Identifying crystal accumulation and melt extraction during formation of high-silica granite
Lu T, He ZY, Klemd R (2022)
Publication Type: Journal article
Publication year: 2022
Journal
Book Volume: 50
Pages Range: 216-221
Journal Issue: 2
DOI: 10.1130/G49434.1
Abstract
High-silica (>70 wt% SiO2) magmas are usually believed to form via shallow crustal-level fractional crystallization of intermediate magmas. However, the broad applicability of this model is controversial, because the required crystal-melt separation processes have rarely been documented globally up to now. The ca. 50 Ma Nyemo composite pluton of the Gangdese batholith belt in southern Tibet, which comprises intrusive rocks with intermediate-to high-silica compositions (65-78 wt%), offers a unique opportunity for substantiating the coexistence of extracted melts and complementary silicic cumulates in one of Earth's most complete transcrustal silicic magmatic systems. The Nyemo pluton intrusive rocks exhibit similar zircon Hf isotopic compositional ranges (mean epsilon(Hf(t)) = +5.7 to +8.3), suggesting a common, non-radiogenic magma source with crustal assimilation in the deep crust. Yet, these rocks have distinct geochemical characteristics. High-silica miarolitic and rapakivi granites are strongly depleted in Ba, Sr, and Eu, and their zircon trace elements show extremely low Eu/Eu* and Dy/Yb. In contrast, monzogranite is relatively enriched in Ba and Sr with minor Eu anomalies, and the zircon trace elements are characterized by relatively high Eu/Eu* and Dy/Yb. Therefore, we propose that the high-silica granites represent highly fractionated melt extracted from a mush reservoir at unusually low storage pressure (similar to 99-119 MPa), and that the monzogranite constitutes the complementary residual silicic cumulates.
Authors with CRIS profile
Tianyu Lu
Professur für Geochemie von Lagerstätten
Reiner Klemd
Professur für Geochemie von Lagerstätten
Involved external institutions
China (CN)How to cite
APA:
Lu, T., He, Z.-Y., & Klemd, R. (2022). Identifying crystal accumulation and melt extraction during formation of high-silica granite. Geology, 50(2), 216-221. https://dx.doi.org/10.1130/G49434.1
MLA:
Lu, Tianyu, Zhen-Yu He, and Reiner Klemd. "Identifying crystal accumulation and melt extraction during formation of high-silica granite." Geology 50.2 (2022): 216-221.
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