Reassessment of the Role of Magmatism in the Evolution of the Catalina MCC: Evidence for a Felsic-Intermediate Pluton at Shallow Depths

Aeromagnetic and Bouguer gravity data from the Catalina metamorphic core complex (MCC) combined with thermochronologic data provide evidence for the presence of a subsurface shallow level pluton in the region. The Catalina MCC located in southeastern Arizona includes the Tortolita, Santa Catalina and Rincon Mountains. The Catalina MCC trends NW-SE and the direction of extension along the Catalina detachment fault was top to the southwest. Aeromagnetic and Bouguer gravity data from the region show large NW-SE-trending highs, bordered to the NE by parallel NW-SE-trending magnetic and gravity lows. The lows can be attributed to the Wilderness granitic suite, which is exposed at the surface and extends up to 12 km below the surface based on previous gravity modeling (Holt et al., 1986). Forward modeling of the aeromagnetic data and Bouguer gravity data was performed in order to: 1) constrain the nature of the contact between the magnetic body and the Wilderness suite, 2) constrain the depth of the magnetic body and 3) distinguish between upwarping of the lower crust and pluton emplacement as mechanisms in MCC formation. Two NE-SW-trending profiles, which transect both the highs and the lows and one NW-SE profile from the magnetic and gravity highs, were modeled. The models indicate that the contact between the magnetic/dense body and the Wilderness suite is near vertical or steeply dipping to the northwest. The preferred models show the depth to the body ranges from <1 km to ~ 4 km. Several models were explored to distinguish between a pluton and upwarping of the lower crust as the cause of the magnetic/gravity high, features that have been incorporated in most models for MCC formation. Modeling shows upwarping of lower crustal is not possible because the density needed to represent the lower crust is too high to fit the observed gravity data. An alternative explanation is that the body represents a felsic to intermediate pluton. The aeromagnetic map patterns suggest the pluton is ~ 30 km wide and ~ 100 km long. The exact timing of pluton emplacement is presently unknown, although available thermochronologic data indicates it has to be >14 Ma. The aeromagnetic map patterns show the body is cut by the Basin and Range high angle Pirate fault, which cuts the NW side of the Santa Catalina Mountains and is assumed to be 12-6 Ma. The NW-SE-trending profile exhibits topographic valleys that cut the top boundary surface of the pluton and correspond to drainages at the surface, interpreted as corrugation surfaces. The axes of the corrugation surfaces trend SW-NE and thus suggests the timing of pluton emplacement is related to the extension along the Catalina detachment fault. Future work will include modeling the heat flow for the region. Several heat flow models will be considered using crystallization ages of magmatic rocks exposed at the surface as initial conditions.