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| Titel: |
Age and emplacement conditions of the Chalmers mafic intrusion deduced from contact melts |
| Auteur: |
Kiel, Helena M. Cornell, David H. Whitehouse, Martin J. |
| Verschenen in: |
GFF |
| Paginering: | Jaargang 125 (2003) nr. 4 pagina's 213-220 |
| Jaar: |
2003-12-01 |
| Inhoud: |
Mineral textures, thermobarometry and ion probe U-Pb dating were used to determine the age and emplacement conditions of a gabbro intrusion in Goteborg, southwest Sweden. Granitic diapirlike structures intruding the gabbro are interpreted as contact-metamorphic melts of ∼1.6 Ga country rock gneiss which back-intruded the mafic magma. Metasomatising fluids from these diapirs triggered garnet growth and hornblende alteration at a late stage of magmatism. Xenocrystic zircons in the diapirs were first partly resorbed, then experienced new growth at the time of the intrusion. Thermobarometric calculations show equilibrium conditions of 800d`C and 10 kbar, reflecting an emplacement depth of 33 km. Zircon and titanite U-Pb analyses were made by secondary ionisation mass spectrometry (SIMS). Zircon cores and rims give a coherent concordia age of 1333±8 Ma (2σ), interpreted as the age of intrusion, at which time most xenocrystic zircon cores were totally reset. Titanite gives an age of 991±16 Ma (2σ) with a trend toward the formation age, reflecting incomplete Sveconorwegian resetting. The Chalmers intrusion was emplaced in a lower crustal environment in a block of ∼1.6 Ga arc-related country rock. The tectonic setting at 1.3 Ga was either anorogenic or a pre-Sveconorwegian rift environment. Subsequent amphibolite grade Sveconorwegian regional metamorphism largely reset the U-Pb system in titanites but did not cause either re-equilibration of the thermobarometric minerals or lead-loss in zircon. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
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