CONSTRAINING INITIATION AND DURATION OF BASIN LINKAGE VIA TRANSFER ZONES IN NORTHERN RIO GRANDE RIFT USING LOW-TEMPERATURE THERMOCHRONOLOGY

Continental rifting begins with the formation of separate basins, which then grow and link together via transfer zones. This growth and linkage affects the sediment distribution, stratigraphy, and drainage pattern within the rift. The Poncha Block in Colorado exemplifies a transfer zone in the northern Rio Gande rift (RGR) that links the upper Arkansas River Valley and San Luis Valley via the Sawatch Range Fault, Poncha Springs Fault, and the Sangre de Cristo Fault. Fault initiation in the RGR began ~25Ma, however, the timing for basin linkage is less well constrained. We used apatite fission track (AFT) dating on samples gathered along the Poncha Springs Fault and at the southern tip of the Sawatch Range Fault to obtain cooling ages to further distinguish the timing of fault exhumation. New AFT ages from basement rock in the footwall of the Poncha Springs Fault are 14.2±1 Ma and 15.6±3 Ma while a sample from the hanging wall is 23.3±3 Ma. The southern Sawatch Range Fault sample dates to 16.8±2.5 Ma. These dates indicate the two faults were active in the Middle Miocene. Through forward modeling thermal histories in QTQt, we also make predictions about what apatite (U-Th-Sm)/He (AHe) and zircon (U-Th)/He (ZHe) dates may be expected depending on the rate and duration of fault exhumation. Anticipated AHe and ZHe dating will verify our different tested scenarios for fault exhumation timing. This will help further constrain the start and duration of tectonic activity in the transfer zone and deepen our understanding of basin linkage and its effects on surface processes within the RGR.