Age and Correlation of the Kobau Group, Mount Kobau, British Columbia

1973 ◽  
Vol 10 (10) ◽  
pp. 1508-1518 ◽  
Author(s):  
Andrew V. Okulitch
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
South Central ◽  
Shuswap Metamorphic Complex ◽  
Basic Volcanic ◽  
Devonian Age ◽  
Tertiary Period ◽  
Okanagan Valley

The Kobau Group, found in south-central British Columbia, consists of highly deformed, low-grade metamorphic rocks derived from a succession of sedimentary and basic volcanic rocks of pre-Cretaceous, likely post-Devonian age. Deformation began in Carboniferous times and recurred with decreasing intensity up to the Tertiary Period. Possible correlative successions are found surrounding Mount Kobau. These include possibly late Paleozoic formations west and northwest of Mount Kobau, the Carboniferous to Permian Anarchist Group found south of the 49th parallel and east of the Okanagan Valley, the pre-Upper Triassic, possibly Mississippian Chapperon Group west of Vernon, and parts of the Shuswap Metamorphic Complex east of the Okanagan Valley. Prior to deposition of the Kobau Group, part of the Shuswap Complex was subjected to deformation, presumably in mid-Paleozoic time.

The petrochemistry of the basic volcanic rocks of the South Connemara Group (Ordovician), western Ireland

1983 ◽  
Vol 120 (2) ◽  
pp. 141-152 ◽  
Author(s):  
P. D. Ryan ◽  
M. D. Max ◽  
T. Kelly
Keyword(s):  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Major And Trace Elements ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
The South ◽  
Northern Margin ◽  
Southern Side ◽  
Western Ireland ◽  
Basic Volcanic

Summary16 samples of Ordovician basic volcanic rocks of the South Connemara Group, which abut the southern side of the metamorphic rocks of the Connemara massif in western Ireland, have been analysed for both major and trace elements. Although subject to low grade regional metamorphism and subsequently hornfelsed by the Galway Granite (400 Ma), their immobile element contents do not appear to be significantly disturbed. These elements characterise the metabasites of the South Connemara Group as ocean floor basalts having their origins in a marginal basin. The Skird Rocks Fault, separating the South Connemara Group from high grade metamorphic rocks of the Connemara massif, is consequently regarded as the northern margin of the vestiges of the lapetus Ocean which can be traced into, and along, the Southern Uplands Fault.

The Triassic unconformity of south-central British Columbia

1977 ◽  
Vol 14 (4) ◽  
pp. 606-638 ◽  
Author(s):  
P. B. Read ◽  
Andrew V. Okulitch
Keyword(s):  
British Columbia ◽  
Regional Metamorphism ◽  
Tholeiitic Basalt ◽  
Upper Triassic ◽  
Late Triassic ◽  
Low Grade ◽  
Early Triassic ◽  
Central Belt ◽  
South Central ◽  
Shuswap Metamorphic Complex

At five localities investigated in south-central British Columbia, Upper Triassic rocks are observed or inferred to unconformably overlie upper Paleozoic and older rocks. Paleozoic rocks beneath the unconformity show polyphase deformation and low-grade regional metamorphism which are absent in overlying rocks. Data from these and other localities define a regional angular unconformity of Late Permian or Early Triassic age on the western and southern margins of the Shuswap Metamorphic Complex. Permian and Triassic rocks preserve evidence of structural, sedimentary, and metamorphic events which permits separation of Triassic rocks into three fault-bounded tectonostratigraphic belts. The Eastern Belt contains the transition from miogeoclinal sedimentation throughout Triassic time in the Canadian Rockies to island arc volcanism in the Late Triassic to the west. Basal beds of the Triassic sequence become younger southwest-ward from the axis of the Early to Middle Triassic depocentre lying west of the Rockies. Rocks preserving Early Triassic deformation and metamorphism are restricted to the southwest corner of the belt and are truncated by the Pasayten Fault. The Central Belt, dominated by the products of Late Triassic volcanism in northern and central British Columbia, consists mainly of Middle (?) and Upper Triassic sediments in the south. Meagre evidence indicates that widespread deformation and low-grade regional metamorphism occurred just prior to the Late Triassic. Evidence for these events is not found beyond the faulted margins of the Central Belt. In the Western Belt, an Upper Triassic sequence of tholeiitic basalt and overlying calcareous sediments disconformably overlies Permian rocks. In the western Cordillera, low-grade regional metamorphism and minor plutonism characterize Triassic orogenies. Early Triassic orogenesis in the southwestern corner of the Eastern Belt is coeval with the Sonoma Orogeny and the Middle–Late Triassic orogenesis of the Central Belt represents the Tahltanian Orogeny.

TEM/AEM characterization of fine-grained clay minerals in very-low-grade rocks: Evaluation of contamination by empa involving celadonite family minerals

1996 ◽  
Vol 54 ◽  
pp. 694-695
Author(s):  
Gejing Li ◽  
D. R. Peacor ◽  
D. S. Coombs ◽  
Y. Kawachi
Keyword(s):  
Electron Microscopy ◽  
Volcanic Rocks ◽  
Analytical Electron Microscopy ◽  
Metamorphic Rocks ◽  
New Mineral ◽  
Chemical Compositions ◽  
Low Grade ◽  
Fine Grained ◽  
Depth Analysis ◽  
Mineral Aggregates

Recent advances in transmission electron microscopy (TEM) and analytical electron microscopy (AEM) have led to many new insights into the structural and chemical characteristics of very finegrained, optically homogeneous mineral aggregates in sedimentary and very low-grade metamorphic rocks. Chemical compositions obtained by electron microprobe analysis (EMPA) on such materials have been shown by TEM/AEM to result from beam overlap on contaminant phases on a scale below resolution of EMPA, which in turn can lead to errors in interpretation and determination of formation conditions. Here we present an in-depth analysis of the relation between AEM and EMPA data, which leads also to the definition of new mineral phases, and demonstrate the resolution power of AEM relative to EMPA in investigations of very fine-grained mineral aggregates in sedimentary and very low-grade metamorphic rocks.Celadonite, having end-member composition KMgFe3+Si4O10(OH)2, and with minor substitution of Fe2+ for Mg and Al for Fe3+ on octahedral sites, is a fine-grained mica widespread in volcanic rocks and volcaniclastic sediments which have undergone low-temperature alteration in the oceanic crust and in burial metamorphic sequences.

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 VII.—Mesozoic Volcanic Rocks of British Columbia and Chile. Relation of Volcanic and Metamorphic Rocks

1877 ◽  
Vol 4 (7) ◽  
pp. 314-317
Author(s):  
George M. Dawson
Keyword(s):  
British Columbia ◽  
South America ◽  
Volcanic Rocks ◽  
Geological Survey ◽  
Metamorphic Rocks ◽  
Coast Range ◽  
Similar Relation

In Chile and adjacent regions of South America, Mr. Darwin, in his “Geological Observations,” has described a great series of Mesozoic rocks, which he calls the “porphyritic formation,” and which shows an interesting resemblance to certain rocks in British Columbia. These I had provisionally designated in my report in connexion with the Geological Survey of Canada for 1875, as the Porphyrite series, without at the time remembering Mr. Darwin's name for the Chilian rocks. Many of Mr. Darwin's descriptions of the rocks of Chile would apply word for word to those of British Columbia, where the formation would also appear to bear a somewhat similar relation to the Cascade or Coast Range, which that of Chile does to the Cordillera.

Seismic and potential‐field imaging of the Guichon Creek batholith, British Columbia, Canada, to delineate structures hosting porphyry copper deposits

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1418-1434 ◽  
Author(s):  
Baishali Roy ◽  
Ron M. Clowes
Keyword(s):  
British Columbia ◽  
Seismic Reflection ◽  
Porphyry Copper ◽  
Regional Scale ◽  
Low Grade ◽  
Depth Range ◽  
Porphyry Copper Deposits ◽  
Near Surface ◽  
Copper Deposits ◽  
South Central

The Guichon Creek batholith (GCB), located in south‐central British Columbia, contains several large, low‐grade copper deposits of considerable economic importance. The surface geology of the Guichon batholith and its surrounding region have been well mapped; however, little information about subsurface features is available. The batholith consists of four major phases, emplaced radially outward, which can be separated on the basis of their texture and composition. Previous interpretation of gravity data suggests a mushroom‐shaped structure for the batholith. Data from Lithoprobe seismic reflection line 88-11, acquired across the batholith in 1988, reveal weakly coherent east‐dipping reflections on the west side and west‐dipping reflections on the east in the upper 10 km. To determine if these are related to structures associated with the batholith, we reprocessed the upper 6 s with particular emphasis on applications of signal enhancement techniques (e.g., pattern recognition methods, refraction statics, dip moveout corrections) and correlation of the improved subsurface images with the geological environment associated with porphyry copper deposits. Low near‐surface velocities correlate well with the phases of the batholith hosting the major copper deposits, which structurally lie in faulted and brecciated regions. Although the top 1.5 km cannot be imaged by the regional‐scale seismic reflection data, the reprocessed seismic section helps define the edges of the batholith, its various concentric phases, and the stem in the depth range of 1.5 to 10 km. The seismic results are complemented by 2.5-D (profile sense) modeling and 3-D inversion of regional‐scale gravity and high‐resolution aeromagnetic data. These show a low‐density and low‐magnetic‐susceptibility region associated with the batholith that extends to more than 10 km depth. The region of active mining interest lies above a circular low‐susceptibility area at 2 km depth and a low‐velocity region. Integrated interpretation of geophysical results and geological observations indicates the GCB is a funnel‐shaped feature in which mineralization is located above the stem of the batholith.

K–Ar and Fission Track Geochronometry of an Eocene Thermal Event in the Kettle River (West Half) Map Area, Southern British Columbia

1975 ◽  
Vol 12 (5) ◽  
pp. 836-843 ◽  
Author(s):  
G. A. Medford
Keyword(s):  
British Columbia ◽  
Abrupt Change ◽  
Fission Track ◽  
Apatite Fission Track ◽  
Thermal Event ◽  
South Central ◽  
Early Tertiary ◽  
Okanagan Valley

The Okanagan and Similkameen plutonic complexes west of the Okanagan Valley of south-central British Columbia yield K–Ar dates that range from 185 to 133 m.y. East of the Okanagan Valley Shuswap gneisses into which the plutonics intrude, and which may be as old as pre-midCarboniferous in age yield K–Ar dates between 59.9 and 47.4 m.y. This abrupt change, which approximately coincides with the Okanagan Valley, is a consequence of an intense thermal event in the early Tertiary which has reset K–Ar dates in the gneisses at shallow depths. Comparison of K–Ar, sphene and apatite fission track dates demonstrates that the heating affected the plutons west of the Okanagan Valley and that cooling of the Shuswap gneisses occurred at a rate in excess of 25 °C. per million years. The scatter observed in the older K–Ar dates of the plutonic complexes could be caused by post-emplacement heating with variable partial argon loss rather than by separate magmatic events. Thus, only the oldesl K–Ar dates obtained from the plutons may be significant as minimum ages for emplacement.

Deformational geometry and tectonic significance of a portion of the Chilliwack Group, northwestern Cascades, Washington

1988 ◽  
Vol 25 (3) ◽  
pp. 433-441 ◽  
Author(s):  
Moira Smith
Keyword(s):  
High Pressure ◽  
Volcanic Rocks ◽  
Ductile Deformation ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
North Cascades ◽  
Clastic Rocks ◽  
Tectonic Significance ◽  
Group A ◽  
Event Based

The northwestern Cascades structural province can be interpreted as an accretionary complex comprising fault-bounded blocks of pre-Tertiary metamorphic rocks of diverse age and lithologic type. This paper documents the deformation in a portion of the Chilliwack Group, a unit in this complex. The Chilliwack Group is a thick sequence of volcaniclastic sedimentary rocks, calc-alkaline volcanic rocks, and limestone that is metamorphosed to low-grade blueschist facies. The rocks underwent ductile deformation during a Late Cretaceous orogenic event, producing a subhorizontal foliation and, in appropriate lithologies, subhorizontal stretching lineations that trend N20°W. Finite strain sustained by coarse clastic rocks produced RXZ values averaging 3.5. The deformation at least partially postdates the high pressure metamorphic event, based on the presence of bent and broken high-pressure mineral grains. Although early studies postulated west-vergent thrust imbrication of units in the northwest Cascades, the N20°W direction of apparent elongation in the Chilliwack Group, consistent with the direction of motion along segments of the Shuksan fault elucidated in other more recent studies, may reflect significant, highly oblique components of convergence during formation of the western North Cascades collisional orogen.

Devonian Plutonism in South-Central British Columbia

1975 ◽  
Vol 12 (10) ◽  
pp. 1760-1769 ◽  
Author(s):  
Andrew V. Okulitch ◽  
R. K. Wanless ◽  
W. D. Loveridge
Keyword(s):  
British Columbia ◽  
Middle Devonian ◽  
Metamorphic Complex ◽  
Western Margin ◽  
South Central ◽  
Minimum Age ◽  
History Of ◽  
Shuswap Metamorphic Complex

An apparently tabular body of granitoid gneiss, 3 to 5 km wide and more than 70 km long, that lies along the western margin of the Shuswap Metamorphic Complex between Shuswap and Admas Lakes, shows intrusive relationships with Palaeozoic and older rocks and has yielded zircons whose minimum age is 372 Ma. This intrusion, together with other granitoid plutons in the area that appear to be related to it, provide evidence of widespread plutonism during Middle Devonian time near the western edge of the Paleozoic Cordillera geosyncline and necessitate significant revisions in the interpretation of the crustal history of this region.

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