Basin-Wide Fluid Flow at Plate Boundaries, Major Fault Zones, and Thrust-Loading Settings: What Do the Data Tell Us

Gerald M. Friedman

Along plate boundaries, such as the Dead Sea transform, hydrothermal fluids form carbonates and evaporites. Modern dolomite from this boundary has a strontium-isotopic signature signifying that it derived from a volcanic mantle source. The extrusive magmatic subsurface source which provides on surface the heat (60°C) and saline fluids to form the dolomite also makes the Mg ²⁺ available. The apparent age of the dolomite is >40,770 C-14 years. The dated carbon of the dolomite is inherited and much older than the dolomite which currently forms, where the springs extrude. In the rock record near major fault zones, such as in the Ordovician Arbuckle Group of Oklahoma, dolomitization of limestone occurs with enrichment in heavier carbon and oxygen isotopes. H drothermal fluids once again were responsible for dolomite formation.

Current concepts of basin-wide fluid flow still need to be tested. As an example, foreland basins are said to create favorable conditions for the migration of mineralizing fluids. In the northern Appalachians four thrust-loading episodes of deformation occurred which may have generated multiple brine migration. MVT mineralization and authigenic feldspar are considered diagenetic products of this migration. Yet if hot brines carried concentrations of elements that generate MVT minerals, like barite, then barium should be present in authigenic feldspar. Yet microprobe analysis shows the presence of barium in the cores of the detrital K-feldspar crystals and its absence in the authigenic overgrowths suggesting that the fluids responsible for authigenic K-feldspar may not have been the sa e that produced MVT mineralization; otherwise, enrichment in barium would have been expected in the overgrowths.

Brine-migration diagenesis is not well understood.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995