PALAEOMAGNETIC AND STRUCTURAL ANALYSIS OF THE METAMORPHIC SOLE ROCKS OF THE MERSIN OPHIOLITE, SOUTHERN TURKEY
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The Mersin ophiolite (Tauride Belt, southern Turkey) is a well-exposed Neo-Tethyan suprasubduction zone ophiolite that formed in the Late Cretaceous. It is underlain by metamorphic sole rocks (predominantly amphibolites) inferred to have formed at the top of the down-going plate during subduction. A recent model for exhumation of such rocks from peak metamorphic depths involves slab flattening caused by removal of material from the mantle wedge during fore-arc spreading, implying significant rotation of the sole after formation. Previous palaeomagnetic analysis of non-metamorphosed dykes cutting the Mersin sole rocks indicates a ~45° clockwise rotation of the sole and dykes around a NE-trending, shallowly plunging, ridge-parallel axis. This study aims to quantify any potential rotation of the Mersin sole rocks prior to dyke intrusion to test models of sole exhumation. The amphibolites carry a stable magnetization that is statistically different from that of the dykes, providing evidence for an earlier phase of rotation. However, tectonic interpretation of these data in the absence of paleohorizontal markers cannot be achieved by using standard palaeomagnetic tilt corrections. Therefore, a Monte Carlo approach was used to model potential net tectonic rotation axes after back-stripping the later rotation of sole-hosted dykes from the palaeomagnetic and structural data and by incorporating statistical uncertainties into the analysis. Results suggest that the sole acquired its remanence while the metamorphic foliation dipped moderately (~30-40°) to the ENE and then underwent an early phase of anticlockwise rotation around an inclined, NW plunging axis. This is consistent with a two-stage model involving an earlier phase of exhumation by slab flattening and rotation followed by a later spreading-related rotation around a ridge-parallel axis after accretion of the sole to the base of the lithosphere (and future ophiolite). These rotations around different axes are consistent with a tectonic setting similar to the modern Andaman Sea subduction zone system, where spreading in the suprasubduction zone environment occurs obliquely to the direction of subduction of the down-going plate.