U-Pb ages and tectono-magmatic evolution of Middle Ordovician volcanic rocks of the Wild Bight Group, Newfoundland Appalachians

1998 ◽  
Vol 35 (9) ◽  
pp. 998-1017 ◽  
Author(s):  
Kate MacLachlan ◽  
Greg Dunning
Keyword(s):  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Complex Form ◽  
Mobile Belt ◽  
Middle Ordovician ◽  
Isotopic Signatures ◽  
Structural Relationships ◽  
Isotopic Analyses ◽  
In The Wild ◽  
Volcanic Succession

The Wild Bight Group and spatially associated South Lake Igneous Complex form one of the Ordovician oceanic terranes of the central mobile belt of the Newfoundland Appalachians. An integrated study of these rocks, involving detailed mapping, geochemistry, Sm-Nd isotopic analyses and U-Pb geochronology, has shown that there are two temporally and genetically distinct volcanic sequences within the Wild Bight Group. The younger sequence comprises a lower volcanic succession associated with coarse volcaniclastic rocks and an upper volcanic succession interbedded with argillite, chert, and minor greywacke. The lower volcanic succession has calc-alkaline affinties, and isotopic evidence for minor crustal contamination. It is interpreted to represent a volcanic arc formed in proximity to the Gondwanan margin, above an east-dipping subduction zone. The age of this volcanic sequence is confined to 472 ± 3 Ma by felsic tuffs which occur stratigraphically above and below it. The upper volcanic unit has predominantly enriched tholeiitic to alkaline geochemical characteristics with isotopic signatures indicative of little or no crustal contamination, and is interpreted to represent arc rifting. The age of this sequence was determined indirectly by dating two geochemically related gabbro sills (472+2-9 Ma and 471 ± 4 Ma). This work shows that despite different lithologies and stratigraphic and structural relationships between Early and Middle Ordovician sequences in the northern and southern Exploits Subzone, they have undergone essentially the same tectono-magmatic events. The age constraints on the magmatic events in the Wild Bight Group provide evidence for the timing of "obduction" of Early Ordovician oceanic sequences and the reversal of subduction polarity along the Gondwanan margin, suggested by previous workers.

Pearya: a composite terrane with Caledonian affinities in northern Ellesmere Island

1987 ◽  
Vol 24 (2) ◽  
pp. 224-245 ◽  
Author(s):  
H. P. Trettin
Keyword(s):  
Deep Water ◽  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Ellesmere Island ◽  
Mobile Belt ◽  
Lower Paleozoic ◽  
Water Basin ◽  
Middle Ordovician ◽  
Angular Unconformity ◽  
Deep Water Basin

In Ellesmere Island, the Canadian Shield and Arctic Platform are flanked on the northwest by the lower Paleozoic Franklinian mobile belt, which comprises an unstable shelf (miogeocline) and a deep-water basin, divisible into an inner sedimentary belt and an outer sedimentary–volcanic belt. Both are tied to the shelf by interlocking facies changes, but additional exotic units may be present in the outer belt.Pearya, bordering the deep-water basin on the northwest, is divisible into four successions. Succession I comprises sedimentary and(?) volcanic rocks, deformed, metamorphosed to amphibolite grade, and intruded by granitic plutons at 1.0–1.1 Ga. Succession II consists mainly of platformal sediments (carbonates, quartzite, mudrock), with smaller proportions of mafic and siliceous volcanics, diamictite, and chert ranging in age from Late Proterozoic (Hadrynian) to latest Cambrian or Early Ordovician. Its concealed contact with succession I is tentatively interpreted as an angular unconformity. Succession III (Lower to Middle Ordovician?) includes arc-type and ocean-floor volcanics, chert, mudrock, and carbonates and is associated with fault slices of Lower Ordovician (Arenig) ultramafic–mafic complexes–possibly dismembered ophiolites. The faulted contact of succession III and the ultramafics with succession II is unconformably overlapped by succession IV, 7–8 km of volcanic and sedimentary rocks ranging in age from late Middle Ordovician (Blackriverian = early Caradoc) to Late Silurian (late Ludlow?). The angular unconformity at the base of succession IV represents the early Middle Ordovician (Llandeilo–Llanvirn) M'Clintock Orogeny, which was accompanied by metamorphism up to amphibolite grade and granitic plutonism. Pearya is related to the Appalachian–Caledonian mobile belt by the Grenville age of its basement, the age of its ultramafic–mafic complexes, and evidence for a Middle Ordovician orogeny, comparable in age and character to the Taconic. By contrast, the Franklinian mobile belt has a Lower Proterozoic (Aphebian) – Archean basement and was not deformed in the Ordovician. Stratigraphic–structural evidence suggests that Pearya was transported by sinistral strike slip as three or more slices and accreted to the Franklinian deep-water basin in the Late Silurian under intense deformation. The inferred sinistral motion is compatible with derivation from the northern Caledonides.

Where is the Iapetus suture in northern New England? A study of the Ammonoosuc Volcanics, Bronson Hill terrane, New Hampshire1This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.

2012 ◽  
Vol 49 (1) ◽  
pp. 189-205 ◽  
Author(s):  
Michael J. Dorais ◽  
Miles Atkinson ◽  
Jon Kim ◽  
David P. West ◽  
Gregory A. Kirby
Keyword(s):  
New England ◽  
Subduction Zone ◽  
Volcanic Rocks ◽  
Middle Ordovician ◽  
Isotopic Signatures ◽  
Basement Rocks ◽  
Iapetus Ocean ◽  
Maritime Canada ◽  
Laurentian Margin ◽  
Back Arc

The ∼470 Ma Ammonoosuc Volcanics of the Bronson Hill terrane of New Hampshire have back-arc basin basalt compositions. Major and trace element compositions compare favorably to coeval volcanic rocks in the Miramichi Highlands of New Brunswick and the Munsangan and Casco Bay volcanics of Maine, back-arc basin basalts of known peri-Gondwanan origins. Additionally, the Ammonoosuc Volcanics have Nd and Pb isotopic compositions indicative of peri-Gondwanan provenance. Thus, the Ammonoosuc Volcanics correlate with Middle Ordovician, peri-Gondwanan, Tetagouche–Exploits back-arc rocks of eastern New England and Maritime Canada. This correlation indicates that the Red Indian Line, the principle Iapetus suture, lies along the western margin of the Bronson Hill terrane. However, the younger (∼450 Ma) Oliverian Plutonic Suite rocks that intruded the Ammonoosuc Volcanics, forming domes along the core of the Bronson Hill anticlinorium, have Laurentian isotopic signatures. This suggests that the Ammonoosuc Volcanics were thrust westwardly over the Laurentian margin, and that Laurentian basement rocks are present under the Bronson Hill terrane. A plausible explanation for these relationships is that an easterly dipping subduction zone formed the Ammonoosuc Volcanics in the Tetagoughe–Exploits oceanic tract, just east of the coeval Popelogan arc. With the closure of the Iapetus Ocean, this terrane was thrust over the Laurentian margin. Subsequent to obduction of the Ammonoosuc Volcanics, subduction polarity flipped to the west, with the Oliverian arc resulting from a westerly dipping subduction zone that formed under the Taconic Orogeny-modified Laurentian margin.

Petrogenesis of the peralkaline Flowers River Igneous Suite and its significance to the development of the southern Nain Batholith

2021 ◽  
pp. 1-26
Author(s):  
Taylor A. Ducharme ◽  
Christopher R.M. McFarlane ◽  
Deanne van Rooyen ◽  
David Corrigan
Keyword(s):  
Trace Element ◽  
Volcanic Rocks ◽  
Second Phase ◽  
Discrete Events ◽  
Volcanic Event ◽  
Volcanic Succession ◽  
Intrusive Suite ◽  
Tectonic Boundaries ◽  
Host Rocks ◽  
Nain Plutonic Suite

Abstract The Flowers River Igneous Suite of north-central Labrador comprises several discrete peralkaline granite ring intrusions and their coeval volcanic succession. The Flowers River Granite was emplaced into Mesoproterozoic-age anorthosite–mangerite–charnockite–granite (AMCG) -affinity rocks at the southernmost extent of the Nain Plutonic Suite coastal lineament batholith. New U–Pb zircon geochronology is presented to clarify the timing and relationships among the igneous associations exposed in the region. Fayalite-bearing AMCG granitoids in the region record ages of 1290 ± 3 Ma, whereas the Flowers River Granite yields an age of 1281 ± 3 Ma. Volcanism occurred in three discrete events, two of which coincided with emplacement of the AMCG and Flowers River suites, respectively. Shared geochemical affinities suggest that each generation of volcanic rocks was derived from its coeval intrusive suite. The third volcanic event occurred at 1271 ± 3 Ma, and its products bear a broad geochemical resemblance to the second phase of volcanism. The surrounding AMCG-affinity ferrodiorites and fayalite-bearing granitoids display moderately enriched major- and trace-element signatures relative to equivalent lithologies found elsewhere in the Nain Plutonic Suite. Trace-element compositions also support a relationship between the Flowers River Granite and its AMCG-affinity host rocks, most likely via delayed partial melting of residual parental material in the lower crust. Enrichment manifested only in the southernmost part of the Nain Plutonic Suite as a result of its relative proximity to multiple Palaeoproterozoic tectonic boundaries. Repeated exposure to subduction-derived metasomatic fluids created a persistent region of enrichment in the underlying lithospheric mantle that was tapped during later melt generation, producing multiple successive moderately to strongly enriched magmatic episodes.

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.

Variable modes of formation for tonalite-trondhjemite-granodiorite-diorite (TTG)-related porphyry-type Cu ± Au deposits in the Neoarchean southern Abitibi subprovince (Canada): Evidence from petrochronology and oxybarometry

2021 ◽  
Author(s):  
Xuyang Meng ◽  
Jeremy P Richards ◽  
Daniel J Kontak ◽  
Adam C Simon ◽  
Jackie M Kleinsasser ◽  
...  
Keyword(s):  
Crustal Contamination ◽  
Edge Structure ◽  
Isotopic Signatures ◽  
Porphyry Cu ◽  
Abitibi Subprovince ◽  
Local Restriction ◽  
Fractionation Trend ◽  
Magma Crystallization ◽  
X Ray Absorption

Abstract Most known porphyry Cu ± Au deposits are associated with moderately oxidized and sulfur-rich, calc-alkaline to mildly alkalic arc-related magmas in the Phanerozoic. In contrast, sodium-enriched tonalite-trondhjemite-granodiorite-diorite (TTG) magmas predominant in the Archean are hypothesized to be unoxidized and sulfur-poor, which together preclude porphyry Cu deposit formation. Here, we test this hypothesis by interrogating the causative magmas for the ~2.7 Ga TTG-related Côté Gold, St-Jude, and Clifford porphyry-type Cu ± Au deposit settings in the Neoarchean southern Abitibi subprovince. New and previously published geochronological results constrain the age of emplacement of the causative magmas at ~2.74 Ga, ~2.70 Ga, and ~2.69 Ga, respectively. The dioritic and trondhjemitic magmas associated with Côté Gold and St-Jude evolved along a plagioclase-dominated fractionation trend, in contrast to amphibole-dominated fractionation for tonalitic magma at Clifford. Analyses of zircon grains from the Côté Gold, St-Jude, and Clifford igneous rocks yielded εHf(t) ± SD values of 4.5 ± 0.3, 4.2 ± 0.6, and 4.3 ± 0.4, and δ18O ± SD values of 5.40 ± 0.11 ‰, 3.91 ± 0.13 ‰, and 4.83 ± 0.12 ‰, respectively. These isotopic signatures indicate that although these magmas are mantle-sourced with minimal crustal contamination, for the St-Jude and Clifford settings the magmas or their sources may have undergone variable alteration by heated seawater or meteoric fluids. Primary barometric minerals (i.e., zircon, amphibole, apatite, and magnetite-ilmenite) that survived variable alteration and metamorphism (up to greenschist facies) were used for estimating fO2 of the causative magmas. Estimation of magmatic fO2 values, reported relative to the fayalite-magnetite-quartz buffer as ΔFMQ, using zircon geochemistry indicate that the fO2 values of the St-Jude, Côté Gold, and Clifford magmas increase from ΔFMQ -0.3 ± 0.6, ΔFMQ +0.8 ± 0.4, to ΔFMQ +1.2 ± 0.4, respectively. In contrast, amphibole chemistry yielded systematically higher fO2 values of ΔFMQ +1.6 ± 0.3 and ΔFMQ +2.6 ± 0.1 for Côté Gold and Clifford, respectively, which are consistent with previous studies that indicate amphibole may overestimate the fO2 of intrusive rocks by up to one log unit. Micro X-ray absorption near edge structure (μ-XANES) spectrometric determination of sulfur (i.e., S6+/ΣS) in primary apatite yielded ≥ΔFMQ -0.3 and ΔFMQ +1.4–1.8 for the St-Jude and Clifford, respectively. The magnetite-ilmenite mineral pairs from the Clifford tonalite yielded ΔFMQ +3.3 ± 1.3 at equilibrium temperatures of 634 ± 21 °C, recording the redox state of the late stage of magma crystallization. Electron probe microanalyses revealed that apatite grains from Clifford are enriched in S (up to 0.1 wt. %) relative to those of Côté Gold and St-Jude (below the detection limit), which is attributed to either relatively oxidized or sulfur-rich features of the Clifford tonalite. We interpret these results to indicate the deposits at Côté Gold and Clifford formed from mildly (~ΔFMQ +0.8 ± 0.4) to moderately (~ΔFMQ +1.5) oxidized magmas where voluminous early sulfide saturation was probably limited, whereas the St-Jude deposit represents a rare case whereby the ingress of externally derived hydrothermal fluids facilitated metal fertility in a relatively reduced magma chamber (~ΔFMQ +0). Furthermore, we conclude that variable modes of formation for these deposits and, in addition, the apparent rarity of porphyry-type Cu-Au deposits in the Archean may be attributed to either local restriction of favorable metallogenic conditions, and/or preservation, or an exploration bias.

Helium isotopes in volcanic rocks from the Okinawa Trough-impact of volatile recycling and crustal contamination

2016 ◽  
Vol 51 ◽  
pp. 376-386 ◽  
Author(s):  
Zenghui Yu ◽  
Shikui Zhai ◽  
Kun Guo ◽  
Yonghua Zhou ◽  
Tong Zong
Keyword(s):  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Helium Isotopes ◽  
The Okinawa Trough
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