T27 Challenges in Tectonics: Planetary Evolution in Four Dimensions—The New Global Tectonics

Sunday, 22 October 2017
8:00 AM - 12:00 PM
Tahoma 4

ZIRCON (U-TH)/HE DATA REVEALS DEEP-TIME THERMAL HISTORIES OF CRATONS AND THE GREAT UNCONFORMITY SURFACE

Paper number: T27-2
Program: Technical Sessions
Time: 8:20 AM – 8:35 AM

Authors

Abstract

Craton interiors preserve a record of Earth’s 4-D evolution that can be used to assess interactions between surface dynamics and deep-Earth processes over billion-year time scales. The burial and exhumation history of these settings reveals the timing and magnitude of surface responses to long-term, long-wavelength vertical motions caused by asthenosphere-lithosphere interactions and supercontinent amalgamation and break-up. Multiple cycles of burial and exhumation produce complex time-temperature (t-T) histories in cratons that can be constrained by low-temperature thermochronology. Previous thermochronology studies have focused on apatite (U-Th)/He and fission-track dates in cratons, but both systems have relatively low temperature sensitivities and record exhumation of only the upper few kilometers of crust, with t-T histories largely confined to the Phanerozoic. Here, we exploit the radiation damage-He diffusivity relationship in the zircon (U-Th)/He system to extend the t-T histories of craton burial and exhumation to over a billion years. Samples come from two intracratonic locations: ~1.8 Ga granitoids from southeastern Sweden (Fennoscandian Shield), and ~1.4 Ga granites and rhyolites from the Ozark Plateau of southeastern Missouri. In these locations, deep-time thermochronology reveals the billion-year t-T paths of Precambrian crystalline basement rocks at or just below the Precambrian-Cambrian (Great Unconformity) boundary surface. Our Fennoscandian Shield zircon (U-Th)/He data constrain two episodes of burial and exhumation: burial to ~220°C between ~940 Ma and ~850 Ma followed by exhumation from 850 to 500 Ma, and burial to ~150°C between 370 Ma and 220 Ma. In the Ozark Plateau, zircon (U-Th)/He data record exhumation from a maximum reheating (burial) temperature of ~260°C at ~850-680 Ma, whereas complementary apatite (U-Th)/He and fission-track data record a younger exhumation episode at ~225-150 Ma. Results from both locations identify phases of denudation related to formation of the Great Unconformity and coincide with Rodinia and Pangaea supercontinent break-up, which has implications for understanding surface responses to the supercontinent cycle, and potentially the effects of increased intracratonic erosion at ~850 Ma on CO2 drawdown and snowball Earth cooling.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-306351

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.