Diagenesis of Oligocene-Miocene vitric tuffs to montmorillonite and K-feldspar deposits, Durango, Mexico

Abstract

The two minerals were formed separately from rhyodacitic to rhyolitic pyroclastic deposits in a closed hydrologic system and diagenetically altered following two different patterns. In material deposited on dry land the glass was completely replaced by K-feldspar, and the interstices between the replaced glass bubbles and shards were filled with chalcedony, quartz, and albite. Pyroclastic material deposited in an alkaline lacustrine environment were diagenetically altered to montmorillonite, which formed the bentonitic tuffs widely exposed beneath the K-feldspar-rich tuff. -from Author