Mississippian assembly of the Nisutlin assemblage: evidence from primary contact relationships and Mississippian magmatism in the Teslin tectonic zone, part of the Yukon–Tanana terrane of south-central Yukon

1996 ◽  
Vol 33 (1) ◽  
pp. 103-116 ◽  
Author(s):  
R. A. Stevens ◽  
P. Erdmer ◽  
R. A. Creaser ◽  
S. L. Grant
Keyword(s):  
Hanging Wall ◽  
Volcanic Rocks ◽  
Quartz Diorite ◽  
Late Paleozoic ◽  
Tectonic Zone ◽  
South Central ◽  
Crustal Block ◽  
Early Mesozoic ◽  
Primary Contact ◽  
Progressive Growth

Metamorphosed and ductilely deformed sedimentary, plutonic, and volcanic rocks of the Nisutlin and Anvil assemblages make up the Yukon–Tanana terrane in the Teslin tectonic zone study area. The Nisutlin assemblage consists of siliceous schist–quartzite and graphitic phyllite that share a primary depositional contact, and Early Mississippian tonalite to quartz diorite that intrudes the siliceous schist–quartzite and possibly the graphitic phyllite. The Anvil assemblage includes metagabbro and mafic schist–greenstone that share an intrusive contact relationship. Tonalite to quartz diorite of the Nisutlin assemblage is characterized by minor zircon inheritance with an average Proterozoic age, εNd(350 Ma) values of −2.5 to −6.2, and Nd model ages of 1.50–1.79 Ga. These data suggest that the magmatic bodies have inherited a component of continentally derived material. Primary contact relationships and age data indicate that the Nisutlin assemblage had formed by Mississippian time, and regional correlations show that this assemblage makes up a large part of the Yukon–Tanana terrane of southern Yukon. Assembly of the Nisutlin assemblage by Mississippian time indicates that it did not form as a late Paleozoic and early Mesozoic subduction melange, and it suggests that its tectonic fabrics did not result from the progressive growth of a Permo-Triassic subduction complex. We suggest that the Nisutlin assemblage was part of a crustal block that lay outboard of North America in Mississippian time, and that it lay in the hanging-wall plate of a Permo-Triassic subduction zone as a relatively coherent assemblage, rather than forming within the zone as a subduction complex.

Nd, Sr, and Pb isotopic evidence for contrasting origins of late Paleozoic volcanic rocks from the Slide Mountain and Cache Creek terranes, south-central British Columbia

1995 ◽  
Vol 32 (4) ◽  
pp. 447-459 ◽  
Author(s):  
Alan D. Smith ◽  
Richard StJ. Lambert
Keyword(s):  
Volcanic Rocks ◽  
Trace Element Composition ◽  
Ocean Basin ◽  
Late Triassic ◽  
Late Paleozoic ◽  
Spreading Ridge ◽  
South Pacific Ocean ◽  
South Central ◽  
Pb Isotopic Composition ◽  
Back Arc

The Slide Mountain and Cache Creek terranes are two prominent oceanic sutures in the Canadian Cordillera. Petrological and isotopic variations between volcanic rocks in these terranes support earlier interpretations from stratigraphic evidence that the Slide Mountain terrane represents the remnant of a late Paleozoic basin situated marginal to western North America, whereas the Cache Creek terrane represents a remnant of a much larger, open-ocean basin. Slide Mountain terrane volcanic rocks, represented by Late Pennsylvanian basalts of the Fennell Formation, resemble normal mid-oceanic ridge basalts but possess an unusual kaersutite- or augite-dominated mineralogy. Their εNd(300 Ma) values of +7.7 to +10.2 are among the highest observed for Paleozoic basalts. The hydrous mineralogy can be reconciled with eruption on a spreading ridge in either a back-arc or marginal basin setting. The latter is preferred from Pb isotope compositions (206Pb/204Pb = 17.7–18.5, 207Pb/204Pb = 15.51–15.61, 208Pb/204Pb = 37.2–38.8), which suggest exchange with high Th/U continental-derived sediment during hydrothermal alteration. Volcanic rocks, probably middle Mississippian, in the Bonaparte subterrane of the Cache Creek terrane include picrites and basalts belonging to a within-plate tholeiite suite. The intraplate suite broadly resembles Hawaiian basalts in major and trace element composition. However, moderate positive εNd values (εNd(340 Ma) +4.2 to +5.6) and a transition toward DUPAL signatures in Pb isotopic composition (206Pb/204Pb = 18.1–19.1, 207Pb/204Pb = 15.54–15.61, 208Pb/204Pb = 37.8–38.6) are features more similar to volcanic rocks from modern South Pacific ocean islands. Basaltic andesite and andesitic tuffs, also found in the Bonaparte subterrane, are tentatively correlated with Late Triassic to Early Jurassic low-K tholeiitic volcanic rocks of the Nicola Group on the Quesnel terrane.

The Central Slave Basement Complex, Part I: its structural topology and autochthonous cover

1999 ◽  
Vol 36 (7) ◽  
pp. 1083-1109 ◽  
Author(s):  
Wouter Bleeker ◽  
John WF Ketchum ◽  
Valerie A Jackson ◽  
Michael E Villeneuve
Keyword(s):  
Detrital Zircon ◽  
Hanging Wall ◽  
Volcanic Rocks ◽  
Iron Formation ◽  
Structural Topology ◽  
Banded Iron Formation ◽  
Basement Complex ◽  
South Central ◽  
Slave Province ◽  
Lake Formation

New field and geochronological data are used to define the distribution of Mesoarchean basement rocks in the south-central Slave Province. This distribution reflects a single contiguous basement terrane that we propose to call the Central Slave Basement Complex. It shows a structural topology that is internally consistent and compatible with known regional folding and faulting events. A sample of a proposed basement gneiss below the Courageous Lake greenstone belt, central Slave Province, has been dated by U-Pb methods and yields an age of 3325 ± 8 Ma, consistent with the new basement distribution. This sample also contains 2723 ± 3 Ma metamorphic zircon and ca. 2680 Ma titanite. The Central Slave Basement Complex is overlain by a thin, discontinuous, but distinctive cover sequence that includes minor volcanic rocks, clastic sedimentary rocks, and banded iron formation. All previously known and some new occurrences of this distinctive cover sequence occur in the immediate stratigraphic hanging wall of the Central Slave Basement Complex, locally overlying a preserved in situ unconformity. We propose to call this post-2.93 Ga cover sequence the Central Slave Cover Group. It is perhaps best typified by detrital chromite-bearing, fuchsitic quartzites. Formal formation names are proposed for the spatially separate occurrences of the Central Slave Cover Group. Detrital zircon ages are presented for one of the formations of the Central Slave Cover Group, the Patterson Lake Formation, which occurs on the western flank of a local basement culmination known as the Sleepy Dragon Complex. The detrital zircon data provide evidence for two discrete basement sources dated at ca. 2943 Ma and ca. 3147-3160 Ma. These detrital ages reinforce the depositional link between the Central Slave Cover Group and underlying crystalline rocks of the Central Slave Basement Complex.

Paleomagnetism of the Triassic Nikolai Greenstone, McCarthy Quadrangle, Alaska

1977 ◽  
Vol 14 (11) ◽  
pp. 2578-2592 ◽  
Author(s):  
J. W. Hillhouse
Keyword(s):  
British Columbia ◽  
High Temperature ◽  
North America ◽  
Vertical Axis ◽  
Upper Triassic ◽  
Present Position ◽  
Stable Component ◽  
South Central ◽  
Early Mesozoic ◽  
Lamellar Texture

Paleomagnetic evidence indicates that the extensive early Mesozoic basalt field near McCarthy, south-central Alaska, originated far south of its present position relative to North America. Results obtained from the Middle and (or) Upper Triassic Nikolai Greenstone suggest that those basalts originated within 15° of the paleoequator. This position is at least 27° (3000 km) south of the Upper Triassic latitude predicted for McCarthy on the basis of paleomagnetic data from continental North America. The Nikolai pole, as determined from 50 flows sampled at 5 sites, is at 2.2° N, 146.1° E (α95 = 4.8°). The polarity of the pole is ambiguous, because the corresponding magnetic direction has a low inclination and a westerly declination. Therefore, the Nikolai may have originated near 15° N latitude or, alternatively, as far south as 15° S latitude. In addition to being displaced northward, the Nikolai block has been rotated roughly 90° about the vertical axis. A measure of the reliability of this pole is provided by favorable results from the following tests: (1) Within one stratigraphic section, normal and reversed directions from consecutive flows are antipolar. (2) Consistent directions were obtained from sites 30 km apart. (3) Application of the fold test indicated the magnetization was acquired before the rocks were folded. (4) The magnetizations of several pilot specimens are thermally stable up to 550 °C. The stable component is probably carried by magnetite with lamellar texture, a primary feature commonly acquired by a basalt at high temperature during initial cooling of the magma. Geologic and paleomagnetic evidence indicates that the Nikolai is allochthonous to Alaska and that, together with associated formations in southern Alaska and British Columbia, it is part of a now disrupted equatorial terrane.

scholarly journals The Nordre Strømfjord shear zone and the Arfersiorfik quartz diorite in Arfersiorfik, the Nagssugtoqidian orogen, West Greenland

2006 ◽  
Vol 11 ◽  
pp. 145-162 ◽  
Author(s):  
Kai Sørensen ◽  
John A. Korstgård ◽  
William E. Glassley ◽  
Bo Møller Stensgaard
Keyword(s):  
Shear Zone ◽  
Volcanic Rocks ◽  
Quartz Diorite ◽  
Ductile Deformation ◽  
Chemical Compositions ◽  
West Greenland ◽  
South West ◽  
Wide Range ◽  
Inland Ice ◽  
Zone Deformation

The Nordre Strømfjord shear zone in the fjord Arfersiorfik, central West Greenland, consists of alternating panels of supracrustal rocks and orthogneisses which together form a vertical zone up to 7 km wide with sinistral transcurrent, ductile deformation, which occurred under middle amphibolite facies conditions. The pelitic and metavolcanic schists and paragneisses are all highly deformed, while the orthogneisses appear more variably deformed, with increasing deformation evident towards the supracrustal units. The c. 1.92 Ga Arfersiorfik quartz diorite is traceable for a distance of at least 35 km from the Inland Ice towards the west-south-west. Towards its northern contact with an intensely deformed schist unit it shows a similar pattern of increasing strain, which is accompanied by chemical and mineralogical changes. The metasomatic changes associated with the shear zone deformation are superimposed on a wide range of original chemical compositions, which reflect magmatic olivine and/ or pyroxene as well as hornblende fractionation trends. The chemistry of the Arfersiorfik quartz diorite suite as a whole is comparable to that of Phanerozoic plutonic and volcanic rocks of calc-alkaline affinity.

scholarly journals Supplemental Material: Rifting and subduction records of the Paleo–Tethys in North Laos: Constraints from Late Paleozoic mafic and plagiogranitic magmatism along the Song Ma tectonic zone

2020 ◽  
Author(s):  
Yuzhi Zhang
Keyword(s):  
Late Paleozoic ◽  
Tectonic Zone ◽  
Analytical Results ◽  
Trace Elemental ◽  
Host Rocks

Table S1: Major, trace elemental and Sr-Nd isotopic analytical results for the mafic and plagiogranitic rocks along the Song Ma tectonic zone in North Laos; Table S2: SIMS and LA-ICPMS zircon U-Pb dating results for the mafic, plagiogranitic and associated granitic host rocks along the Song Ma tectonic zone in North Laos; Table S3: Zircon in-situ Hf and O isotopic analytical results for the mafic and plagiogranitic rocks along the Song Ma tectonic zone in North Laos.

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