THE GEOLOGY OF CENTRAL PIEDMONT, CAROLINA TERRANE, NC

Geologic study and mapping of Rowan (Rw), Davie (De) and Davidson (Dd) counties reveals a long history of sedimentation, volcanism, terrane accretation and at least three tectonic intrusive episodes. The area is Carolina Terrane (CT); western 75 % is Charlotte and about 25% at the eastern boundary is Carolina Slate Belt (CSB). The western boundary of Rw is close to the Bridle Creek Fault, separating CT from Inner Piedmont Cat's Square terrane to the west. The oldest and most widespread rocks are late Protorozoic or early Paleozoic amphibolites and granitic gneiss cut by metagranites and metadiorites. These rocks are intruded by gabbro (400 Ma), leucocratic meta-adamellite (385-415 Ma), post-metamorphic granites (Woodleaf ca 265-290 Ma) and two porphyritic granite plutons (290 Ma) with euhedral microcline phenocrysts, by a 243 Ma orbicular diorite dike, Jurassic diabase dikes and by widespread fracture filling and replacement zeolite alteration (laumontite). Small metamorphosed ultramafic rocks crop out in the western part of Rw County. Outcrops appear to be lenses and are composed of talc, chlorite, and tremolite. A 1 km. long ridge and smaller exposures of quartzite crops out in the western part of Rw County. The 320-330 Ma Salisbury shear zone, an internal tectonic feature in CT, is 45 mile long, 2-5 mile wide; it strikes N 20-60 E. and dips 80-85 NW. It consists of sheared ultramylonite schist, mylonite gneiss, protomylonites, and cataclasites with considerable neomineralization and some fluxion structure plus small to large unsheared blocks of metasedimentary and metavolcanics. It extends from Cabarrus across Rw into middle Dd Counties, NC. The CSB occurs in the SE part of Rw and Dd counties as a thick sequence of lower greenschist facies mafic to intermediate to felsic volcanic (predominantly calc-alkaline) and volcanoclastic rocks interbedded with mudstone, shales, siltstones, and argillites of late Precambrian to Cambrian age. The rocks have been folded into a plunging anticline and syncline cut by the Gold-Hill - Silver-Hill shear zone (400-385 Ma), a northeast trending 120 km. long, 3-7 km wide zone of phyllonites plus unsheared metasedimentary and metavolcanic rocks.