Tectonic framework of the upper Paleozoic and lower Mesozoic Alava sequence: a revised view of the polygenetic Taku terrane in southern southeast Alaska

1991 ◽  
Vol 28 (6) ◽  
pp. 881-893 ◽  
Author(s):  
Charles M. Rubin ◽  
Jason B. Saleeby
Keyword(s):  
Upper Jurassic ◽  
Coarse Grained ◽  
Western Boundary ◽  
Southeast Alaska ◽  
Upper Paleozoic ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Tectonic Framework ◽  
Narrow Belt ◽  
Carbonaceous Phyllite

Fragments of upper Paleozoic and lower Mesozoic metavolcanic and metasedimentary sequences of the Taku terrane are exposed discontinuously along a narrow belt in southeast Alaska and form a distinct lithostratigraphic package in the Ketchikan area called the Alava sequence. Crinoidal and argillaceous marble, carbonaceous phyllite, argillite, mafic flows, pillow breccia, pyroclastic tuff, and quartzite characterize the sequence. These strata are unconformably overlain by Upper Jurassic to Lower Cretaceous fine- to coarse-grained epiclastic rocks of the Gravina sequence. The upper Paleozoic part of the Alava sequence may be correlative with the Yukon–Tanana terrane, whereas the Middle and Upper Triassic portion of the Alava sequence may represent a metamorphic vestige of the Stikine terrane. Both parts are now exposed on the western flank of the Coast Plutonic Complex, in contrast with their correlatives to the east. These relations suggest that the Stikine and Alexander terranes were juxtaposed prior to deposition of the Gravina sequence. The western boundary between rocks of North American affinity and allochthonous ensimatic crustal fragments of the Alexander and Wrangellian terranes lies west of the Coast Plutonic Complex.

Upper Paleozoic to lower Mesozoic strata and their conodonts, western Coast Plutonic Complex, British Columbia

1985 ◽  
Vol 22 (9) ◽  
pp. 1329-1344 ◽  
Author(s):  
G. J. Woodsworth ◽  
M. J. Orchard
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Late Triassic ◽  
Western Coast ◽  
Upper Paleozoic ◽  
Facies Metamorphism ◽  
Volcanic Suite ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Greenschist Facies Metamorphism

Six lithologic units, including two newly named formations, were mapped on Randall, Dunira, and nearby islands. The islands are characterized by greenschist-facies metamorphism and westerly directed thrusting. The oldest unit is a Late Mississippian, massive limestone on Ducie Island. The Dunira Formation, composed of thin-bedded limestone and siltstone, is Early and Middle Pennsylvanian in age. It is unconformably overlain by limestone and dolomite of the Upper Triassic Randall Formation. The Randall Formation grades upwards into a green phyllitic unit of Late Triassic(?) age. Rhyolitic and more mafic volcanic rocks may represent a bimodal volcanic suite of Early Jurassic age, based on a U–Pb date of 188 Ma on zircons. These five units correlate with rocks in the Alexander Terrane in southeastern Alaska. The sixth and presumed youngest unit consists of flysch-like sedimentary rocks of probable Middle Jurassic to Early Cretaceous age that may correlate with rocks of the Gravina–Nutzotin belt. The three older units yielded 15 conodont genera from 29 localities. The 13 Paleozoic genera are described and illustrated.

Geology of the Chatham Sound region, southeast Alaska and coastal British Columbia

2001 ◽  
Vol 38 (11) ◽  
pp. 1579-1599 ◽  
Author(s):  
George E Gehrels
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Upper Jurassic ◽  
The West ◽  
Southeast Alaska ◽  
Coast Mountains ◽  
Early Tertiary ◽  
Metavolcanic Rocks ◽  
Upper Paleozoic ◽  
Coastal British Columbia

The Coast Mountains orogen is thought to have formed as a result of accretion of the Alexander and Wrangellia terranes against the western margin of the Stikine and Yukon–Tanana terranes, but the nature and age of accretion remain controversial. The Chatham Sound area, which is located along the west flank of the Coast Mountains near the Alaska – British Columbia border, displays a wide variety of relations that bear on the nature and age of the boundary between inboard and outboard terranes. Geologic and U–Pb geochronologic studies in this area reveal a coherent but deformed and metamorphosed sequence of rocks belonging to the Yukon–Tanana terrane, including pre-mid-Paleozoic marble, schist, and quartzite, mid-Paleozoic orthogneiss and metavolcanic rocks, and upper Paleozoic metaconglomerate and metavolcanic rocks. These rocks are overlain by Middle Jurassic volcanic rocks (Moffat volcanics) and Upper Jurassic – Lower Cretaceous strata of the Gravina basin, both of which also overlie Triassic and older rocks of the Alexander terrane. This overlap relationship demonstrates that the Alexander and Wrangellia terranes were initially accreted to the margin of inboard terranes during or prior to mid-Jurassic time. Accretion was apparently followed by Late Jurassic – Early Cretaceous extension–transtension to form the Gravina basin, left-slip along the inboard margin of Alexander–Wrangellia, mid-Cretaceous collapse of the Gravina basin and final structural accretion of the outboard terranes, and early Tertiary dip-slip motion on the Coast shear zone.

Paleomagnetism of Mesozoic plutons in the westernmost Coast Complex of British Columbia

1977 ◽  
Vol 14 (9) ◽  
pp. 2127-2139 ◽  
Author(s):  
D. T. A. Symons
Keyword(s):  
North American ◽  
Leading Edge ◽  
Upper Jurassic ◽  
North American Plate ◽  
The North ◽  
Banks Island ◽  
Plutonic Complex ◽  
Normal Polarity ◽  
Coast Plutonic Complex ◽  
North American Craton

The Lower Cretaceous Stephens Island (102 ± 8 Ma) and Captain Cove (109 ± 6 Ma) plutons and the Upper Jurassic Gil Island (136 ± 3 Ma) and Banks Island (144 ± 6 Ma) plutons belong to the western K–Ar age zone of the N 35° W trending Coast plutonic complex southwest of Prince Rupert, B.C. After removal of initial viscous components, AF demagnetization isolates a stable primary remanence at 36 of 49 sites (10 specimens from 5 cores/site) before anhysteretic components are added. All sites have normal polarity which is consistent because their K–Ar ages fall in the predominantly normal Cretaceous and Jurassic Quiet Intervals. The poles for Stephens Island (339° W, 67° N (7°, 10°)), Captain Cove (9° W 72° N (8°, 11°)), and Gil Island (357° N. 70° N (6°, 8°)) lie just north of Britain and are discordant for the North American craton. The tectonic panel including these plutons was tilted [Formula: see text] during the Upper Cretaceous–Paleocene orogeny as the leading edge of the North American plate overrode the subducting oceanic Kula Plate. This interpretation is supported by other arguments including the attitudes of contacts and foliations, plutonic trend directions, distribution of metamorphic grades, and paleomagnetic data from the area to the east. The Banks Island pluton lies in the tectonic panel to the west. Its pole of 210° W, 81° N (33°, 38°) is poorly defined but apparently concordant.

Triassic to Neogene geologic evolution of the Queen Charlotte region

1991 ◽  
Vol 28 (6) ◽  
pp. 854-869 ◽  
Author(s):  
P. D. Lewis ◽  
J. W. Haggart ◽  
R. G. Anderson ◽  
C. J. Hickson ◽  
R. I. Thompson ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Upper Jurassic ◽  
Queen Charlotte Islands ◽  
Upper Paleozoic ◽  
Coast Plutonic Complex ◽  
Present Distribution ◽  
Deformation Event ◽  
Differential Uplift ◽  
Uplift And Erosion ◽  
Block Faulting

A wealth of new geological and geophysical data from recent studies of the Queen Charlotte region are integrated into a coherent model. In this paper, we summarize these new studies and discuss possible correlations with other areas. Four tectonostratigraphic divisions are distinguished by stratigraphic, structural, and magmatic character, and each is separated by a major unconformity. The oldest division comprises widely distributed, upper Paleozoic through Middle Jurassic strata of Wrangellia that accumulated in volcanic-arc and stable shelf and basinal settings. No significant deformation occurred in the Queen Charlotte Islands region during the accumulation of these rocks. A Middle and Upper Jurassic assemblage comprises two plutonic suites and volcanic and epiclastic rocks. The unconformity below the Middle and Upper Jurassic assemblage marks a regional, southwest-vergent contractional deformation that is the most significant Mesozoic or Cenozoic deformation in the region. Jurassic plutons in the Queen Charlotte Islands are the oldest and most primitive members of an eastwardly migrating and evolving Jura-Cretaceous magmatic front recognized by other workers in the Coast Plutonic Complex. Widespread Late Jurassic block faulting led to differential uplift and erosion of northwest-trending fault blocks. A third assemblage consists of Cretaceous marine sedimentary rocks derived principally from subjacent Jurassic volcanic rocks as well as older strata. The present distribution of Cretaceous strata reflects a gradual eastward transgression, briefly interrupted in the Coniacian by progradation of conglomerate fans from the east. A second regional contractional deformation event in latest Cretaceous time was concentrated along a northwest-trending zone coinciding with Jurassic block faults. The early Tertiary marked another distinct shift in sedimentation style, with the inception of local nonmarine deposition on the present islands and widespread volcanism and plutonism on the southern islands. Syntectonic deposition in offshore extensional basins (Hecate Strait and Queen Charlotte Sound) may have commenced at this time. Later in the Tertiary, extensive deposition occurred in offshore regions, coeval with northward migration of plutonism and volcanism on the islands. Contractional structures in Pliocene sediments in Hecate Strait are the youngest deformational features observed.

scholarly journals Age, HF-isotope systemantics of detritial zircons and the source of conglomerates of the mt. Southern Demerdzhy, Mountainous Crimea

2019 ◽  
pp. 36-61
Author(s):  
S. V. Rud’ko ◽  
N. B. Kuznetsov ◽  
E. A. Belousova ◽  
T. V. Romanyuk
Keyword(s):  
Middle Jurassic ◽  
Age Distribution ◽  
Primary Source ◽  
Upper Jurassic ◽  
Detrital Zircons ◽  
Hf Isotope ◽  
Coarse Grained ◽  
East European ◽  
Scythian Plate ◽  
Isotope Systematics

The U–Pb dating and Hf isotope systematics of detrital zircons from a sandstone interbed in the section of the upper conglomerate sequence of the Mt. South Demerdzhi were carried out. The dominant populations of detrital zircons in the studied sample characterize episodes of magmatic activity within the source of the Upper Jurassic conglomerates. Magmatism was manifested in the Vendian-Cambrian, Carbon-Triassic and Late Jurassic. The åHf values of detrital zircons of these ages indicate the insignificant role of the ancient (Archean–Early Proterozoic) continental crust in the protolith of magmatic chambers. The similarity of the detrital zircons age distribution from the Middle Jurassic and Upper Jurassic conglomerate strata suggests that they are molasses of the Cimmerian orogen. The absence of products of Middle Jurassic magmatism in molasses of the Cimmerian orogen, which we fixed, limits position of the Cimmerian orogen in the southern part of the Scythian plate. It is shown that the primary source of the Precambrian detrital zircons were mobilized within the Cimmerian orogen the crustal fragments of the Peri-Gondwanan origin, rather than the basement complexes of the East European Platform, similar to the complexes of the Ukrainian shield. The reconstruction of the main stages of the accumulation of the coarse-grained strata of the Mountaineous Crimea in the context of the tectonic evolution of the southern margin of Laurasia during the Mesozoic is presented.

Magmatic evolution of the eastern Coast Plutonic Complex, Bella Coola region, west-central British Columbia

2009 ◽  
Vol 121 (9-10) ◽  
pp. 1362-1380 ◽  
Author(s):  
J. Brian Mahoney ◽  
Sarah M. Gordee ◽  
James W. Haggart ◽  
Richard M. Friedman ◽  
Larry J. Diakow ◽  
...  
Keyword(s):  
British Columbia ◽  
Eastern Coast ◽  
Magmatic Evolution ◽  
West Central ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Bella Coola

Obducted nappe sequence in the San Juan Islands – northwest Cascades thrust system, Washington and British Columbia

2012 ◽  
Vol 49 (7) ◽  
pp. 796-817 ◽  
Author(s):  
E.H. Brown
Keyword(s):  
British Columbia ◽  
Detrital Zircons ◽  
San Juan ◽  
San Juan Islands ◽  
Tectonic History ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
History Of ◽  
Accreted Terranes ◽  
Thrust System

The San Juan Islands – northwest Cascades thrust system in Washington and British Columbia is composed of previously accreted terranes now assembled as four broadly defined composite nappes stacked on a continental footwall of Wrangellia and the Coast Plutonic Complex. Emplacement ages of the nappe sequence are interpreted from zircon ages, field relations, and lithlogies, to young upward. The basal nappe was emplaced prior to early Turonian time (∼93 Ma), indicated by the occurrence of age-distinctive zircons from this nappe in the Sidney Island Formation of the Nanaimo Group. The emplacement age of the highest nappe in the thrust system postdates 87 Ma detrital zircons within the nappe. The nappes bear high-pressure – low-temperature (HP–LT) mineral assemblages indicative of deep burial in a thrust wedge; however, several features indicate that metamorphism occurred prior to nappe assembly: metamorphic discontinuities at nappe boundaries, absence of HP–LT assemblages in the footwall to the nappe pile, and absence of significant unroofing detritus in the Nanaimo Group. A synorogenic relationship of the thrust system to the Nanaimo Group is evident from mutually overlapping ages and by conglomerates of Nanaimo affinity that lie within the nappe pile. From the foregoing relations, and broader Cordilleran geology, the tectonic history of the nappe terranes is interpreted to involve initial accretion and subduction-zone metamorphism south of the present locality, uplift and exhumation, orogen-parallel northward transport of the nappes as part of a forearc sliver, and finally obduction at the present site over the truncated south end of Wrangellia and the Coast Plutonic Complex.

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