Petrology, age, and tectonic setting of the Seal Island Pluton, offshore southwestern Nova Scotia

2007 ◽  
Vol 44 (10) ◽  
pp. 1467-1478 ◽  
Author(s):  
Patrick C Moran ◽  
Sandra M Barr ◽  
Chris E White ◽  
Michael A Hamilton
Keyword(s):  
Nova Scotia ◽  
Tectonic Setting ◽  
Heavy Rare Earth ◽  
Zircon Age ◽  
Relative Age ◽  
Form Part ◽  
Heavy Rare Earth Elements ◽  
Granitoid Rocks ◽  
Meguma Terrane ◽  
Granite Samples

The Seal Island Pluton outcrops only on small islands located on the continental shelf 45 km south of Nova Scotia, although geophysical data indicate that the pluton is part of large granitoid units that cover thousands of square kilometres farther offshore. Based on the island outcrops, the Seal Island Pluton consists of biotite monzogranite and muscovite–biotite monzogranite of uncertain relative age. Metasedimentary xenoliths combined with characteristic magnetic patterns indicate that the pluton intruded the Cambrian–Ordovician Meguma Group. Compared with the biotite monzogranite, the muscovite–biotite monzogranite is higher in SiO2, more peraluminous, and more depleted in heavy rare-earth elements, and also has lower εNd (–1.39 versus +0.82), possibly the result of more contamination by Meguma Group sedimentary rocks. The biotite monzogranite yielded a Late Devonian U–Pb (zircon) age of 362.8 ± 0.7 Ma. Although the relatively minor petrological differences between the two units do not preclude a co-magmatic relationship, the muscovite–biotite monzogranite could be 10–15 Ma older than the biotite monzogranite, based on its petrological similarities to parts of the onshore ca. 376–372 Ma Shelburne and Port Mouton plutons. Comparison with granite samples in offshore drill core indicates that granitoid rocks similar to those exposed on Seal and surrounding islands form part of large plutons farther offshore in the Meguma terrane. The age and petrochemical data from both onshore and offshore plutons indicate that peraluminous granitoid rocks in the Meguma terrane were derived from similar sources over a span of at least 20 million years. Magma genesis may have been related to mantle upwelling and stepping back of the subduction zone to the southeast subsequent to docking of Meguma terrane with adjacent Avalonia.

Petrochemistry and U–Pb (zircon) age of porphyry dykes at the McKenzie Gulch porphyry–skarn Cu–Ag–Au deposit, north-central New Brunswick, Canada: implications for emplacement age, tectonic setting, and mineralization potential

2020 ◽  
Vol 57 (4) ◽  
pp. 427-452 ◽  
Author(s):  
Ronald Joseph Massawe ◽  
David R. Lentz
Keyword(s):  
Mineral Exploration ◽  
Tectonic Setting ◽  
Geochemical Data ◽  
Upper Ordovician ◽  
Heavy Rare Earth ◽  
North Central ◽  
Zircon Age ◽  
Heavy Rare Earth Elements ◽  
Skarn Deposits ◽  
Subducting Slab

North- to northeast-trending intermediate to felsic porphyry dykes in the McKenzie Gulch (MG) area intrude Upper Ordovician through Silurian calcareous sedimentary rocks of the Matapédia Group. These dykes are spatially associated with numerous copper–silver skarn occurrences. In this area, two distinct suites of dykes are recognized: plagioclase–hornblende porphyry (P–H) and quartz–plagioclase porphyry (Q–P). These suites yielded U–Pb (zircon) ages of 386.2 ± 3.1 Ma and 386.4 ± 3.3 Ma, respectively, indicating a coeval relationship and similar genesis despite slight geochemical and petrographical differences. Geochemical data indicate that the dykes are granodioritic to granitic to slightly tonalitic in composition with I-type and slab failure signatures. When compared with other granitoids in the region, the Murdochville suite in Gaspésie, Québec, is the only intrusion that exhibits slab failure magmatic signatures similar to the MG dykes. Magmas with slab failure signatures are compositionally similar to tonalite–trondhjemite–granodiorite (TTG) suites and adakites. They exhibit low Y and Yb concentrations and subsequent high Sr/Y and La/Yb ratios, which are interpreted to be the result of melting of subducting slab and mantle during the waning stages of collision and consequent slab failure. These processes were followed by assimilation and fractional crystallization of minerals such as hornblende and clinopyroxene (± titanite), which preferentially partition Y and heavy rare earth elements (HREE) in the absence of significant plagioclase. Magmas with similar geochemical characteristics worldwide have been proposed to be an important source for metals in most porphyry Cu and skarn deposits and consequently are a target during mineral exploration.

Offshore continuation of Meguma Terrane, southwestern Nova Scotia

1989 ◽  
Vol 26 (1) ◽  
pp. 176-191 ◽  
Author(s):  
Georgia Pe-Piper ◽  
Bosko D. Loncarevic
Keyword(s):  
South Carolina ◽  
Nova Scotia ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Magnetic Anomalies ◽  
Near Surface ◽  
Rock Formation ◽  
South Mountain Batholith ◽  
Granitoid Rocks ◽  
Meguma Terrane

Eight short drill cores have been examined from the continental shelf southwest of Nova Scotia. Four cores recovered granitoid rocks of two types. Ilmenite-bearing granitoid rocks petrographically and geochemically resemble granodiorites of the South Mountain Batholith and granites of the Seal Island Pluton. Magnetite-bearing granitoid rocks are also peraluminous but have no exact analogues onshore in Nova Scotia. Two cores recovered metamorphic rocks in a small area 50 km south of Seal Island. One consits of chlorite–muscovite–quartz schist, geochemically similar to rocks of the Halifax Formation. The second sampled epidote–chlorite–quartz schist similar to metavolcanic rocks of the White Rock Formation. One further core sampled quartzite, and another sampled a metavolcanic rock (possibly erratic).The regional extent of these lithotypes can be inferred from gravity and aeromagnetic data. Regional gravity data suggest the presence of a large granite body off southwestern Nova Scotia. In this area, magnetic anomalies are irregular, apparently reflecting the presence of magnetite-bearing granites. The layer-stripping method of analyzing the magnetic field shows that the area is underlain at depth by high magnetic anomalies. Large near-surface linear magnetic anomalies are used to map the extent of the volcanic rocks of the White Rock Formation. The area is cut by several northwest-trending faults that postdate Acadian folding but predate the earliest Jurassic magmatism of the Shelburne Dyke and North Mountain basalt. The unusual magnetic signature of the area off southwestern Nova Scotia may reflect a different basement; it is possible that Meguma rocks are thrust over the Avalon Terrane. Alternatively, it may be solely the result of magnetite-bearing granites. These granites may be related to a Permian thermal event in southwest Nova Scotia, and they have some petrographic similarity to young granites of the Piedmont Zone of South Carolina.

Rb–Sr age and geochemical distinctions between the Carboniferous tin-bearing Davis Lake complex and the Devonian South Mountain batholith, Meguma Terrane, Nova Scotia

1989 ◽  
Vol 26 (10) ◽  
pp. 2044-2061 ◽  
Author(s):  
Jean M. Richardson ◽  
Keith Bell ◽  
John Blenkinsop ◽  
David H. Watkinson
Keyword(s):  
Nova Scotia ◽  
Trace Element ◽  
Biotite Granite ◽  
Granitic Magma ◽  
Trace Element Geochemistry ◽  
Magmatic Differentiation ◽  
Element Geochemistry ◽  
South Mountain Batholith ◽  
Granitoid Rocks ◽  
Meguma Terrane

The Davis Lake complex (DLC), composed of biotite monzogranite, leucomonzogranite, and cassiterite–topaz greisen, hosts the East Kemptville tin mine in southwestern Nova Scotia. The DLC monzogranite contains glomeroporphyritic biotite with ilmenite and many rare-earth-element (REE) bearing accessory minerals, zircon-bearing quartz phenocrysts, and xenoliths of biotite granite. Primary muscovite is rare. Major- and trace-element geochemical trends indicate well-defined, but limited, magmatic differentiation trends. REE patterns of the least-evolved granites are flat and show a Ce/Yb ratio of 10.The DLC was previously considered cogenetic with the Devonian South Mountain batholith (SMB) on the basis of its location, lithologies, and similarities in major- and trace-element geochemistry. However, new Rb–Sr whole-rock isotopic data indicate an Rb–Sr date of 330 ± 7 Ma (mean square of weighted deviates (MSWD) = 2.8) for the DLC, implying that it is at least 35 Ma younger than the SMB. The initial 87Sr/86Sr ratio of 0.727 ± 0.004 is significantly higher than those for other Meguma Terrane granites and is the highest yet reported from Appalachian granitoid rocks. Rb–Sr data from biotite indicate open-system behaviour between 260 and 240 Ma and provide more evidence for previously documented tectonothermal events after 300 Ma in the Meguma Terrane.The peraluminous nature of the DLC, its high Rb/Sr and high 87Sr/86Sr ratios, high P, F, and Sn contents, low Ca and B contents, and high differentiation indices indicate that the complex was derived from a highly evolved felsic source. Geochemical distinctions indicate that the DLC is neither derived from nor cogenetic with the SMB. A more probable source for the DLC magma is a dehydrated felsic granulite from which a previous H2O-, B-, Cl-, and Zn-rich granitic magma (perhaps the SMB) had been extracted. Such a source is analogous to that postulated for A-type granites and topaz rhyolites.The DLC shows more similarities to the "stitching" Carboniferous Appalachian volatile- and metal-rich granites than to Devonian Meguma granites. Unlike most of these Appalachian plutons, which occur marginal to terrane boundaries and were probably crystallized from locally generated, anatectic magmas, the DLC was emplaced in the centre of the most-outboard Meguma Terrane, adjacent to the Tobiatic shear zone.

scholarly journals Field relations and petrology of the Trafalgar Plutonic Suite and comparisons with other Devonian granitoid plutons in the Meguma terrane, Nova Scotia, Canada

2020 ◽  
Vol 56 ◽  
pp. 001-017
Author(s):  
Raya C. Puchalski ◽  
Sandra M. Barr ◽  
Chris E. White
Keyword(s):  
Nova Scotia ◽  
Quartz Diorite ◽  
Chemical Characteristics ◽  
Volcanic Arc ◽  
Mafic Rocks ◽  
Metasedimentary Rocks ◽  
Mafic Intrusions ◽  
Coarse Texture ◽  
Granitoid Rocks ◽  
Meguma Terrane

The Trafalgar Plutonic Suite intruded metasedimentary rocks of the Goldenville and Halifax groups in the northeastern part of the Meguma terrane of southern Nova Scotia at about 374 Ma, based on previously published U–Pb and 40Ar/39Ar mineral ages. Using field and petrographic observations, the suite is divided into 20 different plutons on the combined basis of variations in grain size (fine, medium, or coarse), texture (equigranular or porphyritic) and modal mineralogy (quartz diorite/tonalite, granodiorite, monzogranite, and syenogranite). The granodiorite, monzogranite, and syenogranite plutons are relatively uniform in composition with little variation in mineralogy or chemistry within each pluton or between plutons of the same lithology. In contrast the quartz diorite/tonalite plutons show mineralogical and chemical variation, both within and between plutons. The granodiorite, monzogranite, and syenogranite plutons closely resemble other peraluminous granitoid plutons characteristic of the Meguma terrane. The quartz diorite/tonalite plutons are varied but chemically resemble minor Devonian mafic intrusions elsewhere in the Meguma terrane. Like other plutons of the Meguma terrane, the Trafalgar Plutonic Suite has chemical characteristics of volcanic-arc to syn-collisional granitoid rocks and likely has experienced extensive contamination by metasedimentary material as documented by previous studies of plutons in the Meguma terrane. The minor quartz diorite/tonalite plutons are additional examples of the mafic rocks that have been proposed in tectonic models of the Meguma terrane to have facilitated melting of the lower crust to generate granodioritic parent magmas, followed by crystal fractionation and extensive contamination by metasedimentary material.

scholarly journals Geochronology and petrogenesis of granitoid rocks from the Goryczkowa Unit, Tatra Mountains (Central Western Carpathians)

2013 ◽  
Vol 64 (6) ◽  
pp. 419-435 ◽  
Author(s):  
Jolanta Burda ◽  
Aleksandra Gawęda ◽  
Urs Klötzli
Keyword(s):  
Tectonic Setting ◽  
Regional Metamorphism ◽  
Source Material ◽  
Tatra Mountains ◽  
Volcanic Arc ◽  
Zircon Age ◽  
Icp Ms ◽  
Crystalline Core ◽  
Granitoid Rocks ◽  
Central Western Carpathians

Abstract The geochemical characteristics as well as the LA-MC-ICP-MS U-Pb zircon age relationship between two granitoid suites found in the Goryczkowa crystalline core in the Western Tatra Mountains were studied. The petrological investigations indicate that both granitoid suites were emplaced at medium crustal level, in a VAG (volcanic arc granites) tectonic setting. However, these suites differ in source material melted and represent two different magmatic stages: suite 1 represents a high temperature, oxidized, pre-plate collision intrusion, emplaced at ca. 371 Ma while suite 2 is late orogenic/anatectic magma, which intruded at ca. 350 Ma. These data are consistent with a period of intensive magmatic activity in the Tatra Mountain crystalline basement. The emplacement of granitoids postdates the LP-HT regional metamorphism/ partial melting at ca. 387 Ma and at 433-410 Ma, imprinted in the inherited zircon cores.

Geochronology of the Buchans, Roberts Arm, and Victoria Lake groups and Mansfield Cove Complex, Newfoundland

1987 ◽  
Vol 24 (6) ◽  
pp. 1175-1184 ◽  
Author(s):  
G. R. Dunning ◽  
B. F. Kean ◽  
J. G. Thurlow ◽  
H. S. Swinden
Keyword(s):  
Local Field ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Late Ordovician ◽  
Mobile Belt ◽  
Western Boundary ◽  
Zircon Age ◽  
Early Ordovician ◽  
Form Part

Volcanic groups of the Central Mobile Belt of the Newfoundland Appalachians have previously been subdivided into "early" and "late" arc sequences, separated in time by a quiescent Caradocian stage defined in some areas by fossil-bearing black shales.New U–Pb zircon ages of [Formula: see text] and 473 ± 2 Ma for rhyolites of the Buchans and Roberts Arm groups, respectively, show them to be correlative early Ordovician sequences. These ages serve to refute both the previous Rb–Sr whole-rock isochron ages of 447 Ma and the idea that these groups were "late arc" sequences. These new ages corroborate evidence from late Arenig – early Llanvirn conodonts in the Buchans Group and calibrate this fossil occurrence.A new U–Pb zircon age of 479 ± 3 Ma from plagiogranite of the Mansfield Cove Complex immediately west of the Roberts Arm Group shows that this plutonic body is only slightly older than the adjacent volcanic rocks and not Hadrynian as previously supposed. Local field relationships suggest this body may represent part of a disrupted ophiolite. It is coeval with the ophiolitic Annieopsquotch Complex along a strike to the south and may form part of a belt of rocks derived from early Ordovician ocean floor that is discontinuously exposed along the western boundary of the Buchans – Roberts Arm Belt.Zircons from rhyolite at the northeast termination of the Tulks Hill volcanics, part of the extensive Victoria Lake Group, give an age of [Formula: see text]. This dated sequence contains limestone previously dated as Llanvirn–Llandeilo by conodonts. This part of the group is therefore younger than the Buchans Group, and the designations "early" and "late" arc are not appropriate. The thrusting that juxtaposed these groups is no longer constrained to be of Silurian age but could have been middle to late Ordovician. Precambrian zircons included in the Victoria Lake Group rhyolite could have been incorporated from associated sedimentary rocks and suggest that the group may have formed in a tectonic setting transitional between oceanic and continental and received detritus from several sources.

scholarly journals New U-Pb (zircon) age and geochemistry of the Wedgeport pluton, Meguma terrane, Nova Scotia

10.4138/1184 ◽  
2003 ◽  
Vol 39 (3) ◽  
Author(s):  
Natalie J. MacLean ◽  
Sandra M. Barr ◽  
Chris E. White ◽  
John W. F. Ketchum
Keyword(s):  
Nova Scotia ◽  
Zircon Age ◽  
Meguma Terrane

scholarly journals The Litchfield Pluton in South-Central Maine: Carboniferous Alkalic Magmatism in northern New England, USA

2016 ◽  
Vol 52 ◽  
pp. 169
Author(s):  
David P West ◽  
Dwight Bradley ◽  
Raymond Coish
Keyword(s):  
New England ◽  
Nepheline Syenite ◽  
Tectonic Setting ◽  
Coarse Grained ◽  
Zircon Age ◽  
South Central ◽  
Appalachian Orogen ◽  
Granitoid Rocks ◽  
Northern New England ◽  
Geochemical Analyses

The Litchfield pluton is a poorly exposed 7 km2 composite alkalic intrusive complex that cuts previously deformed and metamorphosed Silurian turbidites in south-central Maine.  The pluton includes a variety of alkaline syenites, including the type locality of “litchfieldite”, a coarse-grained cancrinite, sodalite, and lepidomelane bearing nepheline syenite first recognized over 150 years ago and common in many petrologic collections.  A new U-Pb zircon age of 321 ± 2 Ma from the nepheline syenite is interpreted to represent the crystallization age of the plutonic complex.  A new biotite 40Ar/39Ar age of 239 ± 1 Ma from the syenite is similar to previously published mica ages from the surrounding country rocks and dates the time of regional cooling in the area below ~ 300°C.  Whole rock geochemical analyses from rocks of the Litchfield pluton are compatible with strongly alkaline A-type granitoid rocks that formed in a within plate or continental rift tectonic setting.  The age and geochemical characteristics of the alkalic igneous rocks near Litchfield are consistent with a model that invokes the generation of a small volume of alkalic magma beneath south-central Maine during a period of Carboniferous transcurrent tectonism in the northern Appalachian orogen.       

Petrology, age, and tectonic setting of the White Rock Formation, Meguma terrane, Nova Scotia: evidence for Silurian continental rifting

2002 ◽  
Vol 39 (2) ◽  
pp. 259-277 ◽  
Author(s):  
Lisa A MacDonald ◽  
Sandra M Barr ◽  
Chris E White ◽  
John WF Ketchum
Keyword(s):  
Nova Scotia ◽  
Shear Zone ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Chemical Characteristics ◽  
Rock Formation ◽  
Meguma Terrane ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks

The White Rock Formation in the Yarmouth area of the Meguma terrane of southern Nova Scotia consists mainly of mafic tuffaceous rocks with less abundant mafic flows, epiclastic and clastic sedimentary rocks, and minor intermediate and felsic crystal tuff. It is divided into seven map units that appear to young from west to east, inconsistent with a previously assumed synclinal structure. The White Rock Formation is flanked on both northwest and southeast by mainly the Cambrian to Lower Ordovician Halifax Formation; the western contact is interpreted to be a sheared disconformity, whereas the eastern contact appears to be a major brittle fault and shear zone that juxtaposes different crustal levels. The granitic Brenton Pluton forms a faulted lens within the eastern shear zone. A felsic tuff from the upper part of the White Rock Formation yielded a U–Pb zircon age of 438+3–2 Ma, identical within error to published ages for the Brenton Pluton and felsic volcanic rocks near the base of the White Rock Formation in the Torbrook area of western Nova Scotia. The chemical characteristics of the mafic volcanic rocks and associated mafic intrusions consistently indicate alkalic affinity and a continental within-plate setting. The felsic volcanic rocks and Brenton Pluton have chemical characteristics of within-plate anorogenic granitic rocks, and the pluton is interpreted to be comagmatic with the felsic volcanic rocks. The igneous activity may have occurred in response to extension as the Meguma terrane rifted away from Gondwana in the latest Ordovician to Early Silurian. Epsilon Nd values are similar to those in voluminous Devonian plutonic rocks of the Meguma terrane, and the magmas appear to have been derived from similar sources.

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