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| Titel |
Detrital mineral thermochronology of Cenozoic deposits of Central Myanmar and implications for the evolution of the eastern Himalayan orogen |
| VerfasserIn |
Cynthia Brezina, Ruth Robinson, Dan Barfod, Andrew Carter, Myint Thein, Nay Win Oo |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250084181
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| Zusammenfassung |
| Detrital low temperature thermochronology of single grains of white mica using 40Ar/39Ar
methods, and double dating of zircon by fission track and U/Pb combined with Lu-Hf
geochemistry methods, have been applied to a suite of Eocene, Oligocene and Miocene
samples from the Central Myanmar Basin in order to identify the tectonothermal events and
source terranes that are recorded in the sedimentary rocks. By combining multiple
provenance tools, it is possible to determine how changes in provenance from Late Eocene to
early Miocene time are related to exhumation and landscape evolution in the eastern sector of
the Himalayan orogen. To discriminate between source terranes, we compare our ages to
published low temperature thermochronology data from Jurassic-Tertiary bedrock of the
Lhasa terrane, and the Transhimalayan rocks of the eastern syntaxis, eastern to southeastern
Myanmar, and western Thailand.
Detrital white mica 40Ar/39Ar ages for the Eocene and Oligocene deposits reflect a broad
range of cooling events that are Jurassic to Oligocene in age and the majority of the
40Ar/39Ar ages are older than 60 Ma. In contrast, the detrital micas from Miocene deposits
have a narrow range of 40Ar/39Ar ages with one dominant peak of 30 – 40 Ma, and about
90% of the ages are younger than 60 Ma. Multi-modal detrital zircon fission track ages are
evident in all samples and span the last 200 Ma, and the majority are younger than 60
Ma. The combined dataset supports our previous interpretations that the Yarlung
Tsangpo of Tibet and the Irrawaddy River of Myanmar were connected in Late Eocene
and Oligocene time, and that the timing of river disconnection and capture of the
Yarlung Tsangpo by the Brahmaputra is an early Miocene event (between 18 - 19
Ma). The 40Ar/39Ar age distributions of detrital muscovite in Palaeogene samples
reflect multiple sources within the Lhasa terrane and represent episodic cooling
following intrusion of the Gangdese Batholith from the Jurassic to Tertiary time. The
abrupt change in 40Ar/39Ar age spectra observed in the oldest Miocene deposit (and
all the younger Miocene deposits sampled) reflects a change in provenance to a
single source area which is interpreted to be in southeastern Myanmar and western
Thailand. We propose that exhumation and deformation in the syntaxis and along the
boundary between the Burma plate and the Asian margin is associated with the
disconnection of the Yarlung Tsangpo-Irrawaddy river coincident with increased
coupling of the India and Burma plates. The partial resetting of a small proportion
of 40Ar/39Ar mica ages in the oldest Eocene samples, and of some fission track
ages in all the samples analysed, allows us to constrain the depth of burial and
timing of exhumation of the sedimentary sequences within the Central Myanmar
Basin, and link that exhumation to the onset of movement on the Sagaing Fault. |
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