http://www.igg.cas.cn/xwzx/yjcg/200910/W020091020357735122250.pdf

Zircon U-Pb geochronology and Hf isotopic constraints on petrogenesis of the Gangdese batholith, southern Tibet

Cenozoic tectono-magmatic and metallogenic processes in the Sanjiang region, southwestern China

Late Cretaceous charnockite with adakitic affinities from the Gangdese batholith, southeastern Tibet: Evidence for Neo-Tethyan mid-ocean ridge subduction?

[1] The Mogok metamorphic belt (MMB) extends for over 1500 km along the western margin of the Shan-Thai block, from the Andaman Sea north to the eastern Himalayan syntaxis. Previous geochronology has suggested that a long-lasting Jurassic–early Cretaceous subduction-related event resulted in emplacement of granodiorites and orthogneisses (171–120 Ma) and a poorly constrained Tertiary metamorphic event. On the basis of new U-Pb isotope dilution thermal ionization mass spectrometry and U-Th-Pb laser ablation–multicollector–inductively coupled plasma mass spectrometer geochronology presented here, we propose two Tertiary metamorphic events affected the MMB in Burma. The first was a Paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at ∼59 Ma. A second metamorphic event spanned late Eocene to Oligocene (at least from 37, possibly 47, to 29 Ma). This resulted in the growth of metamorphic monazite at sillimanite grade, growth of zircon rims at 47–43 Ma, sillimanite + muscovite replacing older andalusite, and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45.5 ± 0.6 Ma and 24.5 ± 0.7 Ma. These data imply high-temperature sillimanite + muscovite metamorphism peaking at 680°C and 4.9 kbar between 45 and 33 Ma, to around 606–656°C and 4.4–4.8 kbar at 29.3 ± 0.5 Ma. The later metamorphic event is older than 24.5 ± 0.3 Ma, the age of leucogranites that crosscut all earlier fabrics. Our structural and geochronological data suggest that the MMB links north to the unexposed middle or lower crust rocks of the Lhasa terrane, south Tibet, and east to high-grade metamorphic core complexes in northwest Thailand.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006TC002083

Tectonic evolution of the Mogok metamorphic belt, Burma (Myanmar) constrained by U-Th-Pb dating of metamorphic and magmatic rocks

A long‐standing problem in the geological evolution of the India‐Asia collision zone is how and where convergence between India and Asia was accommodated since collision. Proposed collision ages vary from 65 to 35 Ma, although most data sets are consistent with collision being underway by 50 Ma. Plate reconstructions show that since 50 Ma ∼2400-3200 km (west to east) of India‐Asia convergence occurred, much more than the 450-900 km of documented Himalayan shortening. Current models therefore suggest that most post‐50 Ma convergence was accommodated north of the Indus‐Yarlung suture zone. We review kinematic data and construct an updated restoration of Cenozoic Asian deformation to test this assumption. We show that geologic studies have documented 600-750 km of N‐S Cenozoic shortening across, and north of, the Tibetan Plateau. The Pamir‐Hindu Kush region accommodated ∼1050 km of N‐S convergence. Geological evidence from Tibet is inconsistent with models that propose 750-1250 km of eastward extrusion of Indochina. Approximately 250 km of Indochinese extrusion from 30 to 20 Ma of Indochina suggested by SE Asia reconstructions can be reconciled by dextral transpression in eastern Tibet. We use our reconstruction to calculate the required size of Greater India as a function of collision age. Even with a 35 Ma collision age, the size of Greater India is 2-3 times larger than Himalayan shortening. For a 50 Ma collision, the size of Greater India from west to east is ∼1350-2600 km, consistent with robust paleomagnetic data from upper Cretaceous‐Paleocene Tethyan Himalayan strata. These estimates for the size of Greater India far exceed documented shortening in the Himalaya. We conclude that most of Greater India was consumed by subduction or underthrusting, without leaving a geological record that has been recognized at the surface.

/pdf/restoration-of-cenozoic-deformation-in-asia-and-the-size-of-4l5rvppy56.pdf

Restoration of Cenozoic deformation in Asia and the size of Greater India

Situated south of the eastern Himalayan syntaxis at
the western margin of the Shan-Thai terrane the highgrade
Mogok metamorphic belt (MMB) in Myanmar occupies a key position in the tectonic evolution of Southeast Asia The first sensitive high-resolution ion microprobe U-Pb in zircon geochronology for the MMB shows that strongly deformed granitic orthogneisses near Mandalay contain Jurassic (~170 Ma) zircons that have partly recrystallized during ~43 Ma high-grade metamorphism A hornblende syenite
from Mandalay Hill also contains Jurassic zircons with
evidence of Eocene metamorphic recrystallization
rimmed by thin zones of 309 plus or minus 07 Ma magmatic
zircon The relative abundance of Jurassic zircons in
these rocks is consistent with suggestions that southern
Eurasia had an Andean-type margin at that time Mid-
Cretaceous to earliest Eocene (120 to 50 Ma) I-type
granitoids in the MMB, Myeik Archipelago, and Western Myanmar confirm that prior to the collision of India, an up to 200 km wide magmatic belt extended along the Eurasian margin from Pakistan to Sumatra 
Metamorphic overgrowths to zircons in the orthogneiss
near Mandalay date a period of Eocene (~43 Ma)
high-grade metamorphism possibly during crustal
thickening related to the initial collision between
India and Eurasia (at 65 to 55 Ma) This was
followed by emplacement of syntectonic hornblende
syenites and leucogranites between 35 and 23 Ma
Similar syntectonic syenites and leucogranites intruded
the Ailao Shan-Red River shear belt in southern China
and Vietnam during the Eocene-Oligocene to Miocene,
and the Wang Chao and Three Pagodas faults in
northern Thailand (that most likely link with the MMB)
were also active at this time The complex history of
Eocene to early Miocene metamorphism, deformation,
and magmatism in the MMB provides evidence that it
may have played a key role in the network of
deformation zones that accommodated strain during
the northwards movement of India and resulting
extrusion or rotation of Indochina

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002TC001398

M. G. Doyle

Papers

Jurassic to Miocene magmatism and metamorphism in the Mogok metamorphic belt and the India‐Eurasia collision in Myanmar