Bedrock Geology of the Deep River Area, Connecticut

Guidebook for field trips in Connecticut and adjacent areas of New York and Rhode Island: New England Intercollegiate Geological Conference 77th annual meeting, Yale University, New Haven, Connecticut, October 4-6, 1985: Trip A

Structure and Petrology of the Willimantic Dome and the Willimantic Fault, Eastern Connecticut

Guidebook for field trips in Connecticut and south central Massachusetts: New England Intercollegiate Geological Conference 74th annual meeting, University of Connecticut, Storrs Connecticut , October 2 and 3, 1982: Trip P-

Geochemistry of Early Devonian calc-alkaline plutons in the Merrimack Belt: implications for mid-Paleozoic terrane relationships in the New England Appalachians

A series of northeast-trending plutons extending from northeastern Massachusetts to southeastern Maine intruded the metasedimenlary rocks of the Merrimack belt. The Early Devonian Dracut, Sweepstakes, Island Pond. Exeter, and Webhannet plutons are metaluminous and, with the exception of the granitie Webhannet pluton, are dominantly mafic to intermediate in composition. The plutons are calc-alkaline in character and have major, minor, and trace clement compositions typical of magmas generated at destructive plate margins. These characteristics include mid- to high-K contents, enrichment of LII.E, LREE, Ba. and Sr. and negative Nb and Ta anomalies. Whole-rock chemical data indicate that the plutons of the Merrimack belt arc similar in every measured geochemical parameter to ca. 400 Ma mafic to intermediate rocks of the New Hampshire Plutonic Suite. These similarities suggest that both groups of plutons were emplaced within the same magmatic arc and belong to the same magmatic suite. A magmatic suite common to both the Merrimack belt and Central Maine terrane suggests that the two lithotectonic zones were proximal to each other at ca. 400 Ma. Trace element differences between Merrimack belt and Sharpners Pond rocks suggest (hat the Putnam-Nashoba terrane represents a separate arc. Located in the Central Maine terrane of New Hampshire, the Rochester pluton is geochemically distinct from the Siluro-Devonian plutons of the Merrimack belt and New Hampshire Plutonic Suite. The Rochester pluton has alkaline affinities but retains overall calc-alkaline features. High concentrations of incompatible elements (K, Ti, P, Ba, Rb, Zr) in the Rochester pluton are markedly similar to those observed in the 360 Ma Hardwick Tonalite of Massachusetts. The strong geochemical correlation between the Rochester and Hardwick plutons implies derivation from the same magmatic event and a common, Late Devonian origin. We suggest that these plutons may have originated in response to pull-apart rifting related to late-stage Acadian transpression. RÉSUMÉ Une série de plutons orientée vers Ie nord-est s'élendant du nord-est du Massachusetts au sud-est du Maine, fait intrusion dans les roches métasédimentaires de la ceinture de Merrimack. Les plutons du Devonien inférieur Dracut Sweepstakes. Island Pond. Exeter et Webhannet constituent des intrusions métalumincuses et, mis à part le pluton granitique Webhannet, ils ont une composition en prédominance mafique à intermédiare. Les plutons ont une conformation calco-alcalinc et leur composition du point de vue des principaux éléments présents, de ceux présents en quantité restreinie et des éléments traces est représentative des magmas produits aux frontièrs de plaques destructives. Leurs caractéristiques component nolamment une teneur movenne à élevée en potassium, un enrichissement en LILEen éléments de terres rares légères. en BA et en SR. de mème que des anomalies négatives de Nb et Ta. Les données de la roche totale révèlent que les plutons de la ceinture de Merrimack sont semblables. sous le rapport de chacun des paramètres géochimiques mesurés. aux magmas mafiques à intermédiaires d'il y a environ 400 Ma du cortège plutonique du New Hampshire. Ces similarités permeltent de supposer que les deux groupes de plutons ont été insérès à l’intérieur du mème arc magmatique et qu'ils appartienment au mème cortège magmatique. L'existence d'un cortège magmatique commun à la ceinture de Merrimack et au terrane de Central Maine permet de supposer que les deux zones lithotectoniques étaient proximales I'une de 1'autre il y a environ 400 Ma. Les différences par rapport aux éléments traces entre les magmas de la ceinture de Merrimack et ccux de Sharpners Pond laissent supposer que le terrane de Putnam-Nashoba rcprisenie un arc distinct Le pluton Rochester, situé dans le terrane de Central Maine du New Hampshire, est géochimiquement distinct des plutons siluro-dévoniens de la ceinture de Merrimack et du cortège plutonique du New Hampshire. Le pluton Rochester présente des affinités alcalines tout en conservant ses carectéristiques calco-alcalines générales. Les concentrations élevées d'éléments incompatibles (K, Ti, P, Ba, Rb, Zr) dans le pluton Rochester sont manifestement semblables à celles observers dans la tonalite d'il y a 360 Ma de Hardwick, au Massachusetts. La correlation géochimique prononcée entre les plutons Rochester et Hardwick suppose qu'ils découlent du mème phénoméne magmatique et qu'ils ont une origine commune remontant au Dévonien supérieur. Nous pensons que ces plutons tirent probablement leur origine d'une réaction a une distension d'écartemcnt apparentée à une transpression acadienne tardive. Traduit par la rédactio

Insights into the Acadian orogeny, New England Appalachians: a provenance study of the Carrabassett and Kittery formations, Maine

The Central Maine Basin and Merrimack Trough are Silurian basins that formed adjacent to or were accreted to the Laurentian margin during the Acadian orogeny. The Early Devonian Carrabassett Formation of the Central Maine Basin and the Kittery Formation of the Merrimack Trough have major and trace element compositions indicative of a passive continental margin provenance, not unlike the older formations of the Central Maine Basin that are thought to have been derived from Laurentian sources. However, both the Carrabassett and Kittery formations have paleocurrent indicators of outboard sources. The Carrabassett Formation is one of the youngest formations of the Central Maine Basin and was deposited just prior to the Acadian orogeny. The Carrabassett and Kittery formations have major and trace element concentrations suggestive of passive margin turbidites derived from intermediate to felsic sources, inconsistent with a juvenile Avalonian provenance. The Carrabassett Formation contains detrital zircon grains that match the ages of peri-Gondwanan Ganderia. Unlike the dominance of positive bulk-rock εNd values that are characteristic of Avalonia, Ganderia has negative εNd values that are a better match for the negative εNd values of the Carrabassett and Kittery formations. However, Ganderia accreted to Laurentia during the Salinic orogeny, prior to the deposition of the Carrabassett Formation, and was basement to the sediments of the Central Maine Basin upon which the Carrabassett and other formations were deposited. Wedging of Ganderia by Avalonia during the initial stages of the Acadian orogeny may have uplifted Ganderia, forming highlands outboard of the Central Maine Basin that served as the source of the Carrabassett Formation sediments. RÉSUMÉ Le bassin central du Maine et la cuvette de Merrimack constituent des bassins siluriens s’étant formés le long de la marge laurentienne ou s’y étant accrétés au cours de l’orogenèse acadienne. La Formation du Dévonien précoce de Carrabassett, dans le bassin central du Maine, et la Formation de Kittery, de la cuvette de Merrimack, présentent des compositions en éléments majeurs et traces signalant une provenance d’une marge continentale passive, à l’instar des formations plus âgées du bassin central du Maine qu’on pense originaires de sources laurentiennes. Les formations de Carrabassett et de Kittery comportent toutefois des indicateurs de paléocourants de sources extérieures. La Formation de Carrabassett constitue l’une des formations les plus récentes du bassin central du Maine; elle s’est mise en place juste avant l’orogenèse acadienne. Les caractéristiques géochimiques et géochronologique des formations de Carrabassett et de Kittery pourraient par conséquent permettre l’identification du terrane de collision. Les formations de Carrabassett et de Kittery possèdent des concentrations d’éléments majeurs et traces évoquant les turbidites de marge passive en provenance de sources intermédiaires à felsiques, ce qui est contradictoire avec une origine avalonienne juvénile. La Formation de Carrabassett comporte des grains détritiques de zircon correspondant aux âges du Ganderia périgondwanien. Contrairement à la prédominance de concentrations εNd positives de roche en vrac caractéristiques d’Avalonia, Ganderia présentent des concentrations εNd négatives qui cadrent mieux avec les concentrations εNd négatives des formations de Carrabassett et de Kittery. Ganderia s’est toutefois accrété à Laurentia au cours de l’orogenèse salinique, avant le dépôt de la Formation de Carrabassett, et il a constitué le socle des sédiments du bassin central du Maine sur lesquels Carrabassett et d’autres formations se sont déposées. L’enfoncement d’Avalonia sous Ganderia au cours des stades initiaux de l’orogenèse acadienne pourrait avoir soulevé Ganderia, formant un massif à l’extérieur du bassin central du Maine qui a servi de source aux sédiments de la Formation de Carrabassett. [Traduit par la redaction

Evidence for syntectonic crystallization for the mudstone to slate transition at Lehigh gap, Pennsylvania, U.S.A.

Data primarily for phyllosilicates have been obtained for the continuous transitional sequence from mudstone to slate with well-developed slaty cleavage at Lehigh Gap, Pennsylvania, and for slates from quarries in the same area. Samples were studied by optical microscopy, powder X-ray diffraction and electron microprobe analysis, with emphasis on transmission and analytical electron microscopy. Mineral grains are virtually free of deformation-induced strain. Concomitant with the gradual development of cleavage normal to bedding the following changes are observed or confirmed: (1) the orientation of phyllosilicate grains changes discontinuously from being preferentially parallel to bedding to being parallel to cleavage; (2) crystal imperfections as expressed in layer terminations, low angle grain boundary-like features and other defects decrease in density; (3) complex mixed layering is replaced by homogeneous packets of layers of single phases and (4) illite transforms to muscovite, with increase in K + Al and change from a 1Md to 2M polytype. Slaty cleavage apparently develops due in part to pressure solution of phyllosilicates oriented parallel to bedding, mass transport of components, and crystallization to form new grains parallel to cleavage. It reflects transitions from imperfect, metastable phases toward ordered stable phases in a low temperature (~225[deg]C) metamorphic environment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26438/1/0000526.pd

Frictional Instabilities and Carbonation of Basalts Triggered by Injection of Pressurized H2O- and CO2- Rich Fluids

The safe application of geological carbon storage depends also on the seismic hazard associated with fluid injection. In this regard, we performed friction experiments using a rotary shear apparatus on precut basalts with variable degree of hydrothermal alteration by injecting distilled H2O, pure CO2, and H2O + CO2 fluid mixtures under temperature, fluid pressure, and stress conditions relevant for large-scale subsurface CO2 storage reservoirs. In all experiments, seismic slip was preceded by short-lived slip bursts. Seismic slip occurred at equivalent fluid pressures and normal stresses regardless of the fluid injected and degree of alteration of basalts. Injection of fluids caused also carbonation reactions and crystallization of new dolomite grains in the basalt-hosted faults sheared in H2O + CO2 fluid mixtures. Fast mineral carbonation in the experiments might be explained by shear heating during seismic slip, evidencing the high chemical reactivity of basalts to H2O + CO2 mixtures