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Effects of a warmer mantle on the characteristics of Archean passive margins

Andrew Hynes
Effects of a warmer mantle on the characteristics of Archean passive margins (in When did plate tectonics begin on planet Earth?, Kent C. Condie (editor) and Victoria Pease (editor))
Special Paper - Geological Society of America (2008) 440: 149-156


The Archean mantle was probably warmer than the modern one. Continental plates underlain by such a warmer mantle would have experienced less subsidence than modern ones following extension because extension would have led to widespread melting of the underlying mantle and the generation of large volumes of mafic rock. A 200 degrees C increase in mantle temperature leads to the production of nearly 12 km of melt beneath a continental plate extended by a factor of 2, and the resulting thinned plate rides with its upper surface little below sea level. The thick, submarine, mafic-to-ultramafic volcanic successions on continental crust that characterize many Archean regions could therefore have resulted from extension of continental plates above warm mantle. Long-term subsidence of passive margins is driven by thermal relaxation of the stretched continental plate (cf. McKenzie). With a warmer mantle, the relaxation is smaller. For a continental plate stretched by a factor of 2, underlain by a 200 degrees C warmer mantle than at present, the cooling-driven subsidence drops from 2.3 km to 1.1 km. The combined initial and thermal subsidence declines by more than 40%, and by even more than this if initial continental crustal thicknesses were lower. The greatly reduced subsidence results in a concomitant decline in accommodation space for passive-margin sediments and may explain the scarcity of passive-margin sequences in the Archean record. The formation of diamonds in the Archean requires geotherms similar to modern ones, which in turn probably reflect the presence of cool mantle roots beneath the continents. Stretching of continents underlain by cool mantle roots would yield passive margins similar to modern ones. Thus, development of significant passive margins may have occurred only through rifting of continents underlain by cool mantle roots. Furthermore, the widespread subcontinental melting associated with rifting of continents devoid of roots may have been a significant contributor to development of the roots themselves.

ISSN: 0072-1077
EISSN: 2331-219X
Serial Title: Special Paper - Geological Society of America
Serial Volume: 440
Title: Effects of a warmer mantle on the characteristics of Archean passive margins
Title: When did plate tectonics begin on planet Earth?
Author(s): Hynes, Andrew
Author(s): Condie, Kent C.editor
Author(s): Pease, Victoriaeditor
Affiliation: McGill University, Department of Earth and Planetary Sciences, Montreal, QC, Canada
Affiliation: New Mexico Institute of Mining and Technology, Department of Earth and Environmental Science, Socorro, NM, United States
Pages: 149-156
Published: 2008
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Meeting name: Penrose Conference
Meeting location: Lander, WY, USA, United States
Meeting date: 20060613June 14-18, 2006
References: 37
Accession Number: 2008-124318
Categories: Solid-earth geophysics
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus.
Secondary Affiliation: Stockholm University, SWE, Sweden
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200848
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