A petrologic and Rb–Sr isotopic study of intrusive rocks near Fairbanks, Alaska

1985 ◽  
Vol 22 (9) ◽  
pp. 1314-1321 ◽  
Author(s):  
Joel D. Blum
Keyword(s):  
Trace Element ◽  
Shallow Depth ◽  
Early Paleozoic ◽  
Uplift Rate ◽  
Isotopic Study ◽  
Crustal Rocks ◽  
Late Proterozoic ◽  
Intrusive Rocks ◽  
Major Oxide ◽  
Plutonic Rocks

Epizonal granodiorite and granite plutons intrude the northwestern portion of the Yukon Crystalline Terrane near Fairbanks, Alaska. Mineralogic, major-oxide, and trace-element studies indicate that the plutons represent a comagmatic fractionation suite. A Rb–Sr whole-rock isochron for one pluton yields an age of 90.9 ± 0.9 Ma, in agreement with previous K–Ar dating of biotite and hornblende and an initial 87Sr/86Sr ratio of 0.71238 ± 0.00014. The elevated initial 87Sr/86Sr ratio suggests that the plutons may have had a different source from that of the belt of subduction-related, mid-Cretaceous plutonic rocks found farther to the southeast in the Yukon Crystalline Terrane. In contrast, they appear to have been formed at least in part by anatectic melting of Late Proterozoic or early Paleozoic crustal rocks. Comparison of aplite dike compositions with the synthetic granite system, estimates of average uplift rate, and K–Ar cooling ages of surrounding schists all indicate that the magmas that formed the plutons near Fairbanks intruded much higher into the crust after anatectic melting and crystallized at a relatively shallow depth of 3–5 km.

Nd isotopic characteristics of metamorphic and plutonic rocks of the Coast Mountains near Prince Rupert, British Columbia

1998 ◽  
Vol 35 (5) ◽  
pp. 556-561 ◽  
Author(s):  
P J Patchett ◽  
G E Gehrels ◽  
C E Isachsen
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Metamorphic Rocks ◽  
Published Data ◽  
Isotopic Data ◽  
Crustal Component ◽  
Coast Mountains ◽  
Crustal Rocks ◽  
Metasedimentary Rocks ◽  
Plutonic Rocks

Nd isotopic data are presented for a suite of metamorphic and plutonic rocks from a traverse across the Coast Mountains between Terrace and Prince Rupert, British Columbia, and for three contrasting batholiths in the Omineca Belt of southern Yukon. A presumed metamorphic equivalent of Jurassic volcanic rocks of the Stikine terrane gives epsilon Nd = +6, and a number of other metaigneous and metasedimentary rocks in the core of the Coast Mountains give epsilon Nd values from +3 to +7. A single metasedimentary rock approximately 3 km east of the Work Channel shear zone gives a epsilon Nd value of -9. Coast Belt plutons in the traverse yield epsilon Nd from -1 to +2. The Omineca Belt plutons give epsilon Nd from -10 to -17. All results are consistent with published data in demonstrating that (i) juvenile origins for both igneous and metamorphic rocks are common in the Coast Belt; (ii) representatives of a continental-margin sedimentary sequence with Precambrian crustal Nd are tectonically interleaved in the Coast Mountains; (iii) Coast Mountains plutons can be interpreted as derived from a blend of metamorphic rocks like those seen at the surface, or as arc-type melts contaminated with the older crustal component; and (iv) Omineca Belt plutons are dominated by remelted Precambrian crustal rocks.

scholarly journals Major-oxide and trace-element geochemical data from rocks collected in the Tok River area, Tanacross A-5 and A-6 quadrangles, Alaska in 2016

2016 ◽  
Author(s):  
Alicja Wypych ◽  
K. R. Sicard ◽  
R. J. Gillis ◽  
L. L. Lande ◽  
T. J. Naibert ◽  
...  
Keyword(s):  
Trace Element ◽  
Geochemical Data ◽  
Major Oxide

CAMBRIAN AND PRECAMBRIAN PETROLEUM AN APPRAISAL

1965 ◽  
Vol 5 (1) ◽  
pp. 7
Author(s):  
Grover E. Murray
Keyword(s):  
United States ◽  
North Africa ◽  
Sedimentary Rocks ◽  
The United States ◽  
Northern Territory ◽  
Early Paleozoic ◽  
Precambrian Rocks ◽  
Late Proterozoic ◽  
Organic Evolution ◽  
Early Phases

Accumulated evidence indicates that (1) the major portion of chemical and organic evolution occurred during the 3-5 x 109 years of the earth's history preceding the Paleozoic; (2) the basic elements constituting petroleum existed in the early phases of the earth's history; (3) unmetamorphosed Precambrian and Cambrian lithic types are similar to younger ones; and (4) the population of the later Precambrian and early Paleozoic seas was relatively rich and varied, though hard skeletal parts are notably absent in the Precambrian rocks and, in all probability, were not widely developed.As petroleum is now generally considered of organic origin and is a widely disseminated and integral part of most sedimentary rocks, unmetamorphosed Precambrian and Cambrian strata should be prospective for petroleum. Discoveries of large reserves of oil in the Cambrian in parts of North Africa, Russia and the United States support this asserted prospectivity. Shows of indigenous gas in the late Proterozoic of the Amadeus Basin, Northern Territory, Australia, indicate that unmetamorphosed Precambrian strata may also yield commercial amounts of hydrocarbons.

scholarly journals Insights into Polyphase Phanerozoic Tectonic Events in SE China: Integrated Isotopic Microanalysis of Detrital Zircon and Monazite

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
pp. 1-17
Author(s):  
Li-Guang Wu ◽  
Xian-Hua Li ◽  
Weihua Yao ◽  
Xiao-Xiao Ling ◽  
Kai Lu
Keyword(s):  
Detrital Zircon ◽  
Beach Sand ◽  
Sand Sample ◽  
Early Paleozoic ◽  
Isotopic Study ◽  
Tectonic Events ◽  
Crustal Reworking ◽  
Detrital Zircon Ages ◽  
Age Range ◽  
Se China

Abstract Widespread Paleozoic and Mesozoic granites are characteristics of SE China, but the geodynamic mechanisms responsible for their emplacement are an issue of ongoing debate. To shed new light on this issue, we present an integrated geochronological and isotopic study of detrital zircon and monazite from Cambrian metasandstones and modern beach sands in the Yangjiang region, SE China. For the Cambrian metasandstone sample, detrital zircon displays a wide age range between 490 and 3000 Ma, while monazite grains record a single age peak of 235 Ma. The results suggest that a significant Triassic (235 Ma) metamorphic event is recorded by monazite but not zircon. For the beach sand sample, detrital zircon ages show six peaks at ca. 440, 240, 155, 135, 115, and 100 Ma, whereas detrital monazite yields a dominant age peak at 237 Ma and a very minor age peak at 435 Ma. Beach sand zircon displays features that are typical of a magmatic origin. Their Hf–O isotopes reveal two crustal reworking events during the early Paleozoic and Triassic, in addition to one juvenile crustal growth event during the Jurassic–Cretaceous. The beach sand monazite records intense Triassic igneous and metamorphic events with significant crustal reworking. Such early Paleozoic and Triassic geochemical signatures of detrital zircon and monazite suggest they were derived from granitoids and metamorphic rocks which formed in intraplate orogenies, i.e., the early Paleozoic Wuyi–Yunkai Orogeny and Triassic Indosinian Orogeny. The Jurassic–Cretaceous signature of detrital zircon may reflect multistage magmatism that was related to subduction of the Paleo-Pacific Plate beneath SE China.

Structural relations at the eastern margin of the Shuswap Complex, near Revelstoke, southeastern British Columbia

1968 ◽  
Vol 5 (4) ◽  
pp. 831-849 ◽  
Author(s):  
John V. Ross
Keyword(s):  
British Columbia ◽  
Granite Gneiss ◽  
Early Paleozoic ◽  
Final Phase ◽  
Late Proterozoic ◽  
Eastern Margin ◽  
Deformational History ◽  
Facies Metamorphism ◽  
Absolute Age ◽  
Paleozoic Rocks

Three major phases of folding affected rocks of Late Proterozoic and Early Paleozoic age and members long assigned to the Shuswap Complex of southeastern British Columbia. The main and first phase of folding produced a large recumbent anticline, having a northerly trend, overturned to the east, that contains an exotic wedge of granite-gneiss within its core. This gneiss was mechanically emplaced into the Late Proterozoic and Early Paleozoic sediments, and already had a metamorphic and deformational history prior to its emplacement. Its age is possible Hudsonian equivalent. Metamorphism during this recumbent phase of folding was greenschist facies.Phase 2 folding was accompanied by amphibolite facies metamorphism, and caused refolding of the earlier composite recumbent anticline into open folds along southeasterly axes.A third and final phase of folding, associated with waning metamorphism, gave rise to folds along southeasterly striking axial-planes that dip steeply to the northeast. Thus, phase three folds caused tightening-up of the previously formed folds.The absolute age of these deformations is not yet known, but the Shuswap Complex, at its eastern margin, is shown to include Paleozoic rocks and some older gneisses, possibly of Hudsonian age.

Geochemical and isotopic (Nd, O, and Pb) constraints on granite sources in the Humber and Dunnage zones, Gaspésie, Quebec, and New Brunswick: implications for tectonics and crustal structure

1994 ◽  
Vol 31 (2) ◽  
pp. 323-340 ◽  
Author(s):  
Joseph B. Whalen ◽  
George A. Jenner ◽  
Ernst Hegner ◽  
Clément Gariépy ◽  
Frederick J. Longstaffe
Keyword(s):  
Subduction Zone ◽  
Incompatible Element ◽  
Crustal Material ◽  
Early Paleozoic ◽  
Isotopic Data ◽  
Geologic History ◽  
Seismic Reflection Data ◽  
Crustal Rocks ◽  
Isotopic Compositions ◽  
Reflection Data

Siluro–Devonian granitoids span a wide compositional range (~50–76% SiO2) and can be subdivided into two groups: (i) monzonitic or incompatible element enriched with affinities to within-plate magmatism (WPG); and (ii) calc-alkalic or incompatible element depleted with supra-subduction zone affinities (VAG). Granitoid εNd(T = 0.4 Ga) values range from −1 to +5.5; most lie between +3 and +5.5. 207Pb/204Pb isotopic compositions range from 15.52 to 15.61; most fall between ~15.55 and 15.59. Most δ18O values lie between +5.5 and +8‰. No well-established trends exist between SiO2 and isotopic composition, and isotopic compositions do not differ between the two trace element defined granitoid groups.Though Pb isotopic data are consistent with a major contribution to the granitoids from Proterozoic-aged Laurentian plate rocks (i.e., Grenville basement), Nd and O isotopic data are not. These isotopic data are consistent with major source components derived from early Paleozoic depleted or supra-subduction zone affected mantle and (or) crustal rocks derived from the early Paleozoic mantle(s). These protoliths would not have seen significant interaction with time-integrated old crustal material or surficial processes. Granitoid Pb isotopic data can be reconciled with an early Paleozoic mantle–crust origin, but it may also be that the Pb isotopes are decoupled from other isotopic systems. In either case, Nd and O isotopic data clearly prohibit the involvement of significant amounts of Grenville crust and suggest that seismic-reflection data do not define crustal blocks, or at least not blocks having a tectonic and geologic history easily related to the surface geology.

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