12-2 Back Arc Basin Development on the Southern Eurasian Margin Prior to India-Eurasia Collision.

Session: The Geodynamic Evolution of the Himalaya: From Mountain Building to Modern Seismicity and Climate Change

Presenting Author:

Craig Martin

Authors:

Martin, Craig R¹, van Buer, Nicholas², Matchette-Downes, Harry³, Mueller, Paul A.⁴, Cruz-Uribe, Alicia Marie⁵, van Tongneren, Jill⁶, Hanchar, John⁷, Upadhyay, Rajeev⁸, Jagoutz, Oliver⁹

(1) Department of Earth and Planetary Sciences, University of Texas at Austin, Austin, TX, USA, (2) Department of Geological Sciences, Cal Poly Pomona, Pomona, CA, USA, (3) Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA, (4) Dept. of Geological Sciences, University of Florida, Gainesville, FL, USA, (5) School of Earth and Climate Sciences, University of Maine, Orono, ME, USA, (6) Department of Earth and Climate Sciences, Tufts University, Medford, MA, USA, (7) Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL, Canada, (8) Department of Geology, Kumaun University, Nainital, Uttarakhand, India, (9) Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA,

Abstract:

At the start of the India-Eurasia collision the southern Eurasian margin in NW India and Pakistan  likely had a complex Japan-Mariana-style tectonic architecture with extended back-arc basins and oceanic crust separating volcanic arc(s) from the Eurasian continental interior. In this presentation we overview geological constraints on the growth and closure of a back-arc basin that developed on the Eurasian margin in Northwest India and Pakistan in the leadup to the India-Eurasia collision. Our extensive geological mapping and geochronology campaign in the Shyok suture zone, which separates the Kohistan-Ladakh arc from the Karakoram terrane, has demonstrated that the Kohistan-Ladakh arc initially intruded a Jurassic forearc ophiolite at the southern edge of Eurasia. Neotethyan slab rollback caused back-arc basin extension between the Kohistan-Ladakh arc and Eurasia that initiated during the Late Cretaceous. After the accretion of the Kohistan-Ladakh arc onto India, the back arc basin shortened and subducted until the Karakoram terrane was thrust southward over the KLA in the Eocene. This final collision event initiated continental collision orogenesis and it also reactivated the Indus suture zone, overprinting previous structural fabrics associated with KLA-India accretion in the Paleocene. Overall, our results are consistent with geological constraints in Pakistan which also suggest that the India-Eurasia collision in the western Himalaya involved a protracted period of back-arc extension and arc-continent accretion before final continental collision. These findings are also consistent with the Tethyan orogenic system westward into Iran and Europe but less consistent with central Tibet which appears to not have experienced such widespread back-arc extension.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8919

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