A Cretaceous back-arc basin in the Coast Belt of the northern Canadian Cordillera: evidence from geochemical and neodymium isotope characteristics of the Kluane metamorphic assemblage, southwest Yukon

2001 ◽  
Vol 38 (1) ◽  
pp. 91-103 ◽  
Author(s):  
Jochen E Mezger ◽  
Robert A Creaser ◽  
Philippe Erdmer ◽  
Stephen T Johnston
Keyword(s):  
Late Jurassic ◽  
Metamorphic Rock ◽  
Tectonic Setting ◽  
Source Region ◽  
Canadian Cordillera ◽  
Metasedimentary Rocks ◽  
Depleted Mantle ◽  
Metamorphic Assemblage ◽  
Continental Source ◽  
Back Arc

The Coast Belt of the northern Cordillera in Canada is the locus of the boundary between accreted and ancient North American margin rocks. The largest exposure of metasedimentary rocks in the Coast Belt is the Kluane metamorphic assemblage (KMA), a northwest-striking belt 160 km long of graphitic mica–quartz schist and gneiss with minor interfoliated olivine serpentinite. The KMA does not appear to correlate with other sedimentary or metamorphic rock assemblages in the Canadian Cordillera. To determine its tectonic setting and protolith provenance, we analyzed trace element, rare earth elements, and neodymium isotope compositions of the KMA, of the adjacent pericratonic Aishihik metamorphic suite (AMS) of the Yukon–Tanana terrane, and of adjacent slates of the Dezadeash Formation (DF), filling a Late Jurassic – Early Cretaceous flysch basin. The εNd(0) values of analyzed KMA samples range from –1.4 to –5.6 and depleted mantle model ages (TDM) range from 1.16 to 1.45 Ga. KMA samples are intermediate between more evolved AMS samples (average εNd(0) –25, TDM = 2.6 Ga) and more juvenile DF samples (εNd(0) = +1.9, TDM = 0.95 Ga). The intermediate characteristics of the KMA samples cannot be linked to a known source region and are interpreted to reflect homogeneous mixing from predominantly juvenile and minor evolved sedimentary sources. A compatible tectonic setting is a back-arc basin within influence of a continental source. Eastward subduction of the KMA beneath ancient North America collapsed the back-arc basin by latest Cretaceous time.

Geochemical constraints on the tectonic setting of the mafic rocks of the Bathurst Camp, Appalachian Orogen

1990 ◽  
Vol 27 (9) ◽  
pp. 1182-1193 ◽  
Author(s):  
A. Dogan Paktunc
Keyword(s):  
Trace Element ◽  
Gulf Of California ◽  
Tectonic Setting ◽  
Source Region ◽  
Ocean Basin ◽  
Mafic Rocks ◽  
Middle Ordovician ◽  
Element Abundances ◽  
Fine Grained ◽  
Back Arc

Abundant mafic rocks comprising basalts and gabbros occur in the Bathurst Camp, a complexly deformed Ordovician terrane in northeastern New Brunswick. The mafic rocks form a consanguineous suite of aphyric lavas, subvolcanic sills, and (or) dikes. Gabbros and basalts have somewhat similar major-element compositions but differ in terms of their trace-element contents. Medium-grained gabbros display tholeiitic compositions, whereas basalts and fine-grained gabbros have alkalic affinities. In general, trace-element abundances indicate an enriched source region for the Bathurst mafic rocks. Trace-element characteristics of the tholeiitic group point to a transitional setting going from back-arc to ocean basin, whereas the alkalic group has geochemical characteristics in common with within-plate basalts. Mixing between magmas of these contrasting settings could explain some of the trace-element characteristics of both groups. The back-arc-basin setting appears to be ensialic and is characterized by the absence of an underlying subducted slab during the formation of the basin. The tectonic reason for rifting in such a case could be the strike separation along a series of en echelon faults similar to those of the Gulf of California. Calc-alkaline characteristics of the upper mantle underlying the basin seem to have been inherited from southeasterly subduction of the proto-Atlantic Ocean in Early to Middle Ordovician times.

Permian exhumation of the Buffalo Pitts orogenic peridotite massif, northern Cordillera, Yukon

2007 ◽  
Vol 44 (3) ◽  
pp. 275-286 ◽  
Author(s):  
S T Johnston ◽  
D Canil ◽  
L H Heaman
Keyword(s):  
Tectonic Setting ◽  
Geochronological Data ◽  
Magmatic Arc ◽  
Crustal Rocks ◽  
Metasedimentary Rocks ◽  
Geochronological Study ◽  
Orogenic Peridotite ◽  
Element Enrichment ◽  
Peridotitic Mantle ◽  
Back Arc

We report the results of a geochemical and U–Pb zircon geochronological study aimed at constraining the timing and tectonic setting of the exhumation of an orogenic peridotitic mantle massif in central Yukon within northern Canadian Cordillera. The Buffalo Pitts orogenic massif is inferred to have been exhumed into continental metasedimentary rocks within the pericratonic Yukon–Tanana terrane. Structurally admixed with the peridotite were boudins of metaleucogabbro and metatroctolite. A metamorphic aureole, defined by migmatite with abundant leucosome, characterizes the metasedi mentary wall rocks to the massif. Whole-rock chemical analyses indicate significant light rare-earth element enrichment of the leucogabbro and the metatroctolite, characteristics commonly ascribed to within-plate or rift settings. Crystallization of the leucogabbro occurred at 261.5 ± 2.3 Ma. The metatroctolite yields a similar crystallization age. These ages are coeval with metamorphism of the wall rocks to the orogenic massif, as indicated by leucosome crystallization at 262.3 ± 0.43 Ma. These geochemical and geochronological data are consistent with the orogenic massif having been exhumed within a continental rift at about 262 Ma, giving rise to metamorphism of the upper crustal rocks into which the massif was exhumed, and coeval with rift-related magmatism. Regional considerations suggest that rifting occurred within the back arc of a northeast-facing magmatic arc, represented by the Klondike schist. Coeval eclogite and blueschist along the northeast margin of the Yukon–Tanana terrane may mark the paleo-trench, along which a southwest-dipping slab is assumed to have subducted beneath Yukon–Tanana terrane.

Chapter 12 Dolerites (1.27–1.25 Ga) and alkaline ultrabasic dykes (c. 1.14 Ga) related to intracratonic rifting

2020 ◽  
Vol 50 (1) ◽  
pp. 315-323 ◽  
Author(s):  
Magnus Ripa ◽  
Michael B. Stephens
Keyword(s):  
Magnetic Susceptibility ◽  
Mantle Plume ◽  
Coastal Area ◽  
Flow Direction ◽  
Tectonic Setting ◽  
Magma Flow ◽  
Depleted Mantle ◽  
Mantle Component ◽  
Back Arc ◽  
Shear Belt

AbstractDoleritic sills, lopoliths and dykes were emplaced into the Paleoproterozoic craton in central Sweden at 1271–1264, 1259–1256 and c. 1247 Ma, a complex temporal zonation occurring in a WSW–ENE direction. The dolerites are subalkaline to alkaline and show predominantly gabbroic, with a trend towards monzogabbroic and quartz monzodioritic, compositions. Positive ɛNd and ɛHf values suggest a significant depleted mantle component in the source volume of the parental magmas. Dyke orientations indicate extension, at least locally, in a northwesterly direction, consistent with a magma flow direction determined using the anisotropy of magnetic susceptibility values. Intracratonic rifting linked to the break-up of the supercontinent Columbia, back-arc extension above a subduction boundary in a westwards-retreating mode or a mantle plume tail above a continental hotspot have all been proposed for the tectonic setting. Renewed intracratonic rifting at c. 1.14 Ga in the coastal area in northeasternmost Sweden resulted in the emplacement of alkaline ultrabasic dykes, including carbonatites (beforsites), silico-carbonatites and lamprophyres, in a north–south direction along an older shear belt. The broader tectonic setting of this extensional event is not known.

scholarly journals A re-appraisal of the petrogenesis and tectonic setting of the Ordovician Fishguard Volcanic Group, SW Wales

2015 ◽  
Vol 153 (3) ◽  
pp. 410-425 ◽  
Author(s):  
BETHAN A. PHILLIPS ◽  
ANDREW C. KERR ◽  
RICHARD BEVINS
Keyword(s):  
Fractional Crystallization ◽  
Tectonic Setting ◽  
Source Region ◽  
Geochemical Data ◽  
Spinel Lherzolite ◽  
Magma Chamber Processes ◽  
Volcanic Group ◽  
South Wales ◽  
Iapetus Ocean ◽  
Back Arc

AbstractThe Fishguard Volcanic Group represents an excellently preserved example of a volcanic sequence linked to the closure of the Iapetus Ocean. This study re-examines the petrogenesis and proposed tectonic setting for the Llanvirn (467–458 Ma) Fishguard Volcanic Group, South Wales, UK. New major and trace element geochemical data and petrographic observations are used to re-evaluate the magma chamber processes, mantle melting and source region. The new data reveal that the Fishguard Volcanic Group represents a closely related series of basalts, basaltic andesites, dacites and rhyolites originating from a spinel lherzolite source which had been modified by subduction components. The rocks of the Fishguard Volcanic Group are co-genetic and the felsic members are related to the more primitive basalts mainly by low-pressure fractional crystallization. The geochemistry of the lavas was significantly influenced by subduction processes associated with a coeval arc, while significant amounts of assimilation of continental crust along with fractional crystallization appear to have contributed to the compositions of the most evolved lavas. The Fishguard Volcanic Group was erupted into a back-arc basin where extensive rifting but no true seafloor spreading had occurred.

Genesis and implications of the Late Jurassic Hailesitai granites in the northern Greater Khingan Range: evidence from zircon U–Pb dating and Hf isotope

2016 ◽  
Vol 154 (5) ◽  
pp. 963-982 ◽  
Author(s):  
PINGPING ZHU ◽  
QIUMING CHENG ◽  
ZHENJIE ZHANG ◽  
ZIYE WANG
Keyword(s):  
Inductively Coupled Plasma ◽  
Late Jurassic ◽  
Tectonic Setting ◽  
Hf Isotope ◽  
Source Rocks ◽  
High Potassium ◽  
Inductively Coupled ◽  
Depleted Mantle ◽  
Two Stages ◽  
Extensional Collapse

AbstractThe tectonic setting and geodynamic model of the Greater Khingan Range (GKR) is highly controversial due to the lack of reliable geological, isotopic and geochronological evidence. In the current study, the Hailesitai pluton, located at the west of the suture between the northern and southern GKR in the east of the Central Asian Orogenic Belt, is selected to address this issue. These granites of the high potassium calc-alkaline series belong to the A1-type granites with typical geochemical characteristics including high contents of Al2O3, extremely low contents of Ti, P, enriched LREE, LILE, depleted HFSE, and a medium Eu negative anomaly. Laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) zircon U−Pb dating indicates that the granites can be divided into two stages: c. 152 and c. 161 Ma. The intrusion of A1-type granites at ~161 Ma implies that intra-plate orogenesis of the northern GKR started at c. 161 Ma at latest. The Hailesitai pluton has relatively homogeneous Hf isotope compositions with a εHf (t) value (+6.0 − +9.0), and two-stage depleted mantle model ages of 579−738 Ma show that the original magma is a mixture of juvenile and crustal source rocks. Extensional collapse of the Mongol−Okhotsk belt between the Siberia block and the northern GKR resulted in the formation of late Jurassic A1-type granites in the northern GKR. The Hailesitai pluton formed in response to post-orogenic extensional collapse of the Mongol–Okhotsk belt, coupled with back-arc extension related to Palaeo-Pacific plate subduction.

Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland

1999 ◽  
pp. 65-78
Author(s):  
Henrik Rasmussen ◽  
Lars Frimodt Pedersen
Keyword(s):  
Tectonic Setting ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
West Greenland ◽  
North West ◽  
North East ◽  
Metavolcanic Rocks ◽  
Arc Setting ◽  
Area North ◽  
Back Arc

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Rasmussen, H., & Frimodt Pedersen, L. (1999). Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 65-78. https://doi.org/10.34194/ggub.v181.5114 _______________ Two Archaean supracrustal sequences in the area north-east of Disko Bugt, c. 1950 and c. 800 m in thickness, are dominated by pelitic and semipelitic mica schists, interlayered with basic metavolcanic rocks. A polymict conglomerate occurs locally at the base of one of the sequences. One of the supracrustal sequences has undergone four phases of deformation; the other three phases. In both sequences an early phase, now represented by isoclinal folds, was followed by north-west-directed thrusting. A penetrative deformation represented by upright to steeply inclined folds is only recognised in one of the sequences. Steep, brittle N–S and NW–SE striking faults transect all rock units including late stage dolerites and lamprophyres. Investigation of major- and trace-element geochemistry based on discrimination diagrams for tectonic setting suggests that both metasediments and metavolcanic rocks were deposited in an environment similar to a modern back-arc setting.

scholarly journals Geochemical Variation of Miocene Basalts within Shikoku Basin: Magma Source Compositions and Geodynamic Implications

Minerals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 25
Author(s):  
Shuang-Shuang Chen ◽  
Tong Hou ◽  
Jia-Qi Liu ◽  
Zhao-Chong Zhang
Keyword(s):  
Japan Sea ◽  
Isotopic Signature ◽  
Magma Source ◽  
Isotopic Compositions ◽  
Enriched Mantle ◽  
Shikoku Basin ◽  
Depleted Mantle ◽  
Parece Vela Basin ◽  
Back Arc ◽  
Ocean Ridge

Shikoku Basin is unique as being located within a trench-ridge-trench triple junction. Here, we report mineral compositions, major, trace-element, and Sr-Nd-Pb isotopic compositions of bulk-rocks from Sites C0012 (>18.9 Ma) and 1173 (13–15 Ma) of the Shikoku Basin. Samples from Sites C0012 and 1173 are tholeiitic in composition and display relative depletion in light rare earth elements (REEs) and enrichment in heavy REEs, generally similar to normal mid-ocean ridge basalts (N-MORB). Specifically, Site C0012 samples display more pronounced positive anomalies in Rb, Ba, K, Pb and Sr, and negative anomalies in Th, U, Nb, and Ta, as well as negative Nb relative to La and Th. Site 1173 basalts have relatively uniform Sr-Nd-Pb isotopic compositions, close to the end member of depleted mantle, while Site C0012 samples show slightly enriched Sr-Nd-Pb isotopic signature, indicating a possible involvement of enriched mantle 1 (EM1) and EM2 sources, which could be attributed to the metasomatism of the fluids released from the dehydrated subduction slab, but with the little involvement of subducted slab-derived sedimentary component. Additionally, the Shikoku Basin record the formation of the back-arc basin was a mantle conversion process from an island arc to a typical MORB. The formation of the Shikoku Basin is different from that of the adjacent Japan Sea and Parece Vela Basin, mainly in terms of the metasomatized subduction-related components, the nature of mantle source, and partial melting processes.

Le terrane de Slide Mountain (Cordillères canadiennes) : une lithosphère océanique marquée par des points chauds

2003 ◽  
Vol 40 (6) ◽  
pp. 833-852 ◽  
Author(s):  
M Tardy ◽  
H Lapierre ◽  
D Bosch ◽  
A Cadoux ◽  
A Narros ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Island ◽  
Light Rare Earth ◽  
Isotopic Compositions ◽  
Incompatible Elements ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
British Colombia ◽  
Ultramafic Cumulates ◽  
Back Arc

The Slide Mountain Terrane consists of Devonian to Permian siliceous and detrital sediments in which are interbedded basalts and dolerites. Locally, ultramafic cumulates intrude these sediments. The Slide Mountain Terrane is considered to represent a back-arc basin related to the Quesnellia Paleozoic arc-terrane. However, the Slide Mountain mafic volcanic rocks exposed in central British Colombia do not exhibit features of back-arc basin basalts (BABB) but those of mid-oceanic ridge (MORB) and oceanic island (OIB) basalts. The N-MORB-type volcanic rocks are characterized by light rare-earth element (LREE)-depleted patterns, La/Nb ratios ranging between 1 and 2. Moreover, their Nd and Pb isotopic compositions suggest that they derived from a depleted mantle source. The within-plate basalts differ from those of MORB affinity by LREE-enriched patterns; higher TiO2, Nb, Ta, and Th abundances; lower εNd values; and correlatively higher isotopic Pb ratios. The Nd and Pb isotopic compositions of the ultramafic cumulates are similar to those of MORB-type volcanic rocks. The correlations between εNd and incompatible elements suggest that part of the Slide Mountain volcanic rocks derive from the mixing of two mantle sources: a depleted N-MORB type and an enriched OIB type. This indicates that some volcanic rocks of the Slide Mountain basin likely developed from a ridge-centered or near-ridge hotspot. The activity of this hotspot is probably related to the worldwide important mantle plume activity that occurred at the end of Permian times, notably in Siberia.

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.

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