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.

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.

Subduction-related magmatic imprint of most Philippine ophiolites: implications on the early geodynamic evolution of the Philippine archipelago

2004 ◽  
Vol 175 (5) ◽  
pp. 443-460 ◽  
Author(s):  
Rodolfo A. Tamayo* ◽  
René C. Maury* ◽  
Graciano P. Yumul ◽  
Mireille Polvé ◽  
Joseph Cotten ◽  
...  
Keyword(s):  
Partial Melting ◽  
Subduction Zone ◽  
Volcanic Rocks ◽  
The Philippines ◽  
Island Arc ◽  
Island Arcs ◽  
Geodynamic Evolution ◽  
Wide Range ◽  
Opening And Closing ◽  
Back Arc

Abstract The basement complexes of the Philippine archipelago include at least 20 ophiolites and ophiolitic complexes. These complexes are characterised by volcanic sequences displaying geochemical compositions similar to those observed in MORB, transitional MORB-island arc tholeiites and arc volcanic rocks originating from modern Pacific-type oceans, back-arc basins and island arcs. Ocean island basalt-like rocks are rarely encountered in the volcanic sequences. The gabbros from the ophiolites contain clinopyroxenes and plagioclases showing a wide range of XMg and An values, respectively. Some of these gabbros exhibit mineral chemistries suggesting their derivation from basaltic liquids formed from mantle sources that underwent either high degrees of partial melting or several partial melting episodes. Moreover, some of the gabbros display a crystallization sequence where orthopyroxene and clinopyroxene appeared before plagioclase. The major element compositions of coexisting orthopyroxenes and olivines from the mantle peridotites are consistent with low to high degrees of partial melting. Accessory spinels in these peridotites display a wide range of XCr values as well with some of them above the empirical upper limit of 0.6 often observed in most modern mid-oceanic ridge (MOR) mantle rocks. Co-existing olivines and spinels from the peridotites also exhibit compositions suggesting that they lastly equilibrated under oxidizing mantle conditions. The juxtaposition of volcanic rocks showing affinities with modern MOR and island arc environments suggests that most of the volcanic sequences in Philippine ophiolites formed in subduction-related geodynamic settings. Similarly, their associated gabbros and peridotites display mineralogical characteristics and mineral chemistries consistent with their derivation from modern supra-subduction zone-like environments. Alternatively, these rocks could have, in part, evolved in a supra-subduction zone even though they originated from a MOR-like setting. A simplified scenario regarding the early geodynamic evolution of the Philippines is proposed on the basis of the geochemical signatures of the ophiolites, their ages of formation and the ages and origins of the oceanic basins actually bounding the archipelago, including basins presumed to be now totally consumed. This scenario envisages the early development of the archipelago to be largely dominated by the opening and closing of oceanic basins. Fragments of these basins provided the substratum on top of which the Cretaceous to Recent volcanic arcs of the Philippines were emplaced.

Lower–Middle Ordovician stratigraphy of North-East Greenland

2002 ◽  
pp. 117-125 ◽  
Author(s):  
Svend Stouge ◽  
W. Douglas Boyce ◽  
Jørgen L. Christiansen ◽  
David A.T. Harper ◽  
Ian Knight
Keyword(s):  
Passive Margin ◽  
East Greenland ◽  
Middle Ordovician ◽  
North East ◽  
Upper Proterozoic ◽  
Iapetus Ocean ◽  
Rodinia Supercontinent ◽  
Lower Palaeozoic ◽  
Early Palaeozoic ◽  
Laurentian Margin

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Stouge, S., Boyce, W. D., Christiansen, J. L., Harper, D. A., & Knight, I. (2002). Lower–Middle Ordovician stratigraphy of North-East Greenland. Geology of Greenland Survey Bulletin, 191, 117-125. https://doi.org/10.34194/ggub.v191.5138 _______________ The Upper Proterozoic (Riphean) to Lower Palaeozoic succession in North-East Greenland is exposed in a broad N–S-trending belt in the fjord region between 71°38´ and 74°25´N (Fig. 1). The succession comprises mainly marine sediments accumulated during the later stages of the break-up of the Rodinia supercontinent, the subsequent opening of the Iapetus Ocean and formation of the passive margin along the edge of the Laurentian palaeocontinent. Investigations of the sedimentary succession were initiated on Ella Ø in the summer of 2000 as part of a project to investigate the development of the Laurentian margin facing the Iapetus Ocean in the Early Palaeozoic, when studies of the uppermost formations of the Riphean Eleonore Bay Supergroup to the Lower Ordovician Antiklinalbugt Formation on Ella Ø were undertaken (Stouge et al. 2001). Ella Ø was revisited during the summer of 2001, with the focus on the Ordovician formations. In addition, investigations were undertaken in the Albert Heim Bjerge area where the uppermost part of the Ordovician succession is preserved (Fig. 1).

The Ordovician volcanics of the Elmtree–Belledune inlier and their relationship to volcanics of the northern Miramichi Highlands, New Brunswick

1992 ◽  
Vol 29 (7) ◽  
pp. 1430-1447 ◽  
Author(s):  
J. A. Winchester ◽  
C. R. van Staal ◽  
J. P. Langton
Keyword(s):  
New Brunswick ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Late Ordovician ◽  
Igneous Rocks ◽  
Volcanic Arc ◽  
Middle Ordovician ◽  
Marginal Basin ◽  
Tectonic Mélange ◽  
Back Arc

An investigation of the geology and chemistry of the basic igneous rocks in the Elmtree and Belledune inliers in northern New Brunswick shows that the bulk of the Middle Ordovician rocks of the ophiolitic Fournier Group are best interpreted as the products of volcanism and sedimentation in an extensive ensimatic back-arc basin southeast of a volcanic arc. The oceanic back-arc-basin igneous rocks form the basement to renewed arc-related basaltic volcanism in late Middle to Late Ordovician time. The Fournier Group is separated from the structurally-underlying, shale-dominated Elmtree Formation of the Tetagouche Group by an extensive tectonic melange, which incorporates lenses of serpentinite, mafic volcanic rocks, and sedimentary rocks of both the Tetagouche and Fournier groups. The mafic volcanic rocks in the Elmtree Formation correlate best with those intercalated with the lithologically similar sediments of the Llandeilian–Caradocian Boucher Brook Formation in the northern Miramichi Highlands. The melange and the present structural amalgamation of the Tetagouche and Fournier groups result from closure of the marginal basin by northward-directed subduction at the end of the Ordovician. Most mafic suites in the Elmtree and Belledune inliers can be chemically correlated with similar suites in the northern Miramichi Highlands, showing that the two areas are not separated by a terrane boundary.

A Laurentian margin subduction perspective: Geodynamic constraints from phase equilibria modeling of barroisite greenstones, northern USA Appalachians

2020 ◽  
Vol 132 (11-12) ◽  
pp. 2587-2605
Author(s):  
I.W. Honsberger ◽  
J. Laird ◽  
J.E. Johnson
Keyword(s):  
Phase Equilibria ◽  
Continental Margin ◽  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Ocean Basin ◽  
Iapetus Ocean ◽  
Continental Arc ◽  
Slab Tear ◽  
Shallow Subduction ◽  
Laurentian Margin

Abstract Phase equilibria modeling of sodic-calcic amphibole-epidote assemblages in greenstones in the northern Appalachians, USA, is compatible with relatively shallow subduction of the early Paleozoic Laurentian margin along the Laurentia-Gondwana suture zone during closure of a portion of the Iapetus Ocean basin. Pseudosection and isopleth calculations demonstrate that peak metamorphic conditions ranged between 0.65 GPa, 480 °C and 0.85 GPa, 495 °C down-dip along the subducted Laurentian continental margin between ∼20 km and ∼30 km depth. Quantitative petrological data are explained in the context of an Early Ordovician geodynamic model involving shallow subduction of relatively young, warm, and buoyant Laurentian margin continental-oceanic lithosphere and Iapetus Ocean crust beneath a relatively warm and wet peri-Gondwanan continental arc. A relatively warm subduction zone setting may have contributed to the formation of a thin, ductile metasedimentary rock-rich channel between the down-going Laurentian slab and the overriding continental arc. This accretionary channel accommodated metamorphism and tectonization of continental margin sediments and mafic volcanic rocks (greenstones) of the Laurentian margin and provided a pathway for exhumation of serpentinite slivers and rare eclogite blocks. Restricted asthenospheric flow in the forearc mantle wedge provides one explanation for the lack of ophiolites and absence of a well-preserved ultra-high-pressure terrane in central and northern Vermont. Exhumation of the subducted portion of the Laurentian margin may have been temperature triggered due to increased asthenospheric flow following a slab tear at relatively shallow depths.

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.

Geology of the Springdale Group: a newly recognized Silurian epicontinental-type caldera in Newfoundland

1987 ◽  
Vol 24 (6) ◽  
pp. 1135-1148 ◽  
Author(s):  
Marylou Coyle ◽  
D. F. Strong
Keyword(s):  
Large Scale ◽  
Basaltic Magma ◽  
Volcanic Rocks ◽  
Sedimentary Facies ◽  
Volcanic Field ◽  
Silica Content ◽  
Large Area ◽  
Basement Rocks ◽  
Iapetus Ocean ◽  
High Silica

Volcanic–sedimentary facies and structural relationships of the Silurian Springdale Group in west-central Newfoundland are indicative of a large collapse caldera with an area of more than 2000 km2. Basaltic flows, andesite flows and pyroclastic rocks, silicic ash-flow tuffs, high-silica rhyolite domes, and volcanically derived debris flows and breccias, fluviatile red sandstones, and conglomerates make up the group. It is bounded on the east and west by up-faulted basement rocks, which include gneisses, amphibolites, and pillow lavas, and in the northwest it unconformably overlies Lower Orodovician submarine volcanics. These margins are intruded by cogenetic and younger granitoid rocks. The volcanic rocks form a calc-alkaline series, although gaps in silica content at 52–56, 67–68, and 73–74% separate them into four groups: basalts, andesites–dacites, rhyolites, and high-silica rhyolites.The high-silica rhyolites are chemically comparable to melts thought to form the upper parts of large, layered silicic magma chambers of epicontinental regions. Such an environment is also suggested by the large area of the Springdale caldera and the fact that it is one of a number of calderas that make up a large Silurian volcanic field in western Newfoundland. An epicontinental tectonothermal environment for central Newfoundland in Silurian–Devonian times is readily explained by the fact that this magmatic activity followed a period of destruction and closure of the early Paleozoic Iapetus Ocean, with trapped heat and basaltic magma causing large-scale melting of thickened and subducted continental crust in an overall transpressional tectonic regime.

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.

The Taconian orogeny in southern New England: Nd-isotope evidence against addition of juvenile components

1996 ◽  
Vol 33 (12) ◽  
pp. 1612-1627 ◽  
Author(s):  
B. Bock ◽  
S. M. McLennan ◽  
G. N. Hanson
Keyword(s):  
New England ◽  
Sedimentary Rocks ◽  
Late Ordovician ◽  
Nd Isotope ◽  
Middle Ordovician ◽  
Southern New England ◽  
Isotope Evidence ◽  
Juvenile Crust ◽  
Plutonic Rocks ◽  
Laurentian Margin

Nd-isotope data for pre-Taconian (meta)sedimentary and igneous rocks, syn-Taconian (meta)sedimentary rocks, and Late Ordovician–Silurian plutonic rocks indicate that the Ordovician Taconian orogeny did not add significant amounts of juvenile crust to the Laurentian margin in southern New England. Nd-isotope compositions of Grenvillian crust and Late Proterozoic to Early Cambrian rift sediments range from εNd of −3.1 to −6.6 at 450 Ma. Sedimentary rocks deposited during the Cambrian and the early Middle Ordovician, which represent the drift stage of Laurentia, and earliest Taconian sedimentary rocks show more negative εNd(450 Ma), with a range from −11.7 to −13.3. Sedimentary rocks deposited in response to the Taconian orogeny have uniform εNd(450 Ma) values of about −8. Middle to Late Ordovician and Permian plutonic rocks from southwestern Connecticut have εNd(450 Ma) values of −2 to −5, which indicates that these rocks contain older crustal components. Rocks with juvenile Nd characteristics are the early Paleozoic Maltby Lake Volcanics (εNd(450 Ma) +8) from southwestern Connecticut, and Middle Ordovician igneous samples from the Hawley Formation (εNd(450 Ma) +6 to −0.6) in Massachusetts.

Geochemical variations in Middle Ordovician volcanic rocks of the northern Miramichi Highlands and their tectonic significance

1991 ◽  
Vol 28 (7) ◽  
pp. 1031-1049 ◽  
Author(s):  
C. R. Van Staal ◽  
J. A. Winchester ◽  
J. H. Bédard
Keyword(s):  
Volcanic Rocks ◽  
Structural Data ◽  
Middle Ordovician ◽  
Chemical Signatures ◽  
Geochemical Study ◽  
Lower Ordovician ◽  
Geochemical Variations ◽  
Thrust Zone ◽  
Arc Setting ◽  
Back Arc

A detailed geochemical study of Middle Ordovician volcanic rocks, undertaken in the northern Miramichi Highlands of New Brunswick, shows that 10 basaltic suites can be distinguished. These suites are assigned to the Tetagouche and Fournier groups. The contact between these two groups is a major thrust zone, marked for over 70 km by a prominent blueschist zone. All the Tetagouche Group volcanic rocks have chemistries consistent with extrusion in a continental rift, but most Fournier Group basalts in the Miramichi Highlands have chemistries suggestive of an oceanic back-arc setting. The chemical signatures, stratigraphic variations, and structural data indicate that the northern Miramichi Highlands preserve a section across a telescoped Middle Ordovician back-arc basin that initially opened as a result of asthenospheric injection near the rear part of a Lower Ordovician ensialic arc.

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