PARALAVAS IN THE HATRURIM BASIN OF ISRAEL

The origin of high-temperature and low-pressure metasedimentary rocks in the Hatrurim Basin, near the Dead Sea in Israel, has been controversial for decades. The currently accepted hypothesis for the source of heat energy, ultimately responsible for metamorphism, is once-combusting bitumen. Rocks in the basin, from the Hatrurim Formation, record pyrometamorphism with K-Ar ages ranging from 2.5-3.8 Ma (Pliocene).

Calc-silicate assemblages in the Hatrurim Formation produced by the metamorphism of carbonate sediments low in SiO₂ include larnite, spurrite, gehlenite, wollastonite, rankinite, grossite, and brownmillerite. The calc-silicate assemblages formed at temperatures less than 1000°C from protoliths that did not melt.

During the last few years, dark-gray dike-like lenses, up to 1 m long and 5 cm thick, were identified in the “Olive” unit of the Hatrurim. The cryptocrystalline lenses exhibit vesicular and fluidal texture. The main mineral assemblage, identified by electron microprobe analysis, is anorthite + Ti-magnetite + clinopyroxene + K-feldspar ± ilmenite. Ovoids with two different mineral assemblages occur in these rocks. One assemblage consists of Fe-rich corundum + Al-spinel + Al-rich hematite, suggesting a crystallization temperature above 900°C. The other consists of fayalite + Ti-magnetite ± anorthite ± hedenbergite-ferrosilite, usually confined to vesicles. The Ti-magnetite and pyroxene assemblage is associated with a silicate melt and fluid inclusions, suggesting the dikes formed from a melt at temperatures above 1000°C.

Considering the geologic setting, textural features, and mineral composition, the plagioclase-pyroxene dike rocks possibly formed during the local melting of a clay-rich protolith. If so, they are paralavas in the Hatrurim basin.