Forward modeling corona growth in a partially eclogitized leucogabbro, Bourbon Island, North-East Greenland
Abstract Coronitic textures are common in partially eclogitized igneous bodies, such as gabbros, leucogabbros, and anorthosites, east of the Germania Land Deformation Zone in North-East Greenland. Coronas formed by prograde metamorphic processes that transformed the gabbroic bodies to eclogite facie...
| Main Authors: | , , |
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| Format: | Text |
| Language: | English |
| Published: |
2007
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1038.5136 http://myweb.uiowa.edu/ctfoster/publications/Sartini_etalLithos%2095_279_295.pdf |
| Summary: | Abstract Coronitic textures are common in partially eclogitized igneous bodies, such as gabbros, leucogabbros, and anorthosites, east of the Germania Land Deformation Zone in North-East Greenland. Coronas formed by prograde metamorphic processes that transformed the gabbroic bodies to eclogite facies, and record frozen stages of the prograde metamorphic evolution of these rocks. A metaleucogabbro-norite body on Bourbon Island in Jøkelbugt is characterized by three concentric areas: a coronitic core, a mottled inner rim with areas of completely eclogitized material surrounded by a matrix of coronitic metaleucogabbro, and an outer rim of strongly foliated and completely retrogressed amphibolite. The Bourbon body preserves four stages of the prograde metamorphic history: Stage I, Stage II, Stage III, and Eclogite Stage. Stage I coronas are found only in the core of the body, which is the least reacted part of the leucogabbro-norite and the closest to the protolith, and is characterized by the corona sequence Pl rim / Grt + Kfs + Amp/Grt + Amp/Cpx rim . The typical corona sequence for Stage II is Pl rim /Grt + Pl + Zo/Cpx rim /Amp rim . Stage III samples show a Pl rim + Ky + Scp/Grt + Pl + Qtz/Qtz + Pl sequence, with the relict clinopyroxene being replaced in part by microcrystalline aggregates of Cpx + Amp + Pl. The Eclogite Stage shows relict Pl completely replaced by Grt, and the relict Cpx completely replaced by aggregates of Omp + Pl + Kfs + Amp. We tested open-system grain boundary diffusion (OSGBD) theories to model the prograde Stage I symplectitic coronas. The observed ratio of the thickness of the different layers is Pl rim :Grt + Kfs + Amp:Grt + Amp:Cpx rim equal to 3:1.3:0.95:0.5. These ratios are very close to the modeled ones of 2.7:1.1:1:0.5. Furthermore, subtle textural changes within the Grt + Kfs + Amp corona were also reproduced by the model. The model gave us insight into the conditions of the metamorphic system in which the coronas formed. The sequence Pl rim /Grt + Kfs + Amp/Grt + Amp/Cpx rim ... |
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