PLUTONIC-VOLCANIC LINK BETWEEN THE PERUVIAN COASTAL BATHOLITH AND HOST-ROCKS OF THE WESTERN PERUVIAN TROUGH

The conventional igneous history of the central coastal ranges of Peru (8-14° S latitude) suggests that the Peruvian Coastal Batholith (PCB) began forming at around 105 Ma, after volcanic activity had ceased in the Huarmey-Cañete basins at around 110-115 Ma during the Albian-Aptian transition. However, more recent geochronological evidence indicates that a flare-up occurred ~20Ma earlier and suggests considering early volcanic-plutonic connections in the Western Peruvian Through.

To explore the geochronological connection between the PCB and the volcanic host-rocks of the Huarmey-Cañete basins, we examined the westernmost intrusions of the batholith in the central costal ranges of Peru. Fieldwork involved collecting samples for new U-Pb zircon dating which was supplemented by published data.

We acquired a new 131.9 ±1.1 Ma U-Pb zircon age from the Quilmana Pluton establishing a chronological connection with nearby volcanic sequences of the Cañete basin dated by U-Pb zircon analysis at 135-136 Ma and with the ~130 Ma Cerro Media Luna Pluton, which also intrudes volcanic sequences of the Cañete basin.

We conclude that geochronological evidence supports the proposed link between the volcanic rocks of the Western Peruvian Trough and the early intrusions of the PCB. Furthermore, instead of only one volcanic-plutonic transition, geochronological evidence hints at three significant episodes of volcanic-plutonic activity in the central costal ranges of Peru: (1) Some plutons and volcanic rocks preserved in the very early Cretaceous, (2) the well-known Aptian-Albian igneous activity which is dominated by more than 3000 m of volcanic sequences and some plutonic intrusions, and (3) the late Cretaceous flare-ups when the bulk of the PCB was intruded.

These findings suggest the need to revisit the timeline for the formation of the PCB in the central coastal ranges, the history of volcanic activity in the Western Peruvian Trough, and the existing ore mining models for the region.