Geochemical constraints on the tectonic setting of the mafic rocks of the Bathurst Camp, Appalachian Orogen

1990 ◽  
Vol 27 (9) ◽  
pp. 1182-1193 ◽  
Author(s):  
A. Dogan Paktunc
Keyword(s):  
Trace Element ◽  
Gulf Of California ◽  
Tectonic Setting ◽  
Source Region ◽  
Ocean Basin ◽  
Mafic Rocks ◽  
Middle Ordovician ◽  
Element Abundances ◽  
Fine Grained ◽  
Back Arc

Abundant mafic rocks comprising basalts and gabbros occur in the Bathurst Camp, a complexly deformed Ordovician terrane in northeastern New Brunswick. The mafic rocks form a consanguineous suite of aphyric lavas, subvolcanic sills, and (or) dikes. Gabbros and basalts have somewhat similar major-element compositions but differ in terms of their trace-element contents. Medium-grained gabbros display tholeiitic compositions, whereas basalts and fine-grained gabbros have alkalic affinities. In general, trace-element abundances indicate an enriched source region for the Bathurst mafic rocks. Trace-element characteristics of the tholeiitic group point to a transitional setting going from back-arc to ocean basin, whereas the alkalic group has geochemical characteristics in common with within-plate basalts. Mixing between magmas of these contrasting settings could explain some of the trace-element characteristics of both groups. The back-arc-basin setting appears to be ensialic and is characterized by the absence of an underlying subducted slab during the formation of the basin. The tectonic reason for rifting in such a case could be the strike separation along a series of en echelon faults similar to those of the Gulf of California. Calc-alkaline characteristics of the upper mantle underlying the basin seem to have been inherited from southeasterly subduction of the proto-Atlantic Ocean in Early to Middle Ordovician times.

Tectonic setting and regional correlation of Ordovician metavolcanic rocks of the Casco Bay Group, Maine: evidence from trace element and isotope geochemistry

2004 ◽  
Vol 141 (2) ◽  
pp. 125-140 ◽  
Author(s):  
DAVID P. WEST ◽  
RAYMOND A. COISH ◽  
PAUL B. TOMASCAK
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Isotope Geochemistry ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Mafic Magma ◽  
Ocean Basin ◽  
Middle Ordovician ◽  
South Central ◽  
Back Arc

Ordovician metamorphic rocks of the Casco Bay Group are exposed in an approximately 170 km long NE-trending belt (Liberty-Orrington belt) in southern and south-central Maine. Geochemical analysis of rocks within the Spring Point Formation (469±3 Ma) of the Casco Bay Group indicate that it is an assemblage of metamorphosed bimodal volcanic rocks. The mafic rocks (originally basalts) have trace element and Nd isotopic characteristics consistent with derivation from a mantle source enriched by a crustal and/or subduction component. The felsic rocks (originally rhyolites and dacites) were likely generated through partial melting of continental crust in response to intrusion of the mafic magma. Relatively low initial εNd values for both the mafic (−1.3 to +0.6) and felsic (−4.1 to −3.8) rocks suggest interactions with Gander zone continental crust and support a correlation between the Casco Bay Group and the Bathurst Supergroup in the Miramichi belt of New Brunswick. This correlation suggests that elements of the Early to Middle Ordovician Tetagouche-Exploits back-arc basin can be traced well into southern Maine. A possible tectonic model for the evolution of the Casco Bay Group involves the initiation of arc volcanism in Early Ordovician time along the Gander continental margin on the eastern side of the Iapetus Ocean basin. Slab rollback and trenchward migration of arc magmatism initiated crustal thinning and rifting of the volcanic arc around 470 Ma and resulted in the eruption of the Spring Point volcanic rocks in a back-arc tectonic setting.

Age, chemistry, and tectonic setting of Miramichi terrane (Early Paleozoic) volcanic rocks, eastern and east-central Maine, USA

2021 ◽  
Vol 57 ◽  
pp. 239-273
Author(s):  
Allan Ludman ◽  
Christopher McFarlane ◽  
Amber T.H. Whittaker
Keyword(s):  
New Brunswick ◽  
Subduction Zone ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Calc Alkaline ◽  
East Central ◽  
Arc Volcanism ◽  
Middle Ordovician ◽  
Volcanic Suite ◽  
Back Arc

Volcanic rocks in the Miramichi inlier in Maine occur in two areas separated by the Bottle Lake plutonic complex: the Danforth segment (Stetson Mountain Formation) north of the complex and Greenfield segment to the south (Olamon Stream Formation). Both suites are dominantly pyroclastic, with abundant andesite, dacite, and rhyolite tuffs and subordinate lavas, breccias, and agglomerates. Rare basaltic tuffs and a small area of basaltic tuffs, agglomerates, and lavas are restricted to the Greenfield segment. U–Pb zircon geochronology dates Greenfield segment volcanism at ca. 469 Ma, the Floian–Dapingian boundary between the Lower and Middle Ordovician. Chemical analyses reveal a calc-alkaline suite erupted in a continental volcanic arc, either the Meductic or earliest Balmoral phase of Popelogan arc activity. The Maine Miramichi volcanic rocks are most likely correlative with the Meductic Group volcanic suite in west-central New Brunswick. Orogen-parallel lithologic and chemical variations from New Brunswick to east-central Maine may result from eruptions at different volcanic centers. The bimodal Poplar Mountain volcanic suite at the Maine–New Brunswick border is 10–20 myr younger than the Miramichi volcanic rocks and more likely an early phase of back-arc basin rifting than a late-stage Meductic phase event. Coeval calc-alkaline arc volcanism in the Miramichi, Weeksboro–Lunksoos Lake, and Munsungun Cambrian–Ordovician inliers in Maine is not consistent with tectonic models involving northwestward migration of arc volcanism. This >150 km span cannot be explained by a single east-facing subduction zone, suggesting more than one subduction zone/arc complex in the region.

Geochemistry and geochronology of OIB-type, Early Jurassic magmatism in the Zhangguangcai range, NE China, as a result of continental back-arc extension

2018 ◽  
Vol 158 (1) ◽  
pp. 143-157 ◽  
Author(s):  
Guangying Feng ◽  
Yildirim Dilek ◽  
Xiaolu Niu ◽  
Fei Liu ◽  
Jingsui Yang
Keyword(s):  
East Asia ◽  
Trace Element ◽  
Partial Melting ◽  
Early Jurassic ◽  
Ne China ◽  
Mafic Rocks ◽  
Asthenospheric Mantle ◽  
Trace Element Contents ◽  
Pacific Slab ◽  
Back Arc

AbstractThe Zhangguangcai Range in the Xing’an Mongolian Orogenic Belt, NE China, contains Early Jurassic (c. 188 Ma) Dabaizigou (DBZG) porphyritic dolerite. Compared with other island-arc mafic rocks, the DBZG dolerite is characterized by high trace-element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB-type rocks. Analysed rocks have (87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive ɛNd(t) values of 2.3–3.2 and positive ɛHf(t) values of 8.5–17.1. Trace-element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet- to spinel-facies conditions. The occurrence of OIB-like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back-arc environment in the upper plate of a palaeo-Pacific slab subducting W–NW beneath East Asia.

Geodynamic setting, crustal architecture, and VMS metallogeny of ca. 2720 Ma greenstone belt assemblages of the northern Wawa subprovince, Superior Province

2015 ◽  
Vol 52 (3) ◽  
pp. 196-214 ◽  
Author(s):  
Robert W.D. Lodge ◽  
Harold L. Gibson ◽  
Greg M. Stott ◽  
James M. Franklin ◽  
George J. Hudak
Keyword(s):  
Trace Element ◽  
Greenstone Belt ◽  
Tectonic Setting ◽  
Geodynamic Setting ◽  
Trace Element Geochemistry ◽  
Superior Province ◽  
Suprasubduction Zone ◽  
Greenstone Belts ◽  
Arc Setting ◽  
Back Arc

The greenstone belts along the northern margin of the Wawa subprovince of the Superior Province (Vermilion, Shebandowan, Winston Lake, Manitouwadge) formed at ca. 2720 Ma and have been interpreted to be representative of a rifted-arc to back-arc tectonic setting. Despite a common inferred tectonic setting and broad similarities, these greenstone belts have a significantly different metallogeny as evidenced by different endowments in volcanogenic massive sulphide (VMS), magmatic sulphide, and orogenic gold deposits. In this paper, we examine differences in geodynamic setting and crustal architecture as they pertain to the metallogeny of each greenstone belt by characterizing the regional-scale trace-element and isotopic (Nd and Pb) geochemistry of each belt. The trace-element geochemistry of the Vermilion greenstone belt (VGB) shows evidence for a transition from arc-like to back-arc mafic rocks in the Soudan belt to plume-driven rifted arcs in the ultramafic-bearing Newton belt. The Shebandowan greenstone belt (SGB) has a significant proportion of calc-alkalic, arc-like basalts, intermediate lithofacies, and high-Mg andesites, which are characteristic of low-angle, “hot” subduction. Extensional settings within the SGB are plume-driven and associated with komatiitic ultramafic and mid-ocean ridge basalt (MORB)-like basalts. The Winston Lake greenstone belt (WGB) is characterized by a transition from calc-alkalic, arc-like basalts to back-arc basalts upward in the strata and is capped by alkalic ocean-island basalt (OIB)-like basalts. This association is consistent with plume-driven rifting of a mature arc setting. Each of the VGB, SGB, and WGB show some isotopic evidence for the interaction with a juvenile or slightly older differentiated crust. The Manitouwadge greenstone belt (MGB) is characterized by isotopically juvenile, bimodal, tholeiitic to transitional volcanic lithofacies in a back-arc setting. The MGB is the most isotopically juvenile belt and is also the most productive in terms of VMS mineralization. The Zn-rich VMS mineralization within the WGB suggests a relatively lower-temperature hydrothermal system, possibly within a relatively shallow-water environment. The Zn-dominated and locally Au-enriched VMS mineralization, as well as mafic lithofacies and alteration assemblages, are characteristic of relatively shallower-water deposition in the VGB and SGB, and indicate that the ideal VMS-forming tectonic condition may have been compromised by a shallower-water depositional setting. However, the thickened arc crust and compressional tectonics of the SGB suprasubduction zone during hot subduction may have provided a crustal setting more favourable for the magmatic Ni–Cu sulphide and relative gold endowment of this belt.

Mafic and ultrapotassic rocks from the Canyon domain (central Grenville Province): geochemistry and tectonic implications

2012 ◽  
Vol 49 (2) ◽  
pp. 412-433 ◽  
Author(s):  
Carolina Valverde Cardenas ◽  
Aphrodite Indares ◽  
George Jenner
Keyword(s):  
Tectonic Setting ◽  
Source Region ◽  
Crustal Contamination ◽  
Granulite Facies ◽  
Grenville Province ◽  
Mafic Rocks ◽  
Isotopic Signatures ◽  
Late Evolution ◽  
Grenvillian Orogeny ◽  
Laurentian Margin

The Canyon domain and the Banded complex in the Manicouagan area of the Grenville Province preserve a record of magmatic activity from ∼1.4 to 1 Ga. This study focuses on 1.4–1.2 Ga mafic rocks and 1 Ga ultrapotassic dykes. Geochemistry and Sm–Nd isotopic signatures were used to constrain the origin of these rocks and evaluate the changing role of the mantle with time and tectonic setting from the late evolution of the Laurentian margin to the Grenvillian orogeny, in the Manicouagan area. The mafic rocks include layers inferred to represent flows, homogeneous bodies in mafic migmatite, and deformed dykes, all of which were recrystallized under granulite-facies conditions during the Grenvillian orogeny. In spite of the complexities inherent in these deformed and metamorphosed mafic rocks, we were able to recognize suites with distinctive geochemical and isotopic signatures. Integration of this data along with available ages is consistent with a 1.4 Ga continental arc cut by 1.2 Ga non-arc basalts derived from depleted asthenospheric mantle, with varied degrees of crustal contamination and inferred to represent magmatism in an extensional environment. The 1 Ga ultrapotassic dykes postdate the Grenvillian metamorphism. They are extremely enriched in incompatible elements, have negative Nb anomalies, relatively unradiogenic Sr-isotopic compositions (initial 87Sr/86Sr ~ 0.7040) and εNd –3 to –15. Some dykes have compositional characteristics consistent with derivation from the mantle, ruling out crustal contamination as a major process in their petrogenesis. The most likely source region for the ultrapotassic dykes is a metasomatized subcontinental lithospheric mantle, with thermal input from the asthenosphere in association with post-orogenic delamination.

A Cretaceous back-arc basin in the Coast Belt of the northern Canadian Cordillera: evidence from geochemical and neodymium isotope characteristics of the Kluane metamorphic assemblage, southwest Yukon

2001 ◽  
Vol 38 (1) ◽  
pp. 91-103 ◽  
Author(s):  
Jochen E Mezger ◽  
Robert A Creaser ◽  
Philippe Erdmer ◽  
Stephen T Johnston
Keyword(s):  
Late Jurassic ◽  
Metamorphic Rock ◽  
Tectonic Setting ◽  
Source Region ◽  
Canadian Cordillera ◽  
Metasedimentary Rocks ◽  
Depleted Mantle ◽  
Metamorphic Assemblage ◽  
Continental Source ◽  
Back Arc

The Coast Belt of the northern Cordillera in Canada is the locus of the boundary between accreted and ancient North American margin rocks. The largest exposure of metasedimentary rocks in the Coast Belt is the Kluane metamorphic assemblage (KMA), a northwest-striking belt 160 km long of graphitic mica–quartz schist and gneiss with minor interfoliated olivine serpentinite. The KMA does not appear to correlate with other sedimentary or metamorphic rock assemblages in the Canadian Cordillera. To determine its tectonic setting and protolith provenance, we analyzed trace element, rare earth elements, and neodymium isotope compositions of the KMA, of the adjacent pericratonic Aishihik metamorphic suite (AMS) of the Yukon–Tanana terrane, and of adjacent slates of the Dezadeash Formation (DF), filling a Late Jurassic – Early Cretaceous flysch basin. The εNd(0) values of analyzed KMA samples range from –1.4 to –5.6 and depleted mantle model ages (TDM) range from 1.16 to 1.45 Ga. KMA samples are intermediate between more evolved AMS samples (average εNd(0) –25, TDM = 2.6 Ga) and more juvenile DF samples (εNd(0) = +1.9, TDM = 0.95 Ga). The intermediate characteristics of the KMA samples cannot be linked to a known source region and are interpreted to reflect homogeneous mixing from predominantly juvenile and minor evolved sedimentary sources. A compatible tectonic setting is a back-arc basin within influence of a continental source. Eastward subduction of the KMA beneath ancient North America collapsed the back-arc basin by latest Cretaceous time.

Geochemical constraints on the evolution of the early continental crust

1981 ◽  
Vol 301 (1461) ◽  
pp. 423-442 ◽  
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Lower Crust ◽  
Plate Tectonics ◽  
Tectonic Setting ◽  
Mantle Plumes ◽  
Element Abundances ◽  
Ocean Island ◽  
Rock Types ◽  
Greenstone Belts

The most important process affecting both major and trace-element concentrations in the mantle and crust is melting producing silicate liquids which then migrate. Another process whose effects are becoming more apparent is the transport of elements by CO 2 - and H 2 O-rich fluids. Due to the relatively small amounts of fluids involved they have but little effect on the major-element abundances but may severely affect minor- and trace-element abundances in their source and the material through which they travel. The Archaean crust was a density filter which reduced the possibility of komatiite or high FeO melts with relative densities greater than about 3.0 from reaching the surface. Those melts retained in the lower crust or at the crust-mantle boundary would have enhanced the possibility of melting in the lower crust. The high FeO melts may have included the Archaean equivalents of alkali basalt whose derivatives may form an important component in the Archaean crust. The occurrence of ultramafic to basic to alkaline magmas in some Archaean greenstone belts is an assemblage most typical of modern ocean-island suites in continental environments. The rock types in the assemblage were modified by conditions of higher heat production during the Archaean and thus greater extents of melting and melting at greater depths. If modern ocean-island suites are associated with mantle plumes, which even now may be an important way to transport heat upward from the deeper mantle, it is suggested that during the Archaean mantle plumes were an important factor in the evolution of the continental crust. It appears that the Archaean continental crust was of comparable thickness to that of the present based on geobarometeric data. If the freeboard concept applied then, this would suggest that plate tectonics was also an active process during the Archaean. If so, it is probably no more realistic to assume that all Archaean greenstone belts had a similar tectonic setting than to assume that all modern occurrences of basic rocks have a common tectonic setting.

Geochemistry, petrography, and zircon U–Pb geochronology of Paleozoic metaigneous rocks in the Mount Veta area of east-central Alaska: implications for the evolution of the westernmost part of the Yukon–Tanana terrane

2013 ◽  
Vol 50 (8) ◽  
pp. 826-846 ◽  
Author(s):  
Cynthia Dusel-Bacon ◽  
Warren C. Day ◽  
John N. Aleinikoff
Keyword(s):  
Trace Element ◽  
Ocean Basin ◽  
Geochemical Characteristics ◽  
Trace Element Geochemistry ◽  
Alkaline Basalt ◽  
Metamorphic Complex ◽  
Element Geochemistry ◽  
East Central ◽  
Metaigneous Rocks ◽  
Back Arc

We report the results of new mapping, whole-rock major, minor, and trace-element geochemistry, and petrography for metaigneous rocks from the Mount Veta area in the westernmost part of the allochthonous Yukon–Tanana terrane (YTT) in east-central Alaska. These rocks include tonalitic mylonite gneiss and mafic metaigneous rocks from the Chicken metamorphic complex and the Nasina and Fortymile River assemblages. Whole-rock trace-element data from the tonalitic gneiss, whose igneous protolith was dated by SHRIMP U–Pb zircon geochronology at 332.6 ± 5.6 Ma, indicate derivation from tholeiitic arc basalt. Whole-rock analyses of the mafic rocks suggest that greenschist-facies rocks from the Chicken metamorphic complex, a mafic metavolcanic rock from the Nasina assemblage, and an amphibolite from the Fortymile River assemblage formed as island-arc tholeiite in a back-arc setting; another Nasina assemblage greenschist has MORB geochemical characteristics, and another mafic metaigneous rock from the Fortymile River assemblage has geochemical characteristics of calc-alkaline basalt. Our geochemical results imply derivation in an arc and back-arc spreading region within the allochthonous YTT crustal fragment, as previously proposed for correlative units in other parts of the terrane. We also describe the petrography and geochemistry of a newly discovered tectonic lens of Alpine-type metaharzburgite. The metaharzburgite is interpreted to be a sliver of lithospheric mantle from beneath the Seventymile ocean basin or from sub-continental mantle lithosphere of the allochthonous YTT or the western margin of Laurentia that was tectonically emplaced within crustal rocks during closure of the Seventymile ocean basin and subsequently displaced and fragmented by faults.

Geochemistry and petrogenesis of Ordovician arc-related mafic volcanic rocks in the Popelogan Inlier, northern New Brunswick

2003 ◽  
Vol 40 (9) ◽  
pp. 1171-1189 ◽  
Author(s):  
Reginald A Wilson
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Volcanic Rocks ◽  
Type I ◽  
Type Ii ◽  
Pyroclastic Rocks ◽  
Middle Ordovician ◽  
Element Abundances ◽  
Bearing Plate ◽  
Ridge Subduction

The Popelogan Inlier consists mainly of mafic volcanic rocks (lapilli tuffs and massive to amygdaloidal, plagioclase-phyric flows) of the Middle Ordovician Goulette Brook Formation. Pyroclastic rocks include high-MgO–Cr–Ni picritic tuffs (type I) containing, in some cases, >20% MgO, and related high-MgO andesitic tuff (type II). High-MgO rocks were generated by 30–40% partial melting of an enriched mantle source; type II is descended from type I mainly by fractionation of olivine. Mafic flows comprise basaltic andesites (type III) with low trace-element abundances and strongly fractionated, trace-element-enriched andesites (type IV). Types III and IV represent ~20 and ~10% partial melts, respectively, of a mantle source similar to that of the pyroclastic rocks, based on similar ratios of high field strength elements (HFSE). Unlike types I and II, petrogenesis of mafic flows involved fractionation of plagioclase and possibly amphibole. Volcanic arc signatures include negative Nb and Ti anomalies in all basalt types, along with low abundances of HFSE. Trace-element abundances are inconsistent with prior depletion in the back arc and require involvement of a mantle plume or subcontinental lithosphere. The highly magnesian composition of the picrites demands high melting temperatures and rapid transit through the crust, both of which suggest extension of the arc-bearing plate. Compositionally similar rocks in the South Pacific are associated with unusual tectono-magmatic settings involving ridge subduction, which may have established the necessary extensional environment. It is proposed that subduction of a plume-influenced ridge segment could explain the chemistry of the Goulette Brook volcanic rocks.

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