Younger volcanic fields of Yemen with focus on Jabal At-Tair active volcano in the Red Sea

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Mattash, Mohamed Ali
Holding Date 07 October 2008

Rift formation is one of the most important problems of the global tectonics. The Yemen rift-related area is one of these important provinces, which is connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar triple junction. Eight major Quaternary volcanic fields are known. Three of which are found in the western province of Yemen, and four occur along the coastal plain of the Gulf of Aden, whereas the Islands Group is found in the southern Red Sea. It can be inferred that Yemen, the western part in particular is not a stable continental zone. It is characterized by some indications of elevated crustal magmas and physical thermal convective anomaly related to deep crustal fracture systems, as well as by seismic activity.
In Sep. 30, 2007, the Jabal At Tair Volcanic Island has renewed its volcanic eruption. It is located at 15° 33’ N, 41° 50’ E. Jabal At-Tair forms an ellipsic island, with a total area exceeding 10 km2. It is composed of relatively thin basaltic lava flows of different colors. Chemical affinity of these lavas is tholeiitic, with silica content ranging from 46.44 to 48.53%, whereas the silica content of the older lavas ranges between 49 and 50.50%. Jabal At-Tair represents the youngest activity in the whole region and is the lonely active volcano in the Red Sea. The latest activity that happened in the nineteenth century was erupting from a central vent of the volcano, some 244 m above sea level, whereas the present eruption is rising from new central vents, aligned to the north of the former one, from an elevation of less than 230 m above sea level. The recent activity is represented by basaltic lava flows of different colors and appearance. Thickness of these lavas varies between 1 and 3 meters. The greatest part of the volcanic island is covered by pahoehoe as well as by aa lavas, in which the recent lavas are flowing over the older yellowish color pyroclastic materials. Beside the lava flows, the volcano emits fumaroles from the southern and northeastern parts of the new central vents and also bluish color sulfur dioxide, and less commonly carbon dioxide.
Two types of fissures are observed. The first is represented by radial fissures having different strikes, but mainly parallel to the main Red Sea trend, and the second type is represented by a newly formed N-S fissures which are found in the northern part of the island and form a parallel feature with each other. Their width is varying from centimeters to more than 1 meter. Based on our last visit in October 21, 2007; we could compare the type of activity to that of Sromboli, so the activity of Jabal At-Tair volcano will continue for months and probably for years. The basaltic rocks are porphyritic, fine to very fine-grained (aphanitic) in textures, and having porous and vesicular structures. Mineral constituents are represented by dominant plagioclase, clinopyroxene, olivine and opaque minerals.