Tateishi, K. and Tsunogae, T. and Santosh, M. and Janardhan, A. S. (2004) First report of sapphirine plus quartz assemblage from southern India: Implications for ultrahigh-temperature metamorphism. Gondwana Research, 7 (4). pp. 899-912. ISSN 1342-937X
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We report here for the first time, the occurrence of sapphirine+quartz assemblage in textural equilibrium from quartzo-feldspathic and pelitic granulites from southern India. The sapphirine-bearing rocks occur as layered gneisses associated with pink granite within massive charnockite in Rajapalaiyam area in the southern part of Madurai Block. Sapphirine occurs in three associations: (i) fine-grained subhedral mineral associated with quartz enclosed in garnet (ii) intergrowth with Al-rich orthopyroxene (up to 9.7 wt.% Al2O3), and (iii) in symplectitic intergrowth with orthopyroxene (Al2O3= 5.9-6.7 wt.%) and cordierite surrounding garnet. The sapphirine in association with quartz is slightly magnesian (X-Mg = 0.79-0.80) and low in Si content (1.55-1.56 pfu) as compared with those associated with orthopyroxene and cordierite (X-Mg = 0.77-0.79, Si = 1.59-1.63 pfu). The sapphirine+quartz assemblage suggests that the granulites underwent T>10510 degreesC peak metamorphism. Cores of porphyroblastic orthopyroxene in the sapphirine-bearing rocks shows high-Al2O3 content of up to 9.7 wt%, suggesting T = 1040-1060 degreesC and P = 8 kbar. FMAS reaction of sapphirine+quartz-->garnet+sillimanite+cordierite indicates a cooling from sapphirine+quartz stability field after the peak ultrahigh-temperature metamorphism. Slightly lower temperature estimates from ternary feldspar and sapphirine-spinel geothermometers (T = 950-1000 degreesC) also support a post-peak isobaric cooling. Corona textures of orthopyroxene+cordierite (+/-sapphirine), orthopyroxene+sapphirine, and cordierite+spinel around garnet suggest subsequent decompression. The sapphirine-quartz association and related textures reported in this study have important bearing on the ultrahigh-temperature metamorphism and exhumation history of the Madurai Block as well as on the tectonic evolution of the continental deep crust in southern India.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | sapphirine plus quartz; Al-rich orthopyroxene; ultrahigh-temperature metamorphism; Madurai Block; southern India |
| Subjects: | F Earth Science > Geology |
| Depositing User: | Users 23 not found. |
| Date Deposited: | 04 Sep 2019 11:46 |
| Last Modified: | 04 Sep 2019 11:46 |
| URI: | http://eprints.uni-mysore.ac.in/id/eprint/6539 |
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