 |
| Titel |
Identifying the complex melting reaction from 20 Ma to 14 Ma in Tsona leucogranite in Southern Tibet: geochemistry, zircon U-Pb chronology and Hf isotopes evidence |
| VerfasserIn |
Qingshang Shi, Zhidan Zhao, Dong Liu, Di-Cheng Zhu |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250139426
|
| Publikation (Nr.) |
 EGU/EGU2017-2663.pdf |
|
|
|
|
|
| Zusammenfassung |
| The Miocene leucogranites, the record of the evolution of the Himalayan-Tibetan Orogen,
extensively intruded the Greater Himalayan Sequence (GHS), and distributed along the South
Tibetan Detachment System (STDS) (Guo and Wilson, 2012). Here we present a
study of geochemistry, zircon U-Pb chronology and Hf isotopes on the Yamarong
leucogranites from Tsona area, Eastern Himalaya, to explore the petrogenesis of the
rocks, including melting condition and mechanism, and source of fluid within the
magmatism through time. Our new results include: (1) The age of the Yamarong
leucogranites range from 14 Ma to 20 Ma (YM1510-1 = 19.7 ± 0.1 Ma, n = 13;
YM1502-1 = 17.5 ± 0.1 Ma, n = 12; YM1412 =14.2 ± 0.1 Ma, n = 18), which suggest
that the anataxis processes have lasted for more than 6 Ma. (2) The geochemical
features are different between the rocks with changing ages, especially between
20 Ma and 17 Ma. The Rb/Sr value of 20 Ma leucogranites (4.1-6.84) is lower
than that of 17 Ma samples (5.12-19.02). The 20 Ma leucogranites have higher
Ba contents (188-337 ppm) than that of 17 Ma rocks (50-158ppm), which exhibit
different trends in the Rb/Sr versus Ba plot, and reveal different melting reaction
from 20 Ma to 17 Ma. (Inger and Harris, 1993) (3) The ɛHf(t) isotopes of 20 Ma
leucogranites are lower (average ɛHf(t) = -12.5) than that of 17 Ma ones (average
ɛHf(t) = -10), which implies differential dissolution of inherited zircon during
two partial melting events possibly due to different fluid contribution (Gao et al.,
2017); (4) The positive linear relationship of LREEs versus Th in the rocks, with
relatively higher contents of Th and LREEs in the 20 Ma, and lower in the 17 Ma
leucogranites, which suggests the relationship were mostly controlled by monazite. And
this further indicates more monazite was dissolved from the source region in the
early stage (∼20Ma) than the later (17Ma) (Gao et al., 2017). In summary, our
study provides new evidence for the complex melting mechanism, from fluid-fluxed
melting at ∼20 Ma to later fluid-absent melting at ∼17 Ma of muscovite in the
metasedimentary sources. The ∼20 Ma magmatism in Tsona area may represent the
early stage of exhumation, with more fluid possibly came from either the Lesser
Himalayan sequence (LHS) or the Cretaceous – Paleogene molasses beneath the along –
stike extrapolation of the Yamarong leucogranties source (Harrison and Wielicki,
2016).
Reference:
Gao L-E, Zeng L, Asimow PD, 2017. Contrasting geochemical signatures of fluid-absent
versus fluid-fluxed melting of muscovite in metasedimentary sources: The Himalayan
leucogranites. Geology, 45(1):39-42.
Guo Z, Wilson M, 2012. The Himalayan leucogranites: Constraints on the nature of
their crustal source region and geodynamic setting. Gondwana Research, 22(2):
360-376.
Harrison TM, Wielicki MM, 2016. From the Hadean to the Himalaya: 4.4 Ga of felsic
terrestrial magmatism. American Mineralogist, 101(6): 1348-1359.
Inger S, Harris N, 1993. Geochemical Constraints on Leucogranite Magmatism
in the Langtang Valley, Nepal Himalaya. Journal of Petrology, 34(2): 345-368. |
|
|
|
|
|
|