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The end of continental growth by TTG magmatism
Author(s) -
Laurie Angelique,
Stevens Gary,
van Hunen Jeroen
Publication year - 2013
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/ter.12015
Subject(s) - geology , archean , geochemistry , slab , mantle (geology) , felsic , subduction , magmatism , partial melting , continental crust , adakite , mantle wedge , petrology , petrogenesis , crust , oceanic crust , mafic , geophysics , paleontology , tectonics
Terra Nova, 25, 130–136, 2013 Abstract High‐Al 2 O 3 tonalite, trondhjemite and granodiorite (TTG) magmas characterise felsic Archaean crust, yet are uncommon in the post‐Archaean rock record. Consequently, understanding the petrogenesis of these rocks provides valuable insights into early Earth processes. Fluid‐absent slab melting represents the dominant hypothesis for the origin of these rocks; however, the absence of voluminous magmas of intermediate composition formed concurrently with these TTGs is incompatible with expectations of slab water loss prior to slab melting. This study demonstrates that for reasonable Archaean mantle temperatures, slab‐derived water is captured by an anatectic zone near the slab surface, which melts via reactions that consume quartz, clinopyroxene and water to produce high‐Al 2 O 3 Archaean trondhjemite. Late in the Archaean, the mantle cooled sufficiently to prevent wet melting of the slab, allowing slab water to migrate into the wedge and produce intermediate composition magmatism, which has since been associated with subduction zones.