229 D14. Recent Advances in Mineralogy and Petrology (Posters)

Wednesday, 18 October 2023
8:00 AM - 5:30 PM
Hall B

P-T CONDITIONS OF METAMORPHISM OF LITTLE PINE GARNET MINE ROCKS, WESTERN BLUE RIDGE, AS CONSTRAINED BY MINERAL ASSEMBLAGE DIAGRAMS

Paper number: 229-7
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

The Little Pine Garnet Mine (LPGM) in the Western Blue Ridge Province of the Southern Appalachians is located on a large shear zone between the Mars Hill Terrane and the Grenville Basement. Three groups of rocks occur in the LPGM : Group 1 are schists with garnet (Grt) + gedrite (Ged) + anthophyllite (Ath) + chlorite (Chl) + biotite (Bt) + staurolite (St) + plagioclase (Pl) ± sillimanite (Sil) + quartz (Qz) + ilmenite (Ilm) + rutile (Rt). Group 2 are gneisses contain hornblende (Hbl) + Bt + Pl + Ilm + Qz ± Grt ± St ± aluminosilicate (Als). Group 3 granofelses are predominated by either Gd/ Ath or Chl with minor Ilm, Pl ± Sil. The protoliths of these rocks were hydrothermally altered E-MORBs (Groups 1 and 3) and greywackes (Group 2) that likely represented part of an oceanic basin between Mars Hill and Grenville Basement Terranes.

Previous attempts at constraining the P-T conditions using petrogenetic grids, conventional thermobarometry, and multi-equilibrium calculations have resulted in estimates ranging from 450°C to 600°C and 4 to 9 kbar. New mineral assemblage diagrams (MAD) were calculated using Theriak-Domino to help better constrain the P-T history of samples from the LPGM. MA for a Group 1 sample constrains its peak metamorphic temperature between 650°C-700°C and pressures in excess of 6.5 kbar for the assemblage of Grt + St + Bt + Ged + Rt. Retrograde metamorphism between 575°C - 650°C and 3 - 4.5 kbar produced the assemblage Ath + Sil + Ilm + Pl + Chl. MAD for a Group 2 sample shows peak metamorphic conditions of 650°C-750°C and 5.5 kbar - 6.0 kbar based on the peak mineral assemblage of Grt + Hbl + Sil + Bt + Pl + Ilm + Rt. The new mineral assemblage diagrams for the LPGM samples therefore show that peak metamorphism for the samples from the Little Pine Garnet Mine occurred between temperatures of 650°-750°C and pressures in excess of 5.5 kbar whereas retrograde metamorphism occurred between 575°C - 650°C and 3.0 - 4.5 kbar.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-393640

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