HR: 0800h
AN: T31B-0481    [Abstracts]
TI: Quantifying Strain in the Mantle Across a Paleotransform Fault, Bogota Peninsula, New Caledonia
AU: * Titus, S J
EM: stitus@carleton.edu
AF: Carleton College, One North College St., Northfield, MN 55057, United States
AU: Ferre, E
EM: eferre@geo.siu.edu
AF: Southern Illinois University, Mailcode 4324, Carbondale, IL 62901, United States
AU: Tikoff, B
EM: basil@geology.wisc.edu
AF: University of Wisconsin - Madison, 1215 W. Dayton St., Madison, WI 53706, United States
AB: The Massif du Sud in New Caledonia exposes the mantle section of an Eocene-age ophiolite thrust sheet. Field foliations over most of the Massif du Sud are horizontal to shallowly dipping to the SW with horizontal NS-trending lineations. The Bogota Peninsula along the northwest edge of the thrust sheet, in contrast, records moderately dipping to sub-vertical fabrics over a 50-km wide region, with the strongest mylonitic fabrics confined to a narrow 3-km wide zone. Field foliations rotate systematically and steepen across the shear zone; field lineations remain shallowly plunging but follow foliation rotations. Pyroxenite and dunite dikes, interpreted as early intrusions, record similar rotations and many become nearly transposed in the center of the high-strain zone. In contrast, late-stage diabase dikes have consistent NE-SW strikes and dip steeply in both directions at all locations across the shear zone. To quantify strain recorded across the Bogota Peninsula shear zone, we subdivided the region into four zones based on regional fabric consistency. We generated incremental forward models of inclined transpression and transtension and compared model results to the orientations of field foliation, lineation, and pyroxenite dikes within each zone. The triclinic fabrics in the Massif du Sud are consistent with sinistral inclined transpression and interpreted to form during oblique spreading along the south flank of an ~EW-trending ridge. Fabrics in the Bogota Peninsula shear zone, in contrast, have monoclinic symmetry and are interpreted to record dextral transpression along an oceanic transform fault linking two mid-ocean ridge segments. When combined, the modeling results from all four zones can be used to estimate the total fault offset and predict plate motion rates for this former oceanic plate boundary.
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8140 Ophiolites (3042)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting