assistance from Norwegian geologists, will determine the origin and subsequent deformation history of rocks from the roots of the Caledonides, to better understand the processes of mountain building during continental collision. The results of this project will be of particular interest to researchers studying deformation in actively deforming mountain belts like the Himalaya. Field and laboratory analysis of high pressure and ultra-high-pressure (UHP) gneisses from Liverpool Land will be used to test models for the subduction and exhumation of UHP terranes in the overriding plates of collisional orogens. Liverpool Land has been correlated with Laurentia, implying it was situated in the upper plate during the Caledonian Orogeny as Baltica subducted beneath. Previous work by these investigators in LL has identified eclogites and mantle-derived garnet peridotites possibly correlated with Baltica in addition to a tectonostratigraphic suture between a younger UHP terrane and an older mid-crustal gneiss terrane. These discoveries challenge generally accepted models for the formation of UHP terranes where continental lithosphere is pulled to mantle depths by negatively buoyant oceanic lithosphere, as well as models for their exhumation in the footwalls of lithospheric-scale normal faults. We propose a structural, geochemical, and geo-thermo-chronologic study of the LL gneiss complexes to 1) define the tectonic setting and metasomatic history of the mantle wedge incorporated into the LL terrane, 2) determine Laurentian versus Baltic provenance of the LL gneiss complexes, and 3) characterize the kinematics and timing of tectonostratigraphic sutures responsible for exhumation in LL. The proposed work promises to shed light on geodynamic processes including the possibility of multiple UHP events during the closure of ocean basins, crust-mantle interaction and exchange during orogeny, and lower to midcrustal melting.