| Title | Two-stage cooling history of pelitic and semi-pelitic mylonite (sensu lato) from the Dongjiu--Milin shear zone, northwest flank of the eastern Himalayan syntaxis |
| |
| Author | Palin, R M; Searle, M P; St-Onge, M R; Waters, D J; Roberts, N M W; Horstwood, M S A; Parrish, R R; Weller, O M |
| Source | Gondwana Research 2014 p. 1-22, https://doi.org/10.1016/j.gr.2014.07.009 |
| Image |  |
| Year | 2014 |
| Alt Series | Earth Sciences Sector, Contribution Series 20130242 |
| Publisher | Elsevier BV |
| Document | serial |
| Lang. | English |
| Media | on-line; digital |
| File format | html; pdf |
| Area | Dongjiu; Milin; China |
| Lat/Long WENS | 93.5000 95.5000 30.1667 29.7500 |
| Subjects | tectonics; structural geology; mineralogy; geochemistry; geochronology; mylonites; metamorphic rocks; shear zones; structural features; metamorphism; mylonitization; tectonic evolution; deformation;
garnet; mineralogical analyses; geochemical analyses; uranium lead dates; lead lead dates; monazite; thorium lead dates; thermobarometry; tectonic models; Dongjiu--Milin shear zone; Himalayan--Tibetan orogen; Himalayan syntaxis; Namche Barwa Complex;
Tertiary |
| Illustrations | geological sketch maps; geochemical analyses; SEM images |
| Program | GEM: Geo-mapping for Energy and Minerals GEM Tri-Territorial Information Management & databases (Tri-Territorial Bedrock Framework) |
| Released | 2015 09 01 |
| Abstract | he Dongjiu-Milin shear zone located on the northwest flank of the eastern Himalayan syntaxis, southeast Tibet, separates Indian and Asian plate rocks. It is characterized by a thick sequence of highly
strained and ductilely deformed mylonite (sensu stricto and sensu lato) bound between a pair of sub-parallel transtensive brittle normal faults. An integrated geochronological, petrographic, and thermobarometric study of three samples of pelitic and
semi-pelitic mylonite (sensu lato) from the shear zone provides new insights into its thermal and structural evolution, and hence the tectonic processes operating in the region since the India-Asia collision. U-Th-Pb in-situ dating of monazite,
garnet-ilmenite thermometry, and textural relationships show that mylonitization and peak-thermal staurolite-grade metamorphism occurred at 23.4 ± 0.7 Ma at a temperature of at least ~ 610 ± 30 °C. Cooling of these units through 420-500 °C occurred
at c. 11-8 Ma, as constrained by the retrograde breakdown of allanite to form monazite. These data show that the cooling history of mylonite (sensu lato) in the shear zone and the tectonic evolution of the syntaxis region can be divided into two
distinct stages. Slow cooling at a rate of 6-12 °C/Myr during c. 23-8 Ma is attributed to exhumation during ductile deformation and mylonitization caused by the ongoing India-Asia collision. This was followed by a period of significantly faster
cooling at a minimum rate of 57 °C/Myr since c. 8 Ma, most likely associated with brittle normal faulting that facilitated the final stages of excavation to the surface. These new thermochronological data provide evidence of deep-seated
exhumation-related cooling processes occurring in a convergent margin orogenic setting. |
| Summary | (Plain Language Summary, not published)
The Dongjiu-Milin shear zone located in southeast Tibet separates the Indian and Asian plates in the Himalaya. An integrated study of deformed rocks from
this zone provides insight into their thermal and structural evolution and the tectonic processes operating during collision. Dating shows that deformation and metamorphism occurred at 23.4 ± 0.7 Ma at ~560-650 °C. Cooling through the ~450 °C
isotherm occurred between c. 11-8 Ma. These data show that the cooling history of the shear zone can be divided into two distinct stages. Initial slow cooling at a rate of 10 °C/Myr between c. 23-8 Ma interpreted to be the result of exhumation during
collision. This was followed by a period of significantly faster cooling at a minimum rate of 56 °C/Myr likely associated with brittle faulting that facilitated the final stages of excavation to the surface. These new data account for deformation
features found along the length of the Himalaya as well as in older collisional systems, such as the Trans-Hudson Orogen in the eastern Canadian Arctic. |
| GEOSCAN ID | 293071 |
|
|