Geosciences Dept. Seminar: 3D gravity modeling of the Kinneret-Bet She'an basin structure, a relic of a rift-transform intersection

Abstract:

The Kinneret-Bet She'an basin (KBSB) comprises the Sea of Galilee, Kinarot, and Bet She'an sub-basins. Development of this basin originated at the intersection between two major tectonic boundaries: the Oligo-Miocene Sirhan failed rift, that later developed into the southern Galilee basins and Carmel-Gilboa fault system; and the Dead Sea fault plate boundary, a transform that developed since the Miocene. Despite numerous studies, the KBSB still remains one of the enigmatic basins. Its structure, stratigraphy and development are vaguely understood – both inside the basin and in correlation with its surroundings. A new and comprehensive 3D model is presented here for the structure of the KBSB. It is based on all available gravity measurements, adopted from the national gravity database, and new gravity measurements, collected in cooperation with the Geological Survey of Israel. To minimize non-uniqueness, the gravity data were integrated with constraints from wells, surface geology, seismic surveys, and potential field studies. Based on the dense coverage of gravity data, modeling the deep structure was enabled in three dimensions.

The model details the spatial distribution, depth, thickness and density of the following regional units within the KBSB and across its surroundings: upper crust, pre-Senonian sediments, Senonian and Cenozoic sediments, Miocene volcanics, Pliocene and Quaternary volcanics. Additional local units include salt, gabbro and pyroclasts. Results indicate that the KBSB comprises two sub-basins separated by a structural saddle: Kinneret-Kinarot (~6-7 km deep, ~45 km long) and Bet She'an (~4 km deep, ~10 km long). A 500 m thick layer of Miocene volcanics is present across the Bet She'an sub-basin, yet missing from the Kinneret-Kinarot sub-basin. Between the basins Zemah-1 well penetrated a salt unit. The model indicates that this unit is a part of a thick (1250 m) dome-shaped, perhaps diapiric, structure. A relatively thin (350 m) salt unit fills the Kinneret-Kinarot sub-basin. Above, a 700 m thick layer of Pliocene volcanics fills the entire KBSB. These volcanics are uplifted in the Zemah area by ~200 m, and dip northward towards the center of the Sea of Galilee. Further north, the Pliocene volcanics dip southward from Korazim towards the center of the Sea of Galilee. Nearly 3.2 km of vertical depth differences are evident across a horizontal distance of ~15 km, forming a ~12° slope below the younger Quaternary fill of the basin. A low-density, probably pyroclastic, lens is calculated within the uppermost 2 km of the Sea of Galilee fill. Scenarios for the multi-phase evolution of the basin are discussed considering its origin as part of a transform, superimposed on a rift.

Seminar Organizer: Prof. Eyal Haifetz