OVERVIEW OF THE PETROLOGIC RECORD OF FLUID-FLOW DURING REGIONAL METAMORPHISM IN NORTHERN NEW-ENGLAND

Modal, mineral chemical, and whole-rock chemical data for 266 samples of pelitic schist, micaceous sandstone, and micaceous limestone were u sed to determine the amount and direction of fluid flow during Buchan- type regional metamorphism in south-central Maine and during Barrovian -type regional metamorphism in east-central Vermont. Metamorphism occu rred in Maine at pressure almost-equal-to 3.5 kb (10-15 km depth) and temperature increasing from almost-equal-to 400-degrees-C in the bioti te zone to almost-equal-to 550-degrees-C in the sillimanite zone. Meta morphism in Vermont occurred at pressure almost-equal-to 7 to 8 kb (25 -30 km depth) and temperature increasing from almost-equal-to 475-degr ees-C in the biotite zone to almost-equal-to 550-degrees-C in the kyan ite zone. Field, petrologic, and isotopic data suggest that pervasive fluid flow associated with prograde mineral reactions in maine and Ver mont was mostly parallel to lithologic layering, subhorizontal, and in the direction of increasing temperature. Calculated amounts of fluid flow, recorded by progress of prograde devolatilization reactions in t he different lithologies and measured as a volumetric time-integrated flux, are similar in both areas and lie in the following ranges: pelit ic schists, (1-26) . 10(5) cm3 fluid/cm2 rock; micaceous sandstones, ( 1-42) . 10(5) cm3/cm2; micaceous limestones, (0.02-24) . 10(5) cm3/cm2 . Evaluation of errors introduced from a variety of sources suggests t hat calculated values are probably uncertain by no more than an order of magnitude. Substantial reactive fluid flow appears to be a fundamen tal aspect of regional metamorphism to depths of at least 30 km in nor thern New England at grades ranging from those of the biotite zone to those of the sillimanite zone. Although flow was not excluded from any particular rock type, geometry was greatly controlled at the outcrop scale by enhanced flow in more permeable layers (such as pelitic schis ts) and restricted flow in other layers (such as relatively pure carbo nate rocks). In situ metamorphic rock permeability, estimated from val ues of time-integrated flux and Darcy's law, is in the range 6 . 10(-1 6) to 1 . 10(-12) cm2 (0.06-100 mud) with an uncertainty of +/-2 order s of magnitude. Metamorphic fluid flow was an essential driving force of prograde mineral reactions but probably had negligible influence on the thermal history of either terrane.