Chronologie geologique fondee sur la desintegration atomique des mineraux radioactifs

1949 ◽  
Vol S5-XIX (7-9) ◽  
pp. 657-668
Author(s):  
Djalma Guimaraes
Keyword(s):  
Radioactive Decay ◽  
Minas Gerais ◽  
Crystalline Basement ◽  
Early Paleozoic ◽  
Sources Of Error ◽  
Basement Rocks ◽  
Potential Sources ◽  
Radioactive Minerals ◽  
Uranium Minerals ◽  
Age Determinations

Abstract Discusses the use of the rate of radioactive decay of minerals as a criterion for determining the geologic age of crystalline basement rocks, noting potential sources of error, due largely to lack of consideration of petrogenetic factors, and the reliability of data based on analyses of monazite, whose field of stability is greater than that of other uranium minerals. The Precambrian-early Paleozoic chronology of Brazil is summarized on the basis of age determinations of radioactive minerals. Analyses of fresh and weathered djalmaite from Minas Gerais and monazite from numerous localities are included.

La tectonique et la geologie de la partie orientale du bouclier bresilien

1967 ◽  
Vol S7-IX (1) ◽  
pp. 147-152 ◽  
Author(s):  
Edison F. Suszczynski
Keyword(s):  
Lower Devonian ◽  
Sedimentary Cover ◽  
Crystalline Basement ◽  
Early Paleozoic ◽  
Structural Trend ◽  
Coastal Basins ◽  
Geologic Processes ◽  
Age Determinations

Abstract The Brazilian shield comprises two separate units. The Precambrian crystalline basement, in the eastern part of the shield, is divided into three parts distinguished by their lithology, structural trend, and mineralizations. The sedimentary cover contains a folded series of formations ranging in age from terminal Precambrian to early Paleozoic and an unfolded series represented by sediments of lower Devonian to Tertiary age which were deposited in epicontinental, intracratonic, and coastal basins. Four phases are recognized in the evolution of the unfolded sedimentary series. The effects of geologic processes active in the Brazilian shield from the end of the Precambrian to the end of the Mesozoic have been observed in the Parnaba-Sao Francisco intracratonic geosyncline. Results of age determinations are reported.

scholarly journals The first deep heat flow determination in crystalline basement rocks beneath the Western Canadian Sedimentary Basin

2014 ◽  
Vol 197 (2) ◽  
pp. 731-747 ◽  
Author(s):  
Jacek Majorowicz ◽  
Judith Chan ◽  
James Crowell ◽  
Will Gosnold ◽  
Larry M. Heaman ◽  
...  
Keyword(s):  
Heat Flow ◽  
Sedimentary Basin ◽  
Crystalline Basement ◽  
Basement Rocks

40Ar/39Ar incremental-release ages of hornblende and biotite from Grenville basement rocks within the Indian Head Range complex, southwest Newfoundland: their bearing on Late Proterozoic – Early Paleozoic thermal history

1978 ◽  
Vol 15 (8) ◽  
pp. 1374-1379 ◽  
Author(s):  
R. D. Dallmeyer
Keyword(s):  
North America ◽  
Continental Margin ◽  
Thermal History ◽  
Structural Unit ◽  
Elevated Temperatures ◽  
Early Paleozoic ◽  
Present Position ◽  
Thermal Peak ◽  
Basement Rocks ◽  
The Times

Hornblende and biotite from autochthonous basement rocks within the Indian Head Range complex of southwest, insular Newfoundland record undisturbed 40Ar/39Ar release spectra with average total-gas ages of 880 Ma (hornblende) and 825 Ma (biotite). These gas-retention ages date the times when this segment of the western Appalachian basement terrane cooled below hornblende and biotite argon retention temperatures (~500 °C and ~300 °C respectively) following culmination of the ~ 1150–1100 Ma Grenville metamorphism. Although these results indicate that elevated temperatures were maintained for a prolonged period following the Grenville thermal peak, once initiated, cooling must have been relatively rapid because hornblende and biotite record generally similar total-gas dates.The undisturbed release spectra of minerals within the Indian Head Range complex indicate that this segment of the western Appalachian basement terrane was not affected by Paleozoic metamorphism. This is consistent with recent tectonic models that indicate that the overlying Humber Arm allochthon was emplaced into its present position as a cold, already assembled structural unit. Lack of Paleozoic metamorphism within the Indian Head basement rocks is also compatible with suggestions that the obduction site of the Bay of Islands ophiolite lay considerably east of the Early Paleozoic continental margin of North America.

scholarly journals POTENTIAL SOURCES OF ERROR IN CORONARY ARTERIOGRAPHY

1975 ◽  
Vol 124 (3) ◽  
pp. 386-393 ◽  
Author(s):  
DAVID C. LEVIN ◽  
HAROLD A. BALTAXE ◽  
THOMAS A. SOS
Keyword(s):  
Coronary Arteriography ◽  
Sources Of Error ◽  
Potential Sources

scholarly journals Influence of basement rocks on fluid evolution during multiphase deformation: the example of the Estamariu thrust in the Pyrenean Axial Zone

2020 ◽  
Author(s):  
Daniel Muñoz-López ◽  
Gemma Alías ◽  
David Cruset ◽  
Irene Cantarero ◽  
Cédric M. Jonh ◽  
...  
Keyword(s):  
Sedimentary Cover ◽  
Crystalline Basement ◽  
Normal Faults ◽  
Published Data ◽  
Fluid Migration ◽  
Rock Interaction ◽  
Fluid Chemistry ◽  
Vein Formation ◽  
Basement Rocks ◽  
Calcite Veins

Abstract. Calcite veins precipitated in the Estamariu thrust during two tectonic events decipher the temporal and spatial relationships between deformation and fluid migration in a long-lived thrust and determine the influence of basement rocks on the fluid chemistry during deformation. Structural and petrological observations constrain the timing of fluid migration and vein formation, whilst geochemical analyses (δ13C, δ18O, 87Sr/86Sr, clumped isotope thermometry and elemental composition) of the related calcite cements and host rocks indicate the fluid origin, pathways and extent of fluid-rock interaction. The first tectonic event, recorded by calcite cements Cc1a and Cc2, is related to the Alpine reactivation of the Estamariu thrust, and is characterized by the migration of meteoric fluids, heated at depth (temperatures between 56 and 98 °C) and interacted with crystalline basement rocks before upflowing through the thrust zone. During the Neogene extension, the Estamariu thrust was reactivated and normal faults and shear fractures with calcite cements Cc3, Cc4 and Cc5 developed. Cc3 and Cc4 precipitated from hydrothermal fluids (temperatures between 127 and 208 °C and between 102 and 167 °C, respectively) derived from crystalline basement rocks and expelled through fault zones during deformation. Cc5 precipitated from low temperature meteoric waters percolating from the surface through small shear fractures. The comparison between our results and already published data in other structures from the Pyrenees suggests that regardless of the origin of the fluids and the tectonic context, basement rocks have a significant influence on the fluid chemistry, particularly on the 87Sr/86Sr ratio. Accordingly, the cements precipitated from fluids interacted with crystalline basement rocks have significantly higher 87Sr/86Sr ratios (> 0.710) with respect to those precipitated from fluids that have interacted with the sedimentary cover (

Some orogenic episodes in South America by K–Ar and whole-rock Rb–Sr dating

1968 ◽  
Vol 5 (3) ◽  
pp. 633-638 ◽  
Author(s):  
P. M. Hurley ◽  
G. C. Melcher ◽  
W. H. Pinson Jr. ◽  
H. W. Fairbairn
Keyword(s):  
South America ◽  
Minas Gerais ◽  
Igneous Rocks ◽  
Radiometric Dating ◽  
Basement Rocks ◽  
Guayana Shield ◽  
Northern Brazil ◽  
Belo Horizonte ◽  
The Guianas ◽  
Coast Region

Radiometric dating of basement rocks in South America by the M.I.T. geochronology laboratory has indicated the following thermo-tectonic episodes. The gneisses of the Imataca Complex of the Venezuela Guayana Shield are about 3000 m.y.; they have been intruded by igneous rocks of 2000 m.y. age. Ancient rocks between these age values have been found in the Bação Complex in Minas Gerais. The principal cratonic rocks of southeastern Venezuela, the Guianas, northern Brazil in the Amapa district, the coast region between Belém and São Luis, the region west of the Tocantins River, and in the São Francisco area near Salvador all show ages in the range 2000 ± m.y. The region in northeast Brazil represented by the Cariri orogenic belt shows an average Rb–Sr whole-rock isochron age value of 640 m.y. K–Ar age values in the Belo Horizonte district, Minas Gerais, show a metamoprhic overprint value of 500 m.y. A similar value is found in Colombia, east of the Macarena mountains.

scholarly journals The role of geological structures on groundwater occurrence and flow in crystalline basement aquifers: a status review

2018 ◽  
Vol 11 (1) ◽  
pp. 155-164
Author(s):  
M.A. Idris ◽  
M.L. Garba ◽  
S.A. Kasim ◽  
I.M. Madabo ◽  
K.A. Dandago
Keyword(s):  
Hydrological Cycle ◽  
Crystalline Basement ◽  
Geological Structures ◽  
Secondary Porosity ◽  
Groundwater Movement ◽  
Remote Sensing Technique ◽  
Basement Rocks ◽  
Groundwater Occurrence ◽  
Basement Aquifers

The paper is review on the role of geological structures on groundwater occurrence and flow in Crystalline Basement aquifers. The aim was to study the existing available literatures in order to evaluate structural/lineaments (faults, joints/fractures, folds, shear zone etc.) their influences and controls of groundwater occurrence and flow of bedrock of crystalline rocks of igneous and/or metamorphic origin. Groundwater in the basement aquifers resides/occurs within the weathered overburden and fractured bedrocks which originate from rainfall through the process of hydrological cycle. Remote sensing technique uses satellite imagery or aerial photograph to identify linear features on the ground and attempts to relate these lines to geologic structures capable of transmitting and storing large quantities of groundwater. Faults, joints/fractures and folds act as conduit and make rocks excellent aquifers. These features also, served as channels for groundwater movement which may results to an increased in secondary porosity, permeability and therefore, can results as a groundwater prospective/promising zones in crystalline basement rocks. Keywords: Basement Terrain, Groundwater, Lineament, Movement, Occurrence

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