The Nahal Tavor vent: Interplay of Miocene tectonics, dikes, and volcanism in the Lower Galilee, Israel

The upper level of a volcanic vent is exposed along Nahal Tavor, Lower Galilee, Israel. The vent, about 300 m in diameter, was formed within the Middle Miocene Lower Basalt sequence. This is the largest documented volcanic edifice from that widespread formation. The vent consists of pyroclastic rocks (tuff, lapilli, scoria, and volcanic bombs), lava flows, dikes, and irregular-shaped intrusive bodies. The vent was formed along a WNW-striking fault escarpment separating an uplifted block in the north from a subsiding basin in the south. The fault was active before the onset of eruptive activity in the vent and ceased before the deposition of the early Pliocene Gesher Formation. Some neighboring faults with similar strikes and evidence for early history of activity were reactivated after the deposition of the Pliocene Cover Basalt, forming the tilted-blocks structure characteristic of the Lower Eastern Galilee. Two dike sets are exposed in the vent. The dikes are restricted to the vent interior and do not extend into the basaltic country rock. Analyses of flow directions in these dikes by field and anisotropy of magnetic susceptibility (AMS) measurements show that in both sets magma flowed from the center of the vent outwards. K-Ar dating of the different volcanic products within the vent indicates at least three major eruptive and intrusive events during the periods 13.5-13.0 Ma, 11.0 Ma, and 9-7.5 Ma. The first and most dominant eruptive and tectonic phase in the vent is contemporaneous with widespread Lower Basalt flows in the Galilee, with the renewal of volcanic activity in the Harrat-Ash-Shaam volcanic field in Jordan, and with faulting along the Yizre'el Valley margins. The youngest volcanic phase in the vent is contemporaneous with the deposition of the Umm-Sabune Formation and corresponds to the Intermediate Basalt in the Lower Galilee. Some pyroclasts were trapped in lacustrine sediments close to the vent. Paleomagnetic measurements suggest that the block containing the vent was unlikely to have rotated about a vertical axis since the Miocene. There is no clear evidence that the Nahal Tavor vent was a source of the Lower Basalt flows. Yet the vent is the largest edifice known from that age, and it probably marks the initiation of wide-spread tectonic activity of the Yizre'el rift and its associated regional volcanism.