HR: 1400h
AN: V53B-04    [Abstracts]
TI: Petrogenesis of Cenozoic Alkaline Basalts From the Tigris Volcanic Field, NE Syria
AU: * Abdel-Rahman, A
EM: arahman@aub.edu.lb
AF: American University of Beirut, Department of Geology, Bliss Street, P.O.Box 11-0236, Beirut, , Lebanon
AU: Lease, N A
AF: Ministre de l'Agriculture, 200 chemin Sainte-Foy, Quebec, G1R 4X6, Canada
AB: The Tigris volcanic field of NE Syria contains large discontinuous exposures of basanitic and basaltic lava flows of Quaternary age, covering an area of about 2,700 km², and is located near the Bitlis collision suture which forms the boundary between the Arabian and Eurasian plates. The lavas are made up of olivine (Fo_78-89), clinopyroxene (salite and titan-augite), plagioclase (An_57-68), and opaque phases. Chemical data show that the rocks exhibit SiO₂ values ranging from 42.2 to 48.2 wt%, MgO (5.7-9.1 wt%) and are relatively enriched in TiO₂ (1.7-3.2 wt%). Mg-numbers range from 0.51 to 0.62, with an average of 0.58. The rocks are enriched in incompatible trace elements such as Zr (119-231 ppm), Nb (14-43 ppm) and Y (17-22 ppm). The REE patterns are strongly fractionated [(La/Yb)_N = 11], indicative of a garnet-bearing source. The ¹⁴³Nd / ¹⁴⁴Nd isotopic compositions range from 0.512803 to 0.512908, and ⁸⁷Sr / ⁸⁶Sr from 0.70327 to 0.70403. Such compositions are typical of those of HIMU-OIB, with a HIMU-like mantle source. Modeling indicates that the magma was produced by a small degree of partial melting (F = 1 to 2%) of a primitive, garnet-lherzolite mantle source. Elemental ratios such as K/P (4.6), La/Ta (12), La/Nb (0.90), Nb/Y (1.22), and Th/Nb (0.09), suggest that the magma was subjected to minimal crustal contamination. Shear heating at the base of the lithospheric mantle of the northern boundary of the Arabian plate, caused by a change in plate motion as the Arabian plate moved in a more easterly direction during the Plio-Quaternary may have provided the heat necessary for partial fusion and magma generation. The Neogene collision of the Arabian plate with Eurasia along the Bitlis suture resulted in reactivation (beneath the Tigris-Euphrates basin) of deep-seated fractures, along which lavas may have penetrated the crust.
DE: 1037 Magma genesis and partial melting (3619)
DE: 3619 Magma genesis and partial melting (1037)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly