 |
| Titel |
Changing provenance areas of the Cenozoic Central Myanmar Basin sediments discriminated using Hf values of detrital zircons |
| VerfasserIn |
Cynthia Brezina, Ruth A. J. Robinson, Randy R. Parrish, Matthew S. A. Horstwood, Michael I. Bird, Nay Win Oo, Myint Thein |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042836
|
|
|
|
|
|
| Zusammenfassung |
| The syntaxis region of the eastern Himalayas is a complex geological collision
zone where uplift, deformation and erosion have influenced landscape evolution
during the Cenozoic. The syntaxis region has several large river systems draining the
present day configuration of catchments, including the Tsangpo, Brahmaputra,
Irrawaddy, Salween, and Mekong. The Tsangpo follows a circuitous route around
the Namche Barwa before draining into the Brahmaputra, and earlier connections
to the large rivers of southern Asia have been suggested in the literature. Liang
et al. (2008) used the ÉHf values of detrital zircons from a Late Miocene Central
Myanmar Basin sample, and from two Himalayan batholiths in the syntaxis, to
show that the Miocene sediment contain Gangdese-like zircons with positive ÉHf
values from Tibet, rather than more negative ÉHf values of zircons from inside the
syntaxis. They concluded that there was a Tsangpo-Irrawaddy connection in the Late
Miocene.
Here we show, using U/Pb dating and ÉHf analyses of detrital zircons extracted
from Eocene, Oligocene, and a suite of Miocene deposits, that the distribution of
detrital zircon ÉHf values in the different aged rock units change through time,
reflecting a change in provenance, as well as uplift, erosion and mixing of zircons from
previously deposited sediments. We have compared all the published ÉHf data for the
Transhimalayan batholiths in Tibet and Myanmar, and can identify the different
provenance areas for the Cenozoic samples based on the range of ÉHf values and
ages measured for the detrital zircons. Mostly positive ÉHf values for the detrital
zircons contained in Eocene sediments are indistinguishable from Gangdese values
and ages, supporting our hypothesis that the proto-Irrawaddy river was tapping the
Gangdese batholith during the Eocene, and that the Tsango-Irrawaddy connection
dates back to at least 43Ma, approximately the age of our oldest sample from the
Myanmar Central Basin. The Oligocene samples also have a Gangdese provenance.
Significantly, the ÉHf signature of detrital zircons changes in the Miocene deposits and
negative ÉHf values similar to those of the Dianxi-Burma batholith are the dominant
signature, with positive ÉHf values becoming less common for the younger Miocene
samples. We interpret this change in provenance to signal the disconnection of the
Tsangpo-Irrawaddy river system, and that it failed to keep pace with uplift in the syntaxis
about 18-20Ma, coincident with major reorganisation in the orogen, the onset of strike-slip
movement on the Sagaing Fault, and widespread magmatic events in the Gangdese
batholith. It is also earlier than the Late Miocene timing suggested by Liang et
al. (2008). Our results explain why Transhimalayan detritus arrives in the Bay of
Bengal in the Early Miocene, and provides new palaeogeographic reconstructions and
timing upon which landscape evolution tectonic-erosion coupling questions can be
addressed. One such question is why did the Tsango-Irrawaddy connection fail at
18-20Ma?
Reference:
Liang, Y-H. et al. (2008) Detrital zircon evidence from Burma for reorganization of
the Eastern Himalayan river system. American Journal of Science, 308, 618-638. |
|
|
|
|
|
|