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Abstract

Small amounts of felsic, evolved plutonic
rocks, often called oceanic plagiogranites, always occur
as veins or small stocks within the gabbroic section of
the oceanic crust. Four major models are under debate
to explain the formation of these rocks: (1) late-stage
differentiation of a parental MORB melt, (2) partial
melting of gabbroic rocks, (3) immiscibility in an
evolved tholeiitic liquid, and (4) assimilation and partial
melting of previously altered dikes. Recent experimental
data in hydrous MORB-type systems are used
to evaluate the petrogenesis of oceanic plagiogranites
within the deep oceanic crust. Experiments show that
TiO2 is a key parameter for the discrimination between
different processes: TiO2 is relatively low in melts
generated by anatexis of gabbros which is a consequence
of the low TiO2 contents of the protolith, due
to the depleted nature of typical cumulate gabbros
formed in the oceanic crust. On the other hand, TiO2 is
relatively high in those melts generated by MORB
differentiation or liquid immiscibility. Since the TiO2
content of many oceanic plagiogranites is far below
that expected in case of a generation by simple MORB
differentiation or immiscibility, these rocks may be
regarded as products of anatexis. This may indicate
that partial melting processes triggered by water-rich
fluids are more common in the deep oceanic crust than
believed up to now. At slow-spreading ridges, seawater
may be transported via high-temperature shear zones
deeply into the crust and thus made available for
melting processes.

Item Type:	Article
Authors/Creators:	Koepke, J and Berndt, J and Feig, ST and Holtz, F
Keywords:	Oceanic plagiogranite; Gabbro; Oceanic crust; Partial melting; Plagioclase
Journal or Publication Title:	Contributions to Mineralology and Petrology
ISSN:	0010-7999 (Print), 1432-0967 (Online)
DOI / ID Number:	https://doi.org/10.1007/s00410-006-0135-y
Additional Information:	The original publication is available at www.springerlink.com
Item Statistics:	View statistics for this item

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