GEOLOGY AND GRAVITY OF LILESVILLE GRANITE BATHOLITH, NORTH-CAROLINA

The Lilesville Granite is the southernmost granite intrusion of the Eastern Piedmont in North Carolina. It is a sheet or tongue-shaped concordant mass extending to a maximum depth of about 1.75 mi. It is surrounded by a contact aureole of metasedimentary mica schist and mica gneiss and has an areal extent of 125 sq mi. The granite is characterized by a porphyritic rapakivi texture with a medium- to coarse-grained matrix of plagioclase, quartz, and biotite. The intrusion is compositionally zoned and consists of adamellite, granodiorite, and tonalite. The granite is considered to have been emplaced as a crystal mush and to have crystallized in place. The modal variations and textural features of the granite may be due to crystal settling, contamination, and rapid late-stage crystallization (sudden escape of water pressure). A large positive Bouguer anomaly associated with the granite is attributed to two major features: (1) a gabbro body which intrudes the granite near its eastern margin, and (2) a mica gneiss unit which underlies the batholith. The proposed sequence of geologic events is: (1) deposition of felsic volcanic rocks and argillites, (2) formation of the proposed anticline and low-rank regional metamorphism, (3) intrusion and crystallization of the Lilesville Granite and the formation of the mica gneiss and mica schist units by thermal metamorphism, (4) intrusion of gabbro body into the Lilesville Granite, (5) Triassic faulting and sedimentation, (6) intrusion of Triassic or Jurassic dikes, and (7) deposition of Cretaceous and Tertiary sands and gravels. © 1971, The Geological Society of America, Inc.