Maturing arc signatures monitored by trace element and Hf isotope systematics in the Early Cretaceous Zacatecas volcanic field, Mexico

Mesozoic growth of continental crust along the southwestern margin of North America and its southern extension in Mexico has been partly explained by the accretion of terranes. These terranes have been considered to be fragments of exotic, intraoceanic island arcs that approached mainland Mexico after the Early Cretaceous. Trace elements and Lu-Hf isotopic systematics for primitive arc successions of the Zacatecas Volcanic Field indicate a close relationship with parts of the northern Guerrero superterrane. Major and trace element systematics of lava flows and dioritic rocks from laccoliths suggest a cogenetic origin of the Zacatecas Formation and Las Pilas Complex rocks, here combined in the Zacatecas Group. This group represents a single arc succession that evolves from a primitive to mature arc. Initial (super 176) Hf/ (super 177) Hf (age corrected to 130 Ma) ranges from 0.28296 to 0.28307, corresponding to epsilon Hf(t) = +9.3 to +13.4, indicating a source related to a depleted mantle wedge with a superimposed subducted sediment contribution. Based on combined field and geochemical evidence, we propose an arc model and suggest a spatial extension of paleoarc spreading north-south from Baja California beyond the present-day Trans-Mexican Volcanic Belt in the Early Cretaceous.