The Montaña de Comayagua structural belt is a zone trending N. 60° W., more than 130 kilometers long, of exposed earliest Tertiary and older rocks that were complexly deformed during the Laramide orogeny. The Honduras Depression, a discontinuous north-trending graben system, extends from the Pacific coast to the Caribbean. The Comayagua graben, a major segment of the Honduras Depression, intersects the older structural belt in the Comayagua Quadrangle. Paleozoic (?) low-rank metamorphic rocks that record two periods of metamorphism underlie two Mesozoic redbed sequences separated by a carbonate group. Cenozoic volcanic and associated sedimentary rocks nonconformably overlie all older rocks. Red elastic rocks of the Todos Santos Formation accumulated as alluvial fans that filled structural depressions. Minor volcanism and faulting accompanied this deposition. The overlying Yojoa Group of carbonate rocks accumulated during a transgression. Red clastic flood plain and deltaic rocks of the Valle de Angeles Group were derived from a rising region outside the map area (probably to the south). The deformation that terminated Valle de Angeles deposition produced the Montaña de Comayagua structural belt, which is a 20 to 30-kilometer wide, N. 60° W.-trending structural high composed of asymmetrical, N. 70° to 90° W.-trending folds, some of which are cut by reverse faults. The folds and reverse faults may be the consequence of left-lateral shearing. Many of the important mineral deposits in Honduras occur along this structural belt. After this deformation, andesite lava flows and mid-Miocene siliceous ignimbrites, tuffs, and associated volcanic rocks were deposited across the deformed older rocks. Normal faulting along west-northwest, northwest, north, northeast, and east-west trends began during volcanism and continued almost to the present. Approximately 2 kilometers of structural relief resulted from this period of normal faulting in the Comayagua Quadrangle. This episode of normal faulting formed the north-trending Comayagua graben and other grabens comprising the Honduras Depression, as well as similar features elsewhere in Honduras and adjacent parts of Guatemala. The complex pattern of normal faults and grabens seems to be the result of left-lateral simple shear deformation of the northwestern part of the Caribbean plate of lithosphere. This simple shear deformation is a consequence of underthrusting at the Middle America Trench and left-lateral strike-slip movement along the Bartlett Trough fault system. Igneous rocks of various compositions intruded the area in several episodes: one was pre-Mesozoic; others were pre-ignimbrite; and the youngest clearly occurred after the mid-Miocene. The Valle de Comayagua was partially filled with a lake following a major episode of graben faulting. Pediments have been cut on the lake beds since through-flowing drainage was established. Earth resources include ground water, limestone, sand and gravel, dimension stone, and possibly small amounts of silver, lead, zinc, and copper. / text

No description available.

Thesis (Ph.D.)--Boston University / The Kingfield quadrangle is located in north central Maine. Work has been completed in adjacent quadrangles on the east, west, and south. Study of the petrology, stratigraphy, structure, and geomorphology reveals the geologic history of the area. The topography, a result of modification by Pleistocene glaciation imposed on a landscape of late maturity, has been developed on the following formations (from oldest to youngest): Lost Brook, Perry Mountain, Parmachenee, and Madrid. More than 12,000 feet of Orodovician to Mid-Silurian strata constitute a variety of rock types which have undergone the effects of regional and contact metamorphism [TRUNCATED]

Thesis advisor: J. Christopher Hepburn / The Shrewsbury quadrangle was geologically mapped at a scale of 1:24,000. The quadrangle spans the entire Nashoba terrane, a belt of amphibolite-grade rocks related to an early Paleozoic peri-Gondwanan arc. Petrofabric studies of fault-rocks indicated that the final motion on several major shear zones - Ball Hill fault, Sulfur Hill shear zone, and Assabet River fault - was sinistral strike-slip with an oblique NW over SE thrust component. Monazites from these shear zones were dated using an electron microprobe. Regional metamorphism (M1) took place around 420 Ma. A second regional metamorphism (M2) produced anatectic conditions around 394Ma. A group of dates in the range 360-385 Ma indicates that the Nashoba terrane was also affected by Neoacadian metamorphism and/or deformation. Major shear zones were active throughout the Devonian and may have persisted into the Carboniferous. / Thesis (MS) — Boston College, 2007. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Graduation date: 1953

The Matagalpa Formation, the oldest unit exposed (Oligocene? - Early Miocene?), consists of over 300 meters of hydrothermally altered mafic flows and some interbedded sedimentary rocks. Up to 1400 meters of siliceous volcanic and sedimentary rocks (Mid-Miocene-Pliocene?), correlative with the Padre Miguel Group in Guatemala, nonconformably overlie the Matagalpa Formation. The lower 1000 meters of this group consists mainly of rhyolitic to andesitic ignimbrites that were probably erupted from a vertically zoned magma. Faulting accompanied the extrusion of these ignimbrites. These are overlain by up to 400 meters of airfall tuffs, fluvial, lacustrine, and laharic deposits, and a series of structurally-controlled rhyolitic domes. The uppermost unit consists of several thin ignimbrites. Most of the faulting occurred after the deposition of the Padre Miguel Group, probably from Middle Pliocene to Early Pleistocene times. Normal faults trend N50-80°W, N10-25°E, N35°E, and N70°E. They are probably surficial features caused by left-lateral shear in the basement related to movement between the Caribbean and Americas plates. Minor northwest-trending folds formed contemporaneous with and perhaps prior to faulting. Olivine basalt was extruded from structurally-controlled vents after most of the faulting had ceased. Cut terraces and pediments formed adjacent to the ancestral Rio del Hombre, Subsequent downcutting may have been the result of regional uplift, stream capture along the Rio Choluteca, or both. / text

The Agalteca quadrangle is located in the Sierras of Northern Central America and straddles the N60W-trending Montaña de Comayagua structural belt near the southeastern limit of its known 130 km extent. The structural belt may extend into unmapped areas to the northwest toward Guatemala and to the southeast toward Nicaragua. The structural belt has a width of approximately 30 km in the vicinity of the Agalteca quadrangle. Mapping of the Agalteca quadrangle has clarified that the Montaña de Comayagua structural belt consists of a series of left-stepping, en echelon strike-slip faults produced by probable dextral strike-slip displacement of unknown magnitude in the Late Cretaceous to early Tertiary. Associated with these strike-slip faults are syntectonic high-angle reverse faults, thrust faults, folds and antithetic shears. The assemblage is a "flower structure" in cross section, and is believed to be the product of transpression, or wrenching with a component of compression. The axis of the N60W-trending Laramide wrench zone in the Agalteca quadrangle is structurally high and exposes a conformable sequence of highly deformed Mesozoic sedimentary rocks. A Paleozoic (?) metamorphic basement, the Cacaguapa Schist, is known to unconformably underlie the Mesozoic sequence in central Honduras, but is not exposed in the Agalteca quadrangle. The Mesozoic sedimentary rocks include the Upper Jurassic (?) to Lower Cretaceous Todos Santos Formation conglomerate which is conformably overlain by the Valanginian (?) to Albian limestone of the Atima Formation. The Atima Formation is conformably overlain by the Albian to Late Cretaceous redbeds of the Valle de Angeles Group, which includes an intercalated limestone member, the Cenomanian Esquías Formation. The Mesozoic sedimentary rocks are intruded by mafic to felsic stocks and dikes of Late Cretaceous to Tertiary age, and are unconformably overlain by Tertiary volcanic rocks. The volcanic rocks include andesite of the early Tertiary Matagalpa Formation and the Oligocene-Miocene ignimbrites, basalt flows and volcanogenic sediments of the Padre Miguel Group. Terrace deposits of late Tertiary to Quaternary age unconformably overlie the older rocks in the Agalteca quadrangle. The Laramide structures of central Honduras are overprinted by north-trending grabens of the Honduras Depression which began to form in the mid-Miocene and are still active. In a regional context, the western tip of the Caribbean Plate (the Chortis Block) is undergoing east-west extension. North-trending grabens, including the Honduras Depression, cut the Chortis block from the Pacific Volcanic Chain to the Motagua transform boundary. The Honduras Depression is the most complex of these graben systems. The southern part of the Honduras Depression consists of grabens and half-grabens which trend north from the Gulf of Fonseca and are interrupted by the N60W-trending structures of the Montaña de Comayagua structural belt near Tegucigalpa. The northern part of the Honduras Depression trends north to the Caribbean coast from its termination against the Montaña de Comayagua structural belt near Lake Yojóa. The northern and southern segments of the Honduras Depression were born with an apparent left-lateral offset along the Montaña de Comayagua structural belt. The Honduras Depression is a developing rift. A pre-existing zone of weakness along the Montaña de Comayagua structural belt inhibited the formation of a through-going rift and rejuvenated the Laramide structural belt as a dextral transform fault zone. Late Cenozoic magmatic uplifts are present within the rejuvenated structural belt, and economically important base metal concentrations such as the El Mochito and El Rosario deposits are localized at the intersections of the northern and southern segments of the Honduras Depression with the Montaña de Comayagua structural belt. Quaternary alkalic basalt is associated with the Honduras Depression and is also restricted to the intersections of the depression with the structural belt in the vicinity of Tegucigalpa and Lake Yojóa. / text

Thesis (Ph.D.)--Boston University.

A detailed study was made of the James Peak-Sharp Mountain area, in the southern part of the Bear River Range, Utah. The mapped area is located in north-central Utah between lat. 41°22'30" N. and lat. 41°30' N. and long. 111°42'30" W. and long. 111°46' W. It measures about 3.8 miles in the east-west direction and 8.7 miles in the north-south direction. The area is centered about 22 miles south-southeast of Logan, Utah. Stratigraphic units of late Precambrian to Mississippian age underlie the mapped area. The Precambrian units include the Mutual and Browns Hole Formations. The Brigham, Langston, Ute, Blacksmith, Bloomington, Nounan, and St. Charles Formations make up a complete Cambrian section. The Ordovician Garden City and Swan Peak Formations, the Ordovician-Silurian Laketown Formation, the Devonian Water Canyon and Hyrum Formations, and the Mississippian Lodgepole and Humbug Formations overlie the St. Charles in normal succession. The oldest unit the Precambrian Mutual Formation, crops out in the southern part of the area on the eastern side of James Peak. The rock units are progressively younger toward the northern part of the area. Mesozoic rocks are not present. The Salt Lake Formation of Tertiary age directly overlies the Paleozoic rocks. The main structural feature of the area is an asymmetrical north-south-trending anticline. The eastern flank dips more steeply than the western flank. The anticline plunges gently north and dies out southward. This anticline is one of a series of asymmetrical anticlines, all steeper on the east than on the west, that includes the Strawberry Valley anticline to the east and the anticline exposed in upper Wolf Creek Canyon to the west. The late Precambrian and early Paleozoic formations, which dip northeast on the eastern flank of James Peak, make up the northeastern flank of the anticline exposed in upper Wolf Creek Canyon. The early Paleozoic to Devonian formations that form Sharp Mountain and dip gently west make up the western flank of the Strawberry Valley anticline. Low-angle thrust faults have disrupted the Precambrian and Paleozoic formations on the eastern and southeastern flanks of James Peak. Displacement on the thrust fault north of upper Wellsville Creek is about 2,000 feet. Movement was generally from the west. Normal faults have disrupted the Paleozoic and Tertiary formations along the eastern margin of Cache Valley and the Paleozoic formations east of McKenzie Mountain. Displacement is indeterminate along the eastern margin of Cache Valley. Maximum displacement, east of McKenzie Mountain, is about 1,750 feet. The normal faults truncate the folds and thrust faults. The folds and thrust faults were formed during the Laramide orogeny. The normal faults were formed during Basin and Range normal faulting. Basin and Range normal faulting is active at the present time.

The El Rosario Quadrangle, situated 100 kilometers northwest of the capital, Tegucigalpa, on the Carretera del Norte, straddles the boundary between the Volcanic Ranges and Plateaus and the Central American Cordillera morphotectonic units, and includes pre-Mesozoic metamorphic rocks, Mesozoic and Tertiary sedimentary rocks, and Tertiary intrusive and volcanic rocks. The oldest rocks exposed are two facies of the pre-Mesozoic Cacaguapa Schist: the Humuya Member of sheared conglomerate, containing evidence of two metamorphic periods, and schist with interlayered, boudinaged meta-andesite; and the Las Marias Member of sericite-quartz schist with inter-layered marble and quartzite. Nonconformably overlying the metamorphic rock are interbedded conglomerate, sandstone, and shale, with intercalated volcanic rocks of the early Mesozoic Todos Santos Formation. The early Cretaceous Yojoa Group of carbonate rock overlies the Todos Santos Formation. Two formations comprise the Yojoa Group: Cantarranas Formation of thin-bedded, marly limestone and the overlying Atima Formation of massive limestone. The Late Cretaceous to early Tertiary (?) Valle de Angeles Group includes red sandstones and shale with minor conglomerate. Padre Miguel Group (Miocene?) siliceous ignimbrite and reworked pyroclastic rock are represented by the La Sabana and Cerro Le Cañada ignimbrite members. The La Sabana ignimbrite has an olivine basalt flow within its lower part. Intrusive igneous rocks include rhyolite with tuffaceous, devitrified-tuff, or granophyric textures, basalt and gabbro dikes, and intruded gabbro. These rocks record three major episodes of deformation: pre-Mesozoic folding and development of schistosity; the Montaña de Comayagua structural belt, a N. 60° W. structural high with high-angle reverse faults formed during the Laramide orogeny; and Tertiary faulting that formed north-trending grabens. The Opoteca silver mine may be the richest mineral deposit within the El Rosario Quadrangle. / text