Neoproterozoic gabbro–granite association from the Micangshan area, northern Yangtze Block: Implication for crustal growth in an active continental margin

Abstract

Neoproterozoic igneous rocks along the northern Yangtze Block are closely related to the evolution of the Rodinia supercontinent. This paper presents zircon U–Pb dating, whole‐rock geochemistry and Sr‐Nd isotopes of the gabbro–granite association from the Micangshan area, northern Yangtze Block. Zircon LA‐ICP MS U–Pb dating indicates that the tonalite and monzogranite from the Pinghe display identical ages of 869 ± 4 Ma (MSWD = 1.3, 2σ) and 859 ± 8 Ma (MSWD = 1.9, 2σ), respectively. According to the regional geology, the gabbro may be younger. The monzogranite and tonalite display almost identical geochemical features, both of them have high Na2O/K2O ratios, with insignificant negative Eu anomalies, relatively juvenile Sr‐Nd isotopic compositions. The monzogranite has initial (87Sr/86Sr)i ratios of 0.703403 to 0.705218, and positive ɛNd(t) values of +1.23 to +2.98. The tonalite have (87Sr/86Sr)i ratios of 0.700387 to 0.706222, positive ɛNd(t) values of +1.98 to +7.79, indicating that they were derived from juvenile source. The 860 Ma monzogranite–tonalite association suggests crustal growth event in an active continental margin. The gabbro has low (La/Yb)N ratios (1.80 to 7.61) and total rare earth element contents (∑REE = 44.95 to 83.92 ppm), they have initial (87Sr/86Sr)i ratios of 0.701913 to 0.704815, positive ɛNd(t) values of +0.65 to +5.73, indicating an island‐arc affinity. In combination with the other Neoproterozoic igneous rocks along the western and northern margin of the Yangtze Block, we propose that the gabbro and granitoid association from the Micangshan area represent two stage crustal growth events in the active continental margin setting, and these results imply that the Neoproterozoic crustal growth events in the Yangtze Block may be controlled by subduction.