T26 From the Afar Rift to Alaskan Arcs (and the Oregon Plateau in between): Honoring the Career and Contributions of William K. Hart (Posters)

Sunday, 10 October 2021
9:00 AM - 1:00 PM
Exhibit Hall A

THE ORIGIN OF CONTINENTAL ALKALINE MAFIC MAGMATISM: MELT INCLUSIONS PERSPECTIVE ON MESOZOIC LAVAS FROM MAKHTESH RAMON, ISRAEL

Paper number: T26-7
Program: Technical Sessions
Time: 9:00 AM – 1:00 PM

Authors

Abstract

The erosional cirque of Makhtesh Ramon, Negev highlands, Israel, records several cycles of Mesozoic within-plate magmatism. While the late Triassic lavas were related to rifting at the margins of the Tethyan Levant basin, the more abundant, multi-phased, Early Cretaceous magmatism is thought to represent the activity of a hot spot beneath the African plate. However, the geochemical and isotope characteristics of the Cretaceous Ramon lavas, as well as the mantle xenoliths they carry, indicate a lithospheric source. The Makhtesh Ramon suites may thus document temporal variation in the mantle source, melting mechanism and lithospheric deformation in an evolving syn- to post- rift continental environment.

The cirque exposes well preserved alkaline mafic rocks and volcanic edifices of the regional Early Cretaceous ‘Levant’ intra-continental magmatic province, in particular of the latest, Aptian, Ramon volcanics. They constitute a highly diverse rock assemblage of alkali basalts through basanites and nephelinites to melilite nephelinites with a typical OIB-like signature and negligible crustal contribution. Melt inclusions are mostly of an evolved alkali basaltic melt, implying some low-pressure crystallization (2.2-5.7 kb) prior to entrapment. pMELTS-based modelling suggests partial melting at depths greater than 60 km to be the dominant process in which the rocks differentiated, with minor control by fractional crystallization. In Ga’ash Hill, a well preserved concentrically zoned volcano, subvolcanic nephelinite bodies intrude alkaline basalts, suggesting progressively lower amount of partial melting with time. However, partial melting of a homogenous source alone cannot explain some of the observations, mainly with regards to Rb and K. It is therefore suggested that a heterogenous source that is selectively melted or mixing of two distinct sources, combined with a process of batch partial melting, should provide the best explanation for the assemblage. The most likely source candidates are the EM (1 or 2) and HIMU mantle end members.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-371456

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