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Focused radiogenic heating of middle crust caused ultrahigh temperatures in southern Madagascar

Horton, Forrest and Hacker, Bradley and Kylander-Clark, Andrew and Holder, Robert and Jöns, Niels (2016) Focused radiogenic heating of middle crust caused ultrahigh temperatures in southern Madagascar. Tectonics, 35 (2). pp. 293-314. ISSN 0278-7407. doi:10.1002/2015TC004040.

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Internal heating can cause melting, metamorphism, and crustal weakening in convergent orogens. This study evaluates the role of radiogenic heat production (RHP) in a Neoproterozoic ultrahigh-temperature metamorphic (UHTM) terrane exposed in southern Madagascar. Monazite and zircon geochronology indicates that the Paleoproterozoic Androyen and Anosyen domains (i) collided with the oceanic Vohibory Arc at ~630 Ma, (ii) became incorporated into the Gondwanan collisional orogen by ~580 Ma, and (iii) were exhumed during crustal thinning at 525–510 Ma. Ti-in-quartz and Zr-in-rutile thermometry reveals that UHTM occurred over >20,000 km^2, mostly within the Anosyen domain. Assuming that U, Th, and K contents of samples from the field area are representative of the middle to lower crust during orogenesis, RHP was high enough—locally >5 μW/m^3—to cause regional UHTM in <60 Myr. We conclude that, due in large part to the stability and insolubility of monazite at high crustal temperatures, RHP was the principal heat source responsible for UHTM, obviating the need to evoke external heat sources. Focused RHP probably thermally weakened portions of the middle crust, gravitationally destabilizing the orogen and facilitating thinning via lateral extrusion of hot crustal sections.

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Additional Information:© 2016 American Geophysical Union. Received 24 SEP 2015; Accepted 7 JAN 2016; Accepted article online 12 JAN 2016; Published online 12 FEB 2016. This research was funded by NSF EAR-1348003 and a NSF Graduate Research Fellowship awarded to F. Horton. Volker Schenk generously provided samples. We thank Professor Michel Rakotondrazafy and his graduate students Jeremia Ramarijaona and Laurent Rakotondramanana for their exemplary help in the field. We also thank Simon Harley for his thoughtful review of this manuscript. All data are available upon request from the corresponding author.
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NSF Graduate Research FellowshipUNSPECIFIED
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Record Number:CaltechAUTHORS:20160415-080532394
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Official Citation:Horton, F., B. Hacker, A. Kylander-Clark, R. Holder, and N. Jöns (2016), Focused radiogenic heating of middle crust caused ultrahigh temperatures in southern Madagascar, Tectonics, 35, 293–314, doi:10.1002/2015TC004040
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66206
Deposited By: Tony Diaz
Deposited On:16 Apr 2016 16:47
Last Modified:10 Nov 2021 23:54

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