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 similar to 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 similar to 88 km(3) in 162 +/-
11 ka. (C) 2012 Elsevier B.V. All rights reserved.