NDLI: Glass-bearing inclusions in Nakhla(SNC meteorite) augite: heterogeneouslytrapped phases

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U/Pb and Pb/Pb zircon ages from granitoid rocks of Wallagga area: constraints on magmatic and tectonic evolution of Precambrian rocks of western Ethiopia

Mineralogy and Petrology : Volume 71, Issue 1-2, January 2001

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Glass-bearing inclusions in Nakhla(SNC meteorite) augite: heterogeneouslytrapped phases

Content Provider	Springer Nature Link
Author	Varela, M. E. Kurat, G. Clocchiatti, R.
Copyright Year	2001
Abstract	Nakhla augite and olivine grains commonly contain glass-bearing inclusions. In contrast to olivines, augites host only one type of multiphase inclusions which consists of euhedral to subhedral augite, Ti-magnetite and pigeonite plus silica-rich glass and a bubble. No fractures surround these inclusions, making it likely that they are of a pristine composition. Heating experiments with a final temperature of 1150 °C were done for the first time with Nakhla augite inclusions. During heating the glass melted and crystals inside the inclusions were dissolved in the melt whereby its chemical composition changed. The quenched glass is poorer in SiO2 and Al2O3 and richer in CaO, FeO and MgO compared to unheated inclusion glass. Our in situ analyses allowed us to estimate the initial composition of a liquid co-existing with Nakhla augite at 1150 °C and 1 atm pressure. Several features of Nakhla, such as the high Fe/Mg ratio of the augite, which is out of equilibrium with the glass, the highly variable alkali content and the Na/K ratio of the glasses are incompatible with the standard model that states that SNC meteorites are all igneous rocks formed from basaltic magmas. Our results on re-melted glasses suggest a more complex and possibly non-magmatic genesis of Nakhla. Both types of glass-bearing inclusions (those hosted by augite or olivine) could represent heterogeneously trapped mineral + glass inclusions. Those hosted by augites mimic at least in part parental melt inclusions. However, the quenched glass is out of equilibrium with the host with respect to the Fe/Mg ratio and has too much compositional variation to be representative of a parental melt. Glasführende Einschlüsse im Augit von Nakhla (SNC-Meteorit): Heterogeneingeschlossene Phasen Augite und Olivine im Achondriten Nakhla enthalten häufig glasführende Einschlüsse. Im Gegensatz zu den Olivinen enthalten die Augite nur einen Typ Multiphasen-Einschluß, welcher aus idiomorphem bis subidiomorphem Augit, Ti-Magnetit, Pigeonit und einem SiO2-reichen Glas mit Blase besteht. Diese Einschlüsse sind nicht von Sprüngen umgeben, was es wahrscheinlich macht, dass sie ihre ursprüngliche Zusammensetzung unverändert erhalten haben.Erstmals wurden Schmelz-Experimente mit Endtemperaturen von 1150 °C an Nakhla Augiten durchgeführt. In diesen Experimenten schmolz das Glas der Einschlüsse, löste die koexistierenden kristallinen Phasen auf und änderte dabei seine chemische Zusammensetzung. Das durch Abschrecken dieser Schmelze erzeugte Glas ist ärmer an SiO2 und Al2O3 und reicher an CaO, FeO und MgO als das ursprüngliche Einschlußglas. Diese in situ-Analyse erlaubt eine Abschätzung der ursprünglichen Zusammensetzung einer Schmelze im Gleichgewicht mit Nakhla Augit bei 1150 °C und 1 atm Druck. Einige Eigenschaften von Nakhla, wie das hohe Fe/Mg-Verhältnis des Augites, welches nicht im Gleichgewicht mit dem Glas ist, die variablen Alkali-Gehalte und die Na/K-Verhältnisse im Glas sind inkompatibel mit dem Standard-Modell für die SNC-Meteorite, welches diese als magmatische Gesteine basaltischer Herkunft sieht. Unsere Ergebnisse weisen auf eine komplexe, möglicherweise nicht-magmatische Entstehung von Nakhla hin. Sowohl die glasführenden Einschlüsse im Olivin als auch jene im Augit von Nakhla könnten Produkte eines heterogenen Aufsammelns von Mineral plus Glas sein. Die Einschlüsse im Augit imitieren zumindest zum Teil Schmelzeinschlüsse. Allerdings sind sie mit ihrem Fe/Mg – Verhältnis nicht im Gleichgewicht mit dem Augit und sind auch in ihrer Zusammensetzung zu inhomogen, um für ein mögliches Mutter-Magma repräsentativ zu sein.
Starting Page	155
Ending Page	172
Page Count	18
File Format	PDF
ISSN	09300708
Journal	Mineralogy and Petrology
Volume Number	71
Issue Number	3-4
e-ISSN	14381168
Language	English
Publisher	Springer-Verlag
Publisher Date	2001-05-02
Publisher Place	Wien
Access Restriction	One Nation One Subscription (ONOS)
Content Type	Text
Resource Type	Article
Subject	Geophysics Geochemistry and Petrology

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The Nakhla Martian meteorite is a cumulate igneous rock. Comment on “Glass-bearing inclusions in Nakhla (SNC meteorite) augite: heterogeneously trapped phases” (2001) by M. E. Varela, G. Kurat, and R. Clocchiatti

The Nakhla Martian meteorite is a cumulate igneous rock. Comment on “Glass-bearing inclusions in Nakhla (SNC meteorite) augite: heterogeneously trapped phases” (2001) by M. E. Varela, G. Kurat, and R. Clocchiatti

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Glass-bearing inclusions in Nakhla(SNC meteorite) augite: heterogeneouslytrapped phases

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