TY - JOUR

T1 - Petrogenesis of oceanic plagiogranites by partial melting of gabbros

T2 - An experimental study

AU - Koepke, Jürgen

AU - Feig, Sandrin T.

AU - Snow, Jonathan

AU - Freise, Marcus

N1 - Funding Information: Acknowledgements Otto Diedrichs’s careful sample preparation is gratefully acknowledged. Miriam Haack is thanked for the compilation of the plagiogranite database. Sample 923A from MAR was kindly provided by Laura Gaggero, Genova, Italy. This research used samples provided by the Ocean Drilling Program (ODP). ODP is sponsored by the US National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. The manuscript has been substantially improved after thorough reviews by B. Scaillet and M.B. Wolf. Valuable editorial advice from J. Hoefs is also acknowledged. Funding for this research was provided by grants from the Deutsche Forschungsgemeinschaft (KO 1723/3).

PY - 2004/1

Y1 - 2004/1

N2 - We performed hydrous partial melting experiments at shallow pressures (0.2 GPa) under slightly oxidizing conditions (NNO oxygen buffer) on oceanic cumulate gabbros drilled by ODP (Ocean Drilling Program) cruises to evaluate whether the partial melting of oceanic gabbro can generate SiO2-rich melts with compositions typical of oceanic plagiogranites. The experimental melts of the low-temperature runs broadly overlap those of natural plagiogranites. At 940 °C, the normalized SiO2 contents of the experimental melts of all systems range between 60 and 61 wt%, and at 900 °C between 63 and 68 wt%. These liquids are characterized by low TiO2 and FeOtot contents, similar to those of natural plagiogranites from the plutonic section of the oceanic crust, but in contrast to Fe and Ti-rich low-temperature experimental melts obtained in MORB systems at ∼950 °C. The ∼1,500-m-long drilled gabbroic section of ODP Hole 735B (Legs 118 and 176) at the Southwest Indian Ridge contains numerous small plagiogranitic veins often associated with zones which are characterized by high-temperature shearing. The compositions of the experimental melts obtained at low temperatures match those of the natural plagiogranitic veins, while the compositions of the crystals of low-temperature runs correspond to those of minerals from high-temperature microscopic veins occurring in the gabbroic section of the Hole 735B. This suggests that the observed plagiogranitic veins are products of a partial melting process triggered by a water-rich fluid phase. If the temperature estimations for high-temperature shear zones are correct (up to 1,000 °C), and a water-rich fluid phase is present, the formation of plagiogranites by partial melting of gabbros is probably a widespread phenomenon in the genesis of the ocean crust.

AB - We performed hydrous partial melting experiments at shallow pressures (0.2 GPa) under slightly oxidizing conditions (NNO oxygen buffer) on oceanic cumulate gabbros drilled by ODP (Ocean Drilling Program) cruises to evaluate whether the partial melting of oceanic gabbro can generate SiO2-rich melts with compositions typical of oceanic plagiogranites. The experimental melts of the low-temperature runs broadly overlap those of natural plagiogranites. At 940 °C, the normalized SiO2 contents of the experimental melts of all systems range between 60 and 61 wt%, and at 900 °C between 63 and 68 wt%. These liquids are characterized by low TiO2 and FeOtot contents, similar to those of natural plagiogranites from the plutonic section of the oceanic crust, but in contrast to Fe and Ti-rich low-temperature experimental melts obtained in MORB systems at ∼950 °C. The ∼1,500-m-long drilled gabbroic section of ODP Hole 735B (Legs 118 and 176) at the Southwest Indian Ridge contains numerous small plagiogranitic veins often associated with zones which are characterized by high-temperature shearing. The compositions of the experimental melts obtained at low temperatures match those of the natural plagiogranitic veins, while the compositions of the crystals of low-temperature runs correspond to those of minerals from high-temperature microscopic veins occurring in the gabbroic section of the Hole 735B. This suggests that the observed plagiogranitic veins are products of a partial melting process triggered by a water-rich fluid phase. If the temperature estimations for high-temperature shear zones are correct (up to 1,000 °C), and a water-rich fluid phase is present, the formation of plagiogranites by partial melting of gabbros is probably a widespread phenomenon in the genesis of the ocean crust.

UR - http://www.scopus.com/inward/record.url?scp=1642482280&partnerID=8YFLogxK

U2 - 10.1007/s00410-003-0511-9

DO - 10.1007/s00410-003-0511-9

M3 - Article

AN - SCOPUS:1642482280

VL - 146

SP - 414

EP - 432

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 4

ER -