Tourmaline as a recorder of the magmatic-hydrothermal evolution in the formation of pegmatite: In-situ elemental and boron isotopic compositions of tourmaline from the Qinghe pegmatite, Chinese Altay orogen

Zheng，Beiqi1,2; Chen，Bin2; Sun，Keke2; Huang，Chao3

2022-06-15

10.1016/j.jseaes.2022.105224

JOURNAL OF ASIAN EARTH SCIENCES   影响因子和分区

1367-9120

1878-5786

We conducted elemental and boron isotope studies on tourmalines from a single pegmatite dyke of the Altay orogen to investigate its origin and evolution. The pegmatite dyke is composed of border, intermediate and core zones. The border and intermediate zone tourmalines mostly belong to schorl, while the core zone and magmatic hydrothermal tourmalines to dravite. Most tourmalines follow the (Na + Mg) (Al + X), FeMg and MnMg exchange vectors. The core zone tourmalines show positively correlated FeO and MgO, and negatively correlated FeO and AlO, suggesting a rise of f in this zone. Moreover, they show higher B, Mg, Sr and Eu than other tourmalines due to magmatic evolution. Tourmaline from the Altay pegmatite is characterized by extremely low REE abundances (<3 ppm) when compared with those from granites, suggesting an origin from direct melting of metapelitic rocks. The border and intermediate zone tourmalines have comparable boron isotopic compositions with δB = −14.0 to −12.2‰, which are similar to the mica schist (−13.2 ‰ to −12.2‰), but slightly heavier than the core zone and magmatic hydrothermal tourmalines (−14.4‰ to −13.3‰). This suggests derivation of the pegmatite from melting of the metapelite without causing boron isotope fractionation, whereas late-stage fluid exsolution caused somewhat boron fractionation. This may be indicative of only small amounts of fluids being released from the barren pegmatite-forming magma. Tourmalines from mineralized pegmatites basically exhibit heavier boron isotope compositions than those from barren pegmatites, due probably to more involvement of evaporate in the source of the former.

Altay orogeny Boron isotope Pegmatite Tourmaline

SCI

英语

通讯

National Natural Science Foundation of China[41872051];

Geology

Geosciences, Multidisciplinary

WOS:000795921400001

PERGAMON-ELSEVIER SCIENCE LTD

GEOSCIENCES

2-s2.0-85129486844

Scopus

1.School of Environment,Harbin Institute of Technology,Harbin,150006,China
2.Department of Earth and Space Sciences,Southern University of Science and Technology,Shenzhen,518055,China
3.School of Resources and Environmental Engineering,Hefei University of Technology,Hefei,230009,China

Zheng，Beiqi,Chen，Bin,Sun，Keke,et al. Tourmaline as a recorder of the magmatic-hydrothermal evolution in the formation of pegmatite: In-situ elemental and boron isotopic compositions of tourmaline from the Qinghe pegmatite, Chinese Altay orogen[J]. JOURNAL OF ASIAN EARTH SCIENCES,2022,231.

Zheng，Beiqi,Chen，Bin,Sun，Keke,&Huang，Chao.(2022).Tourmaline as a recorder of the magmatic-hydrothermal evolution in the formation of pegmatite: In-situ elemental and boron isotopic compositions of tourmaline from the Qinghe pegmatite, Chinese Altay orogen.JOURNAL OF ASIAN EARTH SCIENCES,231.

Zheng，Beiqi,et al."Tourmaline as a recorder of the magmatic-hydrothermal evolution in the formation of pegmatite: In-situ elemental and boron isotopic compositions of tourmaline from the Qinghe pegmatite, Chinese Altay orogen".JOURNAL OF ASIAN EARTH SCIENCES 231(2022).