1993 Fiscal Year Final Research Report Summary
Metamorphic P-T-t path in the Sphir Rondane Mountains, East Antarctica
| Project/Area Number |
04640739
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | Okayama University |
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Principal Investigator |
ASAMI Masao Okayama University, College of Liberal Arts, Professor, 教養部, 教授 (10033193)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Antarctica / Sphir Rondane Mountains / P-T-t path / Granulite-facies / Contact metamorphism / Relict sapphirine / Retrograde kyanite / Late Proterozoic |
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| Research Abstract |
The Sphir Rondane Mountains are underlain by a high-grade, migmatized gneissic complex, intruded by granitic and syenitic plutonic rocks. Regional metamorphism in the granulite-facies is indicated by the common occurrence of mineral assemblages such as Opx-Cpx-Grt-Hbl-Pl-Qtz-Ilm(〕SY.+-.〔)Mag and Sil-Grt-Bt-Kfs-Pl-Qtz-Ilm(〕SY.+-.〔)Rt, together with P-T estimates of 750-800ﾟC and 7-8 kbar based on mineral compositions. Among the granulite-facies rocks, some pelitic rocks contain mineral associations suggestive of prograde and retrograde episodes during the regional metamorphism of medium-pressure type : relict kyanite, staurolite, sapphirine and gedrite enclosed in garnet and secondary kyanite-bearing biotite aggregates embaying garnet ; for the latter association 530-580ﾟC and about 5.5 kbar are estimated. The regional metamorphism was followed by a low-pressure, contact metamorphic event as suggested by the local development of granoblastic andalusite and cordierite in some pelitic rocks adjacent to the acid plutonic intrusives and by the P-T values around 550ﾟC and 3 kbar obtained from mineral compositions. These observations constrain the Sphir Rondane P-T trajectory to a clockwise type for the regional metamorphism, and a near-isothermal decompression path with subsequent isobaric heating during the contact metamorphism. Geochronologic data suggest ages near 1000 Ma for the earlier, mostly granulite-facies, metamorphism and ages near 500 Ma for the later low-P plutono-metamorphic activity after uplift.
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