The Mid-Atlantic Ridge near 45 °N. VI. Remanent intensity, susceptibility, and iron content of dredged samples

1970 ◽  
Vol 7 (2) ◽  
pp. 226-238 ◽  
Author(s):  
E. Irving ◽  
W. A. Robertson ◽  
F. Aumento
Keyword(s):  
Iron Content ◽  
Rock Type ◽  
Chemical Change ◽  
Sampling Bias ◽  
Axial Zone ◽  
Mean Intensity ◽  
Basaltic Rocks ◽  
Active Volcanism ◽  
Serpentinized Peridotite ◽  
Mid Atlantic Ridge

Results from 27 dredge hauls (75 samples) spaced from 150 km west to 70 km east of the Median Valley of the Mid-Atlantic Ridge at about 45 °N are reported. Basalt is the most common rock type. The basalts have a mean remanent intensity of 92 × 10−4 and a mean susceptibility of 0.9 × 10−4 cgs cm−3. The remanence varies with distance from the axis, samples from the Median Valley (mean 574 × 10−4) being ten times more magnetic than samples at a greater distance. Most of this decrease of intensity occurs within a few kilometers (less than 6 km) of the central axis and within the zone of active volcanism. It is suggested that this dramatic drop in intensity is caused by viscous decay enhanced by thermal cycling or by chemical change in the narrow volcanic axial zone.Certain other properties of the basalts vary with distance; the blocking temperatures and stability (versus a.f. demagnetization) increase, and the ratio FeO/Fe2O3 decreases with distance. These changes are most marked at the inner slopes of the Crestal Mountains not within the narrow axial zone, and it is possible that they reflect sampling bias, the samples from the Median Valley being from flow margins, whereas the collections from the flanks contain material from the centers of flows.Non-basaltic rocks include serpentinized peridotite, greenstone, gabbro, and diabase. Serpentinized peridotite samples are strongly magnetic and have a mean intensity of 23 × 10−4 cgs cm−3. Greenstones, gabbros, and diabases are weakly magnetized, with mean intensities of about 10−4. Moreover, basalt showing partial alteration to greenstone has intermediate intensities showing that such a metamorphic process effectively demagnetizes a rock. This result is more consistent with the idea that Layer 3 is composed predominantly of gabbro and metamorphosed basalt rather than of serpentinized peridotite. The remanence and susceptibilities of 18 "erratic" samples, which are thought from other evidence to have been deposited by Pleistocene icebergs, have a wide and irregular spread.

scholarly journals Genetically different organogenic buildups in isotope values δ 13С and δ 18О

2021 ◽  
Vol 11 ◽  
pp. 27-42
Author(s):  
A. I. Antoshkina ◽  
◽  
L. A. Shmeleva ◽  
L. V. Leonova ◽  
I. G. Dobretzova ◽  
...  
Keyword(s):  
Carbonate Rocks ◽  
Climatic Conditions ◽  
Upper Ordovician ◽  
Axial Zone ◽  
Physical Methods ◽  
Active Volcanism ◽  
The North ◽  
Marine Carbonates ◽  
Mid Atlantic Ridge ◽  
Heavy Carbon

The isotopic composition of carbon and oxygen of 165 samples of carbonate rocks of genetically different organogenic structures: the Upper Ordovician Bol'shaya Kos'yu reef, the Upper Devonian Shar'yu microbial mound, the Kozhym skeletal mound, the Upper Miocene Kazantip bioherm complex and deep-water organogenic-carbonate structures of the north of the Mid-Atlantic Ridge was studied. The reef and microbial mound are characterized by δ 13СPDB values within the limits close to normal-sedimentary marine carbonates (–0.33—3.13 ‰) and (0.8—3.0 ‰), but with significant variations in δ 18ОSMOW — (22.24—30.0 ‰) and (20.4—26.3 ‰), respectively. The most isotopically-heavy carbon composition (5.1—7.3 ‰) in combination with varying δ 18ОSMOWvalues (22.4— 30.0 ‰) is characteristic of limestones and brachiopods of the skeletal mound. Fluctuations of δ 13СPDB and δ 18ОSMOW values in carbonate rocks of the Kazantip bioherm complex are the most expressive (–2.76—7.17 ‰) and (24.20—33.1 ‰), respectively. Deepwater organogenic structures from the bottom of the axial zone with active volcanism, in contrast to others, showed stable δ 13СPDB values (–0.98—0.83 ‰) within the area of normal-sedimentary marine carbonates, whereas for oxygen the values are istopic-heavy (32.27—39.75 ‰). As a result, the specificity of the development of the objects under study, established by lithological-paleoecological and chemical-physical methods, found its substantiation in isotopic values, paleosalinity and paleotemperatures caused by paleogeographic and climatic conditions.

Zircon in gabbroids from the axial zone of the Mid-Atlantic ridge, Markov Deep, 6° N: Correlation of geochemical features with petrogenetic processes

Petrology ◽  
2013 ◽  
Vol 21 (1) ◽  
pp. 1-15 ◽  
Author(s):  
L. Ya. Aranovich ◽  
T. F. Zinger ◽  
N. S. Bortnikov ◽  
E. V. Sharkov ◽  
A. V. Antonov
Keyword(s):  
Axial Zone ◽  
Mid Atlantic Ridge ◽  
Markov Deep

Accretion of crust in the axial zone of the Mid-Atlantic Ridge south of the Martin Vas Fracture Zone, South Atlantic

Geotectonics ◽  
2009 ◽  
Vol 43 (5) ◽  
pp. 358-378
Author(s):  
S. G. Skolotnev ◽  
A. A. Peyve ◽  
N. N. Turko ◽  
M. E. Bylinskaya ◽  
L. A. Golovina
Keyword(s):  
Fracture Zone ◽  
South Atlantic ◽  
Axial Zone ◽  
Mid Atlantic Ridge

PERIDOTITIC INTRUSIONS NEAR QUETICO AND SHEBANDOWAN, NORTHWESTERN ONTARIO: A CONTRIBUTION TO THE PETROLOGY AND GEOCHEMISTRY OF ULTRAMAFIC ROCKS

1964 ◽  
Vol 1 (1) ◽  
pp. 63-98 ◽  
Author(s):  
D. H. Watkinson ◽  
T. N. Irvine
Keyword(s):  
Lake Superior ◽  
Olivine Basalt ◽  
Chemical Change ◽  
Ultramafic Rocks ◽  
Tholeiitic Magma ◽  
Mafic Intrusions ◽  
Northwestern Ontario ◽  
Serpentinized Peridotite ◽  
Small Stock ◽  
Petrology And Geochemistry

A study has been made of several dozen small, stock-like ultramafic to mafic igneous bodies that occur in two clusters, 50 and 75 miles west of the head of Lake Superior. One cluster, the Quetico intrusions, is dominantly hornblende peridotite, hornblendite, and feldspathic hornblendite; the other, the Shebandowan intrusions, comprises serpentinized peridotite and subordinate gabbro. Both intrude eugeosynclinal deposits and are followed by extensive granitic, and minor syenitic intrusions, and both have associated Ni–Cu sulphides containing minor Pt and Pd.The Quetico intrusions are shown to have formed by fractional crystallization of tholeiitic olivine basalt liquid, possibly carrying suspended olivine and clinopyroxene when emplaced. Crystallization was at a water partial pressure of at least 2500 bars and, thus, a depth of 5 or more miles. The Shebandowan intrusions resemble alpine-type peridotite bodies structurally but, chemically and petrographically, are more like the differentiates of stratiform mafic intrusions. Their peridotite has formed from tholeiitic magma by early fractionation of olivine; the gabbro probably represents residual magmatic liquid. Serpentinization, which is postmagmatic, apparently has not caused extensive chemical change beyond addition of H2O, O2, and some CO2, and local redistribution of lime.The rocks in the two groups of intrusions differ appreciably in Cu and Ni, and a correlation between the Cu/Ni ratios of the rocks and their respective ores is illustrated. This correlation, and the sulphur isotopic composition, both indicate derivation of the sulphides from the intrusions.

Morphology and impurity elements of zircon in the oceanic lithosphere at the Mid-Atlantic ridge axial zone (6°–13° N): Evidence of specifics of magmatic crystallization and postmagmatic transformations

Petrology ◽  
2017 ◽  
Vol 25 (4) ◽  
pp. 339-364 ◽  
Author(s):  
L. Y. Aranovich ◽  
N. S. Bortnikov ◽  
T. F. Zinger ◽  
S. E. Borisovskiy ◽  
V. A. Matrenichev ◽  
...  
Keyword(s):  
Oceanic Lithosphere ◽  
Axial Zone ◽  
Mid Atlantic Ridge ◽  
Impurity Elements

Age and composition of the Ruisseau Isabelle Mélange along the Shickshock Sud fault zone: constraints on the timing of mélanges formation in the Gaspé Appalachians

2001 ◽  
Vol 38 (1) ◽  
pp. 21-42 ◽  
Author(s):  
Michel Malo ◽  
Pierre A Cousineau ◽  
Paul E Sacks ◽  
J FV Riva ◽  
Esther Asselin ◽  
...  
Keyword(s):  
Black Shale ◽  
Sedimentary Rock ◽  
Rock Type ◽  
Accretionary Prism ◽  
Structural Features ◽  
Late Ordovician ◽  
Ultramafic Rocks ◽  
Serpentinized Peridotite ◽  
Tectonic Position ◽  
Tectonic Origin

Mélanges are common in the Humber and Dunnage zones of the Quebec Appalachians. Humber Zone mélanges are spatially associated with Taconian nappes and believed to be of tectonic origin. Dunnage Zone mélanges are interpreted as relicts of an Ordovician accretionary prism. The Ruisseau Isabelle Mélange (RIM) in the Gaspé Appalachians was first interpreted as a Dunnage Zone mélange, because of its tectonic position along the Baie Verte – Brompton Line and lithological components, such as dark mudstone, blocks of ultramafic rocks, and greenish chromite-bearing sandstone. The RIM comprises sedimentary rock assemblages (Composite Shale, Black Shale, and Chromite-Bearing Sandstone assemblages), an Exotic Block, a Pebbly Mudstone Assemblage and slivers of Serpentinized Peridotite, and Metamorphic Tectonite. Most mélanges of the Dunnage Zone in the Quebec Appalachians contain partly similar rocks, but their age is not well constrained. Recent work on the RIM and Cap-Chat Mélange of the Humber Zone and new fossil finds in the RIM rock assemblages allow us to conclude that previous distinction between mélanges of the Dunnage and Humber zones on the basis of rock-type associations is not valid. According to the age of the RIM rock assemblages, mélanges in the northern Gaspé Appalachians continued forming after the mid-Caradocian, later than the Dunnage Zone mélanges of southern Gaspé Appalachians. The juxtaposition and structural features of the RIM rock assemblages result from repeated faulting along the Shickshock Sud fault from Late Ordovician to Middle Devonian.

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