T304 Metamorphic Petrology: New Approaches and Outcomes (Posters)

Wednesday, 4 November 2015
9:00 AM - 6:30 PM
Exhibit Hall

METAMORPHIC EVOLUTION OF THE PINKIE UNIT METAPELITES FROM SVALBARD (HIGH ARCTIC): P-T-T STUDY INCLUDING QUARTZ-IN-GARNET BAROMETRY (QUIG)

Paper number: T304-10
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Four metamorphic zones indicating Barrovian type metamorphism have been distinguished within the studied metapelites: (1) garnet+chlorite+muscovite+biotite, (2) garnet+staurolite+muscovite+biotite, (3) garnet+staurolite+kyanite+muscovite+biotite, (4) garnet+kyanite+muscovite+biotite. Garnet is present in two textural positions. Garnet-I forms huge, partly crushed, anhedral porpyroblasts with abundant inclusions of quartz and ilmenite, whereas garnet-II occurs as small, euhedral, almost inclusion-free crystals. The Pinkie rocks are strongly deformed. The M1 assemblages and the D1 structures are overprinted by the D2 mylonitization that was associated with fluid infiltration. Hence, estimation of the P-T conditions using conventional techniques is not straightforward.

Preliminary P-T estimates were obtained using QuiG (quartz-in-garnet) barometry, which is based on the shift of the 464 cm-1 Raman band in quartz. The measured quartz inclusions from the zones (2), (3) and (4) suggest that garnet was growing at c. 7-9 kbar. The discontinuous reactions observed in the Pinkie metapelites have been modeled in the K2O-FeO-MgO-Al2O3-SiO2-H2O system and coupled with the QuiG results to show the P-T evolution of the Pinkie unit. The mineral assemblages from the studied zones were formed along the prograde P-T path at c. 7-9 kbar and 550-650°C.

Age of metamorphism was derived based on monazite chemical dating. Monazite occurs in the matrix and forms inclusions in garnet and staurolite. Occasionally, it is rimmed by the allanite+fluorapatite coronas. Monazite from the zones (2), (3) and (4) yielded the age of metamorphism of c. 370-360Ma. Importantly, our study provides the very first evidence for Barrovian metamorphism of Late Devonian (Ellesmerian) age in the High Arctic. Heretofore only "cold" deformation of this age was recognized in the region.