Age and isotopic character of Early Proterozoic basement gneisses in the southern Monashee Complex, southeastern British Columbia

1991 ◽  
Vol 28 (8) ◽  
pp. 1159-1168 ◽  
Author(s):  
Dave Parkinson
Keyword(s):  
Fault Zone ◽  
Columbia River ◽  
Granite Gneiss ◽  
Biotite Granite ◽  
Early Proterozoic ◽  
Pelitic Schist ◽  
Monashee Complex ◽  
Gray Gneiss ◽  
Proterozoic Basement ◽  
Augen Gneiss

The southern Monashee Complex is a fault-bounded exposure of upper-amphibolite-grade basement gneisses (core gneisses) and unconformably overlying mantling metasedimentary gneisses. The eastern margin is marked by the Early Eocene ductile to brittle Columbia River fault zone; the western and southern margins are marked by the Monashee Decollement and structurally higher Selkirk allochthon.The basement gneisses are exposed in the cores of large, northeast-verging nappes that subsequently have been overprinted towards the east by the Columbia River fault zone. The basement gneisses are a supracrustal sequence intruded by at least two distinct orthogneisses: (i) a biotite granite gneiss ("gray gneiss") dated by U/Pb zircon at 1874 ± 21 Ma; and (ii) a ±hornblende–biotite K-feldspar augen gneiss dated by U/Pb zircon at 1934 ± 6 Ma.The supracrustal gneisses are predominantly heterogeneous biotite–quartz–feldspar gneiss interlayered with less common pelitic schist and calc-silicate gneiss. U/Pb zircon data on detrital zircon populations from this heterogeneous supracrustal sequence give 207Pb*/206Pb* ages of less than 2.2 Ga. Whole-rock Pb isotopic data indicate an age of approximately 2.0 Ga. Whole-rock Sm/Nd model ages on the two intrusive suites indicate separate sources, the 1874 Ma gneiss having been produced from similar-age juvenile Early Proterozoic material (TDM ≈ 2.2 Ga). In contrast, Nd data from the 1934 Ma augen gneiss clearly indicate interaction with a component of older (late Archean) material (TDM ≈ 2.8 Ga). Whole-rock Sm/Nd data from the supracrustal gneisses follow this same pattern, with one group (seven samples) similar to the 1874 Ma gneiss (with TDM ≈ 2.3–2.6 Ga) and a second group (five samples) showing provenance or derivation from an Archean source (TDM = 2.8–3.3 Ga). The age of the intrusive suites, combined with the Nd data, strongly argues for a correlation with the Early Proterozoic Wopmay orogenic belt in northern Canada.

Columbia River fault zone: southeastern margin of the Shuswap and Monashee complexes, southern British Columbia

1981 ◽  
Vol 18 (7) ◽  
pp. 1127-1145 ◽  
Author(s):  
Peter B. Read ◽  
Richard L. Brown
Keyword(s):  
Fault Zone ◽  
Hanging Wall ◽  
Columbia River ◽  
Glacial Sediments ◽  
Monashee Complex ◽  
Southeastern Margin ◽  
Minimum Age ◽  
History Of ◽  
Slip Displacement ◽  
Fault Scarps

The Columbia River fault zone extends for 250 km from south of Nakusp, through Revelstoke, to north of Bigmouth Creek. It is a composite fault zone, which dips 20–30° easterly and separates major tectonic elements. The structurally lowest element is the Monashee Complex, which includes the culminations of Pinnacle Peaks, Thor–Odin, and Frenchman Cap. At Hoskins Creek, the Monashee décollement splays westward from the fault zone and then runs southward along the western margin of the Monashee Complex. On the east side, the Selkirk allochthon is a composite of four tectonic slices. Its western part consists of Clachnacudainn, Goldstream, and French Creek slices forming the hanging wall of the Columbia River fault zone. The remainder of the allochthon forms the highest and largest Illecillewaet slice, which may be composite.The fault zone retains evidence of a long history of movement extending from the mid-Mesozoic to Eocene. Early deformation formed a mylonite zone up to 1 km wide in which rocks recrystallized under greenschist facies conditions. The displacement truncated major folds and metamorphic isograds that had developed in the Middle Jurassic. Orientation of slickensides, fiber growth, and strain features in the mylonite indicates normal, dip-slip displacement with the slices of the hanging wall moving eastward. South of Revelstoke, the Galena Bay stock, dated at 150 Ma, apparently intruded the zone and gives a minimum age for early displacement that must be in the Late Jurassic.Late displacement caused intense fracturing, folding of mylonite, and development of gouge zones. These features are well exposed at the Revelstoke damsite, continue north of Revelstoke, but diminish in importance southward. Late movement was again normal, dip-slip with the hanging wall moving eastward; it probably ended in the Eocene. No fault scarps or disrupted drainages have been observed, and at several localities glacial sediments lie undisturbed across the fault zone, indicating a lack of postglacial movement.Metamorphic zones, juxtaposed along the fault, imply a minimum dip-slip displacement of 15–25 km. Displacement in this range poses stratigraphic and metamorphic problems, which are alleviated if displacement is in excess of 80 km. The tectonic slices east of the Columbia River fault zone are part of an allochthonous cover that was transported at least tens of kilometres eastward over the Shuswap and Monashee complexes during the Late Jurassic.

Age constraints on basement of the Midland Valley of Scotland

1984 ◽  
Vol 75 (2) ◽  
pp. 53-64 ◽  
Author(s):  
M. Aftalion ◽  
O. van Breemen ◽  
D. R. Bowes
Keyword(s):  
Volcanic Rocks ◽  
Potassium Feldspar ◽  
Detrital Zircons ◽  
Early Proterozoic ◽  
Common Lead ◽  
Granite Emplacement ◽  
Isochron Diagram ◽  
Lower Palaeozoic ◽  
Proterozoic Basement ◽  
Age Constraints

ABSTRACTThe existence of a basement of granulite beneath the Midland Valley is supported by investigations of inclusions in volcanic rocks and the geophysical studies of the LISPB experiment. To establish age constraints for this basement, a compilation is presented of available Rb–Sr whole-rock, common lead, U–Pb zircon and Sm–Nd radiometrie data for crystalline rocks in Scotland from the earliest recognised crust (c. 2900 Ma) to 380 Ma (“end” of Caledonian orogeny) including xenoliths in volcanic vents and boulders in conglomerates.For rocks within the Midland Valley, isotopic data provide four lines of evidence. (1) An upper intercept U–Pb age of c. 1700 Ma for detrital zircons from a lower Palaeozoic greywacke from Dalmellington corresponds to a late stage of the Laxfordian orogenic episode (early Proterozoic) with possibly some overprinting during the Grenvillian episode (mid Proterozoic). (2) The common lead composition of the Distinkhorn granite suggests the participation of early Proterozoic basement during granite emplacement. (3) For xenoliths from the Carboniferous Partan Craig vent, one gives a Sm–Nd CHUR model age of 1180 ± 55 Ma, a second yielded a Sm–Nd garnet—potassium feldspar age of 356 ± 6 Ma and an upper intercept U–Pb age from zircons from the third is c. 2200 (± 240) Ma; for xenoliths from other vents, an Rb–Sr whole-rock isochron of 1101 ± 63 Ma and an Sm–Nd model age of c. 1100 Ma arerecorded. (4) A linear array corresponding to an apparent age of 770 ± 180 Ma on a Pb–Pb isochron diagram for Tertiary igneous rocks of Arran points to an underlying basement of late Precambrian orthogneiss.The existence of basement made of products of the Grenvillian episode, or predominantly so, similar to the basement N of the Highland Boundary fault, is not inconsistent with the available evidence. However, zircons and other rock components appear to have an ultimate Lewisian provenance. At least in parts, there is also a strong late Proterozoic imprint. Further studies are required for an unequivocal solution.

Rb–Sr biotite and whole-rock data from the Kapuskasing uplift and their bearing on the cooling and exhumation history

1994 ◽  
Vol 31 (7) ◽  
pp. 1172-1181 ◽  
Author(s):  
J. A. Percival ◽  
Z. E. Peterman
Keyword(s):  
Fault Zone ◽  
Spatial Relationship ◽  
Paleomagnetic Data ◽  
Isotopic Ratios ◽  
The West ◽  
Rapid Cooling ◽  
Early Proterozoic ◽  
Granitoid Rocks ◽  
Relationship Of ◽  
Exhumation History

Rb–Sr isotopic ratios were measured on biotite and whole rocks from a suite of 21 granitoid rocks from the southern Kapuskasing uplift. Results of 18 of the whole-rock analyses fall on an isochron with an age of 2.677 ± 0.057 Ga and Sri = 0.70080. Biotite model ages range from 2.50 to 1.93 Ga in a general spatial relationship of decreasing age with depth in the structural section as calibrated with the igneous hornblende barometer for tonalitic rocks and garnet–pyroxene barometers for granulites. Near the Michipicoten belt in the west, biotite ages of ~ 2 Ga reflect disturbances also recorded by paleomagnetic and whole-rock Rb–Sr systems. To the east, in a 70 km long northwest–southeast transect toward the Ivanhoe Lake fault zone, ages decrease from 2.50 to 1.95 Ga. In a southern transect ages are in the range 2.30–2.38 Ga to within 15 km of the fault, reflecting consistent erosion levels corresponding to ~ 0.53 MPa, but decrease to 1.93 Ga to the east, in concert with paleopressures in the 0.7–1.0 GPa range.A plateau of low Rb–Sr biotite dates is not evident, suggesting that the Kapuskasing uplift event exposed a frozen-in cooling profile, rather than setting the Rb–Sr clock by rapid cooling of the rocks from above their closure temperature. The youngest biotite date of 1.93 Ga therefore provides a maximum age for uplift, consistent with paleomagnetic data from Archean rocks and Early Proterozoic dykes, but in conflict with some K–Ar and 40Ar/39Ar biotite age data.

DENSITIES OF METAMORPHIC ROCKS

Geophysics ◽  
1971 ◽  
Vol 36 (4) ◽  
pp. 690-694 ◽  
Author(s):  
Scott B. Smithson
Keyword(s):  
Metamorphic Rock ◽  
Granite Gneiss ◽  
Biotite Granite ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Rock Density ◽  
Rock Types ◽  
Crystalline Crust ◽  
The Mean ◽  
Few Data

Although metamorphic rocks comprise a large part of the crystalline crust, relatively few data concerning metamorphic rock densities are available. In this paper, we present rock densities from seven different metamorphic terrains. Mean densities for rock types range from [Formula: see text] for biotite granite gneiss to [Formula: see text] for diopside granofels. Mean rock densities for metamorphic terrains range from 2.70 to [Formula: see text]. Rock density may decrease in the lower part of the upper crust. Most mean rock densities for metamorphic terrains fall between 2.70 and [Formula: see text]; the mean density of [Formula: see text] commonly used for the upper crystalline crust is too low.

scholarly journals Rare Earth Elements Assessment in the Granitoids of Part of Southwestern Nigeria

2020 ◽  
Vol 1 (5) ◽  
Author(s):  
Victoria B. Omotunde ◽  
Akinade S. Olatunji ◽  
Maryam O. Abdus-Salam
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Inductively Coupled Plasma ◽  
Granite Gneiss ◽  
Biotite Granite ◽  
Geochemical Data ◽  
Southwestern Nigeria ◽  
Lithological Mapping ◽  
Inductively Coupled ◽  
Gneiss Granite

The Rare Earth Elements (REE) composition of granitoids in and around Ila-Orangun area Southwestern Nigeria was assessed in order to ascertain their potential for possible exploitation. Detailed lithological mapping of the area was undertaken followed by whole rock geochemical analysis of representative samples of the granitoids using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) technique. Petrographic study of the samples was carried out as well as the interpretation of the geochemical data using diverse geochemical discrimination plots. The rock units mapped were biotite granite gneiss, granite gneiss and hornblende biotite granite. Biotite hornblende gneiss, quartzite, talc-chlorite-tremolite-schist, mica schist and pegmatites were the surrounding country rocks. The REE concentrations (in ppm) revealed higher concentrations of the light REEs compared to the heavy REEs. The fractionation ratio, (La/Yb)N ranged from 4.35-15.04 (granite gneiss) and 13.78-18.48 (hornblende biotite granite) indicating enrichment in LREEs over the HREEs. The spider plot for the REEs also showed that the granitoids are LREE-enriched and HREE-depleted suggesting fractional crystallisation and a distinct negative Eu anomaly indicating plagioclase fractionation. Enrichment plot also revealed that the REEs in the granitoids are significantly enriched. Comparison with other areas showed that the granitoids of the study area especially the hornblende biotite granite has higher concentrations of REEs and may be a possible pointer of REE mineralisation.

scholarly journals Pedogenic Forms of Iron in Soils Developed from Four Parent Materials

2020 ◽  
Vol 25 (1) ◽  
pp. 47
Author(s):  
Ayodele Owonubi
Keyword(s):  
Iron Oxides ◽  
Ammonium Oxalate ◽  
Granite Gneiss ◽  
Field Work ◽  
Biotite Granite ◽  
Total Iron ◽  
Basement Complex ◽  
Parent Materials ◽  
Basaltic Rocks ◽  
Forms Of Iron

Information on the distribution of various forms of iron in soils are valuable in the study of soil genesis. The objective of this study was to to evaluate the pedogenic forms of iron in soils developed over basement complex and basaltic parent materials of the study area. Geologic units considered in the basement complex area were granite gneiss, biotite granite and migmatite. Stratified random sampling formed the basis for field work. Soil sampling was carried out by digging at least two soil profile pits in each geologic unit. Organically bound, amourphous and total iron oxides were estimated using 0.1 M sodium pyrophosphate, acidified (pH 3) ammonium oxalate, and dithionite-citrate-bicarbonate method, respectively. The total Fe in the soil samples were determined after a mixed acid digestion. In general, total iron fractions were statistically similar among the soils of basement complex geologic units but significantly lower than those of soils derived from basaltic rocks. However, the distribution of iron oxide fractions was similar among the basement and basaltic geologic units. Furthermore, there were significant differences in the distribution of iron oxides in the B horizons of basement complex derived soils. Consequently, the quantity of iron oxides in the B horizon was in the order migmatite > biotite granite > granite gneiss. About 70% of total iron oxides in the soils over granite gneiss, biotite granite and basaltic rocks was amorphous in nature. Furthermore, total iron oxides constitute less than 20% of total clay both in the basement complex and basaltic soils.

Basement–cover relationships in the East Greenland Caledonides: evidence from the Eleonore Bay Supergroup at Ardencaple Fjord

1993 ◽  
Vol 84 (2) ◽  
pp. 103-115 ◽  
Author(s):  
N. J. Soper ◽  
A. K. Higgins
Keyword(s):  
Shear Zones ◽  
Low Grade ◽  
East Greenland ◽  
Early Proterozoic ◽  
Basement Rocks ◽  
Erosion Level ◽  
Isotopic Studies ◽  
Extensional Faulting ◽  
Proterozoic Basement ◽  
Shed Light

AbstractThe Eleonore Bay Supergroup (EBG) is a 16 km-thick shallow-water sequence of Neoproterozoic age that is preserved within the East Greenland Caledonides in several tracts, surrounded by crystalline gneisses and schistose supracrustal rocks. The apparent downward transition from non-metamorphic EBG into gneiss gave rise to the classic ‘stockwerke’ hypothesis, in which all the metamorphism was regarded as Caledonian, and differences in grade were ascribed to the ascent of a migmatite front to different levels within the orogen. Field and isotopic studies in the 1970s however revealed that the underlying gneisses and schists had undergone orogenic reworking in mid-Proterozoic time; the EBG–basement contact was then interpreted as an approximately bedding-parallel décollement with apparent lag geometry, that is with EBG cover rocks in its hangingwall.Recent work in the northernmost EBG tract, at Ardencaple Fjord, has shed light on the problems posed by the basal relationships of the EBG, and together with regional structural and stratigraphic data leads to the following interpretation. There are two regionally important basement-cover interfaces within the East Greenland Caledonides. The earlier one is between Archaean/early Proterozoic gneisses and early Proterozoic supracrustal rocks, which were pervasively deformed in mid-Proterozoic time and form the basement to the Neoproterozoic Eleonore Bay cover sequence. This was deposited on a vast, continually subsiding shelf that is now preserved in East and NE Greenland and Svalbard, and contains Grenville detritus. EBG deposition was terminated by major extensional faulting of Vendian age; the succeeding Tillite Group is interpreted as a syn-rift sequence, presumably associated with the opening of Iapetus.The EBG–basement contacts that are not late faults are inferred to be extensional shear zones of Vendian age. These were reactivated in compression during the Caledonian orogeny in the Silurian, with metamorphic and fabric convergence, which accounts for the apparent downward transition from sedimentary rocks through schists into gneisses. Caledonian shortening was not large; inversion of the Vendian grabens was incomplete, so that the marginal shear zones retained their lag geometry and large tracts of low grade Eleonore Bay sediments are preserved at the present erosion level, surrounded by Proterozoic basement rocks, within the Caledonian belt of East Greenland.

Isotopic evidence for the extent of early Proterozoic basement in Scotland and northwest Ireland

1991 ◽  
Vol 128 (4) ◽  
pp. 385-388 ◽  
Author(s):  
A. P. Dickin ◽  
D. R. Bowes
Keyword(s):  
Nd Isotope ◽  
Early Proterozoic ◽  
Isotopic Evidence ◽  
Gneiss Complex ◽  
Proterozoic Basement ◽  
Western Ireland ◽  
Isotope Systematics

AbstractTightly clustered Sm–Nd model ages, with an average of 1.96±0.02Ga, for the gneiss complex of Inishtrahull indicate coeval development with the earlyProterozoic gneiss terrane of Islay. The extent of this terrane, largely beneath the Dalradian Supergroup, is argued to be 100×600 km, from northeast Scotland to western Ireland. This is based on the distribution of dated basement in conjunction with Pb, Sr and Nd isotope systematics and inherited zircons in Caledonian granites of the region.

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