In-situ boron isotope and chemical composition of tourmaline in the Gyirong pegmatite, southern Tibet: Implications for petrogenesis and magma source

Abstract

Leucogranitic rocks, mainly including leucogranite-pegmatite systems, have been found to be widely distributed in the South Tibetan Himalaya, and they have received considerable interest because of their significance in crustal evolution and associated rare-metal mineralization. Although the nature and geodynamic setting of the Himalayan leucogranites have been well documented by numerous studies, the pegmatites spatially associated with these leucogranites are still poorly understood. Tourmaline is a ubiquitous phase from the leucogranite to the pegmatite. We have therefore conducted in situ major and trace element and boron isotope investigations of tourmaline from the Gyirong pegmatite, synthesizing published data on the Gyirong leucogranite, to document the origin of tourmaline and its genetic implications. Two types of tourmaline (Tur-Ⅰ & Tur-Ⅱ) have been identified in this contribution and they are enriched in Fe, Si and Al but depleted in Mg and Ca, with Mg/(Mg+Fe) ratios ranging from 0.22 to 0.45. Accordingly, the tourmalines belong to the alkali group and have schorl composition. Trace elements, such as Zn, Ga, V, Sc, Li, Sn, Sr, and Co in the tourmalines are relatively enriched, whereas, other trace elements record low concentrations less than 10 ppm. The trace element concentrations of tourmaline are mainly controlled by melt composition. Morphological and geochemical characteristics reflect that the tourmalines from the Gyirong pegmatite are magmatic in origin. The Gyirong pegmatitic tourmalines have S-type granitoids and pegmatites boron isotopic signatures with a tight range of δ11B values between −11.8 and −9.7‰, which is consistent with the magmatic tourmalines (Mg-poor) of the Gyirong leucogranite. This study suggests that the Gyirong pegmatite was the product of crustal anatexis and that the crustal metapelitic rocks within the Greater Himalayan Crystalline Complex were the most likely source components.

Hydrochemical characteristics analysis and human health assessment in the upper reaches of Zhang Wei River alluvial plain

“…Combining the local hydrological conditions, it is observed that groundwater in the aquifers exhibits low ow velocities and relatively long residence times, providing ample time for water-rock interactions. Additionally, considering prior research ndings, it is clear that ion exchange and mineral dissolution processes play a signi cant role in shaping hydrochemistry and groundwater types (Pei et al, 2023;Yang et al, 2023). To delve deeper into the rock control within water-rock interactions, employing end-member diagrams can elucidate the impact of various rock types on the ion composition of groundwater.…”

Hydrothermal fluid evolution in the Cuonadong Sn–W–Be polymetallic deposit, southern Tibet: indicated by the in–situ element and boron isotope compositions of tourmaline

“…Importantly, continental crust and most clastic metasediments have relatively low Ca contents and negative δ 11 B values (Rudnick and Gao, 2003;Trumbull and Slack, 2018), whereas marble and marine carbonate usually contain high Ca contents and positive δ 11 B values (Melezhik et al, 2005;Marschall and Jiang, 2011). Thus, the tourmalines derived from different sources show significantly different element and boron isotope compositions (Harlaux et al, 2020;Trumbull et al, 2020;Pei et al, 2023). This makes tourmaline an excellent messenger for tracing the origin of fluids (Marschall and Jiang, 2011;Harlaux et al, 2020;Trumbull et al, 2020;Chakraborty, 2021).…”