Fault-assisted vertical pluton growth: Coastal Cordillera, north Chilean Andes

摘要

Extensive tracts of magmatic arc plutonic suites in the Mesozoic Coastal Cordillera of northern Chile imply that large volumes of granitic to dioritic magmas were transferred from a lower crustal source to the upper crust. Space for single intrusions was created by interaction of vertical pluton growth and dip-slip reactivation of arc-parallel faults during episodic emplacement of subhorizontal, compositionally distinct magma pulses. Cross-sectional pluton shapes are broadly tabular in geometry and were controlled by differential subsidence of the pluton floors during fault reactivation and incremental assembly of subhorizontal sheets. Equal amounts of floor subsidence of the fault footwall and hanging wall during magma accommodation led to symmetrical intrusions, whereas differential subsidence caused plutons to grow asymmetrically. Strongly asymmetrical plutons resulted when only the hanging wall was reactivated to accommodate floor subsidence. Late, post-intrusion contractional deformation resulted in open folding of some tabular plutonic units and local inversion of bounding faults, which has modified but not obscured the original syn-emplacement geometry and fault kinematics.