HR: 09:00h
AN: T21E-05    [Abstracts]
TI: Did a proto-Indus fan drain to the west?
AU: * Carter, A
EM: a.carter@ucl.ac.uk
AF: School of Earth Sciences, Birkbeck, University of London, Malet Street, London, WC1E 6BT, United Kingdom
AU: Sherlock, S
EM: S.Sherlock@open.ac.uk
AF: Dept. of Earth and Environmental Sciences, CEPSAR, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
AU: Bahroudi, A
EM: bahroudi@yahoo.com
AF: Mining Engineering Faculty, The University of Tehran P.O. Box 11365-4563, Tehran, 11365-4563, Iran (Islamic Republic of)
AU: Garzanti, E
EM: eduardo.garzanti@unimib.it
AF: Dipartmento di Scienze Geologiche e Geotecnologie, Universita di Milano-Bococca, Plazza della Scienza 4, Milan, 20126, Italy
AB: Use of detrital records to reconstruct orogenic growth history requires understanding any long-term changes in sediment routing. For the western Himalayas a proto-Indus fan (Khojak Fan) has been postulated with a drainage that would have deposited Eocene-Oligocene sediments far to the west (present-day western Pakistan and the Makran region of southern Iran) until uplift of the Murray Ridge-Kirthar fold belt in the Miocene. To test for this we conducted a detailed provenance study on Tertiary turbidites exposed in the Makran of southern Iran. The earliest of these sediments have a paleoflow that indicates they were largely sourced from the northeast, possibly from the Himalayan suture zone. Bulk petrography of the Makran sandstones show a mixed provenance, with a prominent change from dominant arc components in Eocene-Early Oligocene samples to a sharp decrease in volcanic grains and an increase in low-grade metamorphic grains in Late Oligocene-mid-Miocene samples consistent with reduced arc input and greater contribution from metamorphic basement. Detrital thermochronometric data (zircon U-Pb, fission-track and 40Ar/39Ar white mica) record a change in source between samples that span the Late Eocene - Early Oligocene (dominated by detrital age populations between 100-150 Ma) and Miocene samples (most source ages between 30-60 Ma). These age modes are consistent with arc sources as the different closure temperatures record the same ages. Contribution from Paleozoic continental basement sources does not appear to change significantly through time. The distinct change in sediment source from arc dominant in the Paleogene to arc subordinate in the Neogene coincided with Miocene uplift of the Murray-Ridge-Kirthar belt and closure of the Katawaz Ocean, a remnant of Tethys. This process closed off Cretaceous arc sources located in the circum Himalaya suture zone to leave a more localised drainage associated with the Tertiary Chagai arc. Such change is consistent with a west draining Paleo-Indus and the main peaks of zircon U-Pb ages are consistent with Karakoram-Kohistan Suture Zone sources but Cretaceous arc magmatism was fairly ubiquitous across northern Tethys.
DE: 1140 Thermochronology
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3675 Sedimentary petrology
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting