Marland P. Billings

Regional metamorphism of the Littleton-Moosilauke area, New Hampshire

INTRODUCTION The Littleton-Moosilauke area occupies 300 square miles in west-central New Hampshire; it is covered by the Moosilauke topographic sheet and the New Hampshire portion of the Littleton sheet. Most of the area lies west of the White Mountains, but the southeast corner of the Moosilauke quadrangle contains some of the higher summits of this group. The writer has long been interested in the problem of the age of the schists of the White Mountains, and, as the only fossil localities known in New Hampshire at the inception of this study were in the Littleton district, this area was chosen for special investigation. Obviously, the stratigraphy and structure of rocks of known age had to be deciphered first, and then their relations to the schists farther east determined. The study has achieved its major purpose and has shown that the schists in the western part of New Hampshire are of . . .

Ordovician cauldron subsidence of the Blue Hills Complex, eastern Massachusetts

The Blue Hills Complex, which lies south of the Boston Basin in eastern Massachusetts, is composed of Cambrian sedimentary rocks and Late Ordovician alkalic plutonic and volcanic rocks. On the north, the Complex is separated by a fault from the Boston Bay Group, which very recently has been shown to be late Precambrian. On the south, the Complex is overlain unconformably by the Pennsyvanian rocks of the Norfolk Basin. The bedding and volcanic flow structures of the Cambrian, Ordovician, and Pennsylvanian rocks are essentially parallel and dip steeply south. I believe that the Blue Hills Complex is a Late Ordovician cauldron subsidence that was tilted during the Alleghenian Orogeny and was thrust northward over the Boston Bay Group.

DIASTROPHISM AND MOUNTAIN BUILDING

For many years the terms orogeny and mountain building have been used so loosely that they no longer convey definite meanings. Because of this lack of precision, hypotheses of diastrophism are often based on false premises. Folding and thrusting, often referred to as tectogenesis or orogeny, is best displayed by stratified rocks. Some geologists believe that folds and thrusts are due to vertical movements accompanied by lateral spreading, that the strata are stretched an amount commensurate with the intensity of the folding, and that the opposite sides of the sedimentary packet do not move toward each other. Most geologists, however, agree that during folding and thrusting the strata are shortened and that the two opposite sides of the sedimentary packet move toward each other by an amount commensurate with the intensity of the folding. But it is not clear to what extent the entire crust in the deformed belt is shortened. In one extreme view, the two opposite ends of the deformed belt do not move toward each other, and the folds and thrusts result from gravity sliding. At the other extreme, the entire crust is believed to be shortened to the same extent as the sedimentary strata. An excellent example of broad vertical movements (epeirogenesis) that has never been sufficiently emphasized is in eastern North America, involving the Appalachians, Coastal Plain, and Continental Shelf. During the Mesozoic and Cenozoic the Fall-Line surface was depressed as much as 20,000 feet beneath the Continental Shelf, whereas it was uplifted at least 8000 feet over the Appalachians. The northeastern two-thirds of the Appalachian-Ouachita belt has been going up since the Jurassic, whereas the southwestern third has been going down. Thus the present Appalachians are unrelated to the late Paleozoic folding. Certain metamorphic minerals—such as kyanite—or certain metamorphic assemblages—such as jadeite and quartz—form at confining pressures found only at depths of tens of miles, implying tremendous erosion wherever such minerals or assemblages are exposed. Broad vertical movements, accompanied by high-angle faulting, are illustrated by the fault-block mountains of the Basin and Range Province and by such features as the Rhine graben and the Rift Valleys of Africa. Although the nature of the displacement along the San Andreas fault has been known for more than 50 years, only in recent decades have other large strike-slip faults been recognized. But it is now the fad to assign all kinds of faults and even nonexistent faults to the strike-slip category. In recent years seismologists have emphasized the importance of strike-slip faults. The author suggests that in the Fairview Peak-Dixie Valley, Nevada, earthquakes there is evidence that strike-slip movements are invading an area previously characterized by Basin-Range structure. The geologic record indicates that large strike-slip faults have been distinctly subordinate to folding, broad vertical movements, and broad vertical movements accompanied by high-angle faulting. Possible displacement of the crust or the entire earth relative to the axis of rotation has been emphasized in recent years. Continental drift, if it occurs, is one such type of movement. Slipping of the entire crust over the mantle is another. Much research has been accomplished in paleomagnetism in recent years, but the data are too scanty and conflicting to permit any definite conclusions. Among the possible causes of diastrophism are (1) contraction of the earth, (2) convection currents, (3) formation of large pockets of magma, (4) sialic material leaking out of the mantle, (5) conversion of sial to mantle by change of low-pressure minerals to high-pressure minerals, or the reverse, and (6) serpentinization or deserpentinization of the upper part of the mantle. Mountain building is merely one manifestation of vertical movements of the crust. In the past mountain building has been erroneously considered by many to be primarily the result of folding and thrusting. Certainly many modern ranges are the result of vertical uplift unrelated to folding. Many such uplifts are accompanied by high-angle faulting to produce fault-block mountains. Blocks caught between strike-slip faults may be squeezed upward if the blocks move toward each other. Mountainous uplifts have also resulted from folding and thrusting. Conversely, in some folded belts erosion appears to have kept pace with the rise of the folds so that no mountains developed.

GEOLOGY OF THE MT. WASHINGTON QUADRANGLE, NEW HAMPSHIRE

The Mt. Washington quadrangle contains the highest peaks in the northern part of the Appalachian Highlands. This paper presents a brief summary of the geology to accompany a colored geological map that has just been printed. The stratified rocks belong to three formations, the Ordovician (?) Albee formation, the Ordovician (?) Ammonoosuc volcanics, and the Devonian Littleton formation. All these rocks have undergone high-grade metamorphism, and such minerals as andalusite, sillimanite, staurolite, garnet, tourmaline, actinolite, and diopside are present. The intrusive rocks belong to four magma series, ranging in age from Late Ordovician (?) to Mississippian (?). The structure of the whole quadrangle is dominated by a northeasterly trending dome, the center of which is occupied by the intrusive Oliverian magma series. The metamorphosed sedimentary and volcanic rocks on the flanks of this dome are thrown into countless folds, ranging from minor folds seen in single outcrops to larger folds hundreds and thousands of feet in wave length and amplitude. The folding is probably Acadian (middle to late Devonian). The intrusive rocks show a variety of structural forms. The Oliverian magma series apparently consists of a series of concordant lenses. The White Mountain magma series occurs in ring-dikes, stocks, and volcanic vents.

Structure and metamorphism in the Mount Washington area, New Hampshire

The Mt. Washington area of New Hampshire contains the highest peaks in the northern Appalachian Mountains. The metamorphic rocks belong to four stratigraphic units: the Ordovician (?) Ammonoosuc volcanics, chiefly fine-grained biotite gneiss; the Ordovician (?) Partridge formation, largely gneiss derived from shale; the Silurian Fitch formation, consisting of lime-silicate granulite and schist; the Devonian Littleton formation, mostly quartzite and schist. The oldest intrusive rocks are quartz monzonites and granites belonging to the Devonian (?) Oliverian and New Hampshire series. Granite, syenite, tuff, and breccia belong to the Mississippian (?) White Mountains magma series. The chemical composition of some of the minerals differs with the formation. Pyroxene and amphibole in the Fitch formation are magnesia-rich and iron-poor, whereas in the Ammonoosuc volcanics the reverse is true. Oligoclase characterizes the Partridge formation, Littleton formation, and Bickford granite; andesine is typical in the Ammonoosuc volcanics; and bytownite is common in the Fitch formation. Biotite and muscovite are relatively uniform, except for magnesia-rich biotite in the Fitch formation. The Mt. Washington area is on the southeast flank of a large dome, the center of which is occupied by the intrusive Oliverian magma series. The folds in the Presidential Range trend north and northeast. The major folds are en echelon , and upon them are superimposed many minor folds. Schistosity, due to platy minerals, parallels the bedding. Fracture cleavage is essentially parallel to the axial planes of the minor folds. The Pine Mountain fault is the largest of several normal faults. Metamorphism is high-grade (katazonal). Original shales are now andalusite schist, coarse rough pseudo-andalusite schist, fine grained pseudo-andalusite schist, and staurolite schist. Contrasting metamorphic history explains the various types. Metamorphism was syntectonic, and the coarser schists show three major stages in the paragenesis. Many rocks, particularly paraschists, suffered no significant chemical change. Potash was introduced into some of the coarser schists. Many of the gneisses are derived from shale by metamorphic differentiation, and less than 1 per cent of soda, lime, and potash has been introduced. Four or five per cent of soda, lime, and potash has been added to shale to form the lighter colored gneisses.

Glaciation in the Wasatch Plateau, Utah

The Wasatch Plateau, northernmost of the High Plateaus of Utah, was occupied by Pleistocene glaciers. The plateau is a high, rugged mass, deeply dissected. In the glaciated areas the bedrock formations are sandstone, shale, and limestone of late Cretaceous and early Tertiary age. Here, in general, the rocks lie nearly flat, but they are cut by systems of normal faults among which graben are prominent. The drainage system evolved in this bedrock setting gave rise to a geomorphic foundation on which a somewhat unusual group of glacial phenomena developed. The largest group of glaciers issued eastward from deep canyons in the main western body of the plateau into a north-south graben valley, where they coalesced to form large, sheetlike compound moraines. The cirques and other erosional evidences of the glaciation are similar to those usual in the Cordilleran region excepting peculiarities of outline produced by the flat-lying, slightly resistant sedimentary rocks of the plateau, as contrasted with the usual mountain assemblage of strongly disturbed hard rocks. The glaciers were localized, in part independently of altitude, probably in large part because of snow distribution similar to that of today. The glaciation was clearly later than most of the faulting in the plateau, but in the central and southern parts some faulting has occurred since. All moraines so far recognized are unmistakably Wisconsin in age. There is no evidence of older glaciation comparable to that in the nearby Wasatch and Uinta Mountains, where pre-Wisconsin ice was more extensive than the Wisconsin; this raises questions that are only partly answered.

Introduction of potash during regional metamorphism in western New Hampshire

PROBLEM One of the outstanding problems of regional metamorphism concerns the amount of material introduced from external sources. If material is added, it is necessary to determine the stage in the metamorphism when such introduction takes place and to discover the source of the added substances. Goldschmidt (1921) has shown, for example, that alkalis and silica have been added to argillaceous sediments in the Stavanger region of Norway, and Barth (1936) has made similar observations in Dutchess County, New York. In both areas the introduced elements were derived from nearby intrusives. In the Littleton and Moosilauke quadrangles of westernmost New Hampshire (Fig. 1) high-grade metamorphic rocks were developed without any notable introduction of material from external sources (Billings, 1937, p. 544–545). Farther east, however, after high-grade metamorphic rocks were formed by recrystallization, potash was locally introduced in large quantities. It is the purpose of this paper to present the . . .

STRATIGRAPHY AND THE STUDY OF METAMORPHIC ROCKS

In recent years many students of metamorphic rocks have become so preoccupied with minor structures, structural petrology, physical chemistry, and granitization that the stratigraphy of metamorphic rocks has been neglected. There is great danger that the younger men, indoctrinated with the idea that stratigraphy and sedimentation are unrelated to metamorphic geology, will be inadequately trained to study metamorphic rocks in the field. Geologic maps of regions characterized by different grades of metamorphism should be based on stratigraphy. The assignment of the rocks to formations should be based on the inferred lithology prior to metamorphism and should not be based directly on the present lithology. The student of metamorphic rocks should be familiar with modern concepts of stratigraphy and sedimentation, such as deposition in transgressing and regressing seas, changes in sedimentary facies, and time surfaces. Metamorphic geologists should be familiar with the textures, mineralogy, and chemical composition of sedimentary rocks. When sufficiently large areas are studied, the metamorphic geologist should think in terms of the paleogeography and climatic conditions at the time of sedimentation. Stratigraphers and students of historical geology should realize that their concepts of paleogeography will be incorrect if they neglect the wealth of data to be obtained from metamorphic rocks. These facts can be abstracted from the metamorphic rocks only by intensive investigations in the field by a host of metamorphic geologists well-trained in stratigraphy.

Petrology and structure of the Franconia quadrangle, New Hampshire

The Franconia quadrangle of New Hampshire supplements the geology of the Littleton and Moosilauke quadrangles in such a way that a very representative picture of the geology of western and central New Hampshire may be obtained by a knowledge of these three quadrangles. Three groups of rocks occupy the Franconia quadrangle. The oldest group contains highly deformed metamorphic rocks of Ordovician (?) and Devonian age. The second group consists of plutonic rocks of the New Hampshire magma series. This is a subalkaline series, in part syntectonic, and is probably late Devonian. The chief dark mineral is biotite, and the rocks are more or less foliated. The third group is the White Mountain magma series, which is alkaline and probably Mississippian. Such minerals as hedenbergite, fayalite, hastingsite, fluorite, and allanite are characteristic, and biotite is subordinate. The rocks of this group are massive. The structure reflects the genetic differences of the three groups. The metamorphic rocks are thrown into closed, isoclinal folds which trend northeasterly. The New Hampshire magma series occurs as great sheets and lenses, which have forcefully injected the older metamorphic rocks. The White Mountain magma series is represented by both extrusive and intrusive members, the latter occurring in ring-dikes and stocks. The space occupied by the ring-dikes was attained by piece-meal stoping along essentially vertical arcuate fracture zones.

Carboniferous topography in the vicinity of Boston, Massachusetts

The Roxbury conglomerate is a heterogeneous formation composed of conglomerate, sandstone, shale, and interbedded volcanic rocks. The coarseness of the conglomerate and the occurrence of tillite in the overlying Squantum formation have suggested considerable relief in the regions from which the sediments were derived. New data indicate that the Roxbury conglomerate was deposited on a surface of high relief. In the Nantasket area the relief was not less than 565 feet, and was presumably at least 845 feet. In the Hingham area the Roxbury conglomerate increases in thickness within less than a mile from 1340 feet in the southern part to 3440 feet or more in the northern part. This is interpreted to mean that in Carboniferous time there was a relief of not less than 2100 feet, with slopes of fourteen degrees or more.