scholarly journals Petrology and geochemistry of selected talc-bearing ultramafic rocks and adjacent country rocks in north-central Vermont

10.3133/pp345 ◽  
1962 ◽  
Author(s):  
A.H. Chidester
Keyword(s):  
Ultramafic Rocks ◽  
North Central ◽  
Adjacent Country ◽  
Petrology And Geochemistry

Microearthquake surveys in the Central and Northern Philippines

1979 ◽  
Vol 69 (6) ◽  
pp. 1889-1902
Author(s):  
H. K. Acharya ◽  
J. F. Ferguson ◽  
V. Isaac
Keyword(s):  
Short Duration ◽  
Ultramafic Rocks ◽  
Tectonic Feature ◽  
North Central ◽  
Manila Trench ◽  
Highly Active ◽  
West Central ◽  
Manila Bay ◽  
Large Earthquakes

abstract Microearthquake surveys were carried out in three sections of Central and Northern Philippines during 1975-1976 for a period of 5 months. A 4-month survey of Bataan Peninsula identified a major tectonic feature near Manila Bay which could not have been postulated from examination of seismicity maps. This feature appears to be situated near the southern end of ultramafic rocks of West Central Luzon and West Luzon Trough and trends W-SW from east of Corregidor Island toward Manila Trench for a distance of about 100 km. This survey also showed no microearthquake activity beneath two presently inactive volcanoes on Bataan Peninsula. The rate of activity in Bataan Peninsula region was found to be very low (8.4 events/1000 km2/yr). A short-duration survey (16 days) of the Philippine Fault in North Central Luzon revealed no microearthquake activity on the fault. During a third short-duration survey (16 days), the Verde Island Passage area between Luzon and Mindoro was found to be as highly active at the microearthquake level as it is for large earthquakes.

Ultramafic intrusions of the Abitibi area, Ontario

1969 ◽  
Vol 6 (2) ◽  
pp. 281-303 ◽  
Author(s):  
N. D. MacRae
Keyword(s):  
General Structure ◽  
Basaltic Magma ◽  
Tholeiitic Basalt ◽  
Ultramafic Rocks ◽  
The South ◽  
South Side ◽  
Original Order ◽  
Cyclic Unit ◽  
Petrology And Geochemistry ◽  
Group 2

A study has been made of the petrology and geochemistry of a 30-mile (48.3 km) segment of a belt of ultramafic-gabbroic igneous bodies extending past the south side of Lake Abitibi, Ontario. In general, the bodies are sill-like and are differentiated into major layers of peridotite, clinopyroxenite, and gabbro, the layers generally being in that stratigraphic order. In detail, the intrusions fall into four groups: (1) complex sills in which there is a cyclic repetition of layers; (2) simple differentiated sills showing only one sequence of the above rock layers; (3) bodies composed only of peridotite and dunite; and (4) bodies composed wholly of gabbroic rocks.One of the group (2) bodies has a chilled margin equivalent in composition to a tholeiitic basalt. The general structure of the intrusions and their petrographic and chemical features indicate that they are differentiated from basaltic magma by gravity-controlled fractionation. However, it appears that while solidifying, some of the intrusions were open to periodic addition or subtraction of magma. Thus, in the intrusions showing cyclic repetition of layers, it is apparent that the magma was altered prior to the formation of each cyclic unit such that the original order of mineral crystallization was repeated. For other intrusions, it can be inferred that large amounts of partly crystallized liquid were expelled such that each of these intrusions is now largely or wholly represented by ultramafic rocks. The bodies composed wholly of gabbro may be derived from the expelled magma.

Petrology and geochemistry of the Kruuse Fjord Gabbro Complex, East Greenland

1997 ◽  
Vol 134 (1) ◽  
pp. 67-89 ◽  
Author(s):  
JOHN G. ARNASON ◽  
DENNIS K. BIRD ◽  
STEFAN BERNSTEIN ◽  
NICHOLAS M. ROSE ◽  
CRAIG E. MANNING
Keyword(s):  
Tholeiitic Basalt ◽  
Coarse Grained ◽  
Ultramafic Rocks ◽  
Basalt Magma ◽  
Crystallization Sequence ◽  
East Greenland ◽  
Topographic Features ◽  
Layered Gabbro ◽  
Petrology And Geochemistry ◽  
Incompatible Trace Elements

The Kruuse Fjord Gabbro Complex is a composite intrusion of layered gabbro and troctolite with subordinate ultramafic rocks and minor trondhjemitic bodies. It was emplaced into Archaean continental crust of East Greenland during early Tertiary rifting of Greenland from Eurasia. The work to date has identified an outer gabbro series and an inner troctolite series, and these are separated by a narrow zone of trondhjemitic intrusions. In the southeast, the partially crystallized cumulates of the gabbro series were intruded by a lenticular, ultramafic pluton 800 m in thickness. Volumetrically minor, syenite–trachyandesite net-veined dykes and later, diabase dykes cross-cut the plutonic rocks. Structural and topographic features suggest that the layered rocks were affected by synmagmatic subsidence and deformation but not by monoclinal coastal flexure.The gabbro series is composed of a marginal gabbro unit, about 20 m wide, bordering more than a 2 km thickness of layered olivine and magnetite gabbro cumulates. The marginal gabbro is interpreted to be chilled magma. The layered cumulates are the product of repeated injections of magma that fractionated in an open-system magma chamber. Anorthositic and troctolitic layers in the lower part of the sequence may represent inputs of magma and suggest that the order of cumulus mineral crystallization was (1) plagioclase (An39–85), (2) olivine (Fo46–82), (3) augite (Wo28–47En39–58Fs8–18 ) and (4) magnetite. The disappearance of cumulus magnetite and a reversal in mineral compositions at 1.5 km from the base of the succession suggests a major input of magma occurred at this height. In the troctolite series, the composition of cumulus minerals, mineral crystallization sequence and style of emplacement are similar to those in the gabbro series. The ultramafic pluton is composed of coarse-grained wehrlite, olivine melagabbro and troctolite that were formed by at least three injections of magma. The typical mineral crystallization sequence was (1) cumulus chromite and olivine (Fo84–88); (2) poikilitic chrome diopside (Wo29–51En43–63Fs3–13 ); and (3) intercumulus plagioclase (An75–90), phlogopite, apatite and localized disseminated sulphides containing Au and platinum-group elements.Comparison of crystallization sequences and the major and trace element compositions of clinopyroxene suggests that the gabbroic and troctolitic rocks formed from a magma represented by the chilled marginal gabbro, a tholeiitic basalt magma similar to E-MORB, whereas the ultramafic rocks formed from a magma that was relatively enriched in incompatible trace elements and volatiles. The association of these two magma types is an example of bimodal mafic–ultramafic magmatism in a rifting environment.

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.

scholarly journals A Special Issue (Part-II): Mafic-ultramafic rocks and alkaline-carbonatitic magmatism and associated hydrothermal mineralization - dedication to Lia Nikolaevna Kogarko

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Lia N. Kogarko ◽  
Lalchand G. Gwalani ◽  
Peter J. Downes ◽  
Kirtikumar R. Randive
Keyword(s):  
Research Work ◽  
Ultramafic Rocks ◽  
Alkaline Magmatism ◽  
Special Issue ◽  
Origin And Evolution ◽  
Hydrothermal Mineralization ◽  
The Earth ◽  
Advanced Sampling ◽  
History Of ◽  
Petrology And Geochemistry

AbstractThis is the second part of a two-volumespecial issue of Open Geoscience (formerly Central European Journal of Geosciences) that aims to be instrumental in providing an update of Mafic-Ultramafic Rocks and Alkaline- Carbonatitic Magmatism and Associated Hydrothermal Mineralization. Together, these two volumes provide a detailed and comprehensive coverage of the subjects that are relevant to the research work of P.Comin-Chiaramonti (Italy) and LiaN. Kogarko (Russia) towhomPart-I and Part- II have been respectively dedicated. To a significant extent, the development of advanced sampling technologies related to alkaline and carbonatitic magmatism by Lia N. Kogarko, has allowed geoscientists to measure and sample the deep crust of the planet not only for the exploration for the mineral deposits, but also to answer basic scientific questions about the origin and evolution of alkaline rocks (kimberlites, lamproites and related rocks associated with carbonatites). The papers presented in this Part-II of the special issue cover the petrology and geochemistry of the rocks collected from the surface and penetrated by drilling. Lia Kogarko proposed a new theory for the evolution of alkaline magmatism in the geological history of the Earth – that the appearance of alkaline magmatism at the Archaean-Proterozoic boundary (~2.5 – 2.7 Ga), and its growing intensity, was related to changes in the geodynamic regime of the Earth and oxidation of the mantle due to mantle-crust interaction.

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