Ancient continental margin assemblage in the northern Coast Mountains, southeast Alaska and northwest Canada

Geology ◽  
1990 ◽  
Vol 18 (3) ◽  
pp. 208 ◽  
Author(s):  
George E. Gehrels ◽  
William C. McClelland ◽  
Scott D. Samson ◽  
P. Jonathan Patchett ◽  
Jay L. Jackson
Keyword(s):  
Continental Margin ◽  
Northern Coast ◽  
Southeast Alaska ◽  
Coast Mountains

U–Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska

1991 ◽  
Vol 28 (8) ◽  
pp. 1285-1300 ◽  
Author(s):  
George E. Gehrels ◽  
William C. McClelland ◽  
Scott D. Samson ◽  
P. Jonathan Patchett
Keyword(s):  
Continental Margin ◽  
North American ◽  
Detrital Zircons ◽  
Northern Coast ◽  
Coast Mountains ◽  
Metasedimentary Rocks ◽  
The North ◽  
Upper Proterozoic ◽  
Two Samples ◽  
Cordilleran Margin

Metamorphic rocks within and west of the northern Coast Mountains in southeastern Alaska consist of an Upper Proterozoic(?) to upper Paleozoic continental margin assemblage that we interpret to belong to the Yukon-Tanana terrane. U–Pb geochronologic analyses of single detrital zircon grains from four samples of quartzite suggest that the zircons were shed from source regions containing rocks of ~495 Ma, ~750 Ma, 1.05–1.40 Ga, 1.75–2.00 Ga, ~2.3 Ga, 2.5–2.7 Ga, and ~3.0 Ga. Multigrain fractions from two samples yield upper intercepts between 2.0 and 2.3 Ga, but the scarcity of single grains of similar age suggests that these fractions comprise a mixture of < 2.0 and > 2.3 Ga grains. Zircons in these rocks generally overlap in age with (i) detrital zircons in metasedimentary rocks of the Yukon–Tanana terrane in eastern Alaska and Yukon, (ii) detrital zircons in strata of the Cordilleran miogeocline, and (iii) plutonic and gneissic rocks that intrude or are overlain by miogeoclinal strata. In addition, the pre-1.7 Ga grains overlap in age with dated crystalline rocks of the western Canadian Shield. These similarities raise the possibility that metaclastic rocks in the northern Coast Mountains accumulated in proximity to western North America. The younger zircon populations were likely shed from mid-Proterozoic to early Paleozoic igneous rocks that now occur locally (but may have been widespread) along the Cordilleran margin. Recognition of a continental margin assemblage of possible North American affinity in the Coast Mountains raises the possibility that some arc-type and oceanic terranes inboard of the Coast Mountains may be large klippen that have been thrust over the North American margin.

Coastal and offshore provinces of Timor-Leste — Geophysics exploration and drilling

2020 ◽  
Vol 39 (8) ◽  
pp. 543-550
Author(s):  
Roberto Fainstein ◽  
Juvêncio De Deus Correia do Rosário ◽  
Helio Casimiro Guterres ◽  
Rui Pena dos Reis ◽  
Luis Teófilo da Costa
Keyword(s):  
Continental Margin ◽  
Accretionary Prism ◽  
Stratigraphic Correlation ◽  
Accretionary Wedge ◽  
Northern Coast ◽  
Potential Field Data ◽  
The North ◽  
Banda Arc ◽  
Timor Leste ◽  
Well Data

Regional geophysics research provides for prospect assessment of Timor-Leste, part of the Southeast Asia Archipelago in a region embracing the Banda Arc, Timor Island, and the northwest Australia Gondwana continental margin edge. Timor Island is a microcontinent with several distinct tectonic provinces that developed initially by rifting and drifting away from the Australian Plate. A compressive convergence began in the Miocene whereby the continental edge of the large craton collided with the microcontinent, forming a subduction zone under the island. The bulk of Timor Island consists of a complex mélange of Tertiary, Cretaceous, Jurassic, Triassic, Permian, and volcanic features over a basal Gondwana craton. Toward the north, the offshore consists of a Tertiary minibasin facing the Banda Arc Archipelago, with volcanics interspersed onshore with the basal Gondwana pre-Permian. A prominent central overthrust nappe of Jurassic and younger layers makes up the mountains of Timor-Leste, terminating south against an accretionary wedge formed by this ongoing collision of Timor and Australia. The northern coast of the island is part of the Indonesian back arc, whereas the southern littoral onshore plus shallow waters are part of the accretionary prism. Deepwater provinces embrace the Timor Trough and the slope of the Australian continental margin being the most prospective region of Timor-Leste. Overall crust and mantle tectonic structuring of Timor-Leste is interpreted from seismic and potential field data, focusing mostly on its southern offshore geology where hydrocarbon prospectivity has been established with interpretation of regional seismic data and analyses of gravity, magnetic, and earthquake data. Well data tied to seismic provides focal points for stratigraphic correlation. Although all the known producing hydrocarbon reservoirs of the offshore are Jurassic sands, interpretation of Permian and Triassic stratigraphy provides knowledge for future prospect drilling risk assessment, both onshore and offshore.

U–Pb geochronology of Late Cretaceous and early Tertiary plutons in the northern Coast Mountains batholith

1991 ◽  
Vol 28 (6) ◽  
pp. 899-911 ◽  
Author(s):  
George E. Gehrels ◽  
William C. McClelland ◽  
Scott D. Samson ◽  
P. Jonathan Patchett ◽  
David A. Brew
Keyword(s):  
Shear Zone ◽  
Late Cretaceous ◽  
Detrital Zircons ◽  
Northern Coast ◽  
Coast Mountains ◽  
Western Margin ◽  
Early Proterozoic ◽  
Isotopic Signatures ◽  
Metasedimentary Rocks ◽  
Early Tertiary

U–Pb geochronologic studies demonstrate that steeply dipping, sheetlike tonalitic plutons along the western margin of the northern Coast Mountains batholith were emplaced between ~83 and ~57 (perhaps ~55) Ma. Less elongate tonalitic–granodioritic bodies in central portions of the batholith yield ages of 59–58 Ma, coeval with younger phases of the tonalitic sheets. Large granite–granodiorite bodies in central and eastern portions of the batholith were emplaced at 51–48 Ma. Trends in ages suggest that the tonalitic bodies generally become younger southeastward and that, at the latitude of Juneau, plutonism migrated northeastward across the batholith at ~0.9 km/Ma. Variations in the age, shape, location, and degree of fabric development among the various plutons indicate that Late Cretaceous – Paleocene tonalitic bodies were emplaced into a steeply dipping, dip-slip shear zone that was active along the western margin of the batholith. Postkinematic Eocene plutons were emplaced at shallow crustal levels. Inherited zircon components in these plutons range in age from mid-Paleozoic to Early Proterozoic and are coeval with detrital zircons in adjacent metasedimentary rocks. These old zircons, combined with evolved Nd isotopic signatures for most plutons, record assimilation of continental crustal or supracrustal rocks during the generation and (or) ascent of the plutons.

Geothermal Data from the Granduc Area, Northern Coast Mountains of British Columbia

1972 ◽  
Vol 9 (10) ◽  
pp. 1333-1337 ◽  
Author(s):  
W. H. Mathews
Keyword(s):  
Thermal Conductivity ◽  
British Columbia ◽  
Heat Flow ◽  
Thermal Gradient ◽  
Temperature Measurements ◽  
Simplified Model ◽  
Northern Coast ◽  
Rock Glacier ◽  
Coast Mountains

Temperature measurements have been obtained from 80 points along the Granduc haulage tunnel, at depths of as much as 1.5 km below the surface. These fit, within 1 °C, a simplified model assuming, among other things, uniform thermal conductivity of the rocks and a temperature at rock–glacier contacts of 0 °C. For these assumptions a generalized thermal gradient (with effects of topographic irregularity removed) is about 26 mK m−1 (26 °C/km). With the thermal conductivity of a suite of rocks from the tunnel averaging 2.72 ± 12 W m−1K−1 (6.50 ±.28 cal/cm s °C) present heat flow of about 73 mW m−2 (1.74 μcal/cm2 s) can be derived.

Nd and Sr isotopic constraints on the petrogenesis of the west side of the northern Coast Mountains batholith, Alaskan and Canadian Cordillera

1991 ◽  
Vol 28 (6) ◽  
pp. 939-946 ◽  
Author(s):  
Scott D. Samson ◽  
P. Jonathan Patchett ◽  
William C. McClelland ◽  
George E. Gehrels
Keyword(s):  
Late Cretaceous ◽  
Crustal Thickening ◽  
Northern Coast ◽  
Crustal Material ◽  
The West ◽  
Crustal Component ◽  
Coast Mountains ◽  
Early Proterozoic ◽  
Depleted Mantle ◽  
Wrangellia Terrane

Nd and Sr isotopic ratios are reported from 15 samples of plutons of the northern Coast Mountains batholith (CMB), between. the Alexander–Wrangellia terrane and the Stikine terrane of southeastern Alaska. Samples of plutons that are part of the Late Cretaceous – Eocene CMB suite have a range in initial εNd of −3.0 to −0.2 and 87Sr/86Sr of 0.70494–0.70607. There is no correlation of isotopic ratio with age, lithology, or geographic location of these plutons. Two plutons that are probably older than the bulk of the CMB plutons have present-day εNd values of −6.8 and −2.6.The Late Cretaceous – Eocene plutons have Nd depleted-mantle model ages (tDM) of 620–1070 Ma. These data indicate that the northern CMB must contain a significant component of old, evolved continental crust. The presence of an old crustal component is further demonstrated by inherited zircons of average Early Proterozoic age contained in some plutons. The mid to Late Proterozoic tDM ages of the CMB plutons are therefore a result of a mixture of Early Proterozoic crustal material with. younger, juvenile crust. The most likely source of this old crustal component is the Yukon–Tanana terrane, a fragment composed of ancient crustal material that occurs within and directly to the west of the northern CMB. The juvenile component is probably a combination of material derived from the mantle and from anatexis of the surrounding juvenile terranes. Crustal anatexis may have occurred as a result of the intrusion of mafic melts related to subduction along the outboard margin of the Alexander–Wrangellia terrane, by crustal thickening due to the underthrusting of the Alexander–Wrangellia terrane beneath the Yukon–Tanana and Stikine terranes, or by a combination of both processes.

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