Publication Date:
2011-04-19
Description:
Sodic pyroxene is reported from an Ordovician metatrachyte of the Kaczawa Mountains, SW Poland. Its composition ranges from Jd0.98Ae0.02 to Jd0.15Ae0.85. Relict jadeite and phengite (up to 3.75 Si atoms per fomula unit) belong to the peak-pressure assemblage of an early HP-LT event. Later greenschist-facies stages are represented by riebeckite, biotite, chlorite, low-Si potassic white mica and actinolite. P-T pseudosections calculated for the range 200-450{degrees}C, 3-13 kbar allow evaluation of the conditions formation of jadeite in the metatrachyte and derivaton of a P-T path. Considering the position of prograde, peak and retrograde metamorphic assemblages and respective mineral compositions, we can derive the following equilibration stages: 8.5{+/-}0.5 kbar, 270{+/-}20{degrees}C for the pressure maximum, 6.0{+/-}1.0 kbar, 310{+/-}20{degrees}C for the temperature maximum and 3.5{+/-}0.5 kbar, 280{+/-}20{degrees}C as well as
Print ISSN:
0026-461X
Electronic ISSN:
1471-8022
Topics:
Geosciences