EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Geochemical and Sr-Nd isotopic characteristics of the lamprophyre in the Tethyan Himalaya, South Tibet

Zhi-Chao Liu1, Jian-Gang Wang2, and Xiao-Chi Liu2
Zhi-Chao Liu et al.
  • 1School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China (
  • 2Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

A lamprophyre dyke has been found in Ramba area within the Tethyan Himalaya. It intruded into the Late Triassic low-grade metasedimentary rocks (Langjiexue Group) and show typical porphyritic textures, with phlogopite as the dominant phenocrysts. In this study, we performed phlogopite 40Ar/39Ar dating and whole-rock major and trace element as well as Sr and Nd isotope geochemical analyses on the lamprophyre. The 40Ar/39Ar plateau ages (13.1 ± 0.2 Ma and 13.5 ± 0.2 Ma) of the phlogopites from two samples are both in excellent agreement with the inverse isochron ages of 13.1 ±0.3 Ma and 13.6 ± 0.3 Ma, recording the times at which the lamprophyre dyke has cooled below ~300 °C. The lamprophyre has low contents of SiO2 (51.43–55.15 wt%) and Al2O3 (11.10–11.85 wt%), high Fe2O3T (8.57–9.27 wt%) and MgO (9.14–9.49 wt %) contents with Mg# of 66–69, higher content of K2O (3.26–5.57 wt%) relative to Na2O (0.50–1.39 wt%) with K2O/Na2O of 2.3–11.1. Furthermore, the lamprophyre has high abundances of large ion lithophile elements (e.g., Rb, Ba, Sr), shows depletions in high field strength elements (e.g., Nb, Ta, Ti), and displays enrichment in light rare-earth elements over heavy rare earth elements with (La/Yb)N of 42.3~47.0. Besides, the lamprophyre is characterized by high initial 87Sr/86Sr ratios of 0.7196~0.7204 and negative εNd(t) values of -10.7~-10.8. Geochemical data suggest that the Ramba lamprophyre was likely generated by partial melting of a metasomatized, phlogopite-bearing harzburgite lithospheric mantle source, followed by crystal fractionation and varying degree of crustal assimilation. The studied lamprophyre provides a window into the composition of the subcontinental lithospheric mantle (SCLM) in the northern margin of the Indian plate. We suggest that the northern Indian plate might be involved in the Andean-type orogeny from the subduction of the Proto-Tethys Ocean during Cambrian to Early Ordovician.

How to cite: Liu, Z.-C., Wang, J.-G., and Liu, X.-C.: Geochemical and Sr-Nd isotopic characteristics of the lamprophyre in the Tethyan Himalaya, South Tibet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12552,, 2020