LOCATION: The outcrops are located on dirt tracks leading north and west around the prominent hill located 0.2 mile west of the S-42-12 bridge over Fairforest Creek. (Fig. 9, Jonesville quadrangle)
DESCRIPTION: Loose boulders and cobbles of metadiorite and diorite gneiss of the Mean Crossroads complex (Dennis and Shervais, 1991) litter the slopes of this prominent hill. Some samples show little fabric at all with randomly oriented coarse hornblende needles, others have a mylonitic foliation. What is common to all samples is the ubiquitous development of epidote at the expense of plagioclase (Fig. 15). This is interpreted to indicate intrusion of the Mean Crossroads diorite relatively late in the late Precambrian-early CambrianS orogenic event, when rather than a zone of broad, distributed strain, deformation was restricted to narrow bands irregularly distributed through a pluton that was intruded into a semicontinuously deforming zone.
Dennis and Wright (1993, 1996) dated four size fractions of zircon from this site by the U-Pb method. The data plot in a highly linear array with an upper intercept at 538+/-5 Ma, interpreted to be the crystallization age of the diorite and the age of the Mean Crossroads complex.
The Mean Crossroads complex was identified by Dennis (1988) and described by Dennis and Shervais (1991, 1995). The Mean Crossroads complex is zoned intrusive complex that has a hornblendite-clinopyroxenite core, surrounded by varieties of gabbro, and mantled by a thick rind of diorite. This entire package was metamorphosed at greenschist to lower amphibolite facies. It is believed that at least some of the mafic metavolcanic rocks in this area were derived from the Mean Crossroads complex because ankaramite and ultramafic dikes crosscut the plutonic rocks. Dennis (1988) and Dennis and Shervais (1991, 1992, 1995) argue that the Mean Crossroads complex, Wildcat Branch complex, the Hammett Grove Meta-Igneous Suite, York-Chester mafic-ultramafic complex, Davie County Complex (NC), Latimer (SC)-Nancy Hart (GA) complex, and Berner mafic complex represent loci of arc-rifting along the western edge of the Carolina arc while the arc was in a periGondwanide position. Probably the Caswell County complex described by Wilkins and others (1995) also belongs in this group. This arc-rifting occurred in the western Carolina terrane at the same time or slightly younger than eruption of Persimmon Fork Formation, Lincolnton metadacite, Uwharrie Formation, ca. 550 Ma (Dennis, 1995; Dennis and Shervais, 1995).
Fig. 15. Photomicrograph of gneissic metadiorite of Mean Crossroads complex, Stop 7. Whether samples contain a good metamorphic fabric or not, all samples show the ubiquitous development of epidote at the expense of plagioclase. The contact between this pluton and mafic metavolcanic rocks observed at Stop 5 is cut by the undeformed, unmetamorphosed pluton observed at Stop 6.