Low-Potash Lush's Bight Tholeiites: Ancient Oceanic Crust in Newfoundland?

1972 ◽  
Vol 9 (5) ◽  
pp. 574-588 ◽  
Author(s):  
W. G. Smitheringale
Keyword(s):  
Oceanic Crust ◽  
Copper Sulfide ◽  
Alkali Basalt ◽  
Trace Element Content ◽  
Volcanic Origin ◽  
North Central ◽  
Ocean Ridges ◽  
Iron Copper ◽  
Volcanic Pile ◽  
Low K

The Lush's Bight Group of north-central Newfoundland consists mainly of regionally metamorphosed pillowed basalts. Mafic dikes and sills, comagmatic with the basalts, are abundant and dioritic stocks and silicic igneous rocks constitute a small portion of the group. Most rocks belong to a tholeiitic suite derived from low-K tholeiite that has a trace element content similar to oceanic tholeiite. A few rocks are slightly alkaline, implying that alkali basalt may have contributed to the volcanic pile. The thickness, chemical composition, and lithology of the group suggest it represents the upper (dominantly volcanic) part of layer two of oceanic crust. Alternatively, formation as a tholeiitic shield beneath a mid-ocean volcanic island is suggested by the alkaline affinities of some rocks and by a thick pyroclastic sequence that conformably overlies the group.The Lush's Bight Group contains many volcanogenic iron-copper sulfide occurrences.Mid-ocean ridges are recognized as magmatically dominated environments in which hydrothermal fluids of plutonic and volcanic origin might constitute ore fluids.

Crustal structure of the southeast flank of Kilauea Volcano, Hawaii, from seismic refraction measurements

1980 ◽  
Vol 70 (4) ◽  
pp. 1149-1159
Author(s):  
John J. Zucca ◽  
David P. Hill
Keyword(s):  
Oceanic Crust ◽  
Crustal Structure ◽  
Seismic Refraction ◽  
Kilauea Volcano ◽  
Geological Survey ◽  
Pn Velocity ◽  
Kīlauea Volcano ◽  
Volcanic Pile ◽  
Rift Zones ◽  
The U.S

abstract In November 1976, the U.S. Geological Survey, in conjunction with the Hawaii Institute of Geophysics, established a 100-km-long seismic refraction line normal to the southeast coast of Hawaii across the submarine flank of Kilauea Volcano. Interpretation of the data suggests that the oceanic crust dips about 2° toward the island underneath the volcanic pile. The unreversed Pn velocity is 7.9 km/ sec with crustal velocities varying strongly along the profile. Profiles across the rift zones of Kilauea suggest that the velocity in the rifts is higher than the velocity in the surrounding extrusive rocks and that the velocity in the southwest rift (∼6.5 km/sec) is lower than the velocity in the east rift (∼7.0 km/sec). The rift boundaries seem to dip away from the rift such that a large part of the volcanic pile is composed of the higher velocity core of riftzone rock.

scholarly journals Evidence for a Carbonatite-Influenced Source Assemblage for Intraplate Basalts from the Buckland Volcanic Province, Queensland, Australia

Minerals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 546 ◽  
Author(s):  
Joshua J. Shea ◽  
Stephen F. Foley
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Alkali Basalt ◽  
Element Concentration ◽  
Continental Lithosphere ◽  
Alkali Basalts ◽  
Volcanic Province ◽  
Eastern Australia ◽  
Low K ◽  
Similar Enrichment

Eastern Australia contains a widespread suite of primitive (MgO ≥ 7.5 wt.%) intraplate basaltic provinces, including those sited along the longest continental hotspot track on Earth (≈2000 km), the Cosgrove track. The Buckland volcanic province is the most southerly basaltic province on the Cosgrove track before a >1600 km stretch that contains only sparse leucitite volcanism. Buckland is also situated just northeast of the edge of thick cratonic lithosphere where it transitions to a thinner continental lithosphere (<110 km) to the east, which may influence the production of plume-derived melts. Here, analysis of minor and trace elements in olivines in alkali basalts and basanites from the Buckland Province are combined with whole-rock compositions to elucidate the mantle source assemblages, and to calibrate minor and trace element indicators in olivine for application to source mineralogy. Olivine xenocrysts show element concentration ranges typical for peridotites; Mn and Al concentrations indicate that the ambient mantle is spinel, rather than garnet, peridotite. High modal pyroxene content is indicated by high Ni, Zn/Fe, and Fe/Mn in olivines, while high Ti/Sc is consistent with amphibole in the source. Residual phlogopite in the source of the basanites is indicated by low K/Nb in whole rocks, while apatite contains high P2O5 and low Rb/Sr (≥0.015) and Sr/La (≥13). The basanite source assemblage probably contains apatite, phlogopite, olivine, clinopyroxene and orthopyroxene, whereas the alkali basalt source assemblage is probably amphibole, olivine, orthopyroxene and clinopyroxene ± phlogopite ± apatite. Both source assemblages correspond broadly to olivine websterite, with the basanite source lying deeper than that for alkali basalt, explaining the occurrence of phlogopite in the source. This mineralogy, along with whole-rock Ti/Eu, Zr/Hf and P2O5/TiO2 values approaching those of natural carbonatites, provide evidence showing that the Buckland source consists of a peridotite that has interacted with a carbonate-rich melt whose origin may be in the deep lithosphere or asthenosphere beneath the craton. Similar enrichment processes are probably common throughout eastern Australia, controlling trace element characteristics in basaltic provinces. The topography of the underside of the lithosphere may play a significant role in determining mantle source assemblages by diverting and concentrating melt flow, and thus influence the location of basaltic provinces.

New gravitational evidence for the subsurface extent of oceanic crust in north-central Newfoundland

1976 ◽  
Vol 13 (3) ◽  
pp. 459-469 ◽  
Author(s):  
H. G. Miller ◽  
E. R. Deutsch
Keyword(s):  
Oceanic Crust ◽  
Coastal Areas ◽  
Crustal Material ◽  
Two Dimensional ◽  
Ophiolite Complex ◽  
Southern Boundary ◽  
North Central ◽  
Density Data ◽  
Bouguer Anomalies ◽  
Plate Margin

Gravity has been measured at 226 locations having a mean spacing of 2.5 km in the area of western Notre Dame Bay, in north-central Newfoundland. The data reveal that the observed steep seaward positive gradients of the Bouguer anomalies previously found on eastern Notre Dame Bay continue to coastal areas of western Notre Dame Bay. This belt of large gradients correlates spatially with the trace of the Chanceport – Lobster Cove Fault, which is the southern boundary of this belt of ophiolitic and island arc rocks (Belts Cove Ophiolite Complex) on the Burlington peninsula, which forms the basement of this belt. The observed anomalies may represent the gravity signature of a Paleozoic lithospheric plate margin, but a test of this possibility must await data from the bay itself.Interpretation of four profiles, using density data from rock samples and two-dimensional models, leads to the conclusion that oceanic crustal material similar to that found on Notre Dame Bay, zone D, continues inland beneath parts of zones C and E to 5–10 km maximum depth. The interpretation also suggests the desirability of establishing a subzone on the Burlington peninsula.

Oxygen isotope geochemistry of rocks from DSDP Leg37

1977 ◽  
Vol 14 (4) ◽  
pp. 771-776 ◽  
Author(s):  
K. Muehlenbachs
Keyword(s):  
Isotopic Composition ◽  
Oxygen Isotope ◽  
Oceanic Crust ◽  
Isotope Geochemistry ◽  
Altered Rock ◽  
Ocean Ridges ◽  
Dredged Materials ◽  
Mid Ocean Ridge ◽  
Intrusive Rocks ◽  
Ocean Ridge

The isotopic compositions of minerals separated from DSDP Leg 37 samples indicate that the primary, unaltered δ18O of both the intrusive and extrusive rocks are identical (~5.7 ‰, SMOW) to those of unaltered basalts dredged from mid-ocean ridges. All of the analyzed basalts (6 to 10 ‰) have been enriched in 18O due to weathering by cold seawater, whereas the intrusive rocks (2.4 and 5.0 ‰) are depleted of 18O probably as a result of exchange with hot seawater at the mid-ocean ridge. Both kinds of altered rock are also known from the study of dredged materials. 18O is preferentially removed from seawater by the first process, but is added to seawater by the second. Exchange of oxygen between oceanic crust and seawater must be considered in any discussion of the evolution of the isotopic composition of the oceans, because large volumes of rock are altered each year as the oceanic crust is formed.

Geochemistry and tectonic significance of the mafic volcanic blocks in the Dunnage mélange, north central Newfoundland

1985 ◽  
Vol 22 (9) ◽  
pp. 1248-1256 ◽  
Author(s):  
Janusz J. Wasowski ◽  
Robert D. Jacobi
Keyword(s):  
Chemical Composition ◽  
Alkali Basalt ◽  
Volcanic Rocks ◽  
Pillow Lava ◽  
Calc Alkaline ◽  
North Central ◽  
Head Formation ◽  
Tectonic Significance ◽  
Low Potassium ◽  
Tuff Breccia

Abundant volcanic blocks are present in the Dunnage mélange. These mafic volcanic rocks consist predominantly of pillow lava, tuff breccia, isolated pillow–tuff breccia, and minor amounts of ropy lava.Major- and trace-element compositions of the basalts reveal that these volcanics do not resemble calc-alkaline or low-potassium island-arc suites. Rather, the majority of the samples are enriched-type ocean-floor tholeiites, whereas some show alkali basalt affinities. Discrimination diagrams suggest that these basalts may have been erupted as within-plate basalts. However, the chemical composition of the volcanic blocks is most similar to that of basalts generated at bathymetric highs located astride (or slightly off) mid-ocean ridges.The geochemistry of the Dunnage mélange basalts is very similar to that of the mafic volcanic rocks from the nearby Summerford Group and the Lawrence Head Formation. This correlation is further supported by sedimentary and petrographic evidence and by partial age equivalency.

scholarly journals Fragmento tectónico cabo frio: aspectos de campo, petrografía e geoquímica

1994 ◽  
Vol 17 ◽  
pp. 109-131
Author(s):  
Ariadne Do Carmo Fonseca
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Amphibolite Facies ◽  
Intermediate Pressure ◽  
High K ◽  
Low K ◽  
Silicate Rocks ◽  
Cabo Frio

The main lithological units which occur in the "Cabo Frio Tectonic Fragment" are orthogneisses and paragneisses. The orthogneisses have granitic-granodioritic-tonalitic compositions, with amphibolitic enclaves and intercalations and are cutted by granitic aplites. The paragneisses are metapelites, with intercalations of amphibolite, quartzites and calc-silicate rocks, metamorphosed in upper amphibolite facies, in intermediate pressure conditions. Geochemically, the orthogneisses correspond to a metaluminous high-K calc-alkalic series, with monzogabbro, quartz-monzodiorite and monzonite compositions. Otherwise, the petrography indicates a low-K calc-alkalic series, suggesting a pre-collisional granitoids series related to oceanic crust subduction. A divergence between the compositions obtained by the petrography and geochemistry can be the result of problems in the analyses of alkalies. The amphibolites, associated to the orthogneisses, also present calc-alkalic metaluminous character, with basaltic and andesitic compositions, suggestive of orogenic emplacement. The paragneisses show compositions varying between lithoarenite and arkoses, with peraluminous character, probably deposited in a continental are or ative continental margin environment.

Blueschist facies overprint of late Triassic Tethyan oceanic crust in a subduction–accretion complex in north-central Anatolia, Turkey

2018 ◽  
Vol 176 (5) ◽  
pp. 945-957 ◽  
Author(s):  
Ömer Faruk Çelik ◽  
Mutlu Özkan ◽  
Cyril Chelle-Michou ◽  
Sarah Sherlock ◽  
Andrea Marzoli ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Central Anatolia ◽  
Late Triassic ◽  
North Central

Volcanoes of the mid-ocean ridges and the building of new oceanic crust

Endeavour ◽  
1994 ◽  
Vol 18 (2) ◽  
pp. 61-66 ◽  
Author(s):  
Johnson Cann ◽  
Deborah Smith
Keyword(s):  
Oceanic Crust ◽  
Ocean Ridges

Tracing the global consumption of carbon at subduction zones over the last 230 million years

2020 ◽  
Author(s):  
Ben Mather ◽  
Dietmar Müller ◽  
Tobias Keller
Keyword(s):  
Oceanic Crust ◽  
Volcanic Activity ◽  
Subduction Zones ◽  
Oceanic Lithosphere ◽  
Conveyor Belt ◽  
Tectonic Plates ◽  
The Past ◽  
Ocean Ridges ◽  
Plate Reconstruction

&lt;p&gt;&lt;span&gt;Chemical heterogeneities in the mantle are typically introduced by recycling oceanic lithosphere through subduction, which transports volatiles into the mantle. The provenance of volatiles, such as carbon, with the down-going plate is varied; here we show how the &lt;/span&gt;&lt;span&gt;spatial &lt;/span&gt;&lt;span&gt;distribution of carbon evolves through time &lt;/span&gt;&lt;span&gt;with the motion of the tectonic plates&lt;/span&gt;&lt;span&gt;. Carbon is sequestered at mid-ocean ridges, as new oceanic crust forms, and is transported similar to a conveyor belt until it is recycled at subduction zones. We budget the amount of carbon that has been recycled at subduction zones over the past 230 million years using a global plate reconstruction. The present-day distribution of in-plate carbon,&lt;/span&gt;&lt;span&gt; taking into consideration the last 230 million years of plate influx, is predominantly distributed in the Atlantic. &lt;/span&gt;&lt;span&gt;In contrast, most of the carbon that was sequestered in Pacific seafloor from 230 Ma has since been subducted. Therefore, it is likely that the carbon stored in Pacific seafloor&lt;/span&gt; &lt;span&gt;has played an important role in stimulating volcanic activity along the Ring of Fire.&lt;/span&gt;&lt;/p&gt;

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