Mount Pleasant Caldera rock. The Intercaldera Sequence comprises formations that crop out from overlying flows in triangularly shaped area, and includes thick volcanic ash (tuff), thick breccia layers, and intermediate to felsic igneous rocks that tend to intrude the above layers and are typically located along caldera margin faults. The Exocaldera Sequence contains ash flow tuffs, mafic lavas, alluvial redbeds, and porphyritic felsic lavas that are distributed across five different layers. The late Caldera-Fill Sequence contains rocks that are similar to those of the outflows of the other, older layers, and comprises two formations and two relatively minor intrusive lava flows. The volcanic
Archean felsic volcanic rocks heavy rare-earth elements than other Archean felsic volcanic rocks) has no plutonic equivalent in the same period. The composition of felsic volcanic rocks are being altered concurrently with shifting granitoid composition. The older GMS-like felsic volcanic rocks formed with similar age of TTG has two implications: Revealing the relationship between Archean felsic volcanic rocks and the granitoids may be difficult. It is because weathering alters the geochemical signatures of the felsic rocks above the Earth's surface. The earliest weathering record can be traced back to 3.8 Ga during Eoarchean. Potassium is enriched but sodium is depleted in these weathered felsic