Crystalline Rock Mass Research Articles

Geochemical and isotopic imprints of hydrodynamic environments of fissure waters in crystalline rocks

1. Crystalline rock masses are not only permeable, but hydraulically continuous and geochemically active. The mass and energy exchange with host rocks in the migration process of fissure waters alter the physical properties and chemical and isotopic compositions of both fissure waters and their host rocks. It is for this reason that the geochemical peculiarities of both fissure waters and their media contain abundant information about their hydrodynamic environment. The acquisition and interpretation of hydrochemical and isotopic data proved to be an effective way to verify the hydraulic continuity of fissured media. 2. The movement of fissure water is variable both in time and in space. The distribution of sinters and the change of their compositions record the evolution of fissure water flow. The variability of fissure water flow in space, on the other hand, often causes remarkable difference in the chemical and isotopic compositions of fissure waters from the same area. On the premise of the verification of hydraulic continuity, system analysis and numerical modelling of fissure waters can be made on different scales.

Permeability determination in crystalline rocks by standard geophysical logs

The formation factor (ratio of bulk resistivity of rock to resistivity of formation fluid) obtained from the focused‐electrode log can be used to estimate the hydraulic conductivity of the unfractured granitic rock matrix [Formula: see text], using an empirical relationship developed between laboratory measurements of formation factor and permeability. The ratio of the formation factor derived from the focused‐electrode log [Formula: see text] to the formation factor derived from the density log [Formula: see text] may be used to estimate the hydraulic conductivity of fractured zones [Formula: see text], because of the following empirical relationship between the transmissivity [Formula: see text] obtained from the in situ hydrogeologic tests and the ratio of the two formation factors, namely, [Formula: see text] where A and s are coefficients [Formula: see text]. This empirical relationship confirms the usefulness of geophysical logs for identifying intervals of potentially high permeability in boreholes drilled in granitic rock. Estimates of hydraulic conductivity derived using these relationships can help obtain a qualitative understanding of hydrological conditions in a crystalline rock mass.

841187 Hydrogeological problems in unlined rock oil storages excavated in crystalline rock masses : Pan, B T Proc International Symposium on Engineering Geology and Underground Construction, Lisbon, 1983V1, P1.323–1.334. Publ Lisbon: SPG, 1983

841187 Hydrogeological problems in unlined rock oil storages excavated in crystalline rock masses : Pan, B T Proc International Symposium on Engineering Geology and Underground Construction, Lisbon, 1983V1, P1.323–1.334. Publ Lisbon: SPG, 1983

Scanning electron microscopy examples of clay residua from crystalline rocks

This article gives examples of the microstructures of clay residua from various crystalline rocks. Within the scope of engineering-geological classification of crystalline rock masses, the processes of weathering and their products which result in the weakening of rocks have been studied with regard to the construction of large dams and railway reconstruction in the region of the Bohemian Massif. The fundamental factors influencing the origin and the character of clay residua and the morphology of mineral grains have been pointed out. Particular stages of hydrolysis have been studied by means of scanning electron microscopy, differential thermal analyses, X-ray and chemical analyses.

Chutes de pierres et éboulisation dans les parois de l'étage périglaciaire

Abstract. — From intermittent observations and continuous measures taken during 21 months on the rock faces in the Combe de Laurichard (Briançonnian Alps), we have tried to approach the rockfall mechanism triggering the demolishing of walls and the development of screes in mountain environment about 3 000 meters high. The rapid falling of materials from fractured crystalline rock masses, allows rockfall inventory all the year round north and south facings. Temperature recorders set in various sites make it possible to situate the major peak of rockfall activity in spring, i.e. between april and june depending on aspect. As many authors, we emphasize the distinction between primary and secondary falls, which shows how important the topographic pattern is.

Strategy for Radioactive Waste Disposal in Crystalline Rocks

A strategy for waste disposal is proposed in which the repository would be situated in a crystalline rock mass beneath a blanket of sedimentary rocks whose ground-water flow characteristics are well understood. Such an approach exemplifies the concept of multiple barriers to the isolation of radioactive wastes from the biosphere. This strategy has the advantages that (i) ground-water flow within the sedimentary rocks can be investigated and modeled by conventional, well-under-stood theory and technology; (ii) under favorable circumstances, the flow system operates as an active barrier, so that a long migration path and extremely low flow rate to the biosphere can be assured; and (iii) since, in many locations, ground water is nonpotable, the possibility of future human intrusion can be minimized.

Influence of fracture deformation on secondary permeability— A numerical approach

In most crystalline rock masses the fracture conductivity generally exceeds the primary permeability by several orders of magnitude. Originally, discrete models for fractured media assumed the fractures to be rigid but later research has shown that fracture deformability can be an important fluid flow parameter. The present study utilizes existing models to study deformable fracture flow and attempts to define the range of influence of fracture deformation on conductivity and the limitations of the discrete approach. The model was found to be very sensitive to input data especially for dilatant shear problems. A rather straightforward coupling of dilatancy and conductivity was assumed—and this deserves further laboratory and field testing. The results indicate that dilatancy may be the most central parameter affecting conductivity in fracture flow.

Radioactive waste storage in argillaceous and crystalline rock masses : Witherspoon, P A; Gale, J E; Cook, N G W Proc 1st International Symposium on Storage in Excavated Rock Caverns (Rockstore 77), Stockholm, 5–8 Sept 1977, V3, P805–810. Publ Oxford: Pergamon Press, 1978

Radioactive waste storage in argillaceous and crystalline rock masses : Witherspoon, P A; Gale, J E; Cook, N G W Proc 1st International Symposium on Storage in Excavated Rock Caverns (Rockstore 77), Stockholm, 5–8 Sept 1977, V3, P805–810. Publ Oxford: Pergamon Press, 1978

Joint apertures in a pre-cambrian crystalline rock mass in sweden

Physical measurements of joint apertures in blasted rock walls and on rock outcrops give an unreliable result, due to the disturbances created by the blasting operations and in the latter case due to weathering effects. In this paper, hydraulic tests are used in order to obtain more significant values of the joint apertures. On the basis of the results of water-pressure tests, the joint apertures have been calculated in a crystalline rock mass.

Shock-Metamorphic Features in Two Meteorite Impact Structures, Southeastern Libya

Shock-metamorphic effects in sandstone samples from two circular structures about 80 km apart in southeastern Libya demonstrate that these structures formed by meteorite impact. The smaller structure is about 2.8 km in diameter, and the larger is 11.5 km in diameter. Both structures occur in flat-lying Nubian Sandstone (Early Cretaceous) that is intensely disturbed within the structures. Sandstone specimens from both show extensive microscopic shock effects in quartz, including cleavage and planar features (shock lamellae), with prominent orientations in the {0001}, {1¯122}, and {1¯011} planes. A reduced development of planes parallel to {1¯013} and {1¯012}, also typical of shocked Coconino Sandstone from Meteor Crater, Arizona, indicates that slightly porous or cemented sandstone shows significantly different responses to shock waves than massive crystalline rocks show. Both Libyan structures are post-Nubian in age. Their similar degree of erosion suggests a simultaneous origin by a double impact.

Les "konglomeratische Mergel" des Cordilleres betiques

Abstract The so-called "konglomeratische Mergel" (conglomeratic marl) formation of the Betic cordilleras, Spain, is neither a marl nor a conglomerate. A residual origin is suggested, involving solution of the soluble part of older rocks. Study of heavy minerals shows that the source rocks cannot have been the mica schists of the Sierra Nevada or the Mischungszone (zone of tectonic mixing); they were derived from crystalline rock masses which were emergent in the lower Triassic.

Southern Mountain Region: ABSTRACT

The Southern Mountain region, by definition here, includes the San Gabriel Mountains of the Transverse Ranges, and the Peninsular Ranges. The northern and eastern boundary of the region is essentially the San Andreas fault zone; the southwestern boundary is the contact of Cretaceous-Tertiary sedimentary rocks on the older crystalline rocks. The San Gabriel Mountains consist of a complex series of closely related Upper Jurassic (?) plutonic rocks including principally granite, granodiorite, monzonite, diorite, and gabbro. These include End_Page 2384------------------------------ numerous fragments of older intrusive rocks and an older metasedimentary series (Placerita) of possible Paleozoic age. The range is flanked on the north by a thick series of continental sandstones and conglomerates, interbedded with volcanics, of probable Miocene age. Intensely folded and faulted marine Pliocene sediments and continental lower Pleistocene gravels lie on the crystalline rocks along the southwest border of the range. Marine Paleocene Martinez sandstone and conglomerate occur in slivers in the San Gabriel fault zone. In the Peninsular Ranges, rocks of the Lower Cretaceous (?) batholith are exposed, including principally granodiorite, tonalite (quartz diorite), and gabbro. In general, these plutonics have intruded Triassic and Jurassic (?) sediments and volcanics along their western border, and Paleozoic sediments along the eastern border. All pre-Cretaceous formations have been metamorphosed to some extent and are widely distributed through the areas of plutonic rocks. Upper Cretaceous sediments overlie the basement crystalline rocks near the northwestern end of the Santa Ana Mountains and in the Southern Coastal region. Marine and brackish-water sediments of the Paleocene Martinez formation are distributed along the Elsinore fault zone. Continental Miocene sediments and volcanics are found along he San Andreas and San Jacinto fault zones and in the bordering Coachella and Imperial valleys at the east. Evidences of oil and gas have been found only along the margins of the crystalline rock masses, particularly abundant at the western and southwestern borders of the San Gabriel Mountains where there are numerous seepages. A very small amount of high-gravity oil was produced at the turn of the century from several shallow wells in crystalline rocks in the San Gabriel fault zone in the western San Gabriel Mountains 2½ miles east of Placerita oil field. Of a total of more than 70 exploratory wells drilled in the Southern Mountain region, these are the only ones which had any real shows of oil or gas. End_of_Article - Last_Page 2385------------

Applications d'etudes recentes sur les diffusions d'ions et la constitution des mineraux a l'interpretation de faits geologiques

Abstract Discusses some of the structural and metamorphic effects of solid diffusion in crystalline rock masses, with special reference to physicochemical equilibria, the stability of the oxygen lattice and its role in determining the extent of development of new mineral assemblages, and volume changes.

Crocker Flat Landslide Area, Temblor Range, California

The Crocker Flat landslide, located in the vicinity of Recruit Pass and northwest of Fellows, is composed largely of lower Miocene and Oligocene sands and silts and a minor amount of middle Miocene shale which were superimposed upon, and subsequently infolded with, younger Miocene sediments. This landslid mass descended by gravity, in upper Miocene time, from a highland located within or west of the San Andreas Fault zone, prior to the deposition of the Santa Margarita (upper Miocene). During Santa Margarita time coarse clastics derived from crystalline rock masses west of the Temblor Range were deposited unconformably over the Crocker Flat landslide and adjacent areas. The Santa Margarita beds and the Crocker Flat landslid mass were involved in the post-Miocene orogeny w ich elevated the Temblor Range and folded and faulted both of these units. Infolded and downfaulted outliers of Santa Margarita, on top of the Range, have been preserved from later erosion. On the summit of the Range clastics so coarse that they have been mapped as Basement complex by several workers are considered to be Santa Margarita in age because they are intertongued with and grade laterally into sands and boulder beds containing Santa Margarita fossils in adjacent areas. Furthermore a portion of the landslid lower Miocene and Oligocene sediments of the Crocker Flat area are unconformable beneath these coarse clastics. This relationship also tends to preclude the premise of this so-called basement being a part of a huge overthrust sheet. The crystalline rocks previously mapped as Basement complex on the west side of the Range are not in place but are detrital in origin and of Santa Margarita age also; these sediments owe their coarseness to a proximity of source and to possible minor landsliding during deposition. The intercalated lenses of granitoid and schistose boulders and sands in the upper Miocene punky shales on the northeast side of the Temblor Range are equivalent in age to the coarse Santa Margarita conglomerates on the southwest side of the Range. These beds are believed to have had a common western source which must have been near at hand, within or west of the San Andreas Fault zone. The erosional remnants of Santa Margarita conglomerate along the summit and higher parts of the Temblor Range are regarded as being normally depositional in origin and not klippen remnants of an overthrust sheet; these deposits represent an intermediate facies between the interbedded conglomerate and punky diatomaceous Santa Margarita on the northeast and the coarse conglomerates on the southwest side f the Range. The Recruit Pass fault is a normal fault with its western side downthrown; it is thought to be one of the lines along which uplift occurred to give the present elevation of the Temblor Range.

Resurrected Erosion Surface in Central Washington

Results obtained in mapping the geology of the Wenatchee-Chelan and of the Okanogan district suggest modifications of the earlier interpretations regarding the erosional history: 1) The existence of a “Methow Plain” or “Cascade Peneplain” is questioned. Most of the areas formerly considered to be remnants of this peneplain are surfaces controlled by the structure of the Columbia River basalt flows without regard to a widespread base level of erosion. One remnant, which bevels the Columbia River basalt and the Ellensburg formation on the flanks of an anticline in the Yakima district, is believed to be a pediment of very local extent. 2) The mature surface of the “Entiat stage” is well developed only on resistant granodiorite and gneiss and is exceedingly fragmentary or absent in areas underlain by greenstone, phyllite, schist, and Tertiary sedimentary rocks. It has not been recognized in areas underlain by the Columbia River basalt. The writer interprets nearly all the residuals of the “Entiat surface” described in the literature as resurrected fragments of a widespread late mature erosion surface buried beneath the Miocene Columbia River lavas and associated sediments and then partially exhumed in post-Miocene time. Certain fragmentary remnants of this surface on massive crystalline rocks beyond the limit reached by the basalt flows are believed to have been similarly preserved by burial under andesitic pyroclastics erupted from volcanoes in the Cascade Range.

The Ancient Volcanoes of Britain

THE Edinburgh school of geology, when of old it formulated the theory of existing causes of terrestrial change, established the fundamental principle of modern geological science. Thanks to this school, men learnt how rocks were formed, how the strata of the earth's crust were built up, how slow had been the evolution of the continents and oceans, and how important is the conception of time in regard to the past history of the globe. The brilliant representative of this illustrious school who has recently published a history of the volcanoes of Great Britain, sets forth in this remarkable treatise the great features in the volcanic history of the earth, and establishes the principles which will henceforth guide geologists in the study of the massive crystalline rocks. The Ancient Volcanoes of Britain. By Sir Archibald Geikie, Director-General of the Geological Survey. Vol. I., pp. xxiv. + 477; Vol. II., pp. xvi. + 492. (London: Macmillan and Co., Ltd., 1897.)

III.—On a Case in which various massive Crystalline Rocks including Soda-Granite, Quartz-Diorite, Norite, Horn-blendite, Pyroxenite, and different Chrysolitic Rocks, were made through Metamorphic Agencies in one Metamorphic Process

The extent of these bands, their number, uniformity of direction and apparently of dip, and the identity of the material constituting them with beds of the schist, especially the more northern, are such as to warrant the following section (Fig. 15).

III.—On a Case in which various massive Crystalline Rocks including Soda-Granite, Quartz-Diorite, Norite, Hornblendite, Pyroxenite, and different Chrysolitic Rocks, were made through Metamorphic Agencies in one Metamorphic Process

The above brief description of the Cortland rocks prepares the way for a consideration of their relation to the other rocks of the county. The following questions arise: Are they one with the latter in system ? are they rocks of an earlier system ? or are they eruptive rocks, and not metamorphic, and hence, of no bearing on the general question as to the age of the Westchester limestones and the associated schists ?

II.—On a Case in which various massive Crystalline Rocks including Soda–Granite, Quartz–Diorite, Norite, Hornblendite, Pyroxenite, and different Chrysolitic Rocks, were made through Metamorphic Agencies in one Metamorphic Process

The hornblendic and associated rocks referred to in the above title cover a large part of the township of Cortland—the north-western of Westchester County, New York—between Croton River on the south and the parallel of Peekskill on the north, an area of about 25 square miles. They differ widely from the ordinary rocks of the county, and may well be designated the Cortland series. In fact, a series so remarkable in constitution, so diversified in kinds, and so full of geological interest, is seldom found together within so small an area anywhere on the globe. They reach the banks of the Hudson just south of the Peekskill railroad station, and at several points beyond; yet considerable portions of the shore region are occupied by narrow strips of common kinds of mica schist and gneiss, and occasionally limestone.