STRAIN PARTITIONING AND SEGMENT LINKAGE IN A MAJOR EXTENSIONAL DETACHMENT FAULT, NORTHWESTERN ARIZONA: IS THE "GOLDEN RULE" A TRANSVERSE ZONE?

A major, 55 km-long, low-angle normal fault in the Lake Mead region of northwestern Arizona and southeastern Nevada, the South Virgin-White Hills detachment (SVWHD), exhibits variable displacement from north to south along its strike. The SVWHD comprises three segments, the Lakeside Mine, Salt Spring and Cyclopic Mine faults, respectively, from north to south. Displacement along the SVWHD varies from ~20 km at its northernmost end, north of Lake Mead, to ~3 km at its southernmost end. The mechanism by which this variation in displacement is accommodated is not known. It could be accomplished by strike-slip movement along discrete transfer faults, by vertical-axis rotations, or by a combination of the two. The Golden Rule Peak lineament traverses both the hanging wall and the footwall of the Salt Spring segment and may represent a major transverse zone. This lineament is expressed as a local gravity gradient that spans a distance of ~50 km from the Lost Basin Range to the west. It is spatially associated with 1) anomalously east-striking foliation trends in the Lost Basin Range that disrupt the regional north-south trends, 2) the anomalously east-trending Golden Rule Peak, 3) a prominent, 300 m amplitude corrugation in the detachment, and 4) the southern terminus of a series of volcanic tilt blocks in the hanging wall of the detachment. Additionally, we have identified two mylonite zones within the footwall of the SVWHD that are on-strike with the lineament, suggesting that it may be controlled by an older (possibly Proterozoic) structure. Furthermore, preliminary gravity modeling is compatible with the presence of a high-angle fault at the northern flank of Golden Rule Peak, coincident with the gravity gradient. Thus, the Golden Rule Peak lineament may represent a transverse structure, specifically, a transfer fault that formed during the linkage of the Salt Spring and Cyclopic Mine segments. However, much more work is necessary to establish the nature of the lineament and the relative timing of normal fault and strike-slip fault (if any) activity. Such a transverse zone, if it exists, would have served to partition strain within the variably extended crust of northwesternmost Arizona.