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Department of Geology, Indiana University, Bloomington, IN 47405, USA
A survey of detrital opaque Fe-Ti oxide minerals in Holocene sands derived exclusively from known source rocks in the Rocky Mountains, USA (semi-arid climate, high relief) and the Appalachian Mountains, USA (humid climate, low relief) shows that, despite obvious differences in weathering rates, the abundance of detrital ilmenite relative to parent rocks is similar in these two regions. Because ilmenite is very common in many crystalline rocks, ilmenite is considered to be a useful Fe-Ti oxide mineral for varietal studies. About 30% to 50% of detrital Fe-Ti oxide minerals are polymineralic grains with intergrowths of two or more phases. Discriminant function analysis indicates that morphological varieties of detrital Fe-Ti oxide minerals in combination with their chemical compositions are useful guides to provenance. An igneous or metamorphic source of 96% of the Holocene samples is correctly identified by this method.
The method is used to determine the relative contribution of igneous and metamorphic source rocks to the sandstones of the part of the Tertiary Renova Formation, which was deposited within a dissected magmatic arc in southwestern Montana, USA. A separate discriminant function is calculated using the chemical compositions of detrital ilmenite and morphological properties of detrital Fe-Ti oxide minerals in Rocky Mountain Holocene sands. Classification of detrital Fe-Ti oxide minerals in Renova sandstones using this function suggests that igneous and metamorphic rocks contributed 77% and 23% respectively to the Renova sandstones in this area.
