Essay Questions Flashcards
(4 cards)
How does the difference in Mg/Fe and Al/Cr ratios between the Masinloc and Acoje chromite deposits reflect their respective positions in the crystallization sequence, and what does this imply about the geochemical evolution of the ultramafic complex?
The difference in Mg/Fe and Al/Cr ratios between the Masinloc and Acoje chromite deposits reflects their positions in the crystallization sequence. Masinloc, with higher Mg/Fe and Al/Cr ratios, crystallized earlier and is associated with olivine-rich rocks, indicating it is at a lower stratigraphic level. In contrast, Acoje, with lower ratios, crystallized later with more pyroxene-rich rocks, indicating it is positioned higher in the sequence. This reflects the geochemical evolution of the Zambales ultramafic complex.
If the Masinloc and Acoje deposits originated from the same peridotite layer but crystallized at different times, what tectonic or magmatic processes might have caused their separation into distinct deposits on opposite limbs of a synclinal structure?
The Masinloc and Acoje chromite deposits, originating from the same peridotite layer but crystallizing at different times, may have been separated by tectonic processes such as folding and faulting associated with the synclinal structure. The syncline could have caused the peridotite layer to be exposed on opposite limbs, with deformation occurring during or after the emplacement of the chromite deposits. This tectonic activity would have localized the deposits into distinct areas, with Masinloc at a lower stratigraphic level and Acoje at a higher level, influencing their separate crystallization timelines.
Considering that the Masinloc deposit formed earlier than Acoje, how might this timing have influenced the later alteration processes, such as serpentinization and faulting, that affected the host rocks and chromite ores?
Since the Masinloc deposit formed earlier than Acoje, its earlier crystallization likely exposed the chromite ores to more extensive alteration processes, such as serpentinization and faulting. The earlier-formed Masinloc deposit, located at a lower stratigraphic level, experienced greater serpentinization due to proximity to olivine-rich gabbro and intense fracturing, which allowed for the infiltration of fluids. In contrast, the later-formed Acoje deposit, situated higher in the sequence, was likely subjected to less intense alteration, as the later faulting and serpentinization may have been less extensive in the region due to the temporal separation in their formation.
