Geology and geophysics of the foreland fold-thrust belt of northwestern Pakistan

Himalayan collision produced frontal and lateral ramps and associated Pliocene to Quaternary tectonic geomorphic features in the foreland fold-thrust belt of northwestern Pakistan. The transpressional right-lateral Kalabagh tear fault zone displaced the emergent Surghar Range frontal thrust from the western Salt Range by 16-19 km since 1.9-2.1 Ma: the age of youngest Siwalik molasse strata erosionally truncated during the southward advance of decollement thrusting. Folds and fanglomerate deposits resulting from decollement thrusting were also cut by the Kalabagh fault. North of the eastern Surghar Range, the N15W-trending Kalabagh fault bends to the west into north-dipping thrust faults that sole out beneath the southern Kohat Plateau. Foreland subsidence associated with the southward advance of thrusting controlled the distribution of Indus River conglomerates during the late Pliocene and Quaternary. Uplift in the northern Kalabagh fault zone diverted the Indus river eastward to its present course. South of the Main Boundary thrust (MBT) and west of the Indus River, decollement thrusting dominated by layer-parallel slip of as much as 32 km on a single thrust fault emplaced blind thrust sheets and fault-bend folds. Balanced cross sections show over 50% line-length shortening in sedimentary strata between the top of the basement and the base of the elastic wedge of the Murree and Kamlial formations and the Siwalik Group. A NNWtrending basement ridge modeled from Bouguer gravity data may have nucleated the similarly-oriented Kalabagh fault lateral ramp along the western Salt Range. A basement fault may have produced the frontal ramp at the Surghar Range. Low friction along the basal decollement thrust, with rapid underthrusting and internal thickening, produced a subcritical wedge tapering approximately 2° across the 70-km-wide Kohat foreland fold-thrust belt between the MBT and the Surghar Range thrust

Balanced structural cross section of the western Salt Range and Potwar Plateau, Pakistan : deformation near the strike-slip terminus of an overthrust sheet

The Salt Range and Potwar Plateau of northern Pakistan are part of the thin-skinned, active thrust system related to the ongoing collision of the Asian and Indian continental blocks. Platform rocks and orogenic molasse of the Indo-Pakistani shield are deformed in south-verging thrusts and folds, relative to a northward-converging basement. This results in three different styles of deformation along a north-south, balanced cross section in the western Potwar Plateau and Salt Range. This cross section, as well as structure and isopach maps for the entire Salt Range/ Potwar Plateau region, were constructed using surface geologic maps, seismic reflection, drillhole, and gravity data. In the Northern Potwar Deformed Zone (NPDZ), shortening of 68% is accomodated by a trailing imbricate stack of high ad low-angle, south-verging faults. These faults are rooted in a master decollement within an Eocambrian evaporite sequence (Salt Range Fm.), which overlies a north dipping basement surface at a depth of approximately 8 km. Southward progression of regional deformation with time appears to be interrupted by overstep, or back-break, thrusting. The low-angle faults, or a possible basement uplift, may represent the ramp for a protracted interval of imbricate faulting that began in middle to late Miocene ([approximately] 15-10 mybp). Later, the basal detachment propagated rapidly, transporting the NPDZ sequence and the developing Soan Syncline (southern Potwar Plateau) southward, without major internal deformation within the Syncline. Within the last 2.0 my, the older units overlying the Salt Range Fm. have been exposed along the Salt Range, where the basal detachment ramped to the surface. A north-facing, subsurface normal fault, that offsets basement and controls frontal ramping along the central portion of the Salt Range, is not present in the western Salt Range. Rather, the older platform rocks and overlying molasse are carried southward up a basement monocline. This monocline is a protrusion on the northeast flank of the northwest-trending Sargodha Ridge, a buried basement arch that may represent a flexural response to Himalayan tectonic loading. Although the footwall, underlying the thrust plane, has not been drilled in the Salt Range, seismic control and two-dimensional gravity modeling suggest the presence of autochthonous sedimentary rocks, overlain by a thickened layer of evaporites, In the western Salt Range, the leading edge of the Salt Range Thrust (SRT) overrode its footwall block about 34 km. Additional shortening may have been accomodated by a series of imbricate thrusts in the Salt Range Fm., or the footwall strata may be imbricated. This would add northward taper to the basement dip, allowing the SRT to be exposed at the surface. An average shortening rate of approximately 1.3 cm/yr is comparable to the shortening rate for the NPDZ, if thrusting there occurred over a 7-8 my interval. Overthrust shortening along the SRT in the central Salt Range has been estimated at between 19 and 23 km. The larger amount of overthrusting in the western Salt Range, as compared to the central Salt Range, is consistent with the structurally-salient range front along this western edge. Minimum overall shortening, from the southern edge of the Peshawar Basin to the undeformed Jhelum Plain, is estimated at 213 km, a shortening of about 49%. This is comparable to the amount of fold and thrust shortening in other deformed forelands

Geochemistry and provenance of the Lower Siwaliks from southwestern Kohat, western Himalayan Foreland Basin, NW Pakistan

Equivalent to the Lower Siwalik Group, the Late Miocene Chinji Formation in Pakistan consists of interbedded in-channel sandstone (SSt) and overbank mudstone (MSt) sequences. Twelve sandstone and sixteen mudstone samples from three different sections of the formation in southwestern Kohat, NW Pakistan were analyzed for major elements and selected trace elements. The Chinji sandstones are feldspathic and lithic arenites. They are mostly matrix-supported, moderately to well sorted, and contain angular to rounded framework grains. Authigenic carbonate makes up most of the matrix. The framework grains consist of abundant monocrystalline quartz, alkali feldspar, and lithic fragments with subordinate mica and trace to accessory amounts of heavy minerals including epidote, monazite, apatite, garnet, rutile, and brown hornblende. The lithic fragments consist of sedimentary, volcanic, and low-grade metamorphic rocks.The average concentration of Zr, Nb and Y, and the Ba/Sc and Ba/Co ratios in the studied samples are lower than the corresponding values for the upper continental crust (UCC) and Post-Archean Australian Shale (PAAS) indicating the presence of mafic phases in the source area(s). The high average Cr/Zr and Cr/V ratios of the investigated samples relative to UCC and PASS also support the presence of mafic lihtologies, possibly chromite and ultramafic rocks in the source region. The La/Sc and Th/Sc ratios of the Chingi samples are more like the UCC while the Th/Co and Cr/Th ratios suggest a major contribution from mafic rocks. The average percent differences of the Chinji samples from both the UCC and PAAS in terms of critical silicic to basic trace element ratios (Ba/Co, Ba/Sc, La/Co, La/Sc, Th/Co, Th/Sc, Zr/Cr, and Zr/Sc) suggest a mafic contribution of 23 to 47% (mudstone) and 56 to 69% (sandstone). The lower Th/U, Rb/Sr and Zr/Sc ratios in the studied samples than the corresponding values of the UCC and PAAS suggest negligible recycling for the sediments of the Chinji Formation. Petrographic point count data on the Chinji sandstone indicate sediment derivation from a dissected arc, suture belt, and recycled orogen corresponding to the Kohistan-Ladakh Arc, the Indus Suture Zone, and the Himalayan Tectonic units, respectively. The different source rocks identified on the basis of various petrographic and geochemical parameters occur as part of the mentioned tectonic domains

Geochemistry and provenance of the Lower Siwaliks from southwestern Kohat, western Himalayan Foreland Basin, NW Pakistan

Equivalent to the Lower Siwalik Group, the Late Miocene Chinji Formation in Pakistan consists of interbedded in-channel sandstone (SSt) and overbank mudstone (MSt) sequences. Twelve sandstone and sixteen mudstone samples from three different sections of the formation in southwestern Kohat, NW Pakistan were analyzed for major elements and selected trace elements. The Chinji sandstones are feldspathic and lithic arenites. They are mostly matrix-supported, moderately to well sorted, and contain angular to rounded framework grains. Authigenic carbonate makes up most of the matrix. The framework grains consist of abundant monocrystalline quartz, alkali feldspar, and lithic fragments with subordinate mica and trace to accessory amounts of heavy minerals including epidote, monazite, apatite, garnet, rutile, and brown hornblende. The lithic fragments consist of sedimentary, volcanic, and low-grade metamorphic rocks.The average concentration of Zr, Nb and Y, and the Ba/Sc and Ba/Co ratios in the studied samples are lower than the corresponding values for the upper continental crust (UCC) and Post-Archean Australian Shale (PAAS) indicating the presence of mafic phases in the source area(s). The high average Cr/Zr and Cr/V ratios of the investigated samples relative to UCC and PASS also support the presence of mafic lihtologies, possibly chromite and ultramafic rocks in the source region. The La/Sc and Th/Sc ratios of the Chingi samples are more like the UCC while the Th/Co and Cr/Th ratios suggest a major contribution from mafic rocks. The average percent differences of the Chinji samples from both the UCC and PAAS in terms of critical silicic to basic trace element ratios (Ba/Co, Ba/Sc, La/Co, La/Sc, Th/Co, Th/Sc, Zr/Cr, and Zr/Sc) suggest a mafic contribution of 23 to 47% (mudstone) and 56 to 69% (sandstone). The lower Th/U, Rb/Sr and Zr/Sc ratios in the studied samples than the corresponding values of the UCC and PAAS suggest negligible recycling for the sediments of the Chinji Formation. Petrographic point count data on the Chinji sandstone indicate sediment derivation from a dissected arc, suture belt, and recycled orogen corresponding to the Kohistan-Ladakh Arc, the Indus Suture Zone, and the Himalayan Tectonic units, respectively. The different source rocks identified on the basis of various petrographic and geochemical parameters occur as part of the mentioned tectonic domains

Subsurface structural investigation based on seismic data of the north-eastern Potwar basin, Pakistan

1258-1268The north-eastern Potwar is present in the foothills of Himalayas on the northern boundary of the Indian Plate and is filled by the Infra-Cambrian to Pliocene sedimentation. The area is affected by the regional structures of the Potwar and the Salt-Range Structures, such as the North Potwar Deformed Zone (NPDZ), the Soan Syncline, the Main Boundary Thrust (MBT) and the Jhelum Fault. Due to complex tectonic-structural framework, it is extremely significant to understand the subsurface structural mechanisms for further hydrocarbons exploration. The 2D seismic data was acquired in the NE-Potwar in the Rawat area is used for this purpose. The current study helps to present rigorous and mechanically feasible structure understanding of the Rawat and associated local structures of the area in the context of the Sub-Himalayas. The study area mainly comprises on the eastern Potwar with tight anticlines and wide synclines with associated thrusts showing collisional regime of the Himalayan Fold and the thrust belt. The structural interpretation and restoration of paleo-section provide a mechanically feasible model for the Rawat area. The interpretation of seismic data shows that this area is associated with conjugate faults and a triangle zone. The results of this study help us to develop understanding in geological history, structural overprint and future leads for hydrocarbons in this geological province

Geology and combustion perspectives of Pakistani coals from Salt Range and Trans Indus Range

Abundant availability of low rank coals in some developing countries has a great potential for socio-economic development. Pakistan, as a developing country, has taken a number of initiatives some of which are at an advanced stage. Thus, a critical study of regional and local geology of Salt Range and Trans Indus Range coals located in the Kohat–Potwar geologic province is presented in this paper. Permian coal is the oldest coal, which is located in the Western Salt Range in limited quantity while Palaeocene coal is the younger coal and it is mined from the Hangu and Patala formations. The Palaeocene coal is available in abundance and is mined in the Eastern and Central parts of the Salt Range and Trans Indus Range. Additionally, this study presents the thermo-chemical analyses of the coal samples collected from thirty coal mines of Salt Range and Trans Indus Range. The samples were analyzed for ash composition, ash fusion temperatures (AFT), proximate analysis, ultimate analysis and calorific value from two different Labs, i.e. SGS Pakistan and Changsha University of Science and Technology (CUST), China. The average AFT of the samples analyzed is > 1350 °C, which reveals that the coal is non-slagging. On average the coal has low slagging index, medium fouling index, good combustion characteristic parameters and indices. The coal samples have high ash (14–50%), ultra-high sulfur (3.3–11.1%), low moisture (3–10%), high volatile matter (VM, 24–41%), low carbon (23–57%) with low to medium gross calorific value (GCV, 10.2–25.7 MJ/kg). The data gathered from an extensive campaign is compared with the already published data. The study has provided a knowledge on utilization of coal reserves to meet the projected energy demand in Pakistan as well as in other developing countries

Preliminary Resource Potential Assessment of Placer Light Rare Earth Elements (LREEs) from mid-Siwalik Sediments of a late Miocene Himalayan Foreland Basin, Pakistan

The present study has assessed the preliminary placer LREEs resource potential of mid-Siwalik Group Dhok Pathan Formation from Surghar-Shingar Range of NW Himalayan foreland Fold-and-Thrust-Belt and regarded them as indicative resources only. The analytical results of bulk samples of sandstone did not show any anomalous concentration of REEs. However, the ICP-MS results of heavy minerals laminations (black sands) revealed high concentrations (ppm) of LREEs (La: 975, Ce: 2831, Pr: 193, Nd: 746, Sm: 127, Gd: 98.70). We identified monazite-(Ce) [Ce, La, Nd]PO4 as the primary LREEs-bearing mineral through Electron Probe Micro Analysis (EPMA). The representative quantitative micro-mineral analysis of monazite confirmed promising concentration of Rare Earth Oxides (REOs) maximum (in weight %) - La2O3: 16.20, Ce2O3: 37.82, Pr2O3: 4.77, Nd2O3: 21.72, Sm2O3: 5.23, Gd2O3: 4.88. Considering the thickness, lateral extension and depositional setting of host sediments along-with anomalously high concentrations of LREEs, it has been concluded that these Siwalik sediments host good indicative placer resource potential for low-cost recovery of LREEs