Unravelling the fluid flow evolution and precipitation mechanisms recorded in calcite veins in relation to Pangea rifting–Newark Basin, USA

Abstract

Calcite veins hosted in the Triassic Stockton, Lockatong and Passaic formations of the Newark Basin are investigated to reconstruct the fluid evolution. To constrain the parameters of calcite precipitation, a microthermometry study was carried, which reveals precipitation of calcite from a low to moderate saline H2O-NaCl fluid (0.4 to 13.2 wt% NaCl equiv.) under low to moderate hydrothermal (137 °C to 232 °C) conditions. This fluid composition is interpreted to reflect mixing between a deep basement-derived heated diluted fluid and relatively low to moderate saline diagenetic formation waters hosted in the different Triassic formations. Carbon and strontium isotope analysis on the vein calcites suggests that these elements are derived from the pre-Triassic basement and the sedimentary cover through fluid-rock interactions. The aforementioned geochemical findings are supported by Rare Earth Elements and Yttrium (REY) systematics and oxygen isotope data.The Late Triassic extensional activity and gravity-driven fluid flow mechanism facilitated the infiltration of meteoric waters to deeper lithostratigraphic units (i.e., Precambrian-Paleozoic basement-Triassic Stockton Formation) where they became heated. In response to the extensional tectonics, the deep-seated hydrothermal basement-derived diluted fluids migrated upward along the tectonic-related fractures and the major faults to upper shallow crustal levels. Here, the heated, diluted meteoric waters were mixed with low, moderately saline, and relatively cooler formation waters, leading to calcite precipitation. The pH increase is suggested to be a contributing factor in the precipitation of calcite.