THE BOUNDARY ZONE BETWEEN THE NORTHERN AND CENTRAL BASIN & RANGE SUBPROVINCES: A DEVELOPING RIFT SEGMENT BOUNDARY

Segment boundaries accommodate differences in magnitude, distribution and kinematics of extension and are essential components of rifts. Such features rarely have been examined in the Basin & Range province. We delineate and analyze a Miocene-Quaternary boundary zone that contains a concentration of transverse left-lateral faults between the northern and central Basin & Range subprovinces (NBR, CBR, respectively). The boundary zone location and occurrence are based on gravity anomalies, new maps of E- and NE-striking left-lateral faults, calderas, clustering of earthquake epicenters, and GPS velocity differences. Based on these features, the boundary zone total width ranges from 5- ~70 km.

We test the hypothesis that the NBR-CBR boundary evolved through time with (1) older deformation concentrated in the north and center, and younger (Quaternary) deformation concentrated in the center and south, and (2) slip transfer among strike-slip faults via normal faults. On the north side of the boundary zone, E-striking left- and oblique faults of the Timpahute lineament in the Timpahute and Mt. Irish ranges, cut rocks as young as the 18.5 Ma Hiko Tuff. In the central boundary zone, near Alamo, NV, all three main NE-striking left-lateral faults of the Pahranagat shear zone (PSZ) cut rocks as young as the 15.1 Ma Kane Wash Tuff. The most recent scarp of the southern main PSZ fault, offsets a unit younger than sediment dated at 7601-7546 cal BC by 14C. The farthest south left-lateral fault in the boundary zone, the Kane Springs Wash fault, shows offset of a 15.1 Ma tuff and lesser offset of middle to late Pleistocene units. In addition, our new map data show fault geometries and kinematics that document linkages of ~N-striking normal faults to the left-lateral faults during both the Miocene and Quaternary. These linkage zones allow slip transfer among the normal and strike-slip faults which suggests the boundary zone is transtensional.

In summary, we combine new map data with published data and suggest the following. (1) The boundary zone between the NBR and CBR is transtensional and progressed southward from Miocene to Quaternary. (2) This boundary zone is a developing rift segment boundary as evidenced by the Quaternary faulting and linkages.