Structural and thermal setting during emplacement of the Sandia Pluton
— Eric Kirby, Karl E. Karlstrom, and Chris L. Andronicos

Structural and metamorphic studies of the 1.42 Ga Sandia pluton and its aureole document significant deformation and metamorphism synchronous with pluton emplacement. The pluton has a minimum areal extent of ~500 km2 and a 1-2 km wide aureole preserved at its NW and SE margins. Field and microstructural observations indicate that syn-emplacement deformation occurred along a bounding shear zone, within the main body of the pluton, and in the NW and SE aureoles. Kinematic elements of the pluton and aureole all record consistent subhorizontal shortening (ESE) and extension (N-S) directions interpreted to be part of a regional deformation event at ca. 1.4 Ga. Pluton-enhanced low-pressure, high-temperature metamorphism facilitated growth of sillimanite and andalusite in the NW aureole and generated a well-developed metamorphic field gradient. Assemblage data and thermobarometry indicate that temperatures increased toward a maximum of ~750°C at the pluton margin at a pressure of ~0.35 GPa. Similar field gradients occur along the SE margin of the pluton in the Monte Largo Hills and in Tijeras canyon, suggesting that the aureole can be traced across the Phanerozoic Tijeras fault. The Vincent Moore thrust truncates the southern margin of the Sandia aureole, and juxtaposes greenschist grade rocks with the amphibolite grade aureole. Field, microstructural, mineral assemblage and geochronologic data suggest that latest movement along the thrust occurred during or after cooling of the Sandia aureole at ~1.423 Ga, and thus reinforce evidence for regional contractional deformation.