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A.E.J. Engel

Publications and source records attributed to A.E.J. Engel.

18 recordsLinked to original sources
USGS1970

Lunar rock compositions and some interpretations

Samples of igneous "gabbro," "basalt," and lunar regolith have compositions fundamentally different from all meteorites and terrestrial basalts. The lunar rocks are anhydrous and without ferric iron. Amounts of titanium as high as 7 weight percent suggest either extreme fractionation of lunar rocks or an unexpected solar abundance of titanium. The differences in compositions of the known, more "primitive" rocks in the planetary system indicate the complexities inherent in defining the solar abundances of elements and the initial compositions of the earth and moon.

Science↗
USGS1968

Alga-like forms in Onverwacht Series, South Africa: Oldest recognized lifelike forms on earth

Spheroidal and cupshaped, carbonaceous alga-like bodies, as well as filamentous structures and amorphous carbonaceous matter occur in sedimentary rocks of the Onverwacht Series (Swaziland System) in South Africa. The Onverwacht sediments are older than 3.2 eons, and they are probably the oldest, little-altered sedimentary rocks on Earth. The basal Onverwacht sediments lie approximately 10,000 meters stratigraphically below the Fig Tree sedimentary rocks, from which similar organic microstructures have been interpreted as alga-like microfossils. The Onverwacht spheroids and filaments are best preserved in black, carbon-rich cherts and siliceous argillites interlayered with thick sequences of lavas. These lifelike forms and the associated carbonaceous substances are probably biological in origin. If so, the origins of unicellular life on Earth are buried in older rocks now obliterated by igneous and metamorphic events.

Science↗
USGS1965

Igneous rocks of the Indian ocean floor

Four dredge hauls from near the crest and from the eastern flank of the seismically active Mid-Indian Ocean Ridge at 23° to 24°S, at depths of 3700 to 4300 meters, produced only low-potassium tholeiitic basalt similar in chemical and mineralogic composition to basalts characteristic of ridges and rises in the Atlantic and Pacific oceans. A fifth haul, from a depth of 4000 meters on the lower flank of a seamount on the ocean side of the Indonesian Trench, recovered tholeiitic basalt with higher concentrations of K and Ti and slightly lower amounts of Si and Ca than the typical-oceanic tholeiite of the ridge. The last sample is vesicular, suggesting depression of the area since the basalt was emplaced. Many of the rocks dredged are variously decomposed and hydrated, but there is no evidence of important chemical modification toward conversion of the lava flows to spilite during extrusion or solidification.

Science↗
USGS1965

Potassium, rubidium, strontium, thorium, uranium, and the ratio of strontium-87 to strontium-86 in oceanic tholeiitic basalt

The average concentrations of potassium, rubidium, strontium, thorium, and uranium in oceanic tholeiitic basalt are (in parts per million) K, 1400; Rb, 1.2; Sr, 120; Th, 0.2; and U, 0.1. The ratio Sr 87 to Sr 86 is about 0.702, that of K to U is 1.4 x 10 4 , and of Th to U is 1.8. These amounts of K, Th, U, and radiogenic Sr 87 are less than in other common igneous rocks. The ratios of Th to U and Sr 87 to Sr 86 suggest that the source region of the oceanic tholeiites was differentiated from the original mantle material some time in the geologic past.

Science↗
USGS1965

Chemical characteristics of oceanic basalts and the upper mantle

Tholeiitic basalts ( oceanic tholeiites) that form most of the deeply submerged volcanic features in the oceans are characterized by extremely low amounts of Ba, K, P, Pb, Sr, Th, U, and Zr as well as Fe 2 O 3 /FeO < 0.2 and Na/K > 10 in unaltered samples. Oceanic tholeiites also have rare earth abundance-distribution patterns and ratios of K/Rb (1300) and Sr 87 /Sr 86 (0.702) similar to or overlapping those of calcium-rich (basaltic) achondritic meteorites. The close compositional similarities between the oceanic tholeiites and calcium-rich achondrites indicates the relatively primitive nature of the oceanic tholeiites. In contrast, the alkali-rich basalts that cap submarine and island volcanoes are relatively enriched in Ba, K, La, Nb, P, Pb, Pb 206 , Rb, Fe 2 O 3 , Sr, Sr 87 , Ti, Th, U, and Zr; i.e. in the same elements and isotopes that are concentrated in the sialic continental crusts by factors of 5 to 1000 more than the amounts readily inferred in the upper mantle . These analytical data coupled with the field relationships indicate that the alkali-rich basalts are derivative rocks, fractionated from the oceanic tholeiites by processes of magmatic differentiation, and that the oceanic tholeiites are the principal or only primary magma generated in the upper mantle under the oceans. Studies of the abundances and compositions of continental basalts show that essentially identical tholeiitic lavas, contaminated with Si, K, and the chemically coherent trace elements and radiogenic isotopes from the sial, also have been the predominant or only magma generated in the mantle under the continents. The chemical properties of oceanic tholeiites suggest that the upper mantle probably contains less than (in parts per million): Ba, 10; K, 1000; Pb, 0.4; Rb, 10; Th, 0.2; and U, 0.1. The Sr 87 /Sr 86 must be less than 0.7015; Th/U about 2; K/Rb about 1500-2000; and Fe 2 O 3 /FeO less than 0.1. The integration of field and petrochemical data with seismic, density, and shock-wave studies suggests that the oceanic tholeiites are either complete melts of the upper mantle or are generated from a mix of this tholeiite and a magnesium-rich peridotite or dunite in proportions up to perhaps 1:4. The Mohorovičić discontinuity under the oceans appears to mark the transition downward from a largely tholeiitic oceanic crust to either tholeiite reconstituted to blueschist or greenschist or to the ultramafic residue left after expulsion of oceanic tholeiite.

Geological Society of America Bulletin↗
USGS1964

Composition of basalts from the Mid-Atlantic Ridge

Studies of volcanic rocks in dredge hauls from the submerged parts of the Mid-Atlantic Ridge suggest that it consists largely of tholeiitic basalt with low values of K, Ti, and P. In contrast, the volcanic islands which form the elevated caps on the Ridge are built of alkali basalt with high values of Ti, Fe 3+ , P, Na, and K. This distinct correlation between the form of the volcanic structures, elevation above the sea floor, and composition suggests that the islands of alkali basalt are derived from a parent tholeiitic magma by differentiation in shallow reservoirs. The volume of low-potassium tholeiites along the Mid-Atlantic Ridge and elsewhere in the oceans appears to be many times that of the alkali basalts exposed on oceanic islands. Tholeiitic basalts with about 0.2 K 2 O appear to be the primary and predominant magma erupted on the oceanic floor.

Science↗
USGS1964

Igneous rocks of the East Pacific Rise

The apical parts of large volcanoes along the East Pacific Rise (islands and seamounts) are encrusted with rocks of the alkali volcanic suite (alkali basalt, andesine- and oligoclase-andesite, and trachyte). In contrast, the more submerged parts of the Rise are largely composed of a tholeiitic basalt which has low concentrations of K, P, U, Th, Pb, and Ti. This tholeiitic basalt is either the predominant or the only magma generated in the earth's mantle under oceanic ridges and rises. It is at least 1000-fold more abundant than the alkali suite, which is probably derived from tholeiitic basalt by magmatic differentiation in and immediately below the larger volcanoes. Distinction of oceanic tholeiites from almost all continental tholeiites is possible on the simple basis of total potassium content, with the discontinuity at 0.3 to 0.5 percent K 2 O by weight. Oceanic tholeiites also are readily distinguished from some 19 out of 20 basalts of oceanic islands and seamount cappings by having less than 0.3 percent K 2 O by weight and more than 48 percent SiO 2 . Deep drilling into oceanic volcanoes should, however, core basalts transitional between the oceanic tholeiites and the presumed derivative alkali basalts. The composition of the oceanic tholeiites suggests that the mantle under the East Pacific Rise contains less than 0.10 percent potassium oxide by weight; 0.1 part per million of uranium and 0.4 part of thorium; a potassium: rubidium ratio of about 1200 and a potassium: uranium ratio of about 10 4 .

Science↗
USGS1963

Basalts dredged from the northeastern Pacific Ocean

Volcanic rocks dredged from seamounts, fault ridges, and other major geological features of the northeast Pacific Ocean include a wide variety of basalts. Most of these are vesicular, porphyritic types with near analogues in the Hawaiian and other oceanic islands. in addition, aluminous basalts and diabasic tholeiites impoverished in potassium also occur. There is no simple correlation of composition, degree of oxidation, vesiculation, or hydration of these basalts with texture, or depth of dredge site. Most samples appear to have been extruded at much shallower depths than those now pertaining at the dredge site. the distribution of these basalts suggests that the andesite line coincides with or lies on the continent side of the foot of the continental slope.

Science↗
USGS1963

Metasomatic origin of large parts of the Adirondack Phacoliths

A metasomatic origin seems established for large parts of the granite phacoliths in the northwest Adirondack Mountains, New York. This conclusion is based upon the discovery and detailed mapping of a blurred but widespread stratigraphic sequence in the phacoliths . Highly complicated patterns of relict beds are defined by alternations of granitic gneiss, amphibolite, oligoclase-quartz gneiss, and a predominant alaskitic granite. Regional reconstructions indicate these relict beds comprise a major basal formation, probably of arkosic and calcareous quartzites, in the exposed Grenville metasedimentary rocks. The existing amphibolite interlayers formed early in the metasomatic epoch, probably replacing the more calcareous quartzite beds. This mafic metasomatism was overlapped and followed by pervasive granitization of the arkosic and highly quartzose members. Pink alaskitic granite is the final metasomacic product. It tends to replace all pre-existing rock types, especially in the cores of the antiforms. This mafic and granitic metasomatism occurred during the evolution of the major folds in the metasedimentary sequence. As the folds evolved, rising domes in the quartzite probed upward into successively higher horizons in the overlying marbles. At least three quartzite antiforms (California, Clark Pond, and South Edwards phacoliths ) punctured the overlying marble, invading the basal layers of the Adirondack paragneiss. The crests of the evolving folds in the basal quartzite, capped by carbonate-rich marble, acted as traps for aqueous and carbonated, alkali-bearing fluids, and perhaps some associated anatectic granitic magma generated in the deeper, hotter basement to the Grenville.

New York↗
USGS1962

Hornblendes formed during progressive metamorphism of amphibolites, northwest Adirondack Mountains, New York

Hornblendes in amphibolite interlayers in the paragneiss of the northwest Adirondack Mountains undergo systematic changes in color, composition, and density during progressive metamorphism from almandine- amphibolite to hornblende -granulite facies. In contrast, indices of refraction of the hornblendes remain about constant. In the almandine- amphibolite facies the amphibolite layers have the bulk composition of a saturated basalt and consist of bluish-green hornblende , andesine, and quartz. As these layers are traced into the hornblende -granulite facies, their composition undergoes a progressive change to that of an olivine basalt with brownish-green hornblende , clinopyroxene and orthopyroxene, and calcic andesine as major constituents. Compositional changes in the hornblendes with increasing grade of metamorphism include increases in Ti, Na, K, Cr, V, and Sc. Decreases occur in the amounts of Mn, Zn, OH + F + Cl, and in the ratios Fe 2 O 3 /FeO and Fe/Mg. Density of the hornblendes increases from 3.260 to 3.278 with the increasing grade of metamorphism . These changes in the hornblendes with increasing T and P, although well denned, are less pronounced than those measured in biotites and garnets of the enclosing paragneiss. Large variations in the physical and chemical properties of hornblendes in metamafic rocks reconstituted above the epidote- amphibolite facies appear to be induced principally by critical changes in the bulk composition of the total rock, and not by the regional gradients in T, P, or by changes in kind, or composition, of the coexisting minerals.

New York↗
USGS1962

The Precambrian geology and talc deposits of the Balmat-Edwards district, northwest Adirondack Mountains, New York

The Balmat-Edwards, or Gouverneur, mining district is in the Grenville Lowlands of the northwest Adirondacks, St. Lawrence County, New York. In the district, important deposits of talc and zinc and minor deposits of lead are mined from a northeast trending belt of marble. Deposits of pyrite that were prospected and mined during and before World War I occur in schists in the vicinity of Pyrites and Antwerp villages. Fifteen to 50 miles east-southeast is the St. Lawrence County magnetite district, which contains commercially important magnetite deposits.

New York↗
USGS1946

The quartz crystal deposits of western Arkansas

Extensive geological investigations of domestic deposits of quartz crystals were undertaken by the Geological Survey of the United States Department of the Interior in the fall of 1942 in response to the urgent demand for crystals for war purposes. The work was continued throughout 1943 and took survey geologists into some 20 states in which over 1,400 deposits or reports of deposits were examined. Of the numerous highly varied occurrences of quartz examined, only the deposits in western Arkansas, in the Piedmont and Blue Ridge provinces of Virginia, North Carolina and Georgia and the placer quartz of Mokelumne Hill, California, were of sufficient promise to warrant detailed work. Production in 1943 from these areas totaled slightly less than 4 tons of oscillator quartz, over 85 per cent of which came from Arkansas.The Arkansas deposits occur throughout the thick, deformed Paleozoic shales, sandstones, and cherts exposed along the central belt of the Ouachita Mountains. Steeply dipping fractures closely related to the major folds control the deposition of most quartz.Clear quartz is confined largely to the terminal parts of primary crystals, which have developed without disturbance or interference, are commonly elongate parallel to their C axes and are bounded by relatively simple forms. Deposition of silica during and subsequent to the fracturing of crystals resulted in the formation of complex crystals which are characterized by extensive optical twinning and lineage structures, and commonly are bounded by aggregates of the simpler crystal forms. The principal defects in all types of crystals are twinning, smokiness, cavities, solid inclusions and fractures.The Arkansas quartz deposits include veins, sheeted zones and stock-works. They are largely cavity fillings, apparently deposited by rising, attenuated, hydrothermal solutions, at relatively low temperatures and pressures. Minerals associated with the quartz, which constitutes 90 per cent or more of the cavity fillings, include dickite and carbonaceous material, calcite, adularia, and chlorite. The constituents of the cavity fillings could have been derived principally from magmatic sources or more probably from underlying rocks, with small additions from the rocks enclosing the cavities. The complex vein fabrics apparently resulting from intermittent regional deformation during the deposition of the quartz, and certain structural relations of the deposits, indicate that they were formed in the final stages of the Ouachita orogeny, probably in mid-Pennsylvanian time.

Arkansas↗