To better understand paleomagnetic data from the southern massifs, we conducted a detailed paleomagnetic and rock magnetic study of 21 sites in upper gabbros and 5 sites in lower crustal gabbros within the central Semail massif. Paleomagnetic data from northern massifs of the Oman ophiolite demonstrate substantial clockwise rotations prior to or during obduction, yet data from southern massifs are recently suggested to be remagnetized during obduction and show subsequent smaller counterclockwise rotations. New Paleomagnetic Data From Upper Gabbros Supports Limited Rotation of Central Semail Massif in Oman Ophiolite iii) The prevalent sense of shear is normal and slickenfibers ii) The deformation ranges from brittle-ductile, causing local deflection of the magmatic foliation, to brittle offset of the foliation and core and mantle structures in anhydrite veins. Early veins are filled with amphibole, chlorite, epidote, and anhydrite. Near-axis faulting- i) On or near-axis structures consist of epidote-amphibole bearing hydraulic breccias and some zones of intense cataclasis with intensely deformed epidote and seams of clay and chlorite accompanied by syntectonic alteration of the wall rock. Cyclic variation of magmatic foliation dip most likely reflects the process of plate separation at the ridge axis. Key observations include: no simple, systematic shallowing of dip with depth across the foliated-layered gabbro transition and layering is continuous across this transition. 4) There are no high temperature crystal-plastic shear zones in the core. 3) Layering is present throughout both cores, is defined by changes in mode and grain size ranging in thickness from 2 cm to 3 m and is commonly sub-parallel to the foliation.
2) The dip of the magmatic foliation varies cyclically, gradually changing dip by 30o from gentle to moderate over a 50 m wavelength. Magmatic and high temperature history- 1) Both cores exhibit a pervasive, commonly well-defined magmatic foliation delineated by plagioclase, olivine and in places clinopyroxene. Here we report the structural history of the gabbros reflecting formation at the ridge to later obduction. Hole GT2A is cut by a wider zone of brittle deformation and incipient brecciation. Hole GT1A is cut by a discrete fault system including localized thin ultracataclastic fault zones. 400 m of continuous core through a section of the layered gabbros and the foliated-layered gabbro transition. Oman Drilling Project Holes GT1A and GT2A were drilled into the Wadi Tayin massif, Samail ophiolite and both recovered ca. Structural Characterization of the Foliated-Layered Gabbro Transition in Wadi Tayin of the Samail Ophiolite, Oman Oman Drilling Project Holes GT1A and GT2Aĭeans, J. The lower part of the Hole (Units II, III and V) is dominated by medium-grained olivine gabbro, olivine melagabbro and olivine-bearing gabbro. The uppermost part of Hole GT2A (Unit I) is dominated by fine-grained granular olivine gabbro intercalated with less dominant medium-grained granular olivine gabbro and rare coarse-grained varitextured gabbro. On the basis of changes in grain size and/or modal abundance and/or appearance/disappearance of igneous primary mineral(s) five lithological units are defined in Hole GT2A (Unit I to V).
Intensity of alteration vein decreases from the top to the bottom of the hole.
Brittle fracture is observed throughout the core. The top 50 m of Hole GT2A is foliated gabbro whereas the bottom 250 m consists of layered gabbro. The transition zone occurs between 50 and 150 m curation corrected depth (CCD).
Hole GT2A drilled through the transition between foliated and layered gabbro. 33 shipboard scientists were divided into six teams (Igneous, Alteration, Structural, Geochem, Physical Properties, Paleomag) to describe and analyze the cores. The outer surfaces of the cores were imaged and described on site before being curated, boxed and shipped to the IODP drill ship Chikyu, where they underwent comprehensive visual and instrumental analysis. Hole GT2A was diamond cored in to to a total depth of 406.77 m. OmDP is an international collaboration supported by the International Continental Scientific Drilling Program, the Deep Carbon Observatory, NSF, IODP, JAMSTEC, and the European, Japanese, German and Swiss Science Foundations, with in-kind support in Oman from the Ministry of Regional Municipalities and Water Resources, Public Authority of Mining, Sultan Qaboos University, and the German University of Technology. Hole GT2A (UTM: 40Q 655960.7E / 2529193.5N) was drilled by the Oman Drilling Project (OmDP) into Wadi Gideah of Wadi Tayin massif in the Samail ophiolite, Oman. Overview of Hole GT2A: Drilling middle gabbro in Wadi Tayin massif, Oman ophiolite
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