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7461378 
Journal Article 
Peak metamorphic conditions of garnet amphibolites beneath the Semail Ophiolite: Implications for an inverted pressure gradient 
Gnos, E 
1998 
Yes 
International Geology Review
ISSN: 0020-6814 
40 
4 
281-304 
English 
WOS:000073374500001 
Garnet amphibolites beneath the Semail Ophiolite formed at 1.1 +/- 0.2 GPa and green schist-facies rocks in the same metamorphic sole yielded pressure estimates of 0.45 to 0.55 GPa. Thus, in addition to the well-known inverted thermal gradient in subophiolitic metamorphic sequences, an inverted metamorphic pressure gradient of 0.3 to 2.0 MPa/m over <2000 m also exists. Temperature estimates for samples systematically collected every 10 m across a 70 m thick sequence that contains the assemblage garner + plagioclase + amphibole (+/- diopside +/- ilmenite +/- titanite +/- rutile) allowed the determination of an average inverted metamorphic temperature gradient of 1 to 4 degrees C/m, using different thermometers. Pressures in garnet amphibolites were estimated from the presence of cm-sized kyanite, by comparison of the observed assemblage with relevant published experimental results, and by using heterogeneous equilibrium calculations. The different estimations result in peak P-T conditions of 800 +/- 100 degrees C and 1.1 +/- 0.2 GPa, The inverted metamorphic pressure gradient can be explained by the continuous accretion of material formed under different P-T conditions, although there are no obvious structural breaks in outcrop. The less than or equal to 20 km thick overlying Semail Ophiolite is insufficient to produce the computed 1.1 +/- 0.2 GPa lithostatic pressures. Piling of nappes or structural thinning at the base of the nappe and continuous denudation/structural thinning at rates of 0.36 to 0.45 cm per year during emplacement may explain the inverted pressure gradient. 
Physical Sciences - Other Topics; southeastern oman mountains, samail ophiolite, quartz, rocks,; geothermometer, temperature, equilibria, granulites, eclogites, ca