Abstract
Direct dating of maars and their phreatomagmatic deposits is difficult due to the dominance of lithic (host rock) fragments and glassy particles of the juvenile magma. In this paper we demonstrate that optically stimulated luminescence (OSL) dating can be successfully used for age determination of phreatomagmatic deposits. We studied the tuff deposit of Birket Ram, a basanitic maar located at the northern edge of the Golan heights on the western Arabian plate. The maar is underlain by a thick section of Pleistocene basalts, and currently hosts a small lake. It is filled by approximately 90 m of lacustrine sediments with radiocarbon ages extrapolated to 108 ka at the base. OSL was applied to quartz grains extracted from tuffs and paleosols in order to set the time frame of the phreatomagmatism at the site. A maximum age constraint of 179 ± 13 ka was determined for a paleosol that underlies the maar ejecta. Quartz grains from two layers in the tuff section yielded a direct age of 129 ± 6 ka for the phreatomagmatic eruption. A younger age of 104 ± 7 ka, which was determined for a tuff layer underlying a basaltic flow, was attributed to thermal resetting during the lava emplacement. This was confirmed by an 40Ar/ 39Ar age of 101 ± 3 ka determined on the overlying basalt. The internal consistency of the OSL ages and the agreement with the 40Ar/ 39Ar age determination as well as with previous estimates demonstrates the potential of OSL for maar dating.
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