GEOCHEMISTRY OF THE YELLOWKNIFE VOLCANIC ROCKS

1966 ◽  
Vol 3 (1) ◽  
pp. 9-30 ◽  
Author(s):  
W. R. A. Baragar
Keyword(s):  
Bulk Composition ◽  
Volcanic Rocks ◽  
River Section ◽  
Magma Chambers ◽  
Tholeiitic Magma ◽  
Composite Form ◽  
High Level ◽  
Mafic Lavas ◽  
Stratigraphic Height ◽  
Volcanic Cycles

Results of rapid-method chemical analyses of samples taken at about 500-ft stratigraphic intervals through two sections of Yellowknife Group volcanic rocks are presented in graphical and composite form. The Yellowknife section is about 40 000 ft thick with the base undefined; the Cameron River section, about 45 mi northeast, is about 7 000 ft thick and may be complete.Two aspects of the volcanic chemistry considered are (1) variation in composition with stratigraphic height; (2) bulk composition of the volcanic rocks.Chemical data of the Yellowknife section define two volcanic cycles in each of which mafic lavas show a small but significant increase in sialic components with stratigraphic height culminating abruptly in acidic layers. The Cameron River section shows a similar but less well-defined trend. Iron–magnesium ratios stage a succession of systematic increases, each persisting for a few thousand stratigraphic feet, but no overall systematic variation. The two types of chemical variation correspond to calc-alkali and tholeiitic differentiation trends respectively. The tholeiitic trend is attributed to fractionation in high-level magma chambers, demonstrated for Yellowknife magma by the Kam Point sill, and the calc-alkali trend to contamination of tholeiitic magma by sialic crust.Frequency distribution diagrams show Yellowknife volcanic rocks to be similar to Chayes' circumoceanic basalts in TiO2, CaO, and MgO and to his oceanic basalts in Al2O3. The characteristic rock type is basalt.

scholarly journals Filling and plugging of a marine basin by volcanic rocks: the Tunoqqu Member of the Lower Tertiary Vaigat Formation on Nuussuaq, central West Greenland

1996 ◽  
Vol 171 ◽  
pp. 5-28
Author(s):  
A.K Pedersen ◽  
L.M Larsen ◽  
G.K Pedersen ◽  
K.S Dueholm
Keyword(s):  
Volcanic Rocks ◽  
Water Levels ◽  
North Coast ◽  
Magma Chambers ◽  
Tectonic Control ◽  
Crustal Rocks ◽  
The North ◽  
High Level ◽  
Marine Embayment ◽  
Volcanic Cycles

The volcanic Tunoqqu Member formed at the end of the second of three volcanic cycles in the Paleocene Vaigat Formation. The Tunoqqu Member consists of brown aphyric and feldspar-phyric basalts and forms a marker horizon within the grey picritic rocks of the Vaigat Formation. Most of the basalts are siliceous and were produced by contamination with crustal rocks of magmas ranging in composition from picrite to evolved basalt. Some of the basalts were erupted from local volcanic centres of which four have been identified, whereas other basalts form more regional flows. The four identified eruption centres are located along fault lines and zones of uplift and subsidence, indicating tectonic control. Tectonic control is also inferred to be important in terminating the volcanic cycle and causing the development of high-level magma chambers where the magmas stagnated, fractionated, and became contaminated. The basalts of the Tunoqqu Member form subaerial lava flows in western Nuussuaq. Central Nuussuaq constituted a marine embayment in which the volcanics were deposited as eastward prograding foreset-bedded hyaloclastite breccia fans which indicate water depths of up to 160 m. Eastern Nuussuaq was a gneiss highland with a more than 700 m high NW-SE-elongated gneiss promontory stretching into the sea. During Tunoqqu Member time the volcanic rocks reached the gneiss promontory and blocked the outlet from the south to the sea in the north. This resulted in increased water levels in the enclosed embayment and transformation of the outlet into a torrential river. This river eroded the concomitantly forming Tunoqqu Member volcanics and the gneiss promontory and deposited the material in up to more than 250 m thick foreset-bedded boulder conglomerates in the sea where the north coast of Nuussuaq is now situated.

The petrogenetic significance of chemically related plutonic and volcanic rock units

1986 ◽  
Vol 123 (6) ◽  
pp. 619-628 ◽  
Author(s):  
D. Wyborn ◽  
B. W. Chappell
Keyword(s):  
Fractional Crystallization ◽  
Source Region ◽  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Magma Chambers ◽  
Southeastern Australia ◽  
Lachlan Fold Belt ◽  
Magma Compositions ◽  
High Level ◽  
Heterogeneous Crystallization

AbstractComagmatic granitic and volcanic rocks are divided into two types depending on whether or not the primary magma contains restite crystals. Examples of both of these types are discussed from the Lachlan Fold Belt of southeastern Australia.Volcanic rocks containing restite phenocrysts are chemically identical to the associated plutonic rocks containing the same amount of restite. The more mafic granitic rocks correspond in composition to the most phenocryst-rich volcanics (up to 60% phenocrysts), and thus cannot be cumulate rocks produced by fractional crystallization, but must represent true magma compositions. These restite-bearing magmas result from partial melting in a source region up to the rheological critical melt percentage, which we estimate to be about 40% in the S-type Hawkins Suite of volcanics.Melts which escape their restite at the source, before the critical melt percentage is reached, are able to undergo fractional crystallization in high level magma chambers by heterogeneous crystallization on chamber walls. In this case volcanic products from the top of the chamber are more felsic than the plutonic products, the plutonics are crystal cumulates and the volcanics are composed of the complementary fractionated liquid. Those phenocrysts present in the volcanics were probably eroded from the chamber walls and are less abundant (< 20%) than in the restite-retentive volcanic products.

Stratigraphy and eruptive history of the Late Devonian Mount Pleasant Caldera Complex, Canadian Appalachians

1997 ◽  
Vol 134 (1) ◽  
pp. 17-36 ◽  
Author(s):  
S. R. McCUTCHEON ◽  
H. E. ANDERSON ◽  
P. T. ROBINSON
Keyword(s):  
Fractional Crystallization ◽  
Basaltic Magma ◽  
Late Devonian ◽  
Crustal Material ◽  
Basaltic Rocks ◽  
Stratigraphic Subdivision ◽  
Mount Pleasant ◽  
History Of ◽  
High Level ◽  
Mafic Lavas

Stratigraphic, petrographic and geochemical evidence indicate that the volcano-sedimentary rocks of the Late Devonian Piskahegan Group, located in the northern Appalachians of southwestern New Brunswick, represent the eroded remnants of a large epicontinental caldera complex. This complex – the Mount Pleasant Caldera – is one of few recognizable pre-Cenozoic calderas and is divisible into Exocaldera, Intracaldera and Late Caldera-Fill sequences. The Intracaldera Sequence comprises four formations that crop out in a triangular-shaped area and includes: thick ash flow tuffs, thick sedimentary breccias that dip inward, and stocks of intermediate to felsic composition that intrude the volcanic pile or are localized along caldera-margin faults. The Exocaldera Sequence contains ash flow tuffs, mafic lavas, alluvial redbeds and porphyritic felsic lavas that comprise five formations. The Late Caldera-Fill Sequence contains rocks that are similar to those of the outflow facies and comprises two formations and two minor intrusive units. Geochemical and mineralogical data support the stratigraphic subdivision and indicate that the basaltic rocks are mantle-derived and have intraplate chemical affinities. The andesites were probably derived from basaltic magma by fractional crystallization and assimilation of crustal material. The various felsic units are related by episodes of fractional crystallization in a high-level, zoned magma chamber. Fractionation was repeatedly interrupted by eruption of material from the roof zone such that seven stages of caldera development have been identified. The genesis of the caldera is related to a period of lithospheric thinning that followed the Acadian Orogeny in the northern Appalachians.

Rare earth element concentrations in Quaternary volcanic rocks of southwestern British Columbia

1984 ◽  
Vol 21 (6) ◽  
pp. 731-736 ◽  
Author(s):  
Nathan L. Green ◽  
Paul Henderson
Keyword(s):  
British Columbia ◽  
Earth Element ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Lake Area ◽  
Calc Alkaline ◽  
Lower Light ◽  
The Individual ◽  
High Level ◽  
Ree Patterns

A suite of hy-normative hawaiites, ne-normative mugearite, and calc-alkaline andesitic rocks from the Garibaldi Lake area exhibits fractionated, slightly concave-upward REE patterns (CeN/YbN = 4.5–15), heavy REE contents about 5–10 times the chondritic abundances, and no Eu anomalies. It is unlikely that the REE patterns provide information concerning partial melting conditions beneath southwestern British Columbia because they have probably been modified substantially by upper crustal processes including crustal contamination and (or) crystal fractionation. The REE contents of the Garibaldi Lake lavas are not incompatible with previous interpretations that (1) the hawaiites have undergone considerable fractionation of olivine, plagioclase, and clinopyroxene; and (2) the individual andesitic suites were derived from separate batches of chemically distinct magma that evolved along different high-level crystallization trends. In general, however, the andesites are characterized by lower light REE contents than the basaltic andesites. These differences in LREE abundances may reflect different amounts of LREE-rich accessory phases, such as apatite, sphene, or allanite, assimilated from the underlying quartz diorites.

Volcanic rocks of the Blake River Group, Abitibi Greenstone Belt, Ontario, and their sulfur content

1977 ◽  
Vol 14 (4) ◽  
pp. 539-550 ◽  
Author(s):  
A. J. Naldrett ◽  
A. M. Goodwin
Keyword(s):  
Sulfur Content ◽  
Greenstone Belt ◽  
Geometric Mean ◽  
Volcanic Rocks ◽  
Smooth Curve ◽  
Arithmetic Mean ◽  
Arithmetic Means ◽  
Basaltic Rocks ◽  
Abitibi Greenstone Belt ◽  
Stratigraphic Height

Six hundred and ninety samples of volcanic rocks from the Blake River Group of the Abitibi Greenstone Belt have analysed for sulfur on a Leco sulfur analyser. Basaltic rocks have been subdivided into komatiites, Fe-rich tholeiites, Al-rich basalts, and intermediate basalts with more than 1% TiO2 and with less than 1% TiO2. Andesites have been subdivided into Fe-rich types, Al-rich types, and others. All dacites are grouped together as are all rhyolites. Rocks of many of these subdivisions occur at more than one level within the Blake River stratigraphy. Within a given rock subdivision, the sulfur content is distributed log normally. When the geometric mean of the sulfur content of each of the subdivisions outlined above is plotted against the arithmetic mean of the FeO content, a smooth curve is obtained, with sulfur increasing markedly with increase in FeO. The data give no indication of any change in sulfur content of a given rock subdivision with stratigraphic height. The arithmetic mean of the sulfur content of each rock subdivision also increases with the mean FeO content, although less smoothly than the geometric mean. The arithmetic means of sulfur content fall within the scatter of points obtained experimentally for the sulfur content of sulfur saturated basalts, supporting the contention that the Blake River rocks may have been saturated with sulfur at the time of their extrusion.

Cyclical variation in composition in continental tholeiites of East Greenland

1989 ◽  
Vol 26 (3) ◽  
pp. 534-543 ◽  
Author(s):  
A. J. Hogg ◽  
J. J. Fawcett ◽  
J. Gittins ◽  
M. P. Gorton
Keyword(s):  
North Atlantic Ocean ◽  
Tholeiitic Basalt ◽  
Primitive Mantle ◽  
Magma Chambers ◽  
Flood Basalts ◽  
East Greenland ◽  
Continental Flood Basalts ◽  
Tholeiitic Magma ◽  
Small Reservoirs ◽  
The North

The Prinsen of Wales Bjerge (PWB), part of the Tertiary volcanic province of East Greenland, consists of tholeiitic basalts overlain by alkalic basalts that were erupted 100–150 km west of the original axis of continental rifting and active ocean-floor development during the creation of the North Atlantic Ocean. They have many features of continental flood basalts but are somewhat enriched in Fe and in Ti relative to Fe and have slightly lower Al2O3. They have slight enrichments in the light rare-earth elements (La/Yb = 3–4). A nunatak within the PWB displays four cycles of tholeiitic basalt, each about 50 m thick, which are defined by trace-element variations (Ni, Cr, Sr, Zr, and Zr/Y). In three of the four cycles the lowermost flows are the most highly differentiated, and successive flows are increasingly primitive. These changes are thought to be the result of frequent injection of primitive, mantle-derived tholeiitic magma into small crustal magma chambers that contain evolved tholeiitic magma. The resultant mixing and expulsion of hybrid magma produce flows of small volume (0.01–0.03 km3) that display increasingly primitive character upward within each cycle (increasing Mg# and decreasing content of incompatible elements). This process is expected to be more efficient in small reservoirs than in the very large magma chambers that have been invoked by previous exponents of the differentiation–replenishment hypothesis. We suggest that cyclical volcanism in areas well back from the line of active rifting may be more common than is realized and is controlled by the fractionation–magma-replenishment process operating in numerous small reservoirs in an extensively fractured continental crust.

Relationships between silicic plutonism and volcanism: geochemical evidence

1988 ◽  
Vol 79 (2-3) ◽  
pp. 257-263 ◽  
Author(s):  
R. Macdonald ◽  
R. L. Smith
Keyword(s):  
Open Systems ◽  
Mafic Magma ◽  
Geochemical Data ◽  
Magma Chambers ◽  
Magma Body ◽  
Jemez Mountains ◽  
Evolutionary Phase ◽  
Ring Complexes ◽  
High Level ◽  
Melt Evolution

ABSTRACTField associations (voluminous ash flow deposits, rhyolitic stocks and dykes, ring complexes), evidence of repeated influxes of mafic magma, and thermal constraints indicate that many high-level silicic plutons (magma chambers) acted as open systems for considerable parts of their history. The long thermal lifetime, as well as other evidence from the volcanic record, suggests that some such systems reached a quasi-steady state in which magma input was balanced by magma output for times longer than those required for crystallisation. Reconstruction of the evolution of large, long-lived caldera-forming systems, such as that of the Jemez Mountains, New Mexico, indicates that many chambers have lost a highly fractionated silicic cap, in some cases cyclically. Crystallised plutons may contain no obvious record of this evolutionary phase.Geochemical data from silicic ash flow deposits can be used to reconstruct the volcanic stage of pluton development. Many silicic systems, especially of alkaline affinity, apparently pass from a stage in which melt evolution is dominated by crystal-liquid processes to one in which other processes may also contribute to differentiation. Apparently, the transition is most readily achieved in volatile-rich, alkaline silicic systems emplaced in complex, ancient sialic crust of the cratons. Once established, the preservation of highly fractionated caps on magma chambers requires a balance between thermal input and cooling-induced crystallisation. If heat enters the system too quickly, the cap may get stirred into the dominant magma volume by convection. If heat input is too slow, the magma body will crystallise inward from the margins, and the plutonic-consolidation stage will begin.

Fractionation in the feeder system at a Proterozoic rifted margin

1984 ◽  
Vol 21 (4) ◽  
pp. 489-499 ◽  
Author(s):  
Jean H. Bedard ◽  
Donald M. Francis ◽  
Andrew J. Hynes ◽  
Serge Nadeau
Keyword(s):  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Crystallization Mechanism ◽  
Evolutionary Trend ◽  
Titanium Oxides ◽  
Magma Chambers ◽  
Volcanic Stratigraphy ◽  
Volcanic Pile ◽  
Dominant Process ◽  
Rifted Margin

In the Proterozoic Cape Smith Foldbelt of Ungava, Quebec, basal basalts of continental affinity are succeeded upward and basinward by cyclic sequences of MgO-rich (≤ 19 wt.% MgO) to MgO-poor submarine basalts of oceanic affinity belonging to the Chukotat Group. The more primitive komatiitic basalts of the Chukotat Group evolved via fractional crystallization of olivine within a crustal feeder system that is represented by large, layered sills and discordant dyke – sill complexes. These intrusions occupy horizons of mechanical weakness such as sedimentary or hyaloclastite-rich horizons within the volcanic stratigraphy. Peridotite and peridotite – gabbro sills predominate at the base of the Chukotat volcanic pile, whereas gabbroic sills are more common higher in the stratigraphy, reflecting the progressive fractionation within the feeder system. Gravitationally controlled settling of crystals or crystal clots is thought to be the dominant process responsible for fractionation in these crustal sills. Fractional crystallization of olivine within the feeder system produced the olivine-phyric to pyroxene-phyric evolutionary trend observed in the coexisting volcanic rocks. Continuing extraction of clinopyroxene, plagioclase, and iron – titanium oxides in subcrustal sills or magma chambers is thought to have generated the MORB-like upper plagioclase-phyric Chukotat basalts. The compositional gap between the pyroxene-phyric and plagioclase-phyric basalts is a by-product of the fractional crystallization mechanism: liquids with compositions typical of the gap are so highly charged with suspended plagioclase crystals that they resist extrusion.

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