TY - JOUR

T1 - Origin of high-Cr stratiform chromitite in the Fangmayu Alaskan-type ultramafic intrusion, North China Craton

AU - Han, Yue-Sheng

AU - Waterton, Pedro

AU - Szilas, Kristoffer

AU - Santosh, M.

AU - Kirkland, Christopher L

PY - 2021/4

Y1 - 2021/4

N2 - The study of chromite from chromitite-bearing layered intrusions can provide significant insights into their petrogenetic origin and tectonic setting. The Fangmayu Alaskan-type ultramafic intrusion in the North China Craton contains layered and massive chromitite associated with a serpentinized ultramafic suite. This study presents zircon and apatite geochronology, chromite mineral chemistry, platinum-group element (PGE) and Re-Os isotopic data for the purpose of constraining the origin, evolution, and composition of the Fangmayu chromitite parental melts. Zircon U-Pb data from the chromitites define various age populations, with oldest age component (>2.49 Ga) interpreted to represent xenocrystic grains incorporated from crystalline basement. A dominant age component (~2.42 Ga) may represent the age of magma emplacement. Ages in the range of 2375–2068 Ma likely represent variable partial radiogenic Pb-loss during subsequent thermal events. Zircon ages in the range of 1.96–1.90 Ga record metamorphic events, potentially related to the collision between the Eastern Block and Western Block in the North China Craton. Ages of 1.85–1.81 Ga likely represent zircon growth during retrograde metamorphic process in a post-collisional setting; near contemporaneous apatite (~1.8 Ga) tracks cooling through ~500 °C. High Fo contents in olivine (Fo90-92) and high Cr# in chromite (72–77) suggest a low Al2O3 ultramafic parental magma formed by a high degree of partial melting. However, total concentrations of PGEs are abnormally low, and the Re-Os system indicates multiple disturbances during later metamorphic events. Experimental data are used to recover the compositions of parental melts to the chromitite, the calculations yield parental melts with 10–11 wt% Al2O3 and 0.7–1.1 wt% TiO2, which define the arc and IAB affinity. The high Cr#s, low Al2O3 (8–10 wt%), and high TiO2 (0.58–0.96 wt%) contents of chromite, combined with calculated parental melt compositions, suggest that the parental magma of Fangmayu stratiform chromitites was a high-Ti island-arc basalt origin and formed within supra-subduction zone setting.

AB - The study of chromite from chromitite-bearing layered intrusions can provide significant insights into their petrogenetic origin and tectonic setting. The Fangmayu Alaskan-type ultramafic intrusion in the North China Craton contains layered and massive chromitite associated with a serpentinized ultramafic suite. This study presents zircon and apatite geochronology, chromite mineral chemistry, platinum-group element (PGE) and Re-Os isotopic data for the purpose of constraining the origin, evolution, and composition of the Fangmayu chromitite parental melts. Zircon U-Pb data from the chromitites define various age populations, with oldest age component (>2.49 Ga) interpreted to represent xenocrystic grains incorporated from crystalline basement. A dominant age component (~2.42 Ga) may represent the age of magma emplacement. Ages in the range of 2375–2068 Ma likely represent variable partial radiogenic Pb-loss during subsequent thermal events. Zircon ages in the range of 1.96–1.90 Ga record metamorphic events, potentially related to the collision between the Eastern Block and Western Block in the North China Craton. Ages of 1.85–1.81 Ga likely represent zircon growth during retrograde metamorphic process in a post-collisional setting; near contemporaneous apatite (~1.8 Ga) tracks cooling through ~500 °C. High Fo contents in olivine (Fo90-92) and high Cr# in chromite (72–77) suggest a low Al2O3 ultramafic parental magma formed by a high degree of partial melting. However, total concentrations of PGEs are abnormally low, and the Re-Os system indicates multiple disturbances during later metamorphic events. Experimental data are used to recover the compositions of parental melts to the chromitite, the calculations yield parental melts with 10–11 wt% Al2O3 and 0.7–1.1 wt% TiO2, which define the arc and IAB affinity. The high Cr#s, low Al2O3 (8–10 wt%), and high TiO2 (0.58–0.96 wt%) contents of chromite, combined with calculated parental melt compositions, suggest that the parental magma of Fangmayu stratiform chromitites was a high-Ti island-arc basalt origin and formed within supra-subduction zone setting.

KW - Stratiform chromitite

KW - Zircon

KW - Apatite

KW - Mineral chemistry

KW - Platinum-group element

KW - Re-Os

U2 - 10.1016/j.precamres.2021.106096

DO - 10.1016/j.precamres.2021.106096

M3 - Journal article

VL - 355

JO - Precambrian Research

JF - Precambrian Research

SN - 0301-9268

M1 - 106096

ER -