Chilas Complex
Cretaceous (102-85 Ma)
Cretaceous in the time scale →Cited in 8 sources Last reviewed Aug 20, 2026
- Rank
- Not recorded
- Status
- Published
- Age
- Mesozoic · Cretaceous · mid-CretaceousCretaceous (102-85 Ma)
- Named by
- Jan et al.
- Type locality
- Chilas, Gilgit-Baltistan35.4200°N, 74.1000°E
- Thickness
- 8-10 km thick
- Lithology
- Large mafic–ultramafic body — gabbronorite with serpentinized ultramafic rocks (dunite, harzburgite, pyroxenite), dolerite and gabbro; associated with the Babusar Pass mélange.
- Synonyms
- Not recorded
The Chilas Complex — a giant layered gabbro body that was the mid-crustal magma chamber of the Kohistan arc.
Largest mafic-ultramafic plutonic body in Kohistan arc. Represents deep-level arc crust. Contains platinum group elements.
Fossils
Not recorded
Contacts
Band colour = period; texture = dominant rock type. Lines between bands mark the contact type. True scale makes height ∝ recorded thickness; hatched = thickness not recorded. Ages approximate, for ordering.
This unit (highlighted) within its province column; faded ends continue above and below. Line style marks the contact type.
Distribution & setting
- Basin
- Not recorded
- Region
- Not recorded
- Depositional environment
- volcanic-arc, plutonic
- Coordinates
- 35.4200°N, 74.1000°E
Correlation
Not recorded. Compare this unit against other basins on the correlation panel →
Economic significance
Platinum group element potential
Remarks
The Chilas Complex — a huge mafic–ultramafic layered intrusion forming the mid-crustal level of the Kohistan arc, interpreted as a sub-arc magma-chamber complex; one of the world's classic exposures of arc mid-crust.
Research notes (5)
Field-by-field findings drawn from the cited literature. Every statement is traced to a registered source — follow a citation for the full reference.
Name & nomenclature (1)
-
Attested in Shah (2009), Geological Survey of Pakistan Memoir 22 - the Stratigraphic Committee of Pakistan's compiled lexicon (listed in the memoir's contents). Adds the definitional GSP/SCP lexicon citation.
Shah, S.M.I. (2009)
Age & correlation (1)
-
Treloar et al. (1996): the Chilas Complex — a massive calc-alkaline gabbronorite body up to ~50 km wide and ~300 km long (with high-Mg ultramafic–mafic cumulates) — was emplaced at c. 85 Ma (U–Pb zircon 84 ± 0.5 Ma, Zeitler et al. 1981) by intra-arc rifting. Its largely undeformed state, intruding the already-deformed Jaglot Group, indicates emplacement after the main late-Cretaceous suturing deformation; heat from its emplacement drove amphibolite-facies metamorphism, lower-arc melting and Stage-2 batholith plutonism.
Treloar, P.J., Petterson, M.G., Jan, M.Q. & Sullivan, M.A. (1996)
Lithology (1)
-
Coward et al. (1984): the Chilas Complex is a vast stratiform cumulate body over 300 km long and up to 8 km thick, with an upward sequence of hypersthene gabbro, major chromite-layered dunite, norite, gabbro, minor troctolite/harzburgite/dunite and norite at the top; rhythmically phase-graded cumulate layers up to 10 cm thick, slump folds, syn-sedimentation faults and sedimentary breccias occur, with near-pure anorthosite layers and 3 m compact chromitite seams in the basal dunites.
Coward, M.P., Jan, M.Q., Rex, D., Tarney, J., Thirlwall, M. & Windley, B.F. (1984)
Geological significance (2)
-
Khan et al. (1989): the Chilas Complex is the root (deepest exposed level) of the Kohistan island arc — a mafic-ultramafic body >300 km long and up to 40 km wide at the base of the arc. It is dominantly massive to locally layered gabbro-norite, with a central near-base association of layered dunite-peridotite-troctolite-gabbronorite-pyroxenite-anorthosite (graded bedding, slump breccias, syn-depositional faults) representing a more primitive magma batch. It is NOT an ophiolite: trace-element patterns (marked negative Nb, positive Sr-Ba-P, high K/Rb) indicate melting of a hornblende-bearing sub-arc mantle, and the complex is interpreted as the arc root-zone magma chamber or a diapir formed during early intra-arc (back-arc) rifting.
Khan, M.A., Jan, M.Q., Windley, B.F., Tarney, J. & Thirlwall, M.F. (1989)
-
Coward et al. (1984): the Chilas Complex is folded by an F2 isoclinal anticline and interpreted as the lowermost crustal unit of the Kohistan arc sequence - a granulite-grade layered complex forming the base of the crustal section, compared to the Ivrea Zone of the Italian Alps; its intact cumulate stratigraphy would have blocked the passage of the arc's granitic magmas, implying it was one of the latest pre-first-deformation intrusions.
Coward, M.P., Jan, M.Q., Rex, D., Tarney, J., Thirlwall, M. & Windley, B.F. (1984)
Sources (8)
- Malkani, M.S. & Mahmood, Z. (2017). Stratigraphy of Pakistan. Geological Survey of Pakistan, Memoir Vol. 24.
- Kazmi, A.H. & Jan, M.Q. (1997). Geology and Tectonics of Pakistan. Graphic Publishers, Karachi.
- OpenStreetMap contributors and GEOnet Names Server (public geographic gazetteers), used to geolocate named GSP type localities to approximate decimal coordinates.
- Shah, S.M.I. (2009). Stratigraphy of Pakistan. Geological Survey of Pakistan, Memoir Vol. 22.
- Treloar, P.J., Petterson, M.G., Jan, M.Q. & Sullivan, M.A. (1996). A re-evaluation of the stratigraphy and evolution of the Kohistan arc sequence, Pakistan Himalaya: implications for magmatic and tectonic arc-building processes. Journal of the Geological Society, London, 153, 681-693.
- Kazmi, A.H. & Abbasi, I.A. (2008). Stratigraphy and Historical Geology of Pakistan. Department & National Centre of Excellence in Geology, University of Peshawar, Peshawar. 524 pp. ISBN 978-969-9119.
- Khan, M.A., Jan, M.Q., Windley, B.F., Tarney, J. & Thirlwall, M.F. (1989). The Chilas mafic-ultramafic igneous complex; the root of the Kohistan island arc in the Himalaya of northern Pakistan. In: Malinconico, L.L. & Lillie, R.J. (eds) Tectonics of the Western Himalayas. Geological Society of America Special Paper 232, 75-94.
- Coward, M.P., Jan, M.Q., Rex, D., Tarney, J., Thirlwall, M. & Windley, B.F. (1984). Geology of the South Central Karakoram and Kohistan. In: Miller, K.J. (ed.), The International Karakoram Project, Vol. 2, 71-84. Cambridge University Press.
Reviewer confidence: medium
Every fact on this page is source-cited. This entry is part of the peer-archived Pakistan Stratigraphy Dataset (doi.org/10.5281/zenodo.21363991, CC‑BY‑4.0).
Lexicon status: Name attested in the Shah (1977/2009) Geological Survey of Pakistan compilation — the national stratigraphic lexicon. This records where the name is documented; it is not an endorsement of the unit’s definition, age or figures.
Cite this unit
Qudsi, L. (2026). Chilas Complex. In Pakistan Stratigraphy Dataset [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21363991
@misc{stratigraphypk_chilascomplex,
author = {Qudsi, Lareb},
title = {{Chilas Complex} --- Pakistan Stratigraphy Dataset},
year = {2026},
publisher = {Zenodo},
doi = {10.5281/zenodo.21363991},
url = {https://doi.org/10.5281/zenodo.21363991}
} Archived dataset: doi.org/10.5281/zenodo.21363991 (CC‑BY‑4.0) · Direct link to this entry: https://stratigraphy.pk/formation/chilas-complex (accessed October 7, 2026).
To cite the unit's original definition instead, see: Jan et al..
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