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Spatial and temporal trends in exhumation of the eastern Himalaya and syntaxis as determined from a multitechnique detrital thermochronological study of the Bengal Fan

Yani Najman, Chris Mark, Dan N. Barfod, Andy Carter, Randy Parrish, David Chew and Lorenzo Gemignani
Spatial and temporal trends in exhumation of the eastern Himalaya and syntaxis as determined from a multitechnique detrital thermochronological study of the Bengal Fan
Geological Society of America Bulletin (March 2019) Pre-Issue Publication

Abstract

The Bengal Fan provides a Neogene record of Eastern and Central Himalaya exhumation. We provide the first detrital thermochronological study (apatite and rutile U-Pb, mica Ar-Ar, zircon fission track) of sediment samples collected during International Ocean Discovery Program (IODP) Expedition 354 to the mid-Bengal Fan. Our data from rutile and zircon fission-track thermochronometry show a shift in lag times over the interval 5.59-3.47 Ma. The oldest sample with a lag time of <1 m.y. has a depositional age between 3.76 and 3.47 Ma, and these short lag times continue to be recorded upward in the core to the youngest sediments analyzed, deposited at <1 Ma. We interpret the earliest record of short lag times to represent the onset of extremely rapid exhumation of the Eastern Himalayan syntaxial massif, defined as the syntaxial region north of the Nam La Thrust. Below the interval characterized by short lag times, the youngest sample analyzed with long lag times (>6 m.y.) has a depositional age of 5.59-4.50 Ma, and the zircon and rutile populations then show a static peak until >12 Ma. This interval, from 5.59-4.50 Ma to >12 Ma, is most easily interpreted as recording passive erosion of the Greater Himalaya. However, single grains with lag times of <4 m.y., but with high analytical uncertainty, are recorded over this interval. For sediments older than 10 Ma, these grains were derived from the Greater Himalaya, which was exhuming rapidly until ca. 14 Ma. In sediments younger than 10 Ma, these grains could represent slower, yet still rapid, exhumation of the syntaxial antiform to the south of the massif. Lag times <1 m.y. are again recorded from 14.5 Ma to the base of the studied section at 17 Ma, reflecting a period of Greater Himalayan rapid exhumation. Mica (super 40) Ar/ (super 39) Ar and apatite U-Pb data are not sensitive to syntaxial exhumation: We ascribe this to the paucity of white mica in syntaxial lithologies, and to high levels of common Pb, resulting in U-Pb ages associated with unacceptably high uncertainties, respectively.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: Pre-Issue Publication
Title: Spatial and temporal trends in exhumation of the eastern Himalaya and syntaxis as determined from a multitechnique detrital thermochronological study of the Bengal Fan
Affiliation: Lancaster University, Lancaster Environment Centre, Lancaster, United Kingdom
Published: 20190329
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Accession Number: 2019-032178
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2019108
N24°00'00" - N30°00'00", E88°00'00" - E96°00'00"
Secondary Affiliation: Trinity College Dublin, IRL, IrelandScottish Universities Environmental Research Centre, GBR, United KingdomUniversity College London, GBR, United KingdomPortsmouth University, GBR, United KingdomVrije Universiteit Amsterdam, NLD, Netherlands
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201908
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