New Constraints for the On‐Shore Makran Subduction Zone Crustal Structure

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Sobouti, Farhad 
Mokhtarzadeh, Rahil 
A. Irandoust, Mohsen 
Ghods, Reza 

jats:titleAbstract</jats:title>jats:pThe Makran Subduction Zone is the primary seismic/tsunami hazard of the northwestern Indian Ocean, but little is known of its on‐shore seismic structure. We derived a shear wave velocity model extending to <jats:inline-graphic xmlns:xlink="" xlink:href="graphic/jgrb55383-math-0001.png" xlink:title="urn:x-wiley:21699313:media:jgrb55383:jgrb55383-math-0001" />100 km depth beneath a ∼400 km‐long seismic profile oriented parallel to the convergence vector of the Arabian Sea Plate. Receiver function/surface wave analysis shows that the average structure in the coastal region comprises a ∼22–28 km‐thick low wavespeed sedimentary cover and a 6–8 km‐thick gradient zone overlying <jats:inline-graphic xmlns:xlink="" xlink:href="graphic/jgrb55383-math-0002.png" xlink:title="urn:x-wiley:21699313:media:jgrb55383:jgrb55383-math-0002" />100 km‐thick high wavespeed upper mantle. The ocean‐basement interface dips gently northward, remaining a positive impedance contrast to ∼50 km depth at ∼250 km north of the coast where it disappears as the basaltic/gabbroic oceanic crust has probably transformed to eclogite. Further north, a weak arrival at ∼5 s in the receiver functions appears, grading northward into the Moho arrival of the continental Iranian Plateau. This disruption in the seismic signature of the Moho occurs in the forearc region where the dip of the subducting oceanic plate steepens. The southern Iranian Plateau's continental crust has an average jats:italicV</jats:italic>jats:subjats:italics</jats:italic></jats:sub> of 3.55 ± 0.05 km sjats:sup−1</jats:sup>, an almost flat Moho 40–45 km deep, and a sub‐Moho mantle jats:italicV</jats:italic>jats:subjats:italics</jats:italic></jats:sub> of 3.75 ± 0.05 km sjats:sup−1</jats:sup> in the 50–80 km depth range. Weak Moho conversions probably result from ∼20% serpentinization of peridotite in the mantle wedge. Receiver functions indicate a flat continental Moho – no crustal root beneath the high topography region of the volcanic belt, which therefore must be compensated by low upper mantle densities. The high jats:italicV</jats:italic>jats:subjats:italicp</jats:italic></jats:sub>/jats:italicV</jats:italic>jats:subjats:italics</jats:italic></jats:sub> ratio observed for the mantle wedge suggests ∼1%–2% partial melt.</jats:p>


Funder: Institute for Advanced Studies in Basic Sciences; Id:

37 Earth Sciences, 3703 Geochemistry, 3705 Geology, 3706 Geophysics
Journal Title
Journal of Geophysical Research: Solid Earth
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American Geophysical Union (AGU)
Royal Society (ICA/R1/180234)
Natural Environment Research Council (NERC) (NE/J019895/1)