Coupled Basin Evolution and Core-Complex Exhumation in Southeastern Arizona: Another Look Into Subsurface Relations From Seismic Reflection Data

Records of lithospheric extension and mountain-range uplift are most continuously contained within syntectonic sedimentary rocks in basins adjacent to large structural culminations. Although subject to local conditions and other limitations, basin-fill sedimentary assemblages provide essential keys to understanding the sequence and timing of tectonic activity and crustal deformations in the southern Basin and Range Province where metamorphic core complexes document extreme crustal extension. In southeastern Arizona, major core complexes form mountain ranges with the highest elevations in the region and, paradoxically, supposedly much less extended terranes lie at lower elevations. These large structural and topographic culminations are flanked by sedimentary basins that have trapped the products of core-complex formation. Adjacent to the Catalina-Rincon metamorphic core complex, stratigraphic-sequence geometries evident in seismic reflection data within the Tucson Basin suggest a two-phase basin-evolution model. In its earliest stage, Phase I was characterized by voluminous volcanism that coincided with the early stages of crustal extension and tectonically induced collapse of post-Laramide crustal blocks. Extensive faults formed relatively small-scale proto-basins, which coalesced in later stages along larger basin-bounding extensional fault systems. Evidence of synextensional sedimentation within the enlarging basin is provided by sediment growth packages, derived from adjacent footwall material, which fan into brittle hanging-wall faults. During this phase, volcanism remained active, and growth packages contain interbedded sedimentary rocks and volcanic products. Phase II of basin evolution consisted of an overall broader deepening of the central basin, coupled with uplift and initial exposure of the Catalina-Rincon metamorphic core as supported by the introduction of mylonitic clasts present in the basin fill that were not present in the earlier phases of sedimentation. Well-log constraints from the central basin suggest that a significant depositional hiatus exists between the two phases of deformation and sedimentation, consistent with surface geological evidence for late-stage exhumation of the Catalina-Rincon metamorphic core complex. However, seismic sequence analysis suggests that mountain uplift was coupled with basin subsidence over an extended period of time. Moreover, the geometry of upper basin-fill units suggests lateral mass transfer of mid-crustal rocks to the adjacent core complex as exhumation of the crystalline core progressed.