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Episodic heating of continental lower crust during extension: A thermal modeling investigation of the Ivrea-Verbano Zone

Journal article
Authors A. J. Smye
L. L. Lavier
Thomas Zack
D. F. Stockli
Published in Earth and Planetary Science Letters
Volume 521
Pages 158-168
ISSN 0012-821X
Publication year 2019
Published at Department of Earth Sciences
Pages 158-168
Language en
Links dx.doi.org/10.1016/j.epsl.2019.06.0...
Keywords rifting, metamorphism, diffusion, rutile, thermal modeling, small-scale convection, southern alps, cooling history, alpine tethys, rifted margin, western alps, upper-mantle, evolution, zircon, rutile, Geochemistry & Geophysics, hnetger b, 1994, chemical geology, v113, p71, ahle v, 1990, earth and planetary science letters, v101, p196, acey js, 1975, earth and planetary science letters, v26, p207, hmid r, 1976, contributions to mineralogy and petrology, v54, p255, kenzie d, 1978, earth and planetary science letters, v40, p25, hmid sm, 1987, tectonophysics, v135, p47, kenzie d, 1988, journal of petrology, v29, p625
Subject categories Earth and Related Environmental Sciences

Abstract

Rheology of the continental lower crust plays an integral role in governing the style of continental extension. Temperature-dependent creep deformation in the lower crust decreases lithospheric strength and promotes coupling of deformation in the brittle crust and upper mantle; however, few constraints exist concerning the thermal evolution of extending lower crust. Here, we present a high-temperature thermochronological investigation of the Ivrea-Verbano Zone archetypal continental lower crust that was attenuated during opening of the Alpine Tethys oceanic basin. Rutile U-Pb dates collected from three samples spanning the bottom similar to 2-km of the crustal section are between similar to 160 and similar to 180 Ma, and exhibit near-rim zonations in Zr, Hf, Nb and Ta. Thermal-kinematic modeling of these data, combined with existing rutile U-Pb dates, show that the base of the Ivrea-Verbano Zone experienced heating on two timescales: conductive heating over similar to 10 Myr, associated with thinning of the lithospheric mantle, and advective heating over <0.1 Myr, associated with high-temperature infiltration of fluids during crustal exhumation. These constraints match the thermal predictions of geodynamic models that predict high-magnitude thinning of lithospheric mantle during the early stages of extension. Conductive heating of lower crust directly preceded mantle exhumation and crustal excision, suggesting that thermal weakening of the lithosphere promotes focusing of extensional strain. (C) 2019 Elsevier B.V. All rights reserved.

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