Geochemistry permits distinction of two broad groups of volcanic rocks distinguished from the Avalon zone of southeastern New England. An alkalic suite is relatively enriched in K, Rb, Y, Zr, Nb, Zn, La, Ce, but lower in Al, Sr, and Ba compared to a calc-alkaline suite. The alkalic suite is compositionally similar to plutonic rocks that range in age from Late Ordovician to Devonian, whereas the calc-alkaline suite is similar to late Proterozoic plutonic rocks. Geochemical discriminant criteria developed in this chapter indicate that a number of the volcanic units previously have been incorrectly grouped and misinterpreted.
Summary Mid-Devonian to late Palaeozoic igneous activity in the N American Appalachians occurs in the eastern portions of the orogen. Represented radiometric ages are almost continuous from 250 to 370 Ma and older, thus overlapping Acadian and Alleghanian orogenic events. In many instances igneous activity is generally similar to that initiated earlier in the Palaeozoic. Plutonic rocks consist of granitoids with subordinate intermediate to mafic rocks. Plutonism is mainly of ‘Caledonian’ or alkalic variety and is dissimilar to subduction-related magmatism of the Andean type. Regional synthesis indicates that some general distinctions of plutonism occur across strike as well as along strike from S to N within the orogen in eastern N America. In the southern Appalachians granites and minor contemporaneous gabbros occur in all lithotectonic zones between the Blue Ridge and the Coastal Plain. These plutons are commonly syn-kinematic in the eastern Piedmont where Alleghanian deformation and metamorphism are best exhibited, but are late- to post-kinematic to the W. The rocks include metaluminous biotite and megacrystic granites and lesser peraluminous two-mica granites. Late Palaeozoic igneous activity is sparse to absent in the central Appalachians. In New England several kinds of mid-Devonian to Carboniferous igneous activity are represented. Biotite and biotite + muscovite granitoids dominate the central terranes, whereas the more easterly Avalon zone is intruded by alkalic-peralkalic plutonic rocks and contains minor bimodal volcanics. Final Permian plutonism includes intrusion of homogeneous metaluminous to peraluminous granite. Within the Canadian Maritimes biotite and megacrystic granites followed by mildly alkalic varieties dominate the Devonian-Carboniferous plutons of New Brunswick and Newfoundland, whereas muscovite + biotite rocks are prominent in the Meguma terrane of Nova Scotia. Volcanism, which is bimodal, is best documented in New Brunswick and northern Nova Scotia. Igneous activity of Permian age is not recognized in the Canadian Maritimes. The petrological diversity together with the considerable span of time represented by the late Palaeozoic igneous activity in the N American Appalachians indicates repeated and locally prolonged anatexis of a variety of heterogeneous crustal sources. The alkalic and bimodal suites are characteristic of extensional or anorogenic tectonics. The more aluminous rocks are generally compositionally similar to the Caledonian and, to a lesser extent, the Hercynian suites of Europe. Overall the igneous activity may reflect relatively independent rifting and accretion of small crustal plates of diverse thicknesses and compositions in which magmatism was not related to a simple subduction island-arc setting.
Knowledge of surface and subsurface geology and geotechnical properties is fundamental to planning, developing, and modernizing transportation systems. Through dynamic coupling of readily available areal geographic information system coverages and subsurface borehole data stored in a relational database, a spatially referenced digital catalog of borehole data was created for two pilot areas in Rhode Island. The borehole database was populated with data derived from Rhode Island Department of Transportation geotechnical reports and supplemental data from the U.S. Geological Survey groundwater site inventory system and local storm water and sewer projects. Most of these data were previously maintained in paper format, making historical or interproject data comparisons virtually impossible. Unification of these data in a single relational database yields two primary benefits: ( a) historical data are readily accessible for review and therefore can be incorporated easily into the planning stages of new projects and ( b) sophisticated analysis of the region becomes possible with access to data from multiple projects with both spatial and temporal coverage. Geologic data include bedrock geology, surface outcrops, unconsolidated materials, soil type, topographic and orthophotographic base maps, and location of boreholes and wells. Subsurface data include land surface elevation, depth to water table, depth to bedrock, presence of fill, high and low blow-count zones, and organic sediment. The digital catalog is distributed on a CD-ROM that includes ArcView project files and an Access relational database. The borehole data are also accessible through the Internet, with retrieval access for all users and data entry privileges for registered users.
ABSTRACT The Avalon terrane of southeastern New England is a composite terrane in which various crustal blocks may have different origins and/or tectonic histories. The northern part (west and north of Boston, Massachusetts) correlates well with Avalonian terranes in Newfoundland, Nova Scotia, and New Brunswick, Canada, based on rock types and ages, U-Pb detrital zircon signatures of metasedimentary rocks, and Sm-Nd isotope geochemistry data. In the south, fewer data exist, in part because of poorer rock exposure, and the origins and histories of the rocks are less well constrained. We conducted U-Pb laser ablation–inductively coupled plasma–mass spectrometry analysis on zircon from seven metasedimentary rock samples from multiple previously interpreted subterranes in order to constrain their origins. Two samples of Neoproterozoic Plainfield Formation quartzite from the previously interpreted Hope Valley subterrane in the southwestern part of the southeastern New England Avalon terrane and two from the Neoproterozoic Blackstone Group quartzite from the adjacent Esmond-Dedham subterrane to the east have Tonian youngest detrital zircon age populations. One sample of Cambrian North Attleboro Formation quartzite of the Esmond-Dedham subterrane yielded an Ediacaran youngest detrital zircon age population. Detrital zircon populations of all five samples include abundant Mesoproterozoic zircon and smaller Paleoproterozoic and Archean populations, and are similar to those of the northern part of the southeastern New England Avalon terrane and the Avalonian terranes in Canada. These are interpreted as having a Baltican/Amazonian affinity based primarily on published U-Pb and Lu-Hf detrital zircon data. Based on U-Pb detrital zircon data, there is no significant difference between the Hope Valley and Esmond-Dedham subterranes. Detrital zircon of two samples of the Price Neck and Newport Neck formations of the Neoproterozoic Newport Group in southern Rhode Island is characterized by large ca. 647–643 and ca. 745–733 Ma age populations and minor zircon up to ca. 3.1 Ga. This signature is most consistent with a northwest African affinity. The Newport Group may thus represent a subterrane, terrane, or other crustal block with a different origin and history than the southeastern New England Avalon terrane to the northwest. The boundary of this Newport Block may be restricted to the boundaries of the Newport Group, or it may extend as far north as Weymouth, Massachusetts, as far northwest as (but not including) the North Attleboro Formation quartzite and associated rocks in North Attleboro, Massachusetts, and as far west as Warwick, Rhode Island, where eastern exposures of the Blackstone Group quartzite exist. The Newport Block may have amalgamated with the Amazonian/Baltican part of the Avalon terrane prior to mid-Paleozoic amalgamation with Laurentia, or it may have arrived as a separate terrane after accretion of the Avalon terrane. Alternatively, it may have arrived during the formation of Pangea and been stranded after the breakup of Pangea, as has been proposed previously for rocks of the Georges Bank in offshore Massachusetts. If the latter is correct, then the boundary between the Newport Block and the southeastern New England Avalon terrane is the Pangean suture zone.
The proposed work extends and builds upon the researchers' present transportation project, GEOLOGIC TRANSPORTATION MAPS FOR THE 21ST CENTURY. During this early study, their partners from the Rhode Island Department of Transportation (RIDOT), Pare and Haley-Aldrich Engineering companies repeatedly stated that the highest priority geoscience need in the planning of transportation systems are core logs and water-well logs in which the depth to bedrock and other geotechnical information are clearly defined. As a consequence, the researchers propose to develop a digital database for core- and water well-log data that can be accessed through the Internet. The web interface will be designed with both retrieval and data submission capabilities. The interactive web page will permit users to selectively access core data by town, county, quadrangle, major road or transit way, etc. The development of such a web-based database, containing accurate locations and geoscience information of existing cores, will cut costs, speed the planning process, and permit informed decisions for siting additional critical locations for new drill sites. In turn, the computer template can then be used for future logging of water-wells and cores. In addition, the researchers intend to demonstrate how core- and water log data in digital format can be efficiently used to construct subsurface cross-sectional profiles, isopach maps, and other types of maps. Examples of data to be displayed on these figures include depth to bedrock, depth to water table, trends of fractures and other zones of weakness in the bedrock, and stratigraphic cross-sections of Quaternary deposits.
Research Article| November 01, 1978 Significance of fossiliferous Middle Cambrian rocks of Rhode Island to the history of the Avalonian microcontinent J. W. Skehan; J. W. Skehan 1Weston Observatory, Department of Geology, and Geophysics, Boston College, Weston, Massachusetts 02193 Search for other works by this author on: GSW Google Scholar D. P. Murray; D. P. Murray 1Weston Observatory, Department of Geology, and Geophysics, Boston College, Weston, Massachusetts 02193 Search for other works by this author on: GSW Google Scholar A. R. Palmer; A. R. Palmer 2Department of Earth Sciences, State University of New York at Stony Brook, Stony Brook, New York 11794 Search for other works by this author on: GSW Google Scholar A. T. Smith; A. T. Smith 3Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802 Search for other works by this author on: GSW Google Scholar E. S. Belt E. S. Belt 4Department of Geology, Amherst College, Amherst, Massachusetts 01002 Search for other works by this author on: GSW Google Scholar Geology (1978) 6 (11): 694–698. https://doi.org/10.1130/0091-7613(1978)6<694:SOFMCR>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. W. Skehan, D. P. Murray, A. R. Palmer, A. T. Smith, E. S. Belt; Significance of fossiliferous Middle Cambrian rocks of Rhode Island to the history of the Avalonian microcontinent. Geology 1978;; 6 (11): 694–698. doi: https://doi.org/10.1130/0091-7613(1978)6<694:SOFMCR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Middle Cambrian trilobites of Acado-Baltic affinities have been found in southern Narragansett Bay, Rhode Island, in phyllites previously mapped as part of the Pennsylvanian stratigraphy of the Narragansett Basin. The trilobite-bearing phyllites form the basal unit of an approximately 1-km-thick sequence that has undergone four episodes of folding and cleavage formation.Three different trilobites are represented. Badulesia tenera (Hartt), which gives a diagnostic medial Middle Cambrian age, is also known from New Brunswick, eastern Newfoundland, southern Germany, northern Spain, and eastern Turkey. This species in northern Spain characterizes a subzone within the Middle Cambrian Badulesia zone correlating approximately with the lower part of the Paradoxides paradoxissimus zone of northern Europe.Nearby in Newport, Rhode Island, a sequence of maroon and green clastic sediments rests unconformably on Precambrian igneous rocks and sediments. If these should be proven to be Lower Cambrian, this succession in southern Narragansett Bay would be the most complete Cambrian succession yet recognized in southern New England and possibly a nearly complete record of sedimentation for this area for the entire Cambrian Period.These well-exposed rocks are part of a distinctive succession of upper Precambrian and lower Paleozoic rocks and are interpreted as a fragment of the Avalonian platform or microcontinent, closely related to rocks of the eastern margin of the northern Appalachians and the western margin of western Europe. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Includes 14 chapters on the Appalachian orogen, 15 of the Ouachita orogen, and a chapter on the connection between them beneath the eastern Gulf Coastal Plain. The Appalachian chapters synthesize the geologic development of the orogen by tectonostratigraphic intervals (pre-orogenic, Taconic, Acadian, Alleghanian, and post-Alleghanian), and also treat Paleozoic paleontologic control, regional geophysics, thermal history of the crystalline terranes, parts of the orogen buried beneath the Atlantic and eastern Gulf coastal plains, regional geomorphology, mineral and energy resources; an integration chapter also is included. The Ouachita chapters cover physical stratigraphy and biostratigraphy of the Paleozoic rocks, structural geology, a synthesis of the subsurface geology beneath the western Gulf Coastal Plain, a review of the mineral and energy resources, regional geophysics, and a tectonic synthesis. Twelve excellent plates provide four-color geologic maps, structural cross sections, tectonic syntheses, and geophysical maps; a black-and-white synthesis of Appalachian mineral deposits, and a reflection seismic cross section.
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