The Silurian(?) Passamaquoddy Bay mafic dyke swarm, New Brunswick: petrogenesis and tectonic implications

2001 ◽  
Vol 38 (11) ◽  
pp. 1565-1578 ◽  
Author(s):  
Nancy A Van Wagoner ◽  
Matthew I Leybourne ◽  
Kelsie A Dadd ◽  
Miranda LA Huskins
Keyword(s):  
New Brunswick ◽  
Incompatible Element ◽  
Tectonic Setting ◽  
Crustal Contamination ◽  
Dyke Swarm ◽  
Mafic Dyke ◽  
Mafic Dykes ◽  
The North ◽  
Passamaquoddy Bay ◽  
Mafic Dyke Swarm

The volcanic and sedimentary rocks of the Passamaquoddy Bay (PB) area of southeastern New Brunswick are part of the Silurian–Devonian Coastal Volcanic Belt (CVB), an extensive belt of bimodal volcanic rocks. The PB sequence is 4 km thick, has four cycles of mafic and felsic volcanism, and is intruded by mafic dykes at all levels. There are two ages of dykes, those related to the Late Silurian PB volcanism (PB dykes) and Mesozoic dykes (the Minister Island Dyke) related to the opening of the North Atlantic. The PB mafic dykes are subalkalic basalt to basaltic andesite, within-plate tholeiites. The dykes are moderately to highly evolved (Mg# = 66.6 to 26.6), with trends of major and trace elements typical of the fractionation of olivine, pyroxene, plagioclase, and ilmenite. The PB mafic dyke swarm comprises over 155 dykes which represent a greater range of compositions than the associated flows, suggesting that they give a more complete representation of the Late Silurian PB mafic magmas. They exhibit incompatible element characteristics best accounted for by crustal contamination. The dykes plot on a linear array away from mantle mixing lines between depleted and enriched mantle sources and toward the composition of the PB felsic units, suggesting that these felsic units are representative of partial melts and fractionates of the source contaminate. The variable TiO2 contents (1.2–4.3 wt.%) and incompatible element ratio trends plotted against a fractionation index suggest that mantle metasomatism, either fluid or melt derived, may also have influenced the mantle source of the dykes. The dykes dip steeply and have a relatively consistent strike to the north. Most dykes range in thickness from 0.5 to 2 m, but range up to 9 m. The single orientation of the dykes, along with their chemical characteristics and volume, and association with a bimodal intraplate volcanic sequence, are consistent with an extensional tectonic setting. Constraints of the regional geology suggest that this extension was associated with convergence, perhaps in a back-arc setting.

The youngest Neoproterozoic mafic dyke suite in the Arabian Shield: mildly alkaline dolerites from South Jordan – their geochemistry and petrogenesis

2001 ◽  
Vol 138 (3) ◽  
pp. 309-323 ◽  
Author(s):  
G. JARRAR
Keyword(s):  
Tectonic Setting ◽  
Crustal Contamination ◽  
Spinel Lherzolite ◽  
Mafic Dyke ◽  
East African ◽  
Elemental Ratios ◽  
Mafic Dykes ◽  
Nubian Shield ◽  
Igneous Activity ◽  
Arabian Nubian Shield

The Arabian–Nubian Shield evolved through a sequence of tectonomagmatic cycles, which took place during Neoproterozoic time (1000–540 Ma). Dyke emplacement constitutes one of the conspicuous features of the Arabian–Nubian Shield, with mafic dykes being the most abundant. The investigated dykes represent the youngest Neoproterozoic mafic dykes and have been dated in Jordan at 545 ± 13 Ma. Geochemically the studied dykes are mildly alkaline, are enriched in large ion lithophile elements (LILE) and high field strength cations (HFSC), show moderate enrichment of REE, and lack Nb anomaly. These features are consistent with a predominantly extensional continental tectonic setting. Crystallization temperatures of the suite fall between 1050 and 800 °C to as low as 650 °C as deduced from pyroxene thermometry. The investigated dykes were derived from a metasomatized lithospheric mantle by 5 % modal batch partial melting of phlogopite-bearing spinel lherzolite, according to geochemical modelling. The intra-suite geochemical features are explicable by 64 % fractional crystallization of olivine, pyroxene, plagioclase and titanomagnetite and possibly other accessories like apatite at a later stage. The cumulate produced from this fractionation of the investigated dyke suite contributed to the formation of the mafic lower crust of the Arabian–Nubian Shield. Elemental ratios and petrographic evidence indicate possible minor crustal contamination of the suite. The youngest mafic dykes show striking geochemical similarities to the same generation of dolerite dykes in the adjacent countries, to transitional young basalt suites of the Main East African Rift, and to Quaternary Jordanian basalts. The youngest mafic dyke suite, the rhyolites of the Aheimir suite, and St Katherina rhyolites of Sinai represent the last igneous activity in the Arabian–Nubian Shield before the onset of the Cambrian at about 545 Ma ago.

Geochemistry, mineral chemistry and petrogenesis of a Neoproterozoic dyke swarm in the north Eastern Desert, Egypt

2006 ◽  
Vol 143 (1) ◽  
pp. 115-135 ◽  
Author(s):  
M. DAWOUD ◽  
H. A. ELIWA ◽  
G. TRAVERSA ◽  
M. S. ATTIA ◽  
T. ITAYA
Keyword(s):  
Tectonic Setting ◽  
Mineral Chemistry ◽  
Eastern Desert ◽  
Major And Trace Elements ◽  
Dyke Swarm ◽  
Mafic Dyke ◽  
Crustal Rocks ◽  
The North ◽  
Chemical Signatures ◽  
Dyke Swarms

Dyke swarms traverse Neoproterozoic rocks in the Hawashiya region in the extreme northern part of the Eastern Desert of Egypt. They are a suite of basaltic andesite and andesite mafic dykes, and dacitic and rhyolitic felsic dykes. The mafic dyke suite is more abundant in the younger granites (577 ± 6 Ma) than in the older granitoids (614 Ma), in which the felsic dykes are the most common. The dyke swarms trend predominantly NE–SW, and the felsic dyke suite is older than the mafic dyke suite. Both dyke suites are calc-alkaline (alkaline dykes are rare) and are relatively poor in TiO2 and Nb but enriched in the incompatible elements and HFSE. The felsic dyke suite is enriched in REE and is strongly LREE fractionated relative to the mafic dyke suite. Although the Hawashiya dykes were emplaced at the end of the Neoproterozoic era in an extensional tectonic setting, they have geochemical characteristics that are consistent with a subduction-related regime. These chemical signatures were inherited from the lithospheric rocks that produced their host Hawashiya granitoids. The felsic dyke suite magma may be derived from crustal rocks (essential source component) by partial melting. The mafic dyke suite magma was generated from a lithospheric mantle and has undergone fractional crystallization of plagioclase, amphibole, clinopyroxene and magnetite, as documented by major and trace elements fractionation modelling.

The Weekend dykes, a newly recognized mafic dyke swarm on the eastern shore of Nova Scotia, Canada

1990 ◽  
Vol 27 (5) ◽  
pp. 644-648 ◽  
Author(s):  
Alan Ruffman ◽  
John D. Greenough
Keyword(s):  
Nova Scotia ◽  
Stress Field ◽  
Radial Stress ◽  
Dyke Swarm ◽  
Carbonate Apatite ◽  
Mafic Dyke ◽  
Eastern Shore ◽  
Mafic Dykes ◽  
Metasedimentary Rocks ◽  
Mafic Dyke Swarm

A group of related mafic dykes is present along the eastern shore of Nova Scotia from Halifax to Country Harbour. The dykes are generally vertical, strike about 150°, and have an abundance of carbonate, apatite, and hydrous mafic minerals, indicating that the dykes may have formed from an alkaline (lamprophyric) magma. They postdate the Acadian folding of the Cambro-Ordovician Meguma Group metasedimentary rocks but predate Carboniferous faulting. Abundant exotic gneissic and (meta)plutonic xenoliths, representing probable pre-Meguma Group rocks, are found in half of the presently known dykes.The dykes may have formed in a regional tensional field during a shearing event synchronous with docking between the Meguma and Avalonian terranes or in a more local radial stress field around an igneous body, such as the Bog Island Lake or Ten Mile Lake diatreme in the Liscomb Complex. Similar ages suggest that the dykes may be related to the intrusion of the Devono-Carboniferous granites of the Musquodoboit batholith.

Mafic and ultramafic amphibolites from the northwestern Pontiac Subprovince: chemical characterization and implications for tectonic setting

1993 ◽  
Vol 30 (6) ◽  
pp. 1110-1122 ◽  
Author(s):  
G. E. Camiré ◽  
J. N. Ludden ◽  
M. R. La Flèche ◽  
J. -P. Burg
Keyword(s):  
Magma Mixing ◽  
Tectonic Setting ◽  
Crustal Contamination ◽  
Chemical Characterization ◽  
Mantle Metasomatism ◽  
Primitive Mantle ◽  
Mafic Dykes ◽  
Metavolcanic Rocks ◽  
Source Mantle ◽  
Ree Patterns

In the northwestern Pontiac Subprovince, metavolcanic rocks are exposed within a metagraywacke sequence that is intruded by metamorphosed mafic dykes. The metavolcanics are Al-undepleted komatiites ([La/Sm]N = 0.3, [Tb/Yb]N = 0.9) and tholeiitic Fe-basalts ([La/Sm]N = 0.8 and [Tb/Yb]N = 0.8). The nearly flat chondrite-normalized distributions of high field strength elements (HFSE), Ti and P, the constant Zr/Y, Nb/Th, Ti/Zr, and Ti/P ratios, and the lack of depletion of HFSE relative to rare-earth elements (REE) in both ultramafic and mafic metavolcanics, imply that crustal assimilation and magma mixing with crustal melts were not significant during differentiation and argue against the presence of subduction-related magmatic components. Contemporaneous volcanism and sedimentation in the northwestern Pontiac Subprovince are unlikely. The metavolcanics do not show any evidence of crustal contamination and likely represent a structurally emplaced, disrupted assemblage, chemically similar to early volcanics of the adjacent southern Abitibi Subprovince.Metamorphosed mafic dykes intruding the metagraywackes are not genetically related to the metavolcanics. The dykes have high CaO, P2O5, K2O, Ba, Rb, and Sr, intermediate Cr and Ni contents, and strongly fractionated REE patterns ([La/Yb]N = 10.8). Normalized to the primitive mantle, they display pronounced negative Nb, Ta, Ti, Zr, and Hf anomalies. These amphibolites are metamorphosed equivalents of Mg-rich calc-alkaline lamprophyre dykes, most likely derived from a hybridized mantle source. Mantle metasomatism was probably related to a subduction event prior to the peak of compressional Kenoran deformation in the Pontiac Subprovince.

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