Discovery of microdiamonds and associated minerals in the Makhtesh Ramon Canyon (Negev Desert, Israel)

Abstract

The Makhtesh Ramon erosional‐tectonic depression (canyon), 40 km long and approximately 8 km wide, is situated in the Negev Desert (southern Israel), 65 km southwest of the Dead Sea. The canyon rim and center are located at an altitude of 800‐1000 and 400‐ 600 m, respectively. In terms of tectonics, this structure represents the southern margin of the Syrian-Sinai [1] block‐fold belt. A comprehensive analysis of the available regional geophysical data revealed a collisionrelated origin of the belt [2]. Its formation terminated approximately 132 Ma ago, i.e., during the Levantine tectonic phase [3].The subsequent origination of the Levantine marginal volcanic suture [4] promoted the accumulation of postcollisional trap rocks (alkaline basaltic, alkaline gabbroic, and kimberlitic associations). The kimberlitic association, which was first discovered in western Syria, is represented in the study region by diatremes filled with kimberlite-type rocks containing eclogitic xenoliths [5]. Maximal magmatism in the region occurred approximately 120 Ma ago, which corresponds to the epoch of global tectonothermal activation (the Middle Cretaceous maximum in the development of upper mantle hot spots [7]). In the Makhtesh Ramon area, this stage is reflected in central-type volcanoes composed of lava flows, eruptive breccia, and tuffs that suggest wide development of explosive volcanism in the Middle Cretaceous [8]. Vent facies of the central-type Mahale Khahatsmaut Depression contain peridotite xenoliths with spinel-bearing lherzolites [9]. The presence of such rocks indicates significant depths of explosive volcanism. Magmatic rocks of the western Makhtesh Ramon Canyon are represented by picritic and olivine basalts and alkaline picrites. It should be noted that the development of these rocks does not rule out the presence of kimberlites in the study area. Detailed analysis of the magnetic (including quantitative interpretation and 3D modeling) and gravity fields indicated the possibility of discovery of parental diamondiferous bodies in the Makhtesh Ramon area. The low heat flow (~35 mW/m 2 ) in southern Israel [11] is an additional indicator of diamond potential in the area. The first diamond microcrystal discovered in the Negev Desert 30 km north of Makhtesh Ramon (Israel) in the Cretaceous/Paleogene boundary iridium layer was attributed to a meteorite fall. However, the habit, size, and characteristic impurities in the microcrystal suggest that it was washed out of diamondiferous bedrocks.