Late Jurassic A-type granite in Sharhada, West Ujimqin, Inner Mongolia: geochemical characteristics, petrogenesis and geodynamic setting

The Sharhada granite in West Ujimqin, Inner Mongolia intruded into ophiolite in Hegenshan suture. LA-ICP-MS zircon dating indicates that the Sharhada granite was emplaced in the Late Jurassic (154.6±1.2 Ma). The mineral assemblage of the Shardaha granite is mainly composed of quartz, alkali feldspar and plagioclase. The granite is characterized by high SiO₂ (74.86%~75.97%), K₂O(4.4%~4.95%), low MgO (0.044%~0.22%), CaO (0.38%~0.77%), TiO₂ (0.046%~0.18%) and P₂O₅ (0.007%~0.042%), A/CNK = 1.03~1.09 < 1.1. It is strongly depleted in Ba, Sr, Eu, P and Ti, with a typical right dipping "Seagull-type" REE distribution pattern, showing the geochemical characteristics of typical aluminous A-type granite. The Sharhada A-type granite has low (⁸⁷Sr/⁸⁶Sr)_i (0.7014~0.70374), positive ε_Nd(t) values (+ 3.96~+ 4.31) and high ε_Hf(t) (+ 10.54~+ 14.72), which may due to the partial melting of the newly formed intermediate/basic crustal materials and the subsequent crystallization differentiation. Furthermore, together with other A-type granites scattered in the Mongolia-Northern North China block, the Sharhada A-type granite is recognized as the product of the post-orogenic extension of the Mongolian-Okhotsk tectonic domain in the Late Jurassic, which indicates the extensive middle-lower crust extension in the Middle-Late Jurassic.