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    Origin of rocks and rock sequences

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    (i) What environment and processes are involved in the formation of the following rock types:
    Shale or mudstone

    (ii) Using relative dating methods place the following events in the correct chronological order (most recent first). Some events may be used more than once.
    ? A time gap in deposition
    ? Deposition of shale
    ? Intrusion of granite pluton
    ? Folding of shale
    ? Metamorphism of shale
    ? Deposition of limestone
    ? Uplift, weathering and erosion

    (ii) Using the above events and the information in the answer to (i) state a brief geological history of the area starting with the oldest event.

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    Solution Preview

    1. Granite: this is an igneous intrusive (plutonic) rock of felsic to intermediate character. That is to say, it occurs via the intrusion of magma at depth and cools in that environment forming "largish" (phaneritic - meaning visually discernible) crystals due to slow cooling. Its chemistry - being felsic - would refer to it occurring in a continental zone where the intruding mafic magma would interact with the thicker continental crust during ascension (refer in your text to Bowen's reaction series) or see: http://maps.unomaha.edu/Maher/geo117/bowens.html

    Thus in direct answer - intrusion of magma in a continental region followed by slow underground cooling could yield a granite.

    Slate: Slate is a low grade metamorphic rock derived from clay-sized particles (and generally clay minerals - hydrated phyllosilicates mainly see: http://mineral.galleries.com/minerals/silicate/clays.htm for details) along with other secondary minerals/elements that generally add color and/or other minor characteristics. ...

    Solution Summary

    This solution examines the origin of several named rock types, a "Steno's Principles" type reorganization of rock strata and then uses these strata to form a geologic history.