TY - JOUR
T1 - Amphibole fractionation as a key driver for oxidation of magmas in convergent margins
AU - Luo, Chen Hao
AU - Wang, Rui
AU - Nebel, Oliver
AU - Li, Qi Wei
N1 - Funding Information:
This study was supported by National Natural Science Foundation of China projects (42225204 and 42121002). This work was also supported by the Fundamental Research Funds for the Central Universities (2652023001) and the Programme of Introducing Talents of Discipline to Universities (111 Project, B18048).
Publisher Copyright:
© 2024 Elsevier B.V.
PY - 2024/9/1
Y1 - 2024/9/1
N2 - During the process of differentiation, the magmas in convergent margins undergo an increase of oxidized nature, accompanied by a decreased Fe content and concentration of heavy Fe isotopes. Garnet and amphibole are both Fe-rich minerals, which can be responsible for this phenomenon through fractional crystallization. One prevailing hypothesis suggests that Fe2+-rich garnet cumulates in the arc root as a "crustal redox filter." However, the stability of garnets is highly dependent on pressure conditions. In contrast, amphibole can crystallize under a broader range of temperature and pressure conditions and is a more common mineral phase in magmas. As such, the contribution of amphibole might have been underappreciated. Here, we conducted elemental composition, zircon trace element, and high-precision Fe isotope analyses on Miocene magmatic rocks from the Gangdese arc to trace the evolution of magmatic oxidation. The results indicate that the enrichment of heavy Fe isotopes in these magmas is primarily controlled by amphibole-dominated fractional crystallization rather than garnet. This also implies that amphibole fractional crystallization may play a role in enhancing the oxygen fugacity of the magmas. Taking a global perspective, we found a pervasive correlation between amphibole fractional crystallization and Fe isotope fractionation in magmatism at convergent plate margins, indicating its widely applicable influence on oxidation. The influence of garnet cannot be entirely neglected in some specific scenarios, such as within thickened continental arcs, but its impact is generally limited. Continuous amphibole fractional crystallization increases oxidation, facilitating the mobilization and concentration of Cu within the magma, thereby enhancing the potential for porphyry deposit formation. This impact is especially notable in spatiotemporally related magmatic events and could be decisive in determining the magmatic mineralization potential.
AB - During the process of differentiation, the magmas in convergent margins undergo an increase of oxidized nature, accompanied by a decreased Fe content and concentration of heavy Fe isotopes. Garnet and amphibole are both Fe-rich minerals, which can be responsible for this phenomenon through fractional crystallization. One prevailing hypothesis suggests that Fe2+-rich garnet cumulates in the arc root as a "crustal redox filter." However, the stability of garnets is highly dependent on pressure conditions. In contrast, amphibole can crystallize under a broader range of temperature and pressure conditions and is a more common mineral phase in magmas. As such, the contribution of amphibole might have been underappreciated. Here, we conducted elemental composition, zircon trace element, and high-precision Fe isotope analyses on Miocene magmatic rocks from the Gangdese arc to trace the evolution of magmatic oxidation. The results indicate that the enrichment of heavy Fe isotopes in these magmas is primarily controlled by amphibole-dominated fractional crystallization rather than garnet. This also implies that amphibole fractional crystallization may play a role in enhancing the oxygen fugacity of the magmas. Taking a global perspective, we found a pervasive correlation between amphibole fractional crystallization and Fe isotope fractionation in magmatism at convergent plate margins, indicating its widely applicable influence on oxidation. The influence of garnet cannot be entirely neglected in some specific scenarios, such as within thickened continental arcs, but its impact is generally limited. Continuous amphibole fractional crystallization increases oxidation, facilitating the mobilization and concentration of Cu within the magma, thereby enhancing the potential for porphyry deposit formation. This impact is especially notable in spatiotemporally related magmatic events and could be decisive in determining the magmatic mineralization potential.
KW - Amphibole fractionation
KW - Arc magmas
KW - Crustal oxidized nature
KW - Iron isotopes
UR - https://www.scopus.com/pages/publications/85196631307
U2 - 10.1016/j.epsl.2024.118851
DO - 10.1016/j.epsl.2024.118851
M3 - Article
AN - SCOPUS:85196631307
SN - 0012-821X
VL - 641
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
M1 - 118851
ER -