The Development of Subduction Below the Oman-UAE Ophiolite: Detailed Temporal Constraints from High Precision U-Pb Zircon Geochronology

Friday, 19 December 2014: 8:30 AM
Matthew E Rioux1, Samuel A Bowring2, Joshua M Garber1, Peter B Kelemen3, Micheal P Searle4, Sumio Miyashita5 and Yoshiko Adachi5, (1)University of California Santa Barbara, Santa Barbara, CA, United States, (2)MIT, Cambridge, MA, United States, (3)Columbia University of New York, Palisades, NY, United States, (4)Department of Earth Sciences, University of Oxford, Oxford, United Kingdom, (5)Niigata University, Niigata, Japan
The tectonic setting during formation of the Oman-UAE ophiolite is debated. High precision 206Pb/238U zircon dates from gabbros indicate that ridge magmatism responsible for formation of most of the ophiolite crust occurred between ~96.0–95.5 Ma. Here we present new high precision 206Pb/238U zircon dates and whole-rock Nd isotopic data from three rock sequences that constrain the development of thrusting/subduction below the ophiolite: 1. The V2 volcanic sequence and associated plutonic rocks in the ophiolite have geochemical patterns that have been interpreted as a subduction signature. V2 plutonic rocks from both Oman and the UAE have dates of ~95.6–95.0 Ma, consistent with rapid development of thrusting/subduction following formation of the ophiolite crust. 2. Felsic plutonic rocks with εNd < 0 intrude residual mantle harzburgites below the crust-mantle boundary, consistent with derivation of the magmas from a source with time-integrated LREE enrichment, such as continental crust or terrigenous sedimentary rocks. Dates on these rocks in Oman range from ~95.5–95.0, consistent with synchronous thrusting of continent derived rocks below the ophiolite during V2 magmatism. Similar intrusive rocks from the UAE are younger, ranging from ~94–91 Ma, indicating a more protracted history of thrusting and melting in this area. 3. Amphibolite facies metamorphic rocks in the sole of the ophiolite are interpreted as crust thrust beneath the ophiolite during formation or emplacement. Garnet amphibolites and small leucocratic (?) pods and veins from sole exposures in Oman are 96.0–94.7 Ma. The oldest dates are synchronous with ridge magmatism and suggest some sole amphibolites underwent metamorphism and melting while the ridge was active, favoring a supra-subduction zone model for ophiolite formation. Rocks from sole exposures in the UAE are slightly younger, ranging from 94.5–92.5 Ma. In summary, the data strongly support a supra-subduction zone model for formation of the ophiolite. If, as has been proposed, the ophiolite formed during subduction initiation, the new dates provide an unprecedented record of this process, which can be used to test and constrain geodynamic models.