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| Titel |
Postcollisional potassic and ultrapotassic rocks in southern Tibet: Deciphering influences of mantle metasomatism and crustal contamination |
| VerfasserIn |
Dong Liu, Zhidan Zhao, Di-Cheng Zhu, Yaoling Niu, T. Mark Harrison |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091890
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| Publikation (Nr.) |
 EGU/EGU2014-6204.pdf |
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| Zusammenfassung |
| Abstract: Postcollisional potassium-rich magmatism in southern Tibet provides an important
insight into the deep processes inducing accelerated plateau uplift and associated geologic
episodes during early Miocene. As a major outcropping of postcollisional magmatic rocks in
the southwestern Tibet, ultrapotassic and potassic volcanism in Xungba basin occurred
coevally at ca. 23 Ma, consisting of bimodal-like volcanic sequence. The mantle-derived
ultrapotassic rocks (Group 1) are latites and marked by both mantle and crustal geochemical
signatures, similar to other younger (19-10 Ma) ultrapotassic rocks elsewhere in the southern
Tibet. The high Th/Yb ratios, low Ba/La and Hf/Sm ratios observed in ultrapotassic
rocks strongly imply derivation from a metasomatized lithospheric mantle regions
enriched by inputs of pelagic sediment and carbonate during previous Tethyan
oceanic subduction, while their relatively high SiO2 and Dy/Yb, low Ni/MgO and
CaO/Al2O3, and convex upward 87Sr/86Sr-δ18OV -SMOW relationship suggest additional
contributions of overthickened lower crust and ancient basement except for enriched
mantle sources. The potassic rocks (Group 2), which underlie Group 1 rocks, are
intermediate to silicic and exhibit adakitic geochemical affinities with high Sr/Y and
La/Yb ratios, and low Y and Yb contents. The fingerprint of overthickened lower
crust identified both from ultrapotassic and potassic rocks may be an important
feature for magmatism occurred under the background of continental collision. And
the bimodal volcanic sequence of Xungba postcollisional magmatism may further
corroborate that the removal of lower part of over-thickened lithospheric mantle at depth
may have triggered an extension setting associated with Miocene plateau uplift. |
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