Slip vectors and fault mechanics in the Makran Accretionary Wedge, southwest Pakistan

Abstract

The Makran is a broadly east–west trending arcuate accretionary wedge currently forming where the oceanic floor of the Gulf of Oman is being subducted north‐northeastward beneath the south Asian margin. Two traverses across the Makran Coast Ranges, extending about 80 km inland from the coastline (which lies about 100 km north of the wedge front), show that the structure of this region is dominated by large back‐rotated south directed thrust faults and associated folds. Related structures include duplexes, fault gouge containing Reidel shears, and melange along fault zones. These structures are cut by later north directed backthrusts, out‐of‐sequence south directed thrusts, and apparently conjugate sets of NNE trending sinistral and NW trending dextral strike‐slip faults. Slip vectors were determined from slickenlines, fiber lineations, gouge fabrics, and Riedel shears. Vectors from early thrusts and bedding‐parallel slip surfaces, corrected for tectonic rotation, form a broad south directed concentration lying between the normal to the regional strike (varying from 160° to 180°) and the present plate convergence vector (200°). Locally, the concentration is bimodal. This pattern may represent the interaction between plate forces and body forces in the accretionary wedge. The late thrusts have widely variable slip vectors and stair‐step off the early thrusts. They overlap in orientation and slip vector with gently dipping sinistral strike‐slip faults, suggesting that they also stair‐step in plan off the latter. The steep strike‐slip faults represent the final tectonic stage, involving minor N‐S shortening and longitudinal extension. These three stages probably occurred in sequence in any one area but migrated diachronously southward as the wedge grew.

Subduction, accretion, and exhumation of coherent Franciscan blueschist-facies rocks, northern Coast Ranges, California

“…This hinders field investigations of emergent examples as well as seismic studies of currently active complexes in submerged fore-arcs. In spite of this, some excellent seismic studies have demonstrated that the frontal regions of accretionary wedges are dominated by imbricate thrusting (Davey et al, 1986;Davis and Hyndman, 1989;Moore et al, 1990;Morgan and Karig, 1995), and this has been confirmed by detailed studies of some well-exposed emergent examples (Moore and Karig, 1980;Wahrhaftig, 1984;Platt et al, 1988;Meneghini andMoore, 2007, Wakabayashi, 2017). The structure of the more deeply buried interiors of accretionary wedges is less well documented, and in particular the processes driving exhumation of these rocks remain controversial.…”

The transition between Makran subduction and the Zagros collision: recent advances in its structure and active deformation

“…It has been formed by the subduction of the oceanic portion of the Arabian Plate beneath Eurasia and is built up by sediments scraped off the Arabian Plate since early Tertiary (Berberian and King, 1981;Harms et al, 1984;Kopp et al, 2000). Subduction was probably initiated during Palaeocene (Platt et al, 1988) and accretion started during Eocene times (Byrne et al, 1992). The modern Makran accretionary prism has developed since Late Miocene (Platt et al, 1985;Platt et al, 1988), and is still propagating seaward at a rate of ~10 mm yr -1 (White, 1982).…”

“…Subduction was probably initiated during Palaeocene (Platt et al, 1988) and accretion started during Eocene times (Byrne et al, 1992). The modern Makran accretionary prism has developed since Late Miocene (Platt et al, 1985;Platt et al, 1988), and is still propagating seaward at a rate of ~10 mm yr -1 (White, 1982). Two features make this accretionary wedge unusual: (1) the sediment thickness on top of the oceanic crust is extremely high (at least 6 km); and (2) the dip angle of subduction is extremely low (~5 degrees, Jacob and Quittmeyer, 1979;Byrne et al, 1992;Carbon, 1996).…”

Statistical Analysis of Earthquakes and Tsunami of Makran Subduction Zone (MSZ), and Tsunami Hazard Assessment of Gwadar Coast

“…Makran Subduction Zone (MSZ) is distinctive region due to its abnormal behavior of seismicity and structural complexities due to slow rate of subduction. Subduction was probably initiated during Palaeocene time by Platt et al and accretion started during Eocene time [1] and accretion started during Eocene time [2].…”