The Nanga Parbat-Haramosh massif (NPHM) is a north-south trending
structural and topographic high, which interrupts the east-west trend
of the Himalaya in northern Pakistan. Previously, the massif was
thought to be bounded by the Main Mantle thrust (MMT), a north-dipping
thrust along which the Kohistan-Ladakh arc was thrust south over the
northern margin of the Indian continent. This study presents field and
geochemical data suggesting that the eastern boundary of the massif,
the Stak fault zone, is a young feature that displaces the suture zone.
The Stak fault zone marks the boundary between Precambrian
kyanite-sillimanite bearing biotite gneiss of continental affinity and
Cretaceous (?) arc lithologies of the western Ladakh terrane. The arc
complex consists of amphibolitic country rock that has been intruded by
gabbroic to tonalitic plutons. The protolith of the amphibolite is
immature oceanic island arc tholeiitic basalt. The mafic to intermediate plutons are dominantly calc-alkaline and could have formed in either a mature island arc setting or a continental margin setting. The
Ladakh arc terrane exposes the upper section of an arc, below the
sedimentary and volcanic cover.
The Stak fault zone is a 3-5 km wide zone containing at least four
major high angle faults that separate blocks of various lithologies.
The only true mylonite zone occurs along the westernmost fault. A
faulted late stage dike is evidence for recent activity along the
easternmost fault. The units along the western side of the fault zone
are analogous to deep oceanic arc lithologies; tholeiitic amphibolite,
banded gneiss, and a section of a layered mafic complex. The units
along the eastern side of the fault zone are mineralogically and
chemically correlative to the mafic plutons exposed in the western
The geometry of the fault zone, the lack of suture zone lithologies, and the evidence for recent activity suggest that the Stak
fault zone does not represent the suturing event, when the Kohistan-
Ladakh arc was obducted onto the northern margin of India. Instead, the
fault zone is likely formed in response to the recent uplift of the
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