Metamorphosed oceanic lithosphere from the Chunky Gal Mountain complex, Blue Ridge province, North Carolina

Conference · Mon Mar 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5688563

Ranson, W A; Garihan, J M ^[1]

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1. Furman Univ., Greenville, SC (United States). Dept. of Geology

Closely associated dunite and layered troctolite, gabbro, and anorthosite from the Chunky Gal Mountain mafic-ultramafic complex suggest a related ocean floor origin for these lithologies, with regional emplacement by the pre-metamorphic Hayesville-Fries thrust of Taconic age. Anhydrous mineral assemblages of dunitic and troctolitic rocks were more resistant to granulite and upper amphibolite metamorphic episodes, retaining much of their original mineralogy. Dunite consists of fresh polycrystalline olivine with local development of anthophyllite, serpentine, and talc along fractures. Dunite adjacent to mafic amphibolites of the complex contains distinctive cm-scale bands or layers of recrystallized plagioclase( ) of uncertain affinity, possibly veins or rhythmic layers. Troctolitic rocks display reaction textures around fresh olivine and plagioclase. Orthopyroxene growing normal to olivine grain boundaries forms an inner corona, in turn surrounded by a complex symplectite of Cpx + Plag [+-] Grt [+-] Spl. Gabbroic rocks show nearly complete replacement of original mafic minerals. Orthopyroxene survives in a few gabbros but mostly has been replaced by emerald green alumino-magnesio-hornblende. Calcic plagioclase is abundant as subhedral crystals or as oval, polycrystalline clots and pink corundum constitutes an accessory phase. A possible reaction resulting in the observed aluminous assemblage is: Na-Plag + Opx + Di + Spl + fluid = Mg-Hbl + Crn + Ca-Plag. Anorthosites occur as layers 10--50 cm in width within layered troctolites and consist of beautifully recrystallized plagioclase with seriate texture and minor amounts of alumino-magnesio hornblende occurring as fine-grained clots. Contacts between anorthosite and troctolite display the same sort of symplectite formed as an outer corona around olivine in the troctolite.

• OSTI ID: 5688563
• Report Number(s): CONF-9303211--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ANORTHOSITES
DEVELOPED COUNTRIES
EARTH CRUST
GABBROS
GEOLOGIC FAULTS
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
IGNEOUS ROCKS
METAMORPHISM
MINERALOGY
MINERALS
NORTH AMERICA
NORTH CAROLINA
OCEANIC CRUST
OLIVINE
PETROGENESIS
PETROLOGY
PLUTONIC ROCKS
RECRYSTALLIZATION
ROCKS
SILICATE MINERALS
USA