Active mud volcanoes on- and offshore eastern Makran, Pakistan

Abstract

To study the activity, source and driving force of the venting of fluidized mud in the coastal Makran, we carried out reconnaissance surveys of two active onshore mud volcano fields (Chandragup and Jebel-u-Ghurab) and of a newly born (March 1999) offshore mud volcano (Malan Island). All studied onand offshore mud volcanoes line up along one southwest/northeast-trending structural lineament, the axis of the Dhak Anticline. Isotopic data point to a bacterial origin of the gas (mainly methane). Mixed benthic foraminiferal faunas and calcareous nannofloras suggest that the source level of the extruded mud is at a sub-surface depth of 2±3 km. Observed mud discharge varied between 0 and 1.4 m 3 h ±1 and gas discharge rates between negligible amounts to 1 m 3 s ±1 . Mud temperatures in the crater lake of Chandragup I are near-ambient temperatures. They rise slightly (^1.5 C) during episodes of modest mud outflow. An area of 160,000 m 3 of soft mud was vigorously extruded from the sea floor at a water depth of 10 m within days after 15 March 1999, forming Malan Island. The island was destroyed within a few months after its birth by deep-reaching wave action during the SW monsoon. This was possibly aided by local subsidence of the mud volcano structure due to the volume loss following rapid degassing and mud extrusion.Keywords Mud volcano´Makran´PakistanǴ eothermics´Gas analysis´Gas seeps G. Delisle ( ) )´U. von Rad´H. Andruleit

Significance of Mud Volcanism

“…Both the sediment and tectonic loading were discussed as driving forces, with water and gas acting as a lubricant for upward migration [Snead, 1964]. More recently, some of the features were studied in greater detail, like the Chandragup or Jebelu-Garab [Delisle et al, 2002]. Mud discharge varied between 0 and 1.4 m 3 h Ϫ1 , while gas emission ranged from negligible amounts to 1 m 3 s Ϫ1 [Delisle et al, 2002].…”

“…More recently, some of the features were studied in greater detail, like the Chandragup or Jebelu-Garab [Delisle et al, 2002]. Mud discharge varied between 0 and 1.4 m 3 h Ϫ1 , while gas emission ranged from negligible amounts to 1 m 3 s Ϫ1 [Delisle et al, 2002]. The activity of some Makran MVs was correlated with earthquakes in the area [e.g., Skrine, 1936;Harrison, 1944].…”

“…This summary closely resembles the review by Higgins and Saunders [1974], with the more recent discoveries added. Appendix A covers the early description of enigmatic mud features [e.g., Goad, 1816;Abich, 1857] up to the most recent studies [e.g., Bouriak et al, 2000;Delisle et al, 2002;Etiope et al, 2002] and is divided into regional sections.…”

Effects of mass waste events on thrust wedges: Analogue experiments and application to the Makran accretionary wedge

“…Active mud volcanoes [e.g., Harrison, 1944;Snead, 1964;von Rad et al, 2000;Delisle et al, 2002] may indicate that such décollements take advantage of overpressured shales.…”

“…The observed segmentation, two wedges separated by a largely undeformed zone, can only take place in the presence of one or more weak décolle-ments. Mud volcanism and seismic profiles [e.g., Harms et al, 1984;von Rad et al, 2000;Delisle et al, 2002;Grando and McClay, 2007;Ellouz-Zimmermann et al, 2007b] indicate the presence of such décollement(s) in the offshore Makran.…”