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Summary of the Geology of the Makran Coast

By
J.C. Harms
J.C. Harms
Marathon Oil Company
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H.N. Cappel
H.N. Cappel
Marathon Oil Company
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D.C. Francis
D.C. Francis
Marathon Oil Company
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T.J. Shackelford
T.J. Shackelford
Marathon Oil Company
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Published:
January 01, 1983

Abstract

The following summary of the geology of the Makran coastal area is taken, with minor modification, from Harms and others (1982).

Makran comprises the southern part of Pakistan and Iran between Sonmiani Bay, near Karachi, and the Straits of Hormuz (Figure 1). The area consists of a great festoon of folded and faulted Tertiary sediments extending 800 km (497 mi) from the Las Bela fold belt on the east to the Oman Line on the west (Figure 2). These eastern and western boundaries separate Makran from older terranes with deformational styles and histories distinct from that of Makran (Farah and Dejong, 1979). To the east the Las Bela fold belt represents deformation associated with the collision of India with Asia whereas to the west the Zagros Mountains of Iran represent the convergence of the Arabian and Iranian plates. In both cases, blocks of continental crust have moved northward against other continental plates, closing former deep oceanic seaways. In contrast, along Makran, it appears that only oceanic crust has been subducted beneath a continental margin composed of small plates and complex ophiolite zones.

Coastal Makran and the area to the north is an accretionary wedge of deformed sediments ranging in age from perhaps Late Cretaceous to Recent, piled up at an oceanic subduction margin. The structure and depositional setting has been compared to "a typical arc model" composed of upper-slope deposits followed by lower-slope and trench deposits, progressively deformed by continuing subduction (Farhoudi and Karig, 1977). However, as an arc-trench system, Makran is hardly typical; indeed it is perhaps largely anomalous in its characteristics, as pointed out by Jacob and Quittmeyer (1979). The arc-trench gap is on the order of 500 km (311 mi), far wider than most systems. A possible Benioff zone is only weakly developed; shallow focal mechanism solutions indicate instances of tension in the downgoing oceanic slab. Volcanic centers are few and widely spaced along the arc feature. Additionally, a very large part of the accretionary prism is exposed, and a significant volume of post-middle Miocene sediments are shallow shelf deposits, not trench and slope deposits as alleged by Farhoudi and Karig (1977).

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Contents

AAPG Studies in Geology

Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces

A. W. Bally
A. W. Bally
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American Association of Petroleum Geologists
Volume
15
ISBN electronic:
9781629810188
Publication date:
January 01, 1983

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