UC San Diego

The Troodos complex, Cyprus, provides an opportunity to study the structural configuration along a fossil intersection of a spreading axis and a transform fault. We complement studies at Troodos that have reconstructed the brittle deformation of the upper crust by new paleomagnetic data from the gabbro suite. The gabbro suite is exposed at the extinct spreading axis continuing the Solea graben toward the intersection with the fossil Arakapas oceanic transform. This is a unique exposure of deep crustal rocks formed at both an inside-corner and an outside-corner of a ridge-transform intersection. Remanence directions from gabbros (23 sites) were used as indicators for rigid body rotation. The spatial distribution of rotation axes allow recognition of three regions to which deformation is partitioned: 1) a western region (outside corner) that experienced primarily tilt about horizontal axis 2) a central region with minor rotation and, 3) an eastern area (inside corner) where vertical axis rotations are dominant. The absence of significant rotation in the 6 km-wide central domain together with its location between the inside- and the outside corner uncover the root of a fossil axial volcanic zone, a zone sufficiently hot so the upper crust can decouple from the substrate. Clockwise rotation in the gabbro increases from the axial zone eastward, similar to that in the overlying dikes, indicating coupling of the lower crust with the brittle upper oceanic crust. The transition from the decoupled layers of sheeted dikes and gabbro in the axial zone to the dikes-gabbro coupling in the inside corner is in keeping with deepening of the brittle-ductile transition from the dike-gabbro boundary into the lower crust away from the axial zone. Our conclusions are consistent with one of the previous reconstructions in which the Solea spreading axis was orthogonal to the Arakapas trunsform fault, and with recent studies of the present-day lower oceanic crust. However, the newly inferred surface trace of the Solea spreading axis is further to the east, probably reflecting the tilt of axial upper crust rotated blocks. (c) 2006 Elsevier B.V. All rights reserved.