Krienitz, Marc-Sebastian, Haase, K. M., Mezger, K., van den Bogaard, Paul, Thiemann, V. and Shaikh-Mashail, M. A. (2009) Tectonic events, continental intraplate volcanism, and mantle plume activity in northern Arabia: constraints form geochemistry and Ar-Ar dating of Syrian lavas. Geochemistry, Geophysics, Geosystems, 10 (Q04008). DOI 10.1029/2008GC002254.

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Abstract

New (40)Ar/(39)Ar ages combined with chemical and Sr, Nd, and Pb isotope data for volcanic rocks from Syria along with published data of Syrian and Arabian lavas constrain the spatiotemporal evolution of volcanism, melting regime, and magmatic sources contributing to the volcanic activity in northern Arabia. Several volcanic phases occurred in different parts of Syria in the last 20 Ma that partly correlate with different tectonic events like displacements along the Dead Sea Fault system or slab break-off beneath the Bitlis suture zone, although the large volume of magmas and their composition suggest that hot mantle material caused volcanism. Low Ce/Pb (<20), Nb/Th (<10), and Sr, Nd, and Pb isotope variations of Syrian lavas indicate the role of crustal contamination in magma genesis, and contamination of magmas with up to 30% of continental crustal material can explain their (87)Sr/(86)Sr. Fractionation-corrected major element compositions and REE ratios of uncontaminated lavas suggest a pressure-controlled melting regime in western Arabia that varies from shallow and high-degree melt formation in the south to increasingly deeper regions and lower extents of the beginning melting process northward. Temperature estimates of calculated primary, crustally uncontaminated Arabian lavas indicate their formation at elevated mantle temperatures (T(excess) similar to 100-200 degrees C) being characteristic for their generation in a plume mantle region. The Sr, Nd, and Pb isotope systematic of crustally uncontaminated Syrian lavas reveal a sublithospheric and a mantle plume source involvement in their formation, whereas a (hydrous) lithospheric origin of lavas can be excluded on the basis of negative correlations between Ba/La and K/La. The characteristically high (206)Pb/(204)Pb (similar to 19.5) of the mantle plume source can be explained by material entrainment associated with the Afar mantle plume. The Syrian volcanic rocks are generally younger than lavas from the southern Afro-Arabian region, indicating a northward progression of the commencing volcanism since the arrival of the Afar mantle plume beneath Ethiopia/Djibouti some 30 Ma ago. The distribution of crustally uncontaminated high (206)Pb/(204)Pb lavas in Arabia indicates a spatial influence of the Afar plume of similar to 2600 km in northward direction with an estimated flow velocity of plume material on the order of 22 cm/a.

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