Restoration of the elemental and stable-isotopic compositions of diffusionally altered minerals in slowly cooled rocks

Article Abstract:

A simple, versatile material-balance method restores the former elemental and stable-isotopic compositions of diffusionally altered minerals in slowly cooled rocks. The method does not require prior knowledge of thermodynamic conditions. The reconstructed mineral compositions help to understand the petrogenetic processes and conditions during the formation of the rocks. Case studies involving rocks from Skaergaard and the Himalayas demonstrate the efficiency of the technique in deciphering processes of regional crustal dynamics, ore metallogeny and igneous fluid dynamics and petrogenesis.

Observations, Rocks, Metamorphic, Metamorphic rocks

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Pseudotachylyte petrogenesis: constraints from the Sudbury impact structure

Article Abstract:

Frictional comminution and preferential melting of host material have formed the pseudotachylytes in the high-speed slip regions of the Sudbury igneous complex, Ontario, Canada. A meteorite collision 1.85 Ga ago produced the initial fracture. The selective accumulation of hydrous ferromagnesian phases occurred during pseudotachylyte formation. The pseudotachylytes are magmatic rocks, and contain quartz and plagioclase as mineral clast inclusions. They contain pre-impact, syn- to immediately post-impact and post-impact assemblages.

Natural history, Sudbury, Ontario

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The determination of partial melt compositions of peridotitic systems by melt inclusion synthesis

Article Abstract:

The development of a method of melt inclusion synthesis within olivine crystals aims to determine the composition of melt present in a partly molten periodotite assemblage. Melt composition is calculated from the glass inclusion composition through the addition of olivine using the Roeder and Emslie Fe/Mg exchange coefficient, and is close to the dry melting trend established by Falloon and Green.

Analysis, Composition, Olivine, Mineral-melt partitioning

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