Multiple Episodes of Clay Alteration at the Precambrian/Paleozoic Unconformity, Appalachian Basin: Isotopic Evidence for Long-Distance and Local Fluid Migrations

Abstract

Abstract--Chlorite and illite are commonly associated with ubiquitous secondary K-rich feldspar in the rocks located immediately above and below the Precambrian-Paleozoic unconformity in southwestern Ontario, and elsewhere in the mid-continent of North America. This alteration assemblage is attributed to long-distance migration of hot brines driven westward by orogenic processes originating along the eastern seaboard of North America. The ~D and 8180 values of chlorite and illite, plus K-Ar dates for secondary K-rich feldspar and illite, were used to determine the nature, origin, and timing of the fluids that altered Precambrian granites and their overlying rocks in southwestern Ontario. The ~80 values of the chlorite-forming fluids are best explained by initial hot brines (~ 150~ evolved mostly from seawater. Secondary K-rich feldspar formation followed shortly thereafter, as the fluids cooled and perhaps mixed with meteoric water. Regional migration of the brines was induced by Taconic orogenic events to the east. The hydrogen and oxygen isotopic compositions for the secondary illite of the early to mid-Carboniferous indicate its crystallization from local meteoric water at low temperatures (40-55~ Infiltration of local meteoric water into the Paleozoic and uppermost altered Precambrian rocks occurred during uplift, erosion, and subaerial exposure of local arches in southern Ontario. The local basement reactivation and associated secondary illite formation in this portion of the North American hinterland was likely a distal expression of east-coast Acadian and Alleghanian orogenic activity.

The interglacial–glacial cycle and geochemical evolution of Canadian and Fennoscandian Shield groundwaters

“…Unlike most other groundwaters, shield brines plot above the GMWL for d 2 H and d 18 O (Fig. 3f), a result of water-rock interaction and silicate hydration Longstaffe, 2000;Ziegler and Longstaffe, 2000). Fennoscandian fluids in d 18 O-Cl plots clearly show a Baltic or paleo-Baltic seawater end-member as a unique end-member, and not the origin of brines (Fig.…”

The Timing of Diagenesis and Thermal Maturation of the Cretaceous Marias River Shale, Disturbed Belt, Montana

“…The degree of illitization of smectite, indicated by the type of stacking order and the percentage of illite layers in diagenetic mixed-layered illite-smectite (I-S), is well known as a gauge of thermal maturity in basins where conversion of smectite to illite (smectite illitization) was caused by burial, and the timing of the illitization can be determined by K-Ar dating (Hoffman et al, 1976; influence clay diagenesis in foreland basins adjacent to tectonic highlands (Morton, 1985;Elliott and Aronson, 1987;Elliott and Aronson, 1993;Ziegler and Longstaffe, 2000;Elliott and Haynes, 2002;Ś rodoń et al, 2009). The conversion of smectite to illite proceeds either by solid-state transformation or dissolution-precipitation reactions; the latter mechanism prevails in fluiddominated systems (Altaner and Ylagan, 1997).…”

Hydrothermal Alteration and Mineralization in the Neves-Corvo Volcanic-Hosted Massive Sulfide Deposit, Portugal. II. Oxygen, Hydrogen, and Carbon Isotopes

“…Therefore, the δD values of the phyllosilicates may have been acquired at temperatures lower than those indicated in Table 3 (cf. Marumo et al, 1980;Graham, 1981;Ziegler and Longstaffe, 2000). This would have little effect on the δD H 2 O calculations for sericite at the temperatures considered here (see Fig.…”