LOCATION: The outcrops are located on Dutchmans Creek. Access is via S-42-511 (a/k/a S-44-68), and entrance can be gained at the Bridge over the Creek or at gates 0.1 or 1.0 miles from the intersection with SC 56. (Fig. 21, Cross Anchor quadrangle)
DESCRIPTION: A good section of mafic metavolcanic rocks is exposed in this reach of Dutchman Creek. These rocks are thought to be typical, if very well exposed, examples of the mafic metavolcanic rocks that are representative of the Carolina terrane in this area. They are comparable to the McClure Creek section discussed above at Stop 5, even to the extent of being intruded by a foliated 579+/-4 Ma granodiorite (Dennis and Wright, 1993, 1995). The metabasalts here are well foliated, and many contain a strong lineation. These rocks are cut by leucocratic granitic to pegmatite dikes that are clearly unfoliated and undeformed, and cut across the metamorphic fabric (Fig. 22; Dennis, 1995). At this location we are less than 3 km from the surface trace of the central Piedmont suture to the west, and less than 1 km from felsic intrusive rocks associated with the Buffalo gabbro to the east and southeast.
Foliation dips in this area are moderately steep, in the range of 45-55deg. to the south or southeast. Mineral lineations plunge 35deg. to 45deg. within a few degrees of 180. This is comparable to lineations discussed above in the stop 10 description, and the regional pattern of lineations in this segment of the central Piedmont suture (Dennis, 1995) that are subparallel to the pole to a great circle of poles to folded foliations, and are interpreted to represent west-vergent folding of Alleghanian age.
Dennis and Shervais (1995) report whole-rock major and trace element geochemistry from this series of outcrops (their samples 2472, 2473a, b, 2474a, b). Dennis and Shervais interpreted the protoliths of the rocks they analyzed from this location to be high-Mg basalts (hornblende and augite porphyries), basaltic andesites, and basalt.
Dallmeyer and others (1986) report a 40Ar/39Ar biotite plateau age at 289+/-5 Ma from this site (their sample 45). This mineral age is consistent with a hornblende plateau age of 302+/-6 Ma (sample 46B) reported by Dallmeyer and others (1986) 3 km north-northwest of here also on Dutchman Creek (S- - 91 bridge, the same site where the 579+/-4 Ma foliated diorite (Dennis and Wright, 1993, 1996) was collected). Their sample 46A, also from that site, was a biotite plateau at 313 Ma, older than that of the hornblende ands interpreted by these authors as evidence of extraneous argon contamination. Dallmeyer and others (1986) note that variations in the 40Ar/39Ar plateau ages they report for Inner Piedmont - Kings Mountain belt - Charlotte belt samples are "not clearly related to any belt boundary, . . . and are tentatively interpreted to indicate faulting or northwestward tilting of isothermal surfaces between ca. 275 and 300 Ma." Based on the stops presented on this trip, it is suggested that uplift related to northwest-vergent folding accompanied by minor Alleghanian-age faulting in this segment of the central Piedmont suture is responsible for the observed variation.
It is thought that the undeformed felsic dikes here are related to the Buffalo gabbro, and are equivalent to those observed at Stop 8. If the Buffalo gabbro belongs indeed to the Siluro-Devonian array of gabbros, and these dikes are related to the late stages of its intrusion, then it can be said that there has been very little penetrative deformation in the subsequent period. This observation and the proximity to the central Piedmont suture was another line of evidence that led Dennis (1995) to conclude that the primary, significant motion on the central Piedmont suture predates ca. 400 Ma (see also Stop 1). Thus, his interpretation is that significant motion on the central Piedmont suture in this area postdates foliation formation (ca. 535 Ma) and predates intrusion of post-metamorphic rocks ca. 400-380 Ma. Where the strike of this fault is oriented northeast-southwest, to the north and to the south (Kings Mountain shear zone and Middleton-Lowndesville zone respectively), it is reactivated as an Alleghanian, retrograde strike-slip shear zone, but in this area Alleghanian effects are less dramatic. The advantage is that we have a better opportunity to see what this boundary looked like prior to the strong Alleghanian overprint observed in areas to the north and south.
Fig. 22. Mafic metavolcanic rocks cut at a high angle by undeformed granitic dike, parallel to hammer, Dutchman Creek, Stop 12. Note the very sharp, angular contact. Sand and pollen fill in small depressions in the mafic metavolcanic rock. Dike is interpreted to be related to intrusion of the Buffalo gabbro, less than 1 km to the west. Hammer handle is 66 cm.