HR: 0800h
AN: T11C-0398    [Abstracts]
TI: Cordilleran- Versus Tethyan-Type Ophiolites and Global Tectonics
AU: * Dilek, Y
EM: dileky@muohio.edu
AF: Miami University, Department of Geology, 116 Shideler Hall, Oxford, OH 45056 United States
AB: Distinguishing between Cordilleran- vs. Tethyan-type ophiolites is a first-order tectonic problem in studying orogenic belts and their geodynamic evolution. Cordilleran ophiolites (CO) in accretionary-type orogenic belts structurally overlie subduction-accretion complexes and are incorporated into active continental margins via progressive underthrusting of oceanic material and/or through ridge-trench interactions. Tethyan-type ophiolites (TO) structurally overlie passive continental margins, microcontinents or island arcs, and are emplaced via collision of these buoyant crustal entities with trenches and their attempted subduction. This process may lead to induced subduction initiation in the region (via subduction jump and/or flip) and precedes terminal continental collisions, which create intra-continental mountain belts (Alps, Himalayas). Cordilleran-type ophiolites are commonly polygenetic, developed on and across a deformed, heterogeneous oceanic basement and may include fully developed island arc sequences having island arc tholeiite (IAT) to calcalkaline affinities, pyroclastic rocks, and felsic differentiates. Prolonged history of subduction with variable polarity and kinematics may generate nested Cordilleran ophiolites with different ages and chemical compositions that may have been affected by orogen-parallel wrench faulting due to oblique convergence. Ophiolites in the Caribbean region are composed of dismembered mafic-ultramafic rock assemblages, including LIP-generated lithologies, and represent fragments of vertically thickened (via plume activities) oceanic crust with polygenetic histories; these kinds of LIP-related ophiolites may also exist in other accretionary-type orogenic belts and in the Precambrian record. Tethyan-type ophiolites include the Ligurian ophiolites with Hess-type oceanic crust and Eastern Mediterranean ophiolites with Penrose-type oceanic crust, and may contain well-developed sheeted dyke complexes developed due to robust magmatic extension beneath narrow rift zones during their seafloor spreading history. Igneous accretion of typical Tethyan-type ophiolites may have been facilitated by slab rollback and mantle flow that resulted in upper plate extension and further melting of previously depleted asthenosphere, showing a progressive evolution from MORB-like to IAT to boninitic proto-arc assemblages. Rift-drift sequences recording early phases of basin opening may be preserved as m‚lange units beneath Tethyan ophiolites. Thus, Tethyan-type ophiolites may reflect the Wilson cycle evolution of ancient oceans and the timing of rifting-related dismantling and collision-driven assembly of supercontinents. Some of these global events may have been linked to the production of plumes and accelerated LIP formation. Recognition of Cordilleran- vs. Tethyan-type ophiolites in ancient mountain belts and in the Precambrian record can be a useful tool to distinguish between accretionary and collisional orogens and their mode of continental growth.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8140 Ophiolites (3042)
DE: 8178 Tectonics and magmatism
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: Fall Meeting 2005