Mud Diapirism on the Makran , Iran : Case Study on the Napag Mud Volcano

The Napag is the biggest Mud Volcano at Makran in Iran. The main aim of this research is the investigation of geologic setting and geographic situation of Napag Mud Volcano as a well-known mud diapir at Makran on the south eastern margin of Iran. The Napag Mud Volcano has been formed during quaternary of as a conical hill on the flat plain in coastal region Oman Sea. There are badlands area and several mud volcanoes that they have been triggered by longitudinal normal faults. This normal faults have been developed in neotectonic regime by the roll-back of oceanic lithosphere (beneath of Oman Sea). Finally, the main characteristics of the Napag mud diapir are presented.


Introduction
Mud Volcanoes are well-known phenomena whereby fluid-rich, fine-grained sediments ascend within a lithologic succession because of their buoyancy.These processes have long been recognized as being related to the occurrence of petroleum, regional volcanic and earthquake activity, and orogenic belts.Most importantly, mud volcanoes occur along convergent plate margins where fluid-rich sediment is accumulated in deep-sea trenches at high rates.Such deposits then enter the subduction factory, where liquids and volatiles are released due to increasing compaction stress and temperature.
In summary, mud volcanism is most abundant in compressional and, to a lesser extent, in deltas of great rivers.As for the first, tectonic activity is an additional trigger to the buoyant driving mechanism.Fluid for mud volcanism is supplied from various sources, including meteoric and volcanic waters, pore water expulsion, hot springs, mineral dehydration reactions, and gas hydrate destabilization [1].The questions are, why and how mud-volcanoes form provokes a lively discussion.Many researchers have worked in different areas and postulated usually a variety of 4 -7 reasons.All these reasons can be divided into four groups [2]: 1) Geologic reasons; 2) Tectonic reasons; 3) Geochemical reasons and 4) Hydrogeological reasons, i.e. fluid flow along fracture zones.It is easy to see that many of these reasons are closely related to each other or require the presence of each other.In various areas the reasons for mud volcano formation are different.As a consequence, it is pointless to define a universal limited set of reasons.The expedient approach is to determine the key causative factors that can be used to forecast the areas of mud volcanic activity.

Materials and Methods
Using the regularities in the spatial distribution of known and inferred submarine mud volcanoes we can define these two key reasons: 1) the high sediment accumulation rate at passive continental margins; 2) the lateral tectonic compression at active continental margins.All other conditions necessary for the formation of mud volcanoes (density inversion, faulting, fluid migration etc.) result from these two key reasons.In addition it is obvious that plastic clay layers must be present for mud volcanoes to form.In some regions, submarine mud volcanoes form in areas characterized by a spatial combination of rapid sediment accumulation and lateral tectonic compression [2].
Finding the characteristics of mud diapirs in the Makranregion in the south eastern part of Iran is the main aim in this research.This area is located on convergent tectonic setting between Cimmerian and oceanic part of Arabian plate (Figure 1).It contains the accretionary prism or Makran ranges on trench of Oman sea subduction zone.
Previous research on Iran's tectonic setting [4]- [6], salt diapirism [7]- [16], Seismotectonics [17]- [20] have shown that the Zagros belt is the most active zone in Iran [21]- [30].Alborz belt in north Iran [31]- [62] and Central Iran [63]- [75] have been situated in the next orders.But, Makran belt has been formed by the east-west striking accretionary prisms.It has been situated on trench of Oman sea subduction zone and there are several Mud volcanoes along the coastal part of Makranranges.The biggest one is Napag Mud volcano (Figure 2).

Results and Discussion
Based on our investigation, the Napag Mud Volcano have got a conical shape with 35 meters height (Figure 3) and it has been formed on the flat quaternary plain in coastal region (Figure 4) of Oman Sea.Flatted top of this cone has been developed by erosion (Figure 5).There is badlands area (Figure 6) at surrounding parts of mud volcanoes that they have formed by multistage mud eruptions (Figure 7).
In central part of the Napag Mud Volcano, gasbubbles are forming rapidly in a small pound that it has been filled by viscous clay (Figure 8).
Also, there are other badlands area and several mud volcanoes along coastal region Oman Sea that they have been triggered by longitudinal normal faults.The normal faults have been covered in quaternary flat but they have exposed in some place (Figure 9).
This normal faulting can be related to neotectonic regime of the southern flank of the Makran ranges that it has been controlled by the roll-back of oceanic lithosphere.It means that oceanic lithosphere beneath of Makran ranges has been sloped.In the other words, increasing of dip in Benioff zone, caused to recent normal longitudinal faulting on Makran accretionary Prism.The Mud volcanism in this region has been shown below specifications, based on our investigations.
This diapirs has been risefrom Paleocene to Late Miocene Turbidities and probably mud diapirism has been         mud diapirs are expected.Because, during convergent between Cimmerian and oceanic part of Arabian plate, roll-back of oceanic lithosphere in the Makran subducton zone will increase in future.

Figure 3 .
Figure 3.The Napag Mud volcanoat northwest of Konarak city, view to the north west.

Figure 4 .
Figure 4.A view from top of the Napag Mud volcano to the north (Makran Range).

Figure 5 .
Figure 5. Flatted top of the Napag Mud volcano, view to the northwest.started since Early Pliocene, because it has covered quaternary plain.Thrust Faults are the index structures in the makran region, but they have been cut by normal faults.It means that mud diapirs have been triggered by longi-

Figure 6 .
Figure 6.Badlands area at surrounding parts of the Napag Mud volcano, view to the east.

Figure 7 .
Figure 7. Two different view from multistage eruptions of the Napag Mud volcano.

Figure 8 .
Figure 8. Two different view from viscous clay and gas bubbles in the central part of the Napag Mud volcano.tudinal normal faults.There are several dispersed mud diapirs, but all of them are the smaller than Napag diaper.
Tectonic geomorphology and origin of the Napagmud volcano in Makran at South-eastern parts of Iran have been determinated.Mud diapirismin this zone has been controlled by tensional tectonic forces, that they have been cosiderable during roll-back of oceanic lithosphere in the Makran subducton zone.It means that tectonic processes are predominant compared to buoyant driving mechanisms in the coastal parts of the Makran ranges.Therefore, formation of the new mud volcanoes and the more development of the older

Figure 9 .
Figure 9.A normal fault that cropping out in the Makran accretionary Prism, view to the north west.