Time resolved construction of a bimodal laccolith (Torres del Paine, Patagonia)

Granitic and mafic magma pulses were sequentially accreted in the spectacularly exposed shallow crustal Torres del Paine laccolith, in southern Patagonia. This 12.5 Ma pluton forms a composite intrusion with a subvertical feeding system in the west and a laccolith in the east. A key unknown in the formation of sill complexes is how individual magma pulses are assembled over time and the geometry and localization of their feeding system. High resolution zircon CA-ID-TIMS U–Pb dating shows that the laccolith grew first by under-accretion of granitic sills over 90 ± 30 ka, linked to a ‘sheet-like’ feeding system, followed by underplating of mafic sills after ~ 20 ka of quiescence. In the mafic sills complex, individual sills were injected by over-accretion during 41 ± 11 ka. Our data show that successive granitic and mafic magmas emplacement generated a volume of ~ 88 km3 in 162 ± 11 ka.