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Michael W. Higgins

Publications and source records attributed to Michael W. Higgins.

15 recordsLinked to original sources
USGS2013

Upper crustal structure of Alabama from regional magnetic and gravity data: Using geology to interpret geophysics, and vice versa

Aeromagnetic and gravity data sets obtained for Alabama (United States) have been digitally merged and filtered to enhance upper-crustal anomalies. Beneath the Appalachian Basin in northwestern Alabama, broad deep-crustal anomalies of the continental interior include the Grenville front and New York–Alabama lineament (dextral fault). Toward the east and south, high-angle discordance between the northeast-trending Appalachians and the east-west–trending wedge of overlapping Mesozoic and Cenozoic Gulf Coastal Plain sediments reveals how bedrock geophysical signatures progressively change with deeper burial. High-frequency magnetic anomalies in the Appalachian deformed domain (ADD) correspond to amphibolites and mylonites outlining terranes, while broader, lower-amplitude domains include Paleozoic intrusive bodies and Grenville basement gneiss. Fundamental ADD structures (e.g., the Alexander City, Towaliga, and Goat Rock–Bartletts Ferry faults) can be traced southward beneath the Gulf Coastal Plain to the suture with Gondwanan crust of the Suwannee terrane. Within the ADD, there is clear magnetic distinction between Laurentian crust and the strongly linear, high-frequency magnetic highs of peri-Gondwanan (Carolina-Uchee) arc terranes. The contact (Central Piedmont suture) corresponds to surface exposures of the Bartletts Ferry fault. ADD magnetic and gravity signatures are truncated by the east-west–trending Altamaha magnetic low associated with the Suwannee suture. Arcuate northeast-trending magnetic linears of the Suwannee terrane reflect internal structure and Mesozoic failed-rift trends. Geophysical data can be used to make inferences on surface and subsurface geology and vice versa, which has applicability anywhere that bedrock is exposed or concealed beneath essentially non-magnetic sedimentary cover.

Alabama↗
USGS1989

The Macon Complex; An ancient accretionary complex in the southern Appalachians

The Macon Complex, which extends from eastern Alabama to northern North Carolina, is a late Precambrian–Middle Cambrian accretionary complex comparable in size to the Franciscan Complex of California and Oregon. Much of the complex is tectonic, sedimentary, and metamorphic chaos, properly termed mélange, where well-rounded to angular fragments, blocks, and slabs of contrasting metamorphic grades, different igneous parentages, drastically different sedimentary facies, and different degrees of deformation “float” in highly imbricated and tectonized matrices, the whole having been intruded by Devonian mafic plutons and associated syenites, and by Carboniferous granitic plutons. We have divided the complex into three mélanges that probably reflect different structural regimes within the accretionary wedge: (1) the Juliette mélange, with two tectonostratigraphic lithofacies, the clastic-rich, partly olistostromal Potato Creek facies and the Gladesville facies, rich in mafic and ultramaflc fragments, blocks, and slabs; (2) the Po Biddy mélange, characterized by metamorphosed manganiferous sediments, metavolcaniclastic rocks, graphitic schists, and locally by metamorphosed thinly bedded pyritiferous limestones, and a wide variety of mineral deposits; and (3) the Falls Lake mélange, which is quite similar to the Juliette mélange and probably represents the same tectonostratigraphic horizon in the accretionary prism. The matrices of the mélanges contain a wide variety of metaigneous and metasedimentary exotic clasts, including mafic and ultramaflc rocks. The Macon Complex is structurally overlain by the late Precambrian–Middle Cambrian Little River Complex, made up of thick piles of mostly felsic calc-alkaline metavolcanic rocks, and lesser amounts of metaplutonic rocks, that originated in a continental-margin volcanic arc (Little River arc). Trilobites from near the top of one of the youngest sections are restricted to the upper two-thirds of the Middle Cambrian and are characteristic of the Atlantic faunal province. The Little River Complex is overlain, beneath the Atlantic Coastal Plain, by the African cratonic Northern Florida platform sequence; the Macon and Little River complexes and the Northern Florida platform sequence make up the Little River thrust stack. The magmas of the Devonian plutons that have intruded the Macon Complex probably formed when the Little River stack was thrust upon the underlying Georgiabama thrust stack, which was itself still being thrust toward the North American craton. The Macon Complex is interpreted to have formed between a trench and the Little River island arc at the oceanward edge of what was either a microcontinent off the African continent or the core of the present African continent. Many mafic and all ultramaflc bodies in the mélange are probably pieces of Iapetus Ocean crust and mantle offscraped from the downgoing slab and imbricated into the accretionary wedge. Rocks of the Macon Complex have previously been assigned to the “Charlotte,” “Kiokee,” “Kings Mountain,” and “Lowndesville” belts and to parts of the “Uchee,” “Raleigh,” “Pine Mountain,” and “Inner Piedmont” “belts.”

Alabama, Georgia, North Carolina, South Carolina↗
USGS1981

Potential source for crushed granite aggregate in Heard County, Georgia

The production of crushed stone suitable for highway and general construction is a major industry in Georgia. The state ranks eighth in the nation in overall crushed stone production, and first in crushed granite production. Crushed stone production in Georgia in 1979 was 40,902,000 short tons worth $154,021,000 (D.H. White, Jr., US Bureau of Mines, personal commun., Aug. 1980). More than 3,000 people were employed by the crushed stone industry in Georgia during that year. Presently, the only active quarry in Heard County is located in an amphibolite. Amphibolite is not a conventional aggregate. It has a high specific gravity, a tendency to make elongate fragments, and varies considerably in abrasion tests. Because the nearest approved aggregate quarry is more than 25 miles from Franklin, the county seat, the purpose of this brief report is to describe a body of granite gneiss that may provide suitable aggregate for the crushed stone industry, potential quarry operators and various agencies in Heard County. This report is part of a project to study the geology and mineral resources of the Piedmont south of the Brevard Zone, and is not intended to supplant detailed site investigations by industry or consultants. The report is a joint effort between the Georgia Geologic Survey and the Office of Materials and Research of the Georgia Department of Transportation.

Georgia↗
USGS1974

Interpretation of aeromagnetic anomalies bearing on the origin of upper Chesapeake Bay and river course changes in the Central Atlantic Seaboard Region: Speculations

On an aeromagnetic map of the Chesapeake Bay area, the northeastern part of the bay coincides well with a deep, “flat” magnetic low, and the upper part of the Delmarva Peninsula east of the bay coincides with detailed magnetic highs; the two areas are separated by a steep, straight gradient that matches the eastern shore of the bay. On the basis of magnetic and geologic evidence, we interpret the Chesapeake Bay magnetic low as a buried Baltimore Gneiss dome, bounded on the southeast by a normal or reverse fault marked by the steep, straight gradient; mafic and ultramafic plutonic rocks probably underlie the southeast side of the fault zone. The flatness of the Chesapeake Bay magnetic low, as opposed to the detail of the anomalies on either side, however, suggests that an abnormal thickness of nonmagnetic sedimentary rocks also coincides with the low. This could reflect a buried Triassic basin or, more probably, a thickened section of Coastal Plain sedimentary rocks deposited in the fault-bounded basin. The present course of the upper part of Chesapeake Bay is probably inherited from the pre-Pleistocene course of the Susquehanna River, but the river's course may have been determined by the fault zone. Thus, this zone and similar en echelon fault zones along strike may explain the sudden change in course of major rivers in the central Atlantic Seaboard region.

Delaware, Maryland, Pennsylvania, Virginia↗
USGS1973

Petrology of Newberry Volcano, central Oregon

Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement. The eastern flank of the central and southern Cascade Mountains is bordered by a belt of shield volcanoes that appears to be a subprovince of the Oregon high-alumina plateau basalt petrologic province. Most of the volcanoes in this belt are low shields in which differentiation from the parent high-alumina basalt magma has been relatively slight, but several are large complex shield centers where differentiation has been extreme. The location of these large centers, and of some of the smaller volcanoes as well, was largely determined by intersecting concentrations of faults and fault-fissures of three regional fault systems. One of the largest of the complex volcanic centers is Newberry Volcano in central Oregon, a shield volcano with a big caldera at its summit. The stratigraphy of the caldera walls and of features on the caldera floor at Newberry allows detailed interpretation of the history of the younger parts of the volcano and caldera. The formation of Newberry Caldera was apparently a slow process controlled largely by faulting along the three regional fault systems. The magma conduits were probably a gridlike plexus of intersecting dikes and fissures, with larger “magma pockets” at the grid intersections. The magma was trapped in shallow chambers and periodically released by faulting. The entrapment of the magma allowed differentiation in the shallow chambers. The stratigraphy and petrology of the wall sequence also allows determination of the relative time at which the caldera had grown large enough to hold a caldera lake. On differentiation plots, chemical analyses of the Newberry rocks show two trends: rocks erupted before the presence of a lake in the caldera trend toward slight iron enrichment, whereas rocks erupted after water was present in the caldera generally trend toward alkali enrichment. These different trends are attributed to differences in the oxygen fugacity of the magma which, in turn, are related to the presence or absence of large volumes of water in the caldera lake. The interpretation is supported by field, petrographic, petrologic, chemical, trace-element, and isotopic data. Plots of existing data for the Medicine Lake Highland Volcano, another large complex shield center in the belt, show the same type of two-trend relation as those of Newberry Volcano.

Oregon↗
USGS1973

Aeromagnetic discovery of a Baltimore Gneiss dome in the Piedmont of northwestern Delaware and southeastern Pennsylvania

In the central Appalachian Piedmont the “basement complex” is an assemblage of 1,100- to 1,300-m.y.-old gneisses, migmatites, and amphibolites that crops out in “domes” mantled by younger meta-sedimentary rocks of the Glenarm Series. Aeromagnetic data and reconnaissance field work indicate that a previously unknown Baltimore Gneiss dome, here called the Mill Creek dome, is present in southeastern Pennsylvania and northwestern Delaware. The discovery of previously unknown domes of Baltimore Gneiss has bearing on the thickness, structure, and regional relations of the Glenarm Series.

Delaware, Pennsylvania↗
USGS1971

Interpretation of an aeromagnetic strip across the northwestern United States

This report discusses the results of aeromagnetic survey bounded by latitudes 45°30′ N. and 47°00′ N. and extending from the Rocky Mountains, to approximately 120 mi offshore in the Pacific Ocean. East of the Rocky Mountains, a larger area has been surveyed in the Great Plains bounded approximately by latitudes 44°50′ N. and 48°10′ N. and by longitudes 104°W. and 110°W. Throughout the area of the survey, the magnetic map is marked by conspicuous northeast and northwest anomaly trends, lineaments, and breaks in the anomaly pattern. Their regional distribution, over-all magnetic character, and geologic evidence suggest that they are major structural features in the basement rocks. The close correspondence of structural and geologic features in younger rocks with these basement magnetic and structural trends suggest that basement trends controlled or at least greatly influenced intrusion, deposition, and structural history of younger rocks. In some cases, evidence suggests that basement structures have been reactivated during later tectonic activity. Perhaps even more striking than the northeast- and northwest-trending features are large east-west magnetic discontinuities which, in some cases, extend completely across the strip to the edge of the shelf, and which, in some cases, can be correlated with large-scale discontinuities dating back to the Precambrian.

Idaho, Montana, North Dakota, Oregon, South Dakota↗
USGS1971

A further revision of the stratigraphic nomenclature of the Wissahickon Formation in Maryland

The Wissahickon Formation, the thickest and most extensive unit of the Glenarm Series, was divided into lithofacies several years ago. We suggest revision of two of these lithofacies and addition of another. We also suggest that the term lithofacies be shortened to facies. The added facies, the quartzite facies, is distinguished by metamorphosed orthoquartzites and protoquartzites. It corresponds in part to the former Peters Creek quartzite.

Maryland↗
USGS1971

Cataclastic rocks

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Professional Paper↗
USGS1970

A re-evaluation of basalt-obsidian relations at East Lake Fissure, Newberry Caldera, Oregon

Andesite scoria, agglutinate, and small flows formed by thin lava gushes that erupted from East Lake Fissure on the north wall of Newberry Caldera carry numerous inclusions of platy rhyolite, partly melted platy rhyolite, and frothy obsidian. This association of obsidian and “basalt” has been interpreted as the result of intermingling of mafic and siliceous magmas. The locality has been repeatedly cited as an example of a mixed intrusion of the “basalt-rhyolite association.” Field, petrographic, chemical, and experimental evidence suggest, however, that the inclusions of frothy and massive obsidian are melted fragments of platy rhyolite which were ripped from a rhyolite unit forming part of the caldera wall by uncontaminated andesite magma which rose and fountained from the fissure.

Oregon↗