TY - JOUR
T1 - Lithospheric petrology of the eastern Arabian Plate
T2 - Constraints from Al-Ashkhara (Oman) xenoliths
AU - Nasir, Sobhi
AU - Stern, Robert J.
N1 - Funding Information:
S. Nasir acknowledges financial support from the Sultan Qaboos University (HM-Grant SR/Sci/ETHS/06/01 ). Hans-Joachim Massonne and Thomas Theye, Stuttgart University are thanked for their help with the microprobe analysis. Constructive reviews by Michel Gregoire and anonymous referee and the comments of the editor A. Kerr led to substantial improvement in the manuscript.
PY - 2012/2
Y1 - 2012/2
N2 - Mafic granulite and spinel lherzolite xenoliths from Cenozoic alkaline basalts near Al-Ashkhara, eastern Oman, have been selected for a systematic mineralogical, geochemical and Sr-Nd-Pb isotopic study. This is the only place in E Arabia where samples of both lower crust and upper mantle can be examined. Lower crustal xenoliths consist of two mineralogically and chemically distinct groups: gabbronorite (subequal abundances of ortho- and clino-pyroxene and plagioclase) and plagioclase pyroxenite (dominant pyroxene and subordinate plagioclase). Temperature estimates for lower crustal xenoliths using the two pyroxene geothermometer (T-Wells) yield 810-865°C. The mineral assemblage (spinel-pyroxene-plagioclase) and Al content in pyroxene indicate that plagioclase-bearing xenoliths equilibrated at 5-8kbar (13 and 30km depth) in the lower crust. εNd and 87Sr/ 86Sr calculated at 700Ma for Al-Ashkhara lower crustal xenoliths (+6.4 to +6.6; 87Sr/ 86Sr=0.7028 to 0.7039) are consistent with the interpretation that juvenile, mafic melts were added to the lower crust during Neoproterozoic time and that there was no discernible contribution from pre-Neoproterozoic crust. Upper mantle xenoliths consist of both dry and hydrous (phlogopite-bearing) lherzolites. These peridotites are more Fe-rich than expected for primitive mantle or melt residues and probably formed by pervasive circulation of melts that have refertilized pre-existing mantle peridotites. Mineral equilibration temperatures range from 990 to 1070°C. Isotopic compositions calculated at 700Ma are εNd=+6.8 to +7.8 and 87Sr/ 86Sr=0.7016 to 0.7025, indicating depleted upper mantle. Pb isotopic compositions indicate that the metasomatism was relatively recent, perhaps related to Paleogene tectonics and basanite igneous activity. Nd model ages for the spinel peridotite xenoliths range between 0.59 and 0.65Ga. The xenolith data suggest that eastern Arabian lower crust is of hotspot origin, in contrast to western Arabian lower crust, which mostly formed at a convergent plate margin. Geochemical and isotopic differences between lower crust and upper mantle indicate that these are unrelated, possibly because delamination replaced the E Arabian mantle root in Neoproterozoic time.
AB - Mafic granulite and spinel lherzolite xenoliths from Cenozoic alkaline basalts near Al-Ashkhara, eastern Oman, have been selected for a systematic mineralogical, geochemical and Sr-Nd-Pb isotopic study. This is the only place in E Arabia where samples of both lower crust and upper mantle can be examined. Lower crustal xenoliths consist of two mineralogically and chemically distinct groups: gabbronorite (subequal abundances of ortho- and clino-pyroxene and plagioclase) and plagioclase pyroxenite (dominant pyroxene and subordinate plagioclase). Temperature estimates for lower crustal xenoliths using the two pyroxene geothermometer (T-Wells) yield 810-865°C. The mineral assemblage (spinel-pyroxene-plagioclase) and Al content in pyroxene indicate that plagioclase-bearing xenoliths equilibrated at 5-8kbar (13 and 30km depth) in the lower crust. εNd and 87Sr/ 86Sr calculated at 700Ma for Al-Ashkhara lower crustal xenoliths (+6.4 to +6.6; 87Sr/ 86Sr=0.7028 to 0.7039) are consistent with the interpretation that juvenile, mafic melts were added to the lower crust during Neoproterozoic time and that there was no discernible contribution from pre-Neoproterozoic crust. Upper mantle xenoliths consist of both dry and hydrous (phlogopite-bearing) lherzolites. These peridotites are more Fe-rich than expected for primitive mantle or melt residues and probably formed by pervasive circulation of melts that have refertilized pre-existing mantle peridotites. Mineral equilibration temperatures range from 990 to 1070°C. Isotopic compositions calculated at 700Ma are εNd=+6.8 to +7.8 and 87Sr/ 86Sr=0.7016 to 0.7025, indicating depleted upper mantle. Pb isotopic compositions indicate that the metasomatism was relatively recent, perhaps related to Paleogene tectonics and basanite igneous activity. Nd model ages for the spinel peridotite xenoliths range between 0.59 and 0.65Ga. The xenolith data suggest that eastern Arabian lower crust is of hotspot origin, in contrast to western Arabian lower crust, which mostly formed at a convergent plate margin. Geochemical and isotopic differences between lower crust and upper mantle indicate that these are unrelated, possibly because delamination replaced the E Arabian mantle root in Neoproterozoic time.
KW - Arabian Plate
KW - Lherzolite
KW - Lithosphere
KW - Lower crust
KW - Oman
KW - Xenoliths
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U2 - 10.1016/j.lithos.2011.11.011
DO - 10.1016/j.lithos.2011.11.011
M3 - Article
AN - SCOPUS:84055178980
SN - 0024-4937
VL - 132-133
SP - 98
EP - 112
JO - Lithos
JF - Lithos
ER -