Metamorphic grade and porosity and permeability controls on mafic phyllosilicate distributions in a regional zeolite to greenschist facies transition of the North Shore Volcanic Group, Minnesota

A low‐grade metamorphic model for the Miocene volcanic sequences in the Andes of central Chile

“…The changes in assemblage between the massive flow part with rare amygdales (5146) and the highly amygdaloidal zone (5145) is similar to features reported from very low grade metabasites in Minnesota (Schmidt & Robinson 1997). There, the differences were attributed to the effect of high primary porosity in the amygdaloidal flow zones resulting in extensive fluid/rock interaction driven by advective fluid movement allowing extensive mass transfer of components such as Al.…”

“…Similar continuous sequences have also been recorded in mafic phyllosilicates from metabasites of the Point Sal Ophiolite (Bettison-Varga et al 1991), Nesjavellir geothermal field (Schiffman & Fridleifsson 1991), and eastern North Greenland (Robinson et al 1993). Such a continuous transition contrasts with other studies in which the smectite to chlorite transition proceeds via a series of discontinuous steps, involving the discrete phases smectite, corrensite, and chlorite, as in La Palma (Schiffman & Staudigel 1995) and Minnesota (Schmidt & Robinson 1997). To explain these differences, Schiffman (1995) suggested that the continuous mixed-layered chlorite/smectite sequence represents a metastable progression associated with low degrees of fluid/rock interaction, whereas the discontinuous transition is an equilibrium progression associated with high fluid/rock ratios.…”

“…This zonal break was marked by a change from Zone 2 with smectite-only mafic phyllosilicates into Zone 3 where the clay type was dependent on morphological character of the samples, exactly as recorded in the VNSS. This changeover from Zones 2 to 3, was estimated to take place at c. 150°C (Schmidt & Robinson 1997). The change from Zone 3 to Zone 4 in the Minnesota rocks is marked by the appearance of prehnite and pumpellyite, and was estimated to take place over the range 220-260°C; such a change is not observed in the VNSS.…”

“…: achieving a Xf^g value that is being buffered by the wholerock composition, and thus represents the first steps towards attainment of an equilibrated system (Bevins i t al. 1991;Schmidt & Robinson 1997).…”

Chlorite, Corrensite, and Chlorite-Mica in Late Jurassic Fluvio-Lacustrine Sediments of the Cameros Basin of Northeastern Spain

“…Both phases are commonly found as a product of hydrothermal alteration of various types of igneous rocks (Meunier et al, 1988;Shau et al, 1990;Shau and Peacor, 1992;Schiffman and Staudigel, 1995;Bettison-Varga and Mackinon, 1997;Schmidt and Robinson, 1997) or related to diagenesis of volcanoclastic sedimentary materials (Almon et al, 1976;Chang et al, 1986;Peacor, 1994a, 1994b). In addition, they are frequently associated with ancient marine evaporites (Bodine and Madsen, 1987) or lacustrine mudrocks (April, 1981;Hillier, 1993).…”