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Extensive tracts of magmatic arc plutonic suites in the Mesozoic Coastal Cordillera of northern Chile imply that large volumes of granitic to dioritic magrnas 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.

We have reanalyzed the pattern of paleomagnetically detected rotations in the central Andes (the central Andean rotation pattern) in order to investigate the temporal and spatial distributions of rotations. The dominant pattern of rotation is well known with counterclockwise rotations in the northern Andes (clockwise in the southern Andes) linked to Neogene orogenesis and shortening. However, much of the rotation in the forearc of northern Chile (23-30[degrees]S) is distinctly anomalous because of markedly high rotations that appear to predate rotations observed elsewhere in the central Andes. We argue that the data define a domain located in the forearc of northern Chile marked by major (>25[degrees]) clockwise crustal rotations related to late Paleocene--early Eocene highly oblique convergence. This rather diffuse and cryptic deformation style accommodated strong shortening perpendicular to the Andean margin by vertical axis rotations rather than by conventional fold-thrust belts or transpressional fault systems. Keywords: rotation, Andes, convergence, obliquity, timing, Chile.

Three fault systems were responsible for Permian to Late Cretaceous deformation of the overriding plate of the Andean convergent margin in the Coastal Cordillera of northern Chile (25[degrees]30' to 27[degrees]00'S). Displacements were linked to crustal growth expressed by the emplacement of a sequence of magmatic arcs. The Tigrillo Fault System, active from Triassic to Early Cretaceous time, was characterized by arc-normal extension with increasing left-oblique extension (transtension) from Early Jurassic to Early Cretaceous time. Stretching of the crust created space for Triassic, Early Jurassic and Early Cretaceous arc basins where epiclastic, volcaniclastic and volcanic sequences accumulated in continental to shallow marine environments. Tabular plutonic complexes were emplaced by roof uplift--floor subsidence that allowed a vertical transfer of material in the crust without significant horizontal extension. The Atacama Fault System was initiated at c. 132 Ma as a (mainly) left strike-slip fault during left-oblique extension of the margin. Elongate, tabular plutonic complexes were emplaced within the Atacama Fault System between c. 132 and c. 106 Ma, again by roof uplift--floor subsidence mechanisms. Ductile--brittle transitions in synplutonic mylonitic rocks of the Atacama Fault System provided the setting for Kiruna-type Fe-apatite, and Fe oxide (with Cu and/or Au) ores. The Chivato Fault System was active as an extensional fault system at the eastern side of the Coastal Cordillera during displacement on the Tigrillo Fault System and later, between c. 125 and c. 93 Ma, as a partitioned left-oblique extensional fault system. In post-Early Cretaceous time the Chivato Fault System was inverted by left-oblique contraction (transpression) when NW-trending transfer faults, some probably reactivated lateral ramps in the Tigrillo Fault System, accommodated clockwise vertical-axis rotations of 35--45[degrees]. Contraction inverted the Atacama Fault System and Tigrillo Fault System and was responsible for west-vergent, thin-skinned, fold--thrust deformation in stratified rocks throughout the margin. Keywords: Andes, Coastal Cordillera, island arcs, magmatism, faulting.

The Ketilidian orogen in SE Greenland contains a continental magmatic arc (Julianehab batholith) and forearc which formed in the overriding plate of a Palaeoproterozoic oblique subduction boundary between c. 1854 and 1795 Ma. During uplift and deformation of the forearc between c. 1795 and 1780 Ma, its sedimentary sequences were invaded by arc-type magmas and metamorphosed at HT-LP upper amphibolite facies conditions which led to widespread anatexis and generation of abundant S-type granites. Transpression during early deformation ([D.sub.1]) was partitioned into arc-parallel, sinistral strike-slip in the magmatic arc rocks of the batholith and arc-normal contraction in the sedimentary and volcaniclastic sequences of the proximal forearc (Psammite Zone). Subsequently, [D.sub.1] fabrics in the Psammite Zone were overprinted and transposed in an intense, flat-lying, [D.sub.2] ductile shear zone with arc-parallel stretching lineations and top-NE kinematic indicators. The kinematic significance of the [D.sub.2] shear zone is that it accommodated vertical differences in strain and displacement and permitted deformation to be partitioned differently at different levels in the crust. As such, it is an attachment or coupling zone that provided kinematic linkage between deformation at different crustal levels during NE transport of a forearc sliver. Overprinting of the upper crustal domain of [D.sub.1] strike-slip partitioned transpression in the forearc during [D.sub.2] is attributed to migration of the attachment zone to a higher crustal level. This migration was a consequence of an enhanced geothermal gradient in the proximal part of the forearc due to the emplacement of batholith-related plutonic suites during [D.sub.2]. Keywords: Palaeoproterozoic, South Greenland, Ketilidian orogen, transpression, coupling.

During the Late Triassic, Jurassic, and Early Cretaceous, an extensional magmatic arc was formed in the Andean margin of northern Chile. Plutons emplaced at ramps within a hinterland-propagating extensional duplex were fed by dikes that transferred magma through the lower crust from a reservoir in the mantle. Phases of volcanism separated phases of plutonism, and our model demonstrates that plutonism was favored only when upper-plate extensional fault systems were active. When they were not, dikes cut across inactive faults, and magma rose directly to the surface during volcanic phases of arc growth.

Cu-Au-Mo porphyry-type and Cu skarn-type mineralization in the Bingham mining district of Utah are temporally and spatially related to a suite of monzonite and quartz monzonite porphyry intrusions comprising the Bingham complex. Structural control on mineralization at the Bingham Canyon mine has been described at the scale of individual large-scale folds and fracture sets but no integrated pattern for the synmineralization deformation structures has emerged from earlier research. In the work reported here we have investigated hitherto largely unrecognized components of deformation (translations, rotations, and strains) associated with emplacement of many cubic kilometers of granitic rocks in the intrusions of the Bingham district. We have used both the local three-dimensional static mine model and the regional context in digital kinematic two- and three-dimensional forward and reverse modeling to identify a geometrically valid and admissible fault framework for the Bingham district and a kinematic solution for this framework through time. The results indicate that porphyry intrusions and associated mineralization were emplaced during reactivation of a basement-dictated linked system comprising two sets of northwest- and (north)-northeast-trending strike-slip faults. Both sets operated as transfer faults during extensional collapse of the Sevier orogen in the Eocene. Each fault set is characterized by overstep geometries with relay, ramps breached by faults (re)activated in extension. Strike-slip was accompanied by progressive dilation of the extensional faults in fault oversteps to permit emplacement of composite stocklike (low aspect ratio) intrusions. The kinematic fault framework identified provides a new structural context for porphyry- and skarn-type mineralization at the Bingham Canyon mine, with potential for linking mineralizing fluid flow to three-dimensional structure and the development of that structure through time. [ABSTRACT FROM AUTHOR]

The Candelaria Fe oxide Cu-Au ore deposit lies within the thermal aureole of the Lower Cretaceous magmatic are plutonic suite in the Candelaria-Punta del Cobre district, Atacama region, northern Chile (27°30′ S). Economic mineralization is present within a synplutonic ductile shear zone (Candelaria shear zone) containing foliated and potassically altered volcanic and volcaniclastic rocks of the Punta del Cobre Formation. In the Candelaria shear zone, there was a complex interplay in space and time between ductile and brittle deformation during mineralization. At high structural levels brittle, moderately to steeply dipping extensional faults curve downward into gently dipping ductilely deformed rocks in the shear zone. Textural and structural characteristics of the ore and the deformed rocks indicate that the dilation of the sulfide-bearing vein systems occurred at the same time as ductile deformation and implies that ductile-brittle cycling occurred in a cooling hydrothermal system in the thermal aureole of the arc plutonic rocks. The La Brea and the San Gregorio plutonic complexes are ex-posed in the plutonic are immediately adjacent to the Candelaria orebody. The intrusions are interpreted to be fiat-lying, tabular bodies emplaced by roof up-lift- floor depression mechanisms during regional extensional deformation. An 40Ar/39Ar age of 119.6 ± 1.2 Ma and five K-Ar ages between 123 and 117 Ma were obtained for the La Brea pluton, and an 40Ar/39Ar age of 111.5 ± 0.4 Ma was obtained for the San Gregorio plutonic complex. 40At/39Ar ages of 111.0 ± 1.4 and 110.7 ± 1.6 Ma obtained from syntectonic biotite from the Candelaria shear zone are interpreted to be the age of the mineralization. These are indistinguishable from the age of the San Gregorio plutonic complex, and therefore beat from this pluton could have promoted ductile deformation during emplacement of the orebody. This result, together with known isotopic similarities between Candelaria ore and the plutonic rocks, implies that the San Gregorio plutonic complex was the most probable source of the mineralizing fluids at Candelaria, although the critical intrusive unit may not be exposed. The ore deposit is located where a roof-uplift fold in the sidewall of the San Gregorio plutonic complex provided a dilatational site which may have drawn hydrothermal fluids out of the adjacent fractionating magmas into a structural trap in the Punta del Cobre Formation below the carbonate rocks of the Chañarcillo Group. [ABSTRACT FROM AUTHOR]