Details
| Original language | English |
|---|---|
| Pages (from-to) | 67-84 |
| Number of pages | 18 |
| Journal | Contributions to Mineralogy and Petrology |
| Volume | 153 |
| Issue number | 1 |
| Publication status | Published - 16 Sept 2007 |
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.
Keywords
- Gabbro, Oceanic crust, Oceanic plagiogranite, Partialmelting, Plagioclase
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geophysics
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Contributions to Mineralogy and Petrology, Vol. 153, No. 1, 16.09.2007, p. 67-84.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The formation of SiO2-rich melts within the deep oceanic crust by hydrous partial melting of gabbros
AU - Koepke, Juergen
AU - Berndt, Jasper
AU - Feig, Sandrin T.
AU - Holtz, Francois
N1 - Funding Information: Acknowledgment Otto Diedrichs’s careful sample preparation is gratefully acknowledged. The manuscript has been substantially improved after thorough reviews by L. Coogan and an unknown reviewer. We would also like to thank P. Thy and Y. Niu for helpful comments on an earlier version of the manuscript. Valuable editorial advice from J. Hoefs is acknowledged. Funding for this research was provided by grants from the Deutsche Forschungsgemeinschaft. Copyright: Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2007/9/16
Y1 - 2007/9/16
N2 - 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.
AB - 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.
KW - Gabbro
KW - Oceanic crust
KW - Oceanic plagiogranite
KW - Partialmelting
KW - Plagioclase
UR - http://www.scopus.com/inward/record.url?scp=33750891404&partnerID=8YFLogxK
U2 - 10.1007/s00410-006-0135-y
DO - 10.1007/s00410-006-0135-y
M3 - Article
AN - SCOPUS:33750891404
VL - 153
SP - 67
EP - 84
JO - Contributions to Mineralogy and Petrology
JF - Contributions to Mineralogy and Petrology
SN - 0010-7999
IS - 1
ER -