Open AccessEnvironmental and chemical controls on palagonitization
Author(s) -
Pauly Bruce D.,
Schiffman Peter,
Zierenberg Robert A.,
Clague David A.
Publication year - 2011
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2011gc003639
Subject(s) - geology , diagenesis , mineralogy , geochemistry , dissolution , chemistry
Palagonitized sideromelane from submarine volcaniclastic, seafloor volcanic, marine phreatomagmatic, lacustine phreatomagmatic, and subglacial volcanic settings was investigated using in situ microanalysis to test if palagonite composition and texture are related to depositional environment. Palagonitization extent varies linearly and inversely with original sample porosity, suggesting that porosity is a controlling factor of palagonitization. Water absorbance of reflected infrared light varies linearly with water content derived from electron microprobe totals. Palagonite water content has a linear, inverse relationship to palagonitization extent. REEs are immobile during palagonitization, so they can be used to construct isocon diagrams for estimating major‐element concentration changes. Major‐element and overall mass changes during palagonitization vary widely (particularly for FeO and TiO 2 ) and indicate that palagonitization cannot be an isovolumetric process. These parameters depend strongly on original sideromelane composition, thus requiring composition to be taken into account when performing global oceanic cation flux calculations. Subalkaline sideromelane dissolves much more rapidly than alkaline sideromelane during palagonitization. Two styles of palagonitization, burial‐diagenesis (relatively long‐duration, low water/rock; passive fluid circulation) and hydrothermal (relatively short‐duration, high water/rock; hydrothermal fluid circulation), are recognized. Observed palagonite REE concentration gradients indicate that sideromelane dissolution must continue in the zone behind the advancing palagonitization front. MgO was found to be highly mobile during palagonitization. Observed palagonite MgO gradients are not developed during sideromelane dissolution, but instead record initiation of syn‐ and/or post‐palagonitization conversion of the gel‐palagonite layer to a phyllosillicate layer, consistent with evolution of sideromelane alteration layers toward equilibrium with the solution.