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.

The Mings Bight Ophiolite Complex, Newfoundland: Appalachian oceanic crust and mantle

1978 ◽  
Vol 15 (5) ◽  
pp. 781-804 ◽  
Author(s):  
W. S. F. Kidd ◽  
John F. Dewey ◽  
John M. Bird
Keyword(s):  
Volcanic Rocks ◽  
Pillow Lava ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Ophiolite Complex ◽  
Pillow Lavas ◽  
Late Cambrian ◽  
Head Formation ◽  
Lava Sequence ◽  
Thrust Sheets

The Mings Bight Ophiolite Complex, of probable early Ordovician age, is disposed in four major thrust sheets with an eastward vergence at the northern end of the Baie Verte Lineament. This narrow ophiolitic belt, and (to the south) an adjacent zone of early Devonian volcanic rocks and sediments, were affected by a strong Acadian (Middle Devonian?) deformation between more resistant blocks consisting mainly of rocks that were deformed and regionally metamorphosed, prior to the development of the ophiolites and overlying mafic sediments and volcanic rocks, probably in Late Cambrian to earliest Ordovician. The ophiolite sequence and conformably overlying sedimentary and volcanic sequence define an overturned synclinal structure with an eastward vergence; the three western thrust sheets contain an inverted sequence, the eastern sheet is upright. The thick mafic volcaniclastic and pillow lava sequence overlying the ophiolite complex suggests that the ophiolite complex was generated as the the floor of a small rear-arc or intra-arc basin. The ophiolite complex, although dissected by faults, consists of an ordered sequence from non-cumulate tectonite harzburgite through cumulate ultramafic rocks, gabbro and sheeted dike complex to pillow lavas. The continuous, coastal exposures show the relationships between the lithologies of the ophiolite complex unusually clearly, and these are described in some detail. In particular, the relationships between the sheeted dikes and both the homogeneous upper gabbro and the pillow lavas, and the intrusive complexities and the high-temperature deformation in the layered gabbros and ultramafics, are very clearly displayed. An ocean floor fault containing diapiric serpentinite is preserved in one thrust sheet. Two new formations are proposed, for the mafic volcaniclastic sediments (Big Head Formation) and for the overlying pillow lavas (Barry–Cunningham Formation) above the ophiolite complex.

Late Cenozoic volcanic rocks of the Clearwater – Wells Gray area, British Columbia

1984 ◽  
Vol 21 (3) ◽  
pp. 267-277 ◽  
Author(s):  
Catherine J. Hickson ◽  
J. G. Souther
Keyword(s):  
British Columbia ◽  
Volcanic Activity ◽  
Olivine Basalt ◽  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Pillow Lava ◽  
Late Cenozoic ◽  
Gray Area ◽  
High Level ◽  
Tuff Breccia

The Clearwater – Wells Gray area of east-central British Columbia includes a succession of late Cenozoic, alkali olivine basalt flows that lie east of the extensive Chilcotin lavas and define the eastern end of the Anahim Volcanic Belt. The rocks are petrographically similar to but less altered than the Chilcotin basalts. The volcanic activity spanned at least two episodes of glacial advance and produced both subaerial flows and a subaqueous facies comprising pillow lava, pillow breccia, and tuff breccia, locally intercalated with fluvial gravels and sand. Four morphological assemblages have been recognized. An early glacial assemblage, characterized by tuyalike forms, gives K – Ar dates of 0.27 – 3.5 Ma. These circular features are surrounded by a deeply dissected valley-filling assemblage of subaerial and minor subaqueous flows and tuff breccia that rest locally on lag gravel and till. Subaerial flows in this assemblage give K – Ar dates of 0.15 – 0.56 Ma. Whitehorse Bluffs, a volcanic centre composed of crudely laminated tuff cut by high-level dykes, may be a source of some of these valley-filling flows. A late interglacial assemblage is composed of subaerial pyroclastic material, transitional deposits, and deposits that are clearly subaqueous. Volcanic activity in the area culminated with the formation of pyroclastic cones, blocky lava flows, and pit craters that postdate the last Cordilleran glaciation.

Geology, geochronology, and geochemistry of Archean rocks in the Eqe Bay area, north-central Baffin Island, Canada: constraints on the depositional and tectonic history of the Mary River Group of northeastern Rae Province

2003 ◽  
Vol 40 (8) ◽  
pp. 1137-1167 ◽  
Author(s):  
K M Bethune ◽  
R J Scammell
Keyword(s):  
Hanging Wall ◽  
Volcanic Rocks ◽  
Dyke Swarm ◽  
Baffin Island ◽  
Calc Alkaline ◽  
North Central ◽  
Bay Area ◽  
Gneiss Complex ◽  
Southeastern Margin ◽  
Greenstone Belts

Results of stratigraphic, U–Pb geochronological, and geochemical study are reported for rocks in a 2800 km2 area along the southeastern margin of the Archean Rae Province on north-central Baffin Island. Archean rocks include a gneiss complex, two greenstone belts of the Mary River Group, and various younger plutonic rocks. The 3000–2800 Ma gneiss complex contains intrusions of orthogneiss, dated at 2780–2770 Ma. Intermediate-felsic volcanism in overlying greenstone belts occurred at 2740–2725 Ma and was accompanied and outlasted by calc-alkaline plutonism (2730–2715 Ma). Peraluminous plutonism at ca. 2700 Ma, possibly associated with low- to medium-pressure metamorphism, represents the culmination of the Archean tectonic cycle. Dating of metamorphic zircon and titanite in Archean gneissic rocks indicates that overprinting, high-grade metamorphism in the northwest part of the area (footwall of the Isortoq fault zone) is Paleoproterozoic (ca. 1820 Ma). A weaker, somewhat older thermal disturbance (ca. 1850–1840 Ma with large errors) is recorded in the hanging wall of this zone. Additional tectonothermal events at ca. 1500–1400 Ma and ca. 700 Ma may, respectively, correlate with Mesoproterozoic faulting and emplacement of the Franklin dyke swarm. Unlike their age-correlative counterparts in the Mary River area and on the mainland to the southwest, the greenstone belts at Eqe Bay lack abundant orthoquartzite and komatiitic volcanic rocks: calc-alkaline volcanic rocks predominate, suggesting a fundamentally different tectonic environment. Striking similarities, both in lithology and age, to greenstone belts of the Minto block of the Superior Province raises the question of Rae–Superior correlation.

Early Cretaceous crust–mantle interaction linked to rollback of the Palaeo-Pacific flat-subducting slab: constraints from the intermediate–felsic volcanic rocks of the northern Great Xing’an Range, NE China

2021 ◽  
pp. 1-22
Author(s):  
Jia-Hao Jing ◽  
Hao Yang ◽  
Wen-Chun Ge ◽  
Yu Dong ◽  
Zheng Ji ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Volcanic Rocks ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
Ne China ◽  
Asthenospheric Mantle ◽  
High K ◽  
Wide Range ◽  
Great Xing’An Range ◽  
Subducting Slab

Abstract Late Mesozoic igneous rocks are important for deciphering the Mesozoic tectonic setting of NE China. In this paper, we present whole-rock geochemical data, zircon U–Pb ages and Lu–Hf isotope data for Early Cretaceous volcanic rocks from the Tulihe area of the northern Great Xing’an Range (GXR), with the aim of evaluating the petrogenesis and genetic relationships of these rocks, inferring crust–mantle interactions and better constraining extension-related geodynamic processes in the GXR. Zircon U–Pb ages indicate that the rhyolites and trachytic volcanic rocks formed during late Early Cretaceous time (c. 130–126 Ma). Geochemically, the highly fractionated I-type rhyolites exhibit high-K calc-alkaline, metaluminous to weakly peraluminous characteristics. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depleted in high-field-strength elements (HFSEs), with their magmatic zircons ϵHf(t) values ranging from +4.1 to +9.0. These features suggest that the rhyolites were derived from the partial melting of a dominantly juvenile, K-rich basaltic lower crust. The trachytic volcanic rocks are high-K calc-alkaline series and exhibit metaluminous characteristics. They have a wide range of zircon ϵHf(t) values (−17.8 to +12.9), indicating that these trachytic volcanic rocks originated from a dominantly lithospheric-mantle source with the involvement of asthenospheric mantle materials, and subsequently underwent extensive assimilation and fractional crystallization processes. Combining our results and the spatiotemporal migration of the late Early Cretaceous magmatic events, we propose that intense Early Cretaceous crust–mantle interaction took place within the northern GXR, and possibly the whole of NE China, and that it was related to the upwelling of asthenospheric mantle induced by rollback of the Palaeo-Pacific flat-subducting slab.

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