The relationship of argon retentivity and chemical composition of hornblende

Leake, Bernard Elgey; Elias, Elias M.; Farrow, Colin

doi:10.1016/0016-7037(88)90195-0

Cited by 9 publications

(1 citation statement)

References 3 publications

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“…The age of cooling through the Ar closure temperature is derived from the stable 'plateau' stage of gas release. A closure temperature of c. 300 "C is typically accepted for biotite (Harrison et al 1985), whereas c. 500 "C is representative of most hornblende, despite the potential complexities introduced by exsolution and composition (Harrison & FitzGerald 1986;Leake et al 1988). Biotite ages show a spread of 44-49 Ma, whereas the single hornblende yielded an older (52 Ma) age.…”

Section: ~R / 3 9~r Geochronologymentioning

confidence: 99%

Constraints on India-Eurasia collision in the Arabian Sea region taken from the Indus Group, Ladakh Himalaya, India

et al. 2002

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The Indus Group is a Paleogene, syntectonic sequence from the Indus Suture Zone of the Ladakh Himalaya, India. Overlying several pre-collisional tectonic units, it constrains the timing and nature of India's collision with Eurasia in the western Himalaya. Field and petrographic data now allow Mesozoic-Paleocene deep-water sediments underlying the Indus Group to be assigned to three pre-collisional units: the Jurutze Formation (the forearc basin to the Cretaceous-Paleocene Eurasian active margin), the Khalsi Flysch (a Eurasian forearc sequence recording collapse of the Indian continental margin and ophiolite obduction), and the Lamayuru Group (the Mesozoic passive margin of India). Cobbles of neritic limestone, deepwater radiolarian chert and mafic igneous rocks, derived from the south (i.e. from India), are recognized within the upper Khalsi Flysch and the unconfomably overlying fluvial sandstones of the Chogdo Formation, the base of the Indus Group. The Chogdo Formation is the first unit to overlie all three pre-collisional units and constrains the age of India-Eurasia collision to being no younger than latest Ypresian time (>49 Ma), consistent with marine magnetic data suggesting initial collision in the Arabian Sea region at c. 55 Ma. The cutting of equatorial Tethyan circulation north of India at that time may have been a trigger to the major changes in global palaeoceanography seen at the Paleocene-Eocene boundary. New 4 0~r / 3 9~r , apatite fission-track and illite crystallinity data from the Ladakh Batholith and Indus Group show that the batholith, representing the old active margin of Eurasia, experienced rapid Eocene cooling after collision, but was not significantly reheated when the Indus Group basin was inverted during north-directed Miocene thrusting (23-20 Ma). Subsequent erosion has preferentially removed 5-6 km (c. 200 "C) over much of the exposed Indus Group, but only c. 2 krn from the Ladakh Batholith. Reworking of this material into the Indus fan may complicate efforts to ' interpret palaeo-erosion patterns from the deep-sea sedimentary record.

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Section: ~R / 3 9~r Geochronologymentioning

confidence: 99%