Structural control of young basaltic fissure eruptions in the plateau basalt area of the Arabian Plate, northeastern Jordan

Abstract

Abstract In the El Hamadieh region, part of the large intracontinental basalt plateau extending NW-SE from Syria to Jordan and Saudi-Arabia in the northern part of the Arabian Plate, young volcanic edifices formed by fissure eruptions have been investigated; all geometrical dimensions and parameters of the ridges have been measured, the field relationships documented, the data evaluated and the structural patterns analysed. Using the attitude of the fissures as palaeostress indicators, a stress-strain-model is introduced, showing the superimposition of stress fields. Magma was extruded at the intersection of two regional structures: the NE-SW-striking Amman-Hallabat fold belt and the NW-SE-trending Azraq-Sirhan graben. A first effusion with a relatively fluid magma took place in reactivated fold-related conjugated hk 0-shear fractures with a compressional σ 1 -stress trending NW-SE. A second phase of fissure effusions produced a more viscous lava. These fissures represent (a) hk 0-planes with an acute angle about the fold axis, and (b) planes of normal faults along the southwestern shoulder of the Azraq-Sirhan graben in the position of fold-related reactivated conjugated 0 hl -shear planes. The geometrical relationships between the Amman-Hallabat folds, the Azraq-Sirham faults and the volcanic fissures indicate a rotation of the local stress field with the originally NW-SE-trending compressional σ 1 - and the NE-SW-trending, σ 3 -stress changing into a NE-SW-acting tensional σ 1 -stress.