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Geological Society, London, Special Publications; 2003; v. 218; p. 129-145;
DOI: 10.1144/GSL.SP.2003.218.01.08
© 2003 Geological Society of London

Tethyan Ophiolites in the Alpine-Himalayan Orogenic System

Structural and microstructural analysis of a palaeo-transform fault zone in the Neyriz ophiolite, Iran

Khalil Sarkarinejad

Department of Earth Sciences, College of Sciences, University of Shiraz, Shiraz, Iran Sarkarinejad{at}geology.susc.ac.ir sarkarinejad{at}yahoo.com

The Neyriz ophiolite in SW Iran includes a NNW-SSE-trending, steeply dipping oceanic palaeo-transform fault zone that consists mainly of deformed and sheared gabbros and peridotites. Mylonitic rocks within the fossil palaeo-transform fault display C-, C'- and S-band shear cleavages containing green hornblende- and feldspar-rich bands. Deformed hornblendemantled porphyroclasts have symmetrical tails or {sigma}-type porphyroclast systems, which show clockwise stair-stepping rotation and oblique foliation with asymmetrical complex stripes and wings. These microstructures indicate dextral shearing on the palaeo-transform fault. The c-axes of hornblende in high-grade S-C mylonitic rocks exhibit strong lattice-preferred orientation (LPO) patterns with M- and G-type origin. These LPO patterns are asymmetrical with respect to the shear zone foliation and also indicate dextral shearing. The NNW-SSE trend of the palaeo-transform fault is perpendicular to the general NE strike of sheeted dykes and is parallel to the average harzburgite foliation. These observations suggest a noncoaxial shear orientation of mantle flow, which progressively rotated toward parallelism with the fossil fracture zone. This dextral transform fault is inferred to have connected ENE-trending oceanic spreading centre segments in a Neo-Tethyan ocean basin.





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[Abstract] [PDF]