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The evolution of Mesozoic magmatism in the Levant margins: melt inclusions perspective on source composition and geodynamic processes

Haran Hennig1 , Yevgeny Vapnik1, Sharon Hazan1, Bar Elisha1, Noriko T. Kita2, Yaron Katzir1

  • Affiliations:  1Department of Earth and Environmental Sciences, Ben Gurion University of the Negev, Be\'er Sheva, Israel. 2 WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA.

  • Presentation type: Talk

  • Presentation time: Monday 16:15 - 16:30, Room R280

  • Programme No: 1.7.11

  • Theme 1 > Session 7

Abstract

Continental rifts are considered a hallmark of intraplate alkaline magmatism as they provide the tectonic, thermal, and compositional conditions necessary for magma generation. However, the structural evidence does not always support extensional tectonism when it comes to prolonged magmatism. The opening of the Neo-Tethys Ocean during the Late Paleozoic--Early Mesozoic exemplifies this, as the southern Levant margin evolved from syn- to post-rift settings. This geodynamic transition is recorded by sequential intraplate mafic magmatism in Makhtesh Ramon, Negev Desert, S Israel. Here, using multiple microanalytical techniques we analyzed olivine-hosted melt inclusions from two volcanic sequences: the late Triassic Saharonim sub-alkalic basalt, and the early Cretaceous alkali basalt-basanite-nephelinite at Ga'ash Hill. Triassic rifting produced voluminous magmatism with a narrow compositional range, dominated by a CO2-metasomatized peridotite source. Pyroxenite formation during this period contributed to the diverse, low-degree melts of the early Cretaceous. Both formations host CO2-rich melt inclusions (up to 3.15 wt.%, some of the highest levels documented in continental OIB-like magmas), indicating a carbon-rich source with up to 850--640 ppm C. Combined with ~0.5 wt.% H2O, entrapment pressures ranged from 6--8 kbar (late Triassic) to 8--11 kbar (early Cretaceous), suggesting melt storage at lower crust--lithospheric mantle depths. The continental Moho likely functioned as a buoyancy barrier for ascending melts. While melting in the Triassic was initiated by mantle decompression, small changes in the tectonic or internal heat regimes could have caused melting of the readily fusible carbonate and pyroxenite bearing early Cretaceous mantle.