Publication: Geochemical and isotopic disequilibrium in crustal melting:
An insight from the anatectic granitoids from Toledo, Spain
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Publication Date
1995
Authors
Barbero González, Luis C.
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American Geophysical Union
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Abstract
In the Hercynian Anatectic Complex of Toledo (ACT) the anatectic granitoids include
leucogranitic leucosomes, leucogranitic massifs, and restite-rich granites. They show a broad range of
initial Sr and Nd isotope ratios from 0.71 I to 0.720 and 0.51164 to 0.51203, respectively, which clearly
indicate the absence of isotopic homogenization in the melts. Broadly, the ranges reflect the isotopic
variation of the metapelitic protoliths. If crusta! melting occurs under water-undersaturated conditions,
as is the case of the ACT, the generated melts do not isotopically and chemically equilibrate with the
granulitic residuum. The preservation of heterogeneities could arise through a number of pmcesses. (1)
duration of the process:in which the presence of melts with disequilibrium features, and the high solid
content of several of the granites in the ACT point to a very short-lived magmatic system, (2) limited
diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted
opportunity for isotopic and chemical homogenization, and (3) magma dynamics in which the low
melting rates, the high restite and low water contents, and the silica-rich composition of these granites,
together with the small volume and high viscosity values of the melts, seriously restrict the physical
processes leading to homogenization.