U–Pb geochronology of Jurassic to early Tertiary granitic intrusives from the Nelson–Castlegar area, southeastern British Columbia, Canada

1995 ◽  
Vol 32 (10) ◽  
pp. 1668-1680 ◽  
Author(s):  
Dipak K. Ghosh
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Middle Eocene ◽  
Biotite Granite ◽  
Published Data ◽  
Crustal Material ◽  
Granitoid Magmatism ◽  
Continental Arc ◽  
Two Samples ◽  
Deformation Event

Eleven U–Pb zircon dates from seven intrusives in the Nelson–Castlegar area provide new age constraints on the granitoid magmatism in southeastern British Columbia. Four samples from the Nelson Batholith date three distinct intrusive phases spanning ca. 10 Ma. One sample from the eastern porphyritic phase (Coffee Creek) yields the oldest age at 172.5 ± 5.0 Ma. Two samples from the central K-feldspar megacrystic phase (Crescent Bay) give precise ages at 162.0 ± 1.0 and 161.5 ± 1.5 Ma, and possibly date the youngest phase of the batholith. An intermediate age of emplacement at 166.0 ± 3.0 Ma is suggested for the southern tail of the batholith. The new and published data suggest that the Nelson Batholith was emplaced in roughly concentric zones. In contrast, the southern quartz diorite phase and the northwestern granodiorite phase of the Bonnington Pluton were emplaced coevally during the Middle Jurassic at 167.4 ± 2.0 and 165.0 ± 3.0 Ma, respectively. Middle Jurassic ages were also obtained for a sample of hornblende orthogneiss (166.0 ± 7.5 Ma) that intrudes the Trail Gneiss, and for a leucocratic gneiss sample (156.6 ± 6.0 Ma), a remnant from the Kinnaird Gneiss. A biotite granite sheet that intrudes the Kinnaird Gneiss yields a Middle Eocene age (40.5 ± 6.0 Ma), and possibly dates the youngest deformation event in the region. The Early Eocene ages (55.1 ± 3.7 and 50.6 ± 0.5 Ma) obtained from the Ladybird Granite and Coryell Syenite agree with previous estimates. Early Proterozoic ages of inherited zircon components in most of the samples agree with Nd–Sr isotopic evidence for incorporation of old crustal material in the intrusives empiaced in continental-arc settings.

Eocene age for Ag–Pb–Zn–Au vein and replacement deposits of the Kokanee Range, southeastern British Columbia

1992 ◽  
Vol 29 (1) ◽  
pp. 3-14 ◽  
Author(s):  
G. Beaudoin ◽  
J. C. Roddick ◽  
D. F. Sangster
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Middle Eocene ◽  
Hanging Wall ◽  
Spatial Association ◽  
High Heat ◽  
Time Interval ◽  
Genetic Link ◽  
Metasedimentary Rocks ◽  
Magmatic Event

The Ag–Pb–Zn–Au vein and replacement deposits of the Kokanee Range, southeastern British Columbia, are hosted by the Middle Jurassic Nelson batholith and surrounding Cambrian to Triassic metasedimentary rocks in the hanging wall of the transcrustal Slocan Lake Fault, Field relations indicate that mineralization is younger than the Nelson batholith and a Middle Jurassic foliation in the Ainsworth area but coeval or older than Eocene unroofing of the Valhalla metamorphic core complex in the footwall of the Slocan Lake Fault. Lamprophyre and gabbro dykes are broadly coeval with mineralization and have biotite and hornblende K–Ar ages defining a short-lived Middle Eocene alkaline magmatic event between 52 and 40 Ma. An older, Early Cretaceous alkaline magmatic event (141 – 129 Ma) is possible but incompletely documented.K–Ar and step-heating 40Ar/39Ar analyses on hydrothermal vein and alteration muscovite indicate that hydrothermal fluids were precipitating vein and replacement deposits 58–59 Ma ago. Crosscutting relationships with lamprophyre dykes indicate the Kokanee Range hydrothermal system lasted for more than 15 Ma. Eocene crustal extension resulted in a high heat flow and structures which were probably responsible for hydrothermal fluid movement and flow paths.A 100 Ma time interval is documented between batholith emplacement and spatially associated mineralization, ruling out any genetic link between the two. Similar large age differences between granite intrusion and peripheral mineralization have recently been documented for two world-sea le Ag–Pb–Zn vein districts, which suggest that spatial association between granite and Ag–Pb–Zn mineralization is not sufficient to infer a genetic link.

Age and origin of Late Jurassic and Paleocene granitoids, Nelson Batholith, southern British Columbia

1993 ◽  
Vol 30 (12) ◽  
pp. 2305-2314 ◽  
Author(s):  
J. H. Sevigny ◽  
R. R. Parrish
Keyword(s):  
British Columbia ◽  
Rare Earth ◽  
Rare Earth Elements ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Alkaline Earth ◽  
Biotite Granite ◽  
Isotopic Data ◽  
Quartz Monzonite ◽  
Early Late

In the Middle Jurassic Nelson Batholith, southern British Columbia, young 40Ar/39Ar ages (i.e., 50–60 Ma) and distorted isobaric surfaces in the batholith suggest the possibility of Paleocene granitic plutonism. We present the results of a study undertaken to evaluate this possibility. Geochemical criteria successfully distinguish a suite of granitoids within the Nelson Batholith that differ from Nelson granites of similar SiO2 content. The granitoid suite is composed of 71.6–75.7 wt.% SiO2 leucocratic biotite granite and quartz monzonite with strong enrichments in alkaline, alkaline earth, and rare earth elements. Nd and Pb isotopic compositions suggest that biotite granite and quartz monzonite are not related. Biotite granite yields a U–Pb age of 158.9 ± 0.6 Ma (concordant zircons). Quartz monzonite crystallized at 61 ± 1 Ma, based on interpretation of titanite and zircon analyses. Zircons from this sample lie along a line from 61 to 160 Ma and demonstrate the presence of Middle Jurassic inheritance. Based on its petrographic and isotopic similarity to other Middle Jurassic plutons in the Nelson Batholith – Valhalla Complex area, we include the 159 Ma biotite granite with the Jurassic plutonic suite. This result demonstrates that magmatism in southern British Columbia was active at least until the early Late Jurassic (Oxfordian). The Paleocene (61 Ma) quartz monzonite that intrudes the southern Nelson Batholith is the structurally highest occurrence of "Ladybird" granite yet documented in southern British Columbia. Comparison of new and published geochemical and isotopic data for Paleocene granitoids throughout the southern Omineca Belt, British Columbia, suggests that these granitoids were not derived from a single, old crustal source.

Fossil Mosses from the Bisaccate Zone of the Mid-Eocene Allenby Formation, British Columbia

1974 ◽  
Vol 11 (3) ◽  
pp. 409-421 ◽  
Author(s):  
Marian Kuc
Keyword(s):  
British Columbia ◽  
Middle Eocene ◽  
Plant Tissues ◽  
Plant Remains ◽  
Lake Bottom ◽  
White Colour

New fossil taxa (Ditrichites fylesi, Muscites maycocki, M. ritchiei, Palaeohypnum jovet-asti and P. steerei); unnamed moss and moss-like fossils, detrital fragments of various plant tissues, and paleobotanical evidence of the bisaccate zone are described from the Middle Eocene Allenby Formation near Princeton, British Columbia. These remains occur in laminated, tuffaceous, silty and pyroclastic shale, deposited under lacustrine conditions.Detailed examination of the various laminae indicates that beds of white colour and composed of coarser silt grains are poor in fossils and could be related to periods of decreasing bioproduction; less silty and darker coloured beds are rich in macro- and microfossils and could be related to periods of extensive bioproduction. The rock features, lamination, and distribution of macrofossils indicate the slow and undisturbed accumulation of plant remains on a lake bottom.

scholarly journals Paleoclimate and precipitation seasonality of the Early Eocene McAbee megaflora, Kamloops Group, British Columbia

2016 ◽  
Vol 53 (6) ◽  
pp. 591-604 ◽  
Author(s):  
Cale A.C. Gushulak ◽  
Christopher K. West ◽  
David R. Greenwood
Keyword(s):  
British Columbia ◽  
North American ◽  
Leaf Size ◽  
Early Eocene ◽  
Precipitation Seasonality ◽  
Two Samples ◽  
Fossil Site ◽  
Fossil Floras ◽  
Climate Analysis ◽  
Early Cenozoic

Early Eocene fossil floras from British Columbia are a rich resource for reconstructing western North American early Cenozoic climate. The best known of these floras reflect cooler (MAT ≤ 15 °C) upland forest communities in contrast to coeval (MAT ≥ 18 °C) forests in lowland western North American sites. Of particular interest is whether Early Eocene climates were monsoonal (highly seasonal precipitation). The McAbee site is a 52.9 ± 0.83 Ma 0.5 km outcrop of bedded lacustrine shale interbedded with volcanic ash. In this report two historical megaflora collections that were collected independently from different stratigraphic levels and (or) laterally separated by ∼100–200 m in the 1980s (University of Saskatchewan) and 2000s (Brandon University) are investigated to (i) assess whether they represent the same leaf population, (ii) assess whether a combined collection yields more precise climate estimates, and (iii) reconstruct paleoclimate to assess the character of regional Early Eocene precipitation seasonality. Combined, the two samples yielded 43 dicot leaf morphotypes. Analysis of leaf size distribution using ANOVA showed no difference between the two samples, and thus they were combined for climate analysis. Climate analysis using leaf physiognomy agrees with previous estimates for McAbee and other regional megafloras, indicating a warm (MAT ∼8–13 °C), mild (CMMT ∼5 °C), moist (MAP > 100 cm/year) ever-wet, non-monsoonal climate. Additionally, we recommend that climate analyses derived from leaf fossils should be based on samples collected within a stratigraphically constrained quarry area to capture a snapshot of climate in time rather than time-averaged estimates derived from multiple quarry sites representing different stratigraphic levels within a fossil site.

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.

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