Petrogenesis and duration of a protracted mafic eruptive episode in the northern Harrat Rahat volcanic field, Kingdom of Saudi Arabia
摘要
We integrate new mineral geochemistry with field relations, 36Cl surface-exposure ages, whole-rock geochemistry, and paleomagnetic directions to understand the petrogenesis and eruption duration of three young basaltic lava flows in northern Harrat Rahat, a distributed volcanic field in central-western Saudi Arabia. These lavas, informally referred to as the Five Fingers, erupted at ~ 24 ka from three elongate vent complexes that define a common lineament. Paleomagnetic data from the northern and central fingers are consistent with penecontemporaneous eruption, while the southern fingers erupted at a different time. Based on paleomagnetic data, the eruptive interval for this set of lava flows is estimated to be 160 ± 70 years. Mineral and whole-rock chemistry suggest that the southern fingers magma was deeply sourced and near-primitive, whereas the northern fingers magma had fractionated a gabbroic assemblage in the mid-crust prior to eruption. The central finger has a whole-rock composition nearly identical to the northern fingers but contains crystals compositionally similar to those present in both the southern and northern fingers, suggesting mixing between a deeply sourced magma and a magma stalled in the mid-crust. These data suggest that the Five Fingers eruptive episode reflects renewed injection of mantle-derived magma into the crust ca. 24 ka, in which basalts from different crustal levels interacted and erupted in two discrete events separated by 160 ± 70 years. Compared with similar datasets from other distributed volcanic fields, our results show that the duration of eruption episodes involving multiple eruption events can span from months to > 100 years.