| Abstract |
- The Gandghar Range and Kherimar Hills, located in the Hill Ranges of northern
Pakistan, contain rocks that are transitional between unmetarnorphosed foreland-basin
strata to the south and high-grade metamorphic and plutonic rocks to the north. The
southern Gandghar Range is composed of a succession of marine strata of probable
Proterozoic age, consisting of a thick basal argillaceous sequence (Manki Formation)
overlain by algal limestone and shale (Shahkot, Utch Khattak, and Shekhai
formations). These strata are intruded by diabase dikes and sills that may correlate
with the Panjal Volcanics. Southern Gandghar Range strata occur in two structural
blocks juxtaposed along the Baghdarra fault. The hanging wall consists entirely of
isoclinally-folded Manki Formation, whereas the footwall consists of the complete
Manki-Shekhai succession which has been deformed into tight, northeast-plunging,
generally southeast (foreland) verging disharmonic folds. Phyllite near the Baghdarra
fault displays kink bands, a poorly-developed S-C fabric, and asymmetric
deformation of foliation around garnet porphyroblasts. These features are consistent
with conditions of dextral shear, indicating reverse-slip displacement along the fault.
South of the Gandghar Range, the Panjal fault brings the Gandghar Range
succession over the Kherimar Hills succession, which is composed of a basal
Precambrian arenaceous sequence (Hazara Formation) unconformably overlain by
Jurassic limestone (Samana Suk Formation) which in turn is unconformably overlain
by Paleogene marine strata (Lockhart Limestone and Patala Formation). The Hazara
and Manki formations, considered to be stratigraphically equivalent, show an increase
in metamorphic grade to the north. In the Kherimar Hills, the Hazara Formation is
unmetamorphosed, whereas in the Gandghar Range, the Manki Formation is metamorphosed to the greenschist-lower epidote-amphibolite grade. Younger strata
in both areas show little to no evidence of metamorphism.
The Gandghar Range succession is identical to the succession in the hanging
wall of the Khairabad fault in the Attock-Cherat Range, and the Kherimar Hills
succession resembles the succession in the footwall of the Khairabad fault. These
relationships indicate that the Panjal and Khairabad faults are continuous and
juxtapose two major, laterally continuous structural blocks. South of the Kherimar
Hills, the Nathia Gali fault brings the Kherimar Hills succession, in which rocks as
old as Precambrian are exposed, over the Margala Hills succession, in which the
oldest rocks exposed are Mesozoic. To the west, the Cherat and Hissartang faults are
considered to be bifurcations of the Nathia Gall fault. The Paleocene Lockhart
Limestone is common to the stratigraphic successions on both sides of the
Hissartang, Cherat, and Nathia Gali faults. Pre-Paleocene successions differ across
the Hissartang and Cherat faults, indicating large amounts of displacement and
juxtaposition of the successions in Late Cretaceous time. Pre-Paleocene successions
juxtaposed along the Nathia Gali fault indicate that most of the displacement along the
fault occurred prior to deposition of the Jurassic Samana Suk Formation. Tertiaty
faulting has occurred on the Hissartang, Cherat, and Nathia Gali faults, although this
displacement is small relative to the pre-Paleocene displacement. Pre-Paleocene
displacement along the Khairabad-Panjal fault cannot be demonstrated due to the
absence of Tertiary strata to the north.
The Hill Ranges fault system, composed of the Main Boundary thrust and
Murree, Nathia Gall, Cherat, Hissartang, Khairabad, Panjal, and Baghdarra faults,
forms a hinterland-dipping duplex. The estimated minimum total horizontal
separation on the Hill Ranges fault system is 85 km. based on the restoration of
projected Paleozoic hanging-wall and footwall cutoffs on a balanced cross section.
Crystalline basement is not involved in the Hill Ranges fault system. The
sedimentary cover is decoupled from the basement along a detachment that
corresponds to the Salt Range thrust.
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