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letters to nature NATURE |VOL 411 |28 JUNE 2001 |www.nature.com 1039

Summary: letters to nature
NATURE |VOL 411 |28 JUNE 2001 |www.nature.com 1039
Comparable textural features are observed in granites. For
example, feldspar crystals often display rapakivi texture with an
alkali feldspar core mantled by a rim of plagioclase feldspar19
. The
plagioclase mantle could form from quenching of hotter ma®c
magma abruptly mixed with felsic magma20
; convective self-mixing,
however, could also be responsible. Mantled and unmantled feld-
spar crystals are observed in the same thin section21
which could
result from localized thermal variations produced by self-mixing.
Granites can display, on a local scale, grains of the same phase with
contrasting textures, such as large phenocrysts of quartz near to
small interstitial grains. There are skeletal and acicular crystal
shapes, which are indicative of rapid undercooling and growth,
and are consistent with rapid Żuctuations in magma conditions22
Orogenic granites are also commonly associated with ma®c syn-


Source: Achenbach, Laurie A. - Department of Microbiology, Southern Illinois University


Collections: Environmental Sciences and Ecology; Environmental Management and Restoration Technologies; Biology and Medicine