HR: 0800h
AN: T41D-1343    [Abstracts]
TI: Fault-related Oceanic Serpentinization in a Fossil Ridge-Transform Intersection: the Troodos Ophiolite
AU: * Nuriel, P
EM: perach@bgu.ac.il
AF: Dept. of Geological and Environmental Sciences, Ben Gurion Univ. of the Negev, Beer Sheva, 84105 Israel
AU: Katzir, Y
EM: ykatzir@bgu.ac.il
AF: Dept. of Geological and Environmental Sciences, Ben Gurion Univ. of the Negev, Beer Sheva, 84105 Israel
AU: Abelson, M
EM: meira@mail.gsi.il
AF: Geological Survey of Israel, Israel30 Malkhe Israel St., Jerusalem, 95501 Israel
AU: Valley, J W
EM: valley@geology.wisc.edu
AF: Dept. of Geology and Geophysics, University of Wisconsin, Madison WI, 53706 United States
AU: Matthews, A
EM: alan@vms.huji.ac.il
AF: Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem, 91904 Israel
AB: A domal structure cored by gabbros and ultramafics occurs at the fossil Ridge Transform Intersection (RTI) preserved in the Turonian Troodos ophiolite of Cyprus. The off-axis location and outside corner position of the ultramafics relative to the palaeo-RTI resemble the geometry of modern oceanic core complexes. Within the RTI, highly- serpentinized ultramafic rocks are juxtaposed against gabbros along a major ridge-parallel normal fault, the Amiandos Fault. Along strike, the fault was described as a listric splay of a low-angle detachment. Field, petrographic and stable isotope data are used to determine the spatial distribution, temperature and the type of water involved in serpentinization in the Troodos RTI. Petrographic and isotope tracers (δ D, δ¹⁸O) of hydrothermal alteration were examined in three profiles across the Amiandos Fault. At all sites the modal amounts of hydrous minerals in both gabbro and ultramafic rocks increase towards the fault, indicating a higher degree of alteration. Oxygen isotope ratios of serpentine (Srp) along a 2.5 km transect in the central part of the serpentinite exposure range from 10.6 to 12.6‰, among the highest δ¹⁸O values measured in ophiolite serpentine, and in agreement with the pioneering work of Magaritz & Taylor (1974). Entirely different, much lower δ¹⁸O (Srp) values of 4.6 to 6.6‰ were measured in a detailed, 150 m long, profile perpendicular to the Amiandos fault in the northern part of the serpentinite domain. Hydrogen isotope ratios also vary: whereas the δD values in the central transect range from -86 to -70‰, those of the northern transect are significantly higher ranging from -75 to -57‰. The bimodal distribution of isotope ratios in these transects calls for two distinct serpentinization events: low-temperature hydration recorded in the central area and high-temperature interaction with seawater in the northern part. Superposition of the two serpentinization events is evident at the third, southernmost transect, where δ¹⁸O (Srp) values decrease gradually from 10.7‰ 2 km away from the fault to 5.0‰ in the fault area. Hydrogen isotope ratios of serpentine are homogenous throughout the southern transect (-63 ±2 ‰),but increase to -51‰ at the fault plane. It is thus suggested that the Troodos peridotites were locally serpentinized due to fault-assisted deep infiltration of seawater during seafloor spreading. This early tectono-hydrothermal history was later overprinted by low- temperature serpentinization, either on the seafloor or in continental conditions during emplacement. These observations suggest that the ridge-parallel Amiandos fault was active during seafloor spreading. In addition to several previous observations, this conclusion implies that a core complex structure is fossilized in the Troodos ophiolite.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Tectonophysics [T]
MN: Fall Meeting 2005