摘要
The combined use of conventional, isotopic and geochemical techniques provides a powerful tool with which to determine sedimentary provenance, from which interpretations on Himalayan evolution and tectonics can be made.Here we present the results of conventional bulk\|composition petrography, single grain isotopic (Ar\|Ar white mica ages, U\|Pb ages and Sm\|Nd on monazite) and whole rock Sm\|Nd, Sr (in prep) study on the Dharamsala formation (Early to Middle Miocene molasse) of Northern India. The petrography and mica cooling ages show an abrupt shift in the provenance with higher\|grade metamorphic source\|rocks replaced by sedimentary and very low\|grade metasedimentary source\|rocks up\|section. The break in composition corresponds to the transition between the Lower and Upper members of the unit, which took place between 17 5 and 17Ma (depositional ages constrained by magnetostratigraphy, Maithani and Burbank unpublished data). This event, with all likelihood tectonic in nature, interrupted and reversed the unroofing trend well documented in the classic Dagshai\|Kasauli sandstone suite of the Indian foreland basin (Najman 2000) and continued through the Lower Dharamsala. In addition U\|Pb ages and Sm\|Nd ratios on single detrital monazite grain suggest three sources, High Himalayan Series which has been effected by the earliest Himalayan metamorphism, low\|grade or un\|metamorphosed High Himalayan equivalents and grains in the youngest sediments which carry ENd(0) values identical to the Lesser Himalayan Series.
The combined use of conventional, isotopic and geochemical techniques provides a powerful tool with which to determine sedimentary provenance, from which interpretations on Himalayan evolution and tectonics can be made.Here we present the results of conventional bulk\|composition petrography, single grain isotopic (Ar\|Ar white mica ages, U\|Pb ages and Sm\|Nd on monazite) and whole rock Sm\|Nd, Sr (in prep) study on the Dharamsala formation (Early to Middle Miocene molasse) of Northern India. The petrography and mica cooling ages show an abrupt shift in the provenance with higher\|grade metamorphic source\|rocks replaced by sedimentary and very low\|grade metasedimentary source\|rocks up\|section. The break in composition corresponds to the transition between the Lower and Upper members of the unit, which took place between 17 5 and 17Ma (depositional ages constrained by magnetostratigraphy, Maithani and Burbank unpublished data). This event, with all likelihood tectonic in nature, interrupted and reversed the unroofing trend well documented in the classic Dagshai\|Kasauli sandstone suite of the Indian foreland basin (Najman 2000) and continued through the Lower Dharamsala. In addition U\|Pb ages and Sm\|Nd ratios on single detrital monazite grain suggest three sources, High Himalayan Series which has been effected by the earliest Himalayan metamorphism, low\|grade or un\|metamorphosed High Himalayan equivalents and grains in the youngest sediments which carry ENd(0) values identical to the Lesser Himalayan Series.
作者
Nikki White 1, Eduardo Garzanti 2, Malcolm Pringle 3, Randy Parrish 4,5 , Geoff Nowell 4, Yani Najman 6,Mike Bickle 1, Peter Friend 1, Hazel Chapman 1, Doug Burbank 7, Ashok Maithani 8
出处
《地学前缘》
EI
CAS
CSCD
2000年第S1期62-63,共2页
Earth Science Frontiers
