Journal article
Oligocene-Miocene middle crustal flow in southern Tibet; geochronology of Mabja Dome
Geological Society Special Publications, Vol.268(1), pp.445-469
2006
DOI: 10.1144/GSL.SP.2006.268.01.21
Abstract
New U-Pb zircon, monazite, (super 40) Ar/ (super 39) Ar, and apatite fission track ages provide constraints on the timing of formation and exhumation of the Mabja Dome, southern Tibet, shed light on how this gneiss dome formed, and provide important clues on the tectonic evolution of middle crustal rocks in southern Tibet. Zircons from a deformed leucocratic dyke swarm yield a U-Pb age of 23.1+ or -0.8 Ma, providing the first age constraint on the timing of middle crustal ductile horizontal extension in the North Himalayan gneiss domes. Zircons and monazite from a post-tectonic two-mica granite yield ages of 14.2+ or -0.2 Ma and 14.5+ or -0.1, respectively, indicating that vertical thinning and subhorizontal stretching had ceased by the middle Miocene. Mica (super 40) Ar/ (super 39) Ar ages from schists and orthogneisses increase structurally down-section from 12.85+ or -0.13 Ma to 17.0+ or -0.19 Ma and then decrease at the deepest structural levels to 13.29+ or -0.09 Ma. Micas from the leucocratic dyke swarm and post-tectonic two-mica granites yield similar (super 40) Ar/ (super 39) Ar cooling ages of 13.48+ or -0.13 to 12.84+ or -0.08 Ma. The low-temperature steps of potassium feldspar (super 40) Ar/ (super 39) Ar spectra yield ages of c. 11.0-12.5 Ma and apatite fission track analyses indicate the dome uniformly cooled below c. 115 degrees C at 9.5+ or -0.6 Ma. Based on these data, calculated average cooling rates across the dome range from c. 40-60 degrees C/million years in schist and orthogneiss and following emplacement of the leucocratic dyke swarm, to c. 350 degrees C/million years following emplacement of the two-mica granites. The mylonitic foliation, peak metamorphic isograds, and mica (super 40) Ar/ (super 39) Ar chrontours are domed, whereas the low-temperature step potassium feldspar (super 40) Ar/ (super 39) Ar and apatite fission track chrontours are not, suggesting that doming occurred between 13.0 and 12.5 Ma and at temperatures between 370 and 200 degrees C. Our new ages, along with field, structural and metamorphic data, indicate that the domal geometry observed at Mabja developed by middle-Miocene southward-directed thrust faulting upward and southward along a north-dipping ramp above cold Tethyan sediments. The structural, metamorphic and geochronologic histories documented at Mabja Dome are similar to those of Kangmar Dome, suggesting a common mode of occurrence of these events throughout southern Tibet. Vertical thinning and horizontal stretching, metamorphism, generation of migmatites, and emplacement of leucogranites in the domes of southern Tibet are synchronous with similar events in the Greater Himalayan Sequence that underlie the high Himalaya. These relations are consistent with previously proposed models for a ductile middle-crustal channel bounded above by the South Tibetan detachment system and below by the Main Central thrust in the High Himalaya that extended northward beneath southern Tibet.
Details
- Title: Subtitle
- Oligocene-Miocene middle crustal flow in southern Tibet; geochronology of Mabja Dome
- Creators
- J Lee - Central Washington UniversityW McClelland - University of IdahoY Wang - China University of GeosciencesA Blythe - University of Southern CaliforniaM McWilliams - Stanford UniversityR. D Law - Virginia Polytechnic Institute and State University, Department of Geological Sciences Blacksburg, VA USA United StatesM. P Searle - University of OxfordL Godin - Queen's University
- Resource Type
- Journal article
- Publication Details
- Geological Society Special Publications, Vol.268(1), pp.445-469
- Publisher
- Geological Society of London
- DOI
- 10.1144/GSL.SP.2006.268.01.21
- ISSN
- 0305-8719
- eISSN
- 2041-4927
- Alternative title
- Channel flow, ductile extrusion and exhumation in continental collision zones
- Language
- English
- Date published
- 2006
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984229165302771
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