Tectonic setting of Avalonian volcanic and Plutonic rocks in the Caledonian Highlands, southern New Brunswick, Canada

1996 ◽  
Vol 33 (2) ◽  
pp. 156-168 ◽  
Author(s):  
S. M. Barr ◽  
C. E. White
Keyword(s):  
New Brunswick ◽  
Subduction Zone ◽  
Continental Margin ◽  
Tectonic Setting ◽  
Sedimentary Rocks ◽  
Igneous Activity ◽  
Appalachian Orogen ◽  
Group Form ◽  
Plutonic Rocks ◽  
Clastic Sedimentary

The Caledonian Highlands of southern New Brunswick consist of Late Proterozoic to Cambrian rocks generally considered typical of the Avalon terrane of the northern Appalachian Orogen. Mainly tuffaceous volcanic and sedimentary rocks of the Broad River Group and cogenetic dioritic to granitic plutons with ages ca. 620 Ma form most of the eastern Caledonian Highlands. They have petrological features indicative of origin in a continental margin subduction zone. Significantly younger ca. 560–550 Ma dacitic to rhyolitic lapilli tuffs and flows, laminated tuffaceous siltstone, basaltic and rhyolitic flows, and clastic sedimentary rocks of the Coldbrook Group form most of the western highlands, and occur locally throughout the highlands. The mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group. This voluminous subaerial magmatism may have formed during postorogenic extension in the earlier ca. 620 Ma subduction zone complex represented by the Broad River Group and associated plutons. This tectono-magmatic model differs from other interpretations that related most of the igneous units to ca. 630–600 Ma subduction, and did not recognize the importance of ca. 560–550 Ma magmatism. The ca 620 Ma subduction-related volcanic and plutonic rocks of the Caledonian Highlands are comparable to units in other parts of the Avalon terrane, but voluminous ca. 560–550 Ma igneous activity like that represented by the Coldbrook Group and related plutons has not been documented yet in other Avalonian areas.

Structural Succession, Nomenclature, and Interpretation of Transported Rocks in Western Newfoundland

1975 ◽  
Vol 12 (11) ◽  
pp. 1874-1894 ◽  
Author(s):  
Harold Williams
Keyword(s):  
North America ◽  
Subduction Zone ◽  
Continental Margin ◽  
North American ◽  
Sedimentary Rocks ◽  
Eastern North America ◽  
Stacking Order ◽  
Ophiolite Suite ◽  
Plutonic Rocks

The Humber Arm and Hare Bay Allochthons of Western Newfoundland are made up of a variety of sedimentary rocks and volcanic and plutonic rocks that originated toward the east and record the evolution and destruction of the ancient continental margin of Eastern North America. Five contrasting rock assemblages that constitute different structural slices are defined and delineated in the Humber Arm Allochthon. Six contrasting rock assemblages constitute the Hare Bay Allochthon. In each allochthon, the lower structural slices consist of sedimentary rocks and the highest structural slice consists of the ophiolite suite. The stacking order and mode of assembly indicate that progressively higher slices travelled increasingly greater distances, so that their present vertical superposition represents a former west-to-east juxtaposition.Most of the transported rocks have direct lithic correlatives in central Newfoundland. These occur west of the Dunnage Mélange, so that if the Dunnage marks the vestige of a North American subduction zone, then all the transported sequences once lay between a continental margin and a nearby oceanic trench.

Geochemistry and tectonic setting of late Precambrian volcanic and plutonic rocks in southeastern Cape Breton Island, Nova Scotia

1993 ◽  
Vol 30 (6) ◽  
pp. 1147-1154 ◽  
Author(s):  
Sandra M. Barr
Keyword(s):  
Subduction Zone ◽  
Continental Margin ◽  
Tectonic Setting ◽  
Volcanic Arc ◽  
Cape Breton Island ◽  
Late Precambrian ◽  
Cape Breton ◽  
Coastal Belt ◽  
Plutonic Rocks ◽  
Mountain Belts

Late Precambrian volcanic–sedimentary belts in the Mira (Avalon) terrane of southeastern Cape Breton Island display differences in rock types, petrochemistry, and age, showing that they did not form contemporaneously above a single northwest-dipping subduction zone, as proposed in earlier models. The oldest rocks are 680 Ma mafic and felsic flows and tuffs, and abundant, mainly tuffaceous, sedimentary rocks in the Stirling belt. They are interpreted to have formed in a trough within or peripheral to a volcanic-arc complex. Northwest of the Stirling belt, the East Bay Hills, Coxheath Hills, and Sporting Mountain belts consist of ca. 620 Ma mafic to felsic subaerial pyroclastic rocks and flows and contemporaneous dioritic to granitic plutons. Both volcanic and plutonic rocks are calc-alkalic to high-K calc-alkalic suites, formed in a continental margin volcanic arc. A correlative 620 Ma plutonic suite intruded the western margin of the Stirling belt, suggesting that subduction may have been toward the present southeast. The ca. 575 Ma Coastal belt, located southeast of the Stirling belt, is significantly younger than the other belts and appears to represent a less evolved calc-alkalic to low-K continental margin volcanic-arc and intra-arc basin formed above a northwest-dipping subduction zone. These various volcanic–sedimentary belts were juxtaposed by lateral movements along major faults in the late Precambrian to form this part of the Avalon composite terrane. Subduction-related, calc-alkalic magmatism at ca. 620 Ma was apparently widespread throughout the Avalon terrane of the northern Appalachian Orogen. However, ca. 680 Ma magmatism like that in the Stirling belt has been documented elsewhere only in the Connaigre Bay Group of Newfoundland. Circa 575 Ma and younger subduction-generated igneous activity like that in the Coastal belt has been recognized in southern New Brunswick, but alkaline magmas were forming in extensional regimes in other areas of the Avalon terrane at that time.

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.

Ophiolitic mélange and its significance in the Fleur de Lys Supergroup, northern Appalachians

1977 ◽  
Vol 14 (5) ◽  
pp. 987-1003 ◽  
Author(s):  
Harold Williams
Keyword(s):  
Continental Margin ◽  
Full Range ◽  
Sedimentary Rocks ◽  
Ultramafic Rocks ◽  
Eastern North America ◽  
Plate Boundaries ◽  
Polyphase Deformation ◽  
Ophiolitic Mélange ◽  
Ophiolite Suite ◽  
Clastic Sedimentary

Ophiolitic mélange consists of a chaotic mixture of sedimentary rocks and igneous rocks derived from the ophiolite suite of rock units. Its formation involves surficial mass wastage, gravity sliding, and tectonism at consuming plate boundaries. Most worldwide examples relate to ophiolite obduction and the destruction of stable continental margins.The Fleur de Lys Supergroup of the northern Appalachians consists of polydeformed and metamorphosed, mainly clastic sedimentary rocks that accumulated at the Hadrynian to early Paleozoic stable continental margin of eastern North America. Greenschists at or near the top of the succession in the east (Birchy Complex) contain zones of typical ophiolitic mélange. These contain large blocks of serpentinized ultramafic rocks, actinolite–fuchsite alterations of smaller ultramafic blocks, altered gabbro, a variety of clastic sedimentary blocks, and marble. All of the rocks are multideformed and metamorphosed so that the mélange was subjected to the full range of Fleur de Lys deformations.The presence of polydeformed and metamorphosed ophiolitic mélange in the Fleur de Lys Supergroup implies an early disruption or imbrication of its rock units. This disruption and mélange formation are interpreted to be related to transport of ophiolite complexes such as the Bay of Islands Complex across an initially undisturbed continental rise prism, the Fleur de Lys Supergroup. Later polyphase deformation and metamorphism of the Fleur de Lys Supergroup are possible results of continued structural submergence and telescoping of the continental margin beneath a thick cover of transported ophiolite rock units.

Geochemistry and tectonic discrimination of Late Proterozoic arc-related volcaniclastic turbidite sequences, Antigonish Highlands, Nova Scotia

1993 ◽  
Vol 30 (12) ◽  
pp. 2273-2282 ◽  
Author(s):  
J. Brendan Murphy ◽  
Deborah L. MacDonald
Keyword(s):  
Nova Scotia ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Widespread Application ◽  
Isotopic Signatures ◽  
Late Proterozoic ◽  
Felsic Volcanic ◽  
Clastic Sedimentary ◽  
End Members

The Late Proterozoic (ca. 618–610 Ma) Georgeville Group of northern mainland Nova Scotia lies within the Avalon Composite Terrane and consists of subgreenschist- to greenschist-facies mafic and felsic volcanic rocks overlain by volcaniclastic turbidites that were deposited in an ensialic basin within a rifted volcanic arc. Geochronological data indicate that the volcanic and sedimentary rocks are coeval. The geochemical and isotopic signatures of the sedimentary rocks are attributed to erosion of the coeval Avalonian volcanic rocks that flank the basin and are consistent with synorogenic deposition. There is no evidence of significant chemical contribution from Avalonian basement.Knowledge of the tectonic setting facilitates the testing of published geochemical discriminant diagrams for clastic sedimentary rocks. Discrimination diagrams using ratios such as K2O/Na2O and Al2O3/(CaO + Na2O) give inconclusive results, probably due to elemental mobility during secondary processes. Plots involving MgO, TiO2, and Fe2O3 detect the chemical contribution of mafic detritus, give much tighter clusters of data, and plot between Aleutian- and Cascade-type arc-derived sediments, suggesting a moderate thickness of continental crust beneath the arc.The arc-related signature of the Georgeville sedimentary rocks is clearly recognizable on ternary plots involving inter-element ratios of high field strength elements (e.g., Ti–Y–Zr, Nb–Y–Zr, and Hf–Ta–Th) in which the samples plot as mixing trends between mafic and felsic end members. Diagrams of this type may have widespread application to tectonic discrimination of sedimentary rocks because in most suites these ratios are relatively insensitive to sedimentary and metamorphic processes.

Structural setting and age of the Partridge Island block, southern New Brunswick, Canada: a link to the Cobequid Highlands of northern mainland Nova Scotia

2014 ◽  
Vol 51 (1) ◽  
pp. 1-24 ◽  
Author(s):  
Adrian F. Park ◽  
Robert L. Treat ◽  
Sandra M. Barr ◽  
Chris E. White ◽  
Brent V. Miller ◽  
...  
Keyword(s):  
Nova Scotia ◽  
New Brunswick ◽  
Tectonic Setting ◽  
Sedimentary Rocks ◽  
Alkali Feldspar ◽  
Early Carboniferous ◽  
Late Devonian ◽  
Island Formation ◽  
Lake Formation ◽  
Saint John

The Partridge Island block is a newly identified tectonic element in the Saint John area of southern New Brunswick, located south of and in faulted contact with Proterozoic and Cambrian rocks of the Ganderian Brookville and Avalonian Caledonia terranes. It includes the Lorneville Group and Tiner Point complex. The Lorneville Group consists of interbedded volcanic and sedimentary rocks, subdivided into the Taylors Island Formation west of Saint John Harbour and West Beach Formation east of Saint John Harbour. A sample from thin rhyolite layers interbedded with basaltic flows of the Taylors Island Formation at Sheldon Point yielded a Late Devonian – Early Carboniferous U–Pb (zircon) age of 358.9 +6/–5 Ma. Petrological similarities indicate that all of the basaltic rocks of the Taylors Island and West Beach formations are of similar age and formed in a continental within-plate tectonic setting. West of Saint John Harbour, basaltic and sedimentary rocks of the Taylors Island Formation are increasingly deformed and mylonitic to the south, and in part tectonically interlayered with mylonitic granitoid rocks and minor metasedimentary rocks of the Tiner Point complex. Based on magnetic signatures, the deformed rocks of the Tiner Point complex can be traced through Partridge Island to the eastern side of Saint John Harbour, where together with the West Beach Formation, they occupy a thrust sheet above a redbed sequence of the mid-Carboniferous Balls Lake Formation. The Tiner Point complex includes leucotonalite and aegirine-bearing alkali-feldspar granite with A-type chemical affinity and Early Carboniferous U–Pb (zircon) ages of 353.6 ± 5.7 and 346.4 ± 0.7 Ma, respectively. Based on similarities in age, petrological characteristics, alteration, iron oxide – copper – gold (IOCG)-type mineralization, and deformation style, the Partridge Island block is correlated with Late Devonian – Early Carboniferous volcanic–sedimentary–plutonic rocks of the Cobequid Highlands in northern mainland Nova Scotia. Deformation was likely a result of dextral transpression along the Cobequid–Chedabucto fault zone during juxtaposition of the Meguma terrane.

Geochemistry of the Laiyang Group from outcrops and Lingke-1 core on Lingshan Island, Shandong Province, Eastern China: implications for provenance, tectonic setting and palaeo-environment

2021 ◽  
pp. 1-18
Author(s):  
Qing Ma ◽  
Yaoqi Zhou ◽  
Hongyu Mu ◽  
Tengfei Zhou ◽  
Hanjie Zhao ◽  
...  
Keyword(s):  
Continental Margin ◽  
Lower Cretaceous ◽  
Tectonic Setting ◽  
Eastern China ◽  
Active Continental Margin ◽  
Sedimentary Rocks ◽  
Source Rocks ◽  
Oceanic Anoxic Event ◽  
Weathering Processes ◽  
Geochemical Indices

Abstract Lower Cretaceous sedimentary rocks of Lingshan Island, located along the continental margin of East Asia, have received increased attention. The Lingke-1 core mainly belongs to the Lower Cretaceous Laiyang Group. We investigate provenance, tectonic setting, palaeoclimate and palaeoredox conditions in the study area using elemental geochemistry, thereby elucidating the depositional history of the Lower Cretaceous sediments and reconstructing the palaeo-environment. To achieve this, 90 siltstones and 76 mudstones were sampled from this core and other outcrops on Lingshan Island. The chemical index of alternation (CIA) values for the majority of the samples and the bivariate diagrams indicate that the sedimentary rocks were subjected to minor weathering processes. Geochemical results suggest that source rocks for the region are felsic igneous and metamorphic rocks, along with minor proportions of intermediate igneous rocks. Major- and trace-element discrimination diagrams, deciphering the tectonic history, indicate that source rocks mainly originated from the continental island-arc and active continental margin. Several representative geochemical indices and the bivariate plots based on elemental contents show that the Laiyang Group was predominantly deposited in arid conditions. Sr/Ba values suggest a palaeosalinity transition from brackish to saline, demonstrating a depositional transformation from lacustrine facies for the lower Laiyang Group to marine facies in the upper Laiyang Group. U/Th and V/(V+Ni) ratios and Ce anomalies in the rocks indicate anoxic conditions. We conclude that the conspicuous decline in the trends of the above three geochemical indices, ranging between 400 and 800 m, may be related to the latest Hauterivian oceanic anoxic event.

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