HR: 15:25h
AN: T43D-08    [Abstracts]
TI: Ridge Transform Intersection at Troodos: Implications for 3D Time-dependent Accretion and Deformation in the Oceanic Crust
AU: * Granot, R
EM: rgranot1@pob.huji.ac.il
AF: Institute of Earth Sciences, Hebrew University, Givat Ram, Jerusalem, 91904 Israel
AU: Abelson, M
EM: meira@mail.gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem, 95501 Israel
AU: Ron, H
EM: hagairon@vms.huji.ac.il
AF: Institute of Earth Sciences, Hebrew University, Givat Ram, Jerusalem, 91904 Israel
AU: Agnon, A
EM: amotz@huji.ac.il
AF: Institute of Earth Sciences, Hebrew University, Givat Ram, Jerusalem, 91904 Israel
AB: Structural features of fossil ridge transform intersection (RTI) are best exposed in the Troodos ophiolite, Cyprus. Previous works have reconstructed the two-dimensional configuration of the ophiolite. In order to understand the evolution of the crust adjacent to the RTI, we investigated deformation and magma flow patterns near and away from the key structural elements: a paleo-spreading axis and a fossil transform fault. The investigation methods included 3D paleomagnetic reconstructions and AMS surveys focused on the gabbro layer of the oceanic lithosphere. We have collected 238 oriented field drilled cores at 42 sites. The stable magnetization was measured and used to reconstruct the deformation within the lower crust. The fabric of the gabbro was determined by measuring the anisotropy of magnetic susceptibility (AMS) on all samples. Directions of magmatic flow in the axial magma chamber, as recorded by the AMS, have changed from vertical to along-axis and vice versa. Three provinces of coherent flow directions are mapped, each 5-10 km across. A province showing vertical flow is right on an orthogonal spreading axis, and the changeover to along-axis flow was accompanied by abrupt transition to a curved RTI. This study also demonstrates that the upper crust, along the spreading axis, is decoupled from the lower crust by detachment. Hence, the precise location of the ridge axis is defined where the gabbro shows no deformation. As the spreading continues and the oceanic lithosphere cools and thickens, the detachment faults at either side of the axis migrate downward into the lower parts of the lithosphere. Rotations of the paleomagnetic vectors at the outside corner reveal an extensional detachment fault, i.e., block rotation about a horizontal axis on the hanging wall of the detachment. On the other hand, the inside corner reveals a torsional detachment fault, i.e., block rotation about a vertical axis on the hanging wall of the detachment. This new type of fault formed as a result of shearing along the transform fault.
DE: 8122 Dynamics, gravity and tectonics
DE: 5475 Tectonics (8149)
DE: 3035 Midocean ridge processes
DE: 1518 Magnetic fabrics and anisotropy
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting