scholarly journals The Petrology and Petrochemistry of Andesite and Dacite Volcanoes in Eastern Bay of Plenty, New Zealand

2021 ◽  
Author(s):  
◽  
Andrew Rae Duncan
Keyword(s):  
Volcanic Rocks ◽  
Taupo Volcanic Zone ◽  
Geochemical Data ◽  
Crustal Material ◽  
Volcanic Zone ◽  
Element Abundances ◽  
Three Samples ◽  
Chemical Trends ◽  
Variation Trends ◽  
White Island

<p>The volcanic rocks of Edgecumbe, Whale Island, White Island and Manawahe are andesites and dacites, which are collectively termed the Bay of Plenty volcanics. Edgecumbe is a comparatively young volcano, being active between 1700 and 8000 years B.P.; Whale Island has probably been inactive for at least the last 36,000 years; White Island has probably been active for much of the late Pleistocene, and is still in a stage of solfataric activity with intermittent tephra eruptions; and Manawahe is probably of the order of 750,000 year old (K-Ar date by J.J. Stipp). The geology of Edgecumbe, Whale Island and White Island is discussed, and the petrography and mineralogy of the Bay of plenty volcanics is discussed and compared. The rocks of Edgecumbe and Whale Island are extremely similar petrographically, but the rocks of White Island and Manawahe are sufficiently different that they can be distinguished both from one another and from Edgecumbe and Whale Island rocks. Most of the Bay of Plenty volcanics are plagioclase andesites or plagioclase dacites. New total rock analyses for 28 elements in 44 samples of the Bay of Plenty volcanics are presented, together with analyses of 4 samples from elsewhere in the Taupo Volcanic Zone. Three samples were analysed for an additional 17 elements. The Bay of Plenty volcanics are calc-alkaline and are predominantly dacites (greater than or equal to 63% SiO2) by Taylor et al.'s (1969) definition, but there is chemical continuity from samples with about 61% SiO2 to samples with about 66% SiO2. Major and trace element variation trends cannot be explained entirely by a crystal fractionation hypothesis, and assimilation of upper crustal material of rhyolitic composition best explains the variation trends for Edgecumbe and Whale Island. The variation trends and certain element abundances in White Island rocks suggest the assimilation of marine sediments, and introduction of seawater into the magma. Taken as a whole, the Bay of Plenty volcanics fit the chemical trends which have been established for the Taupo Zone by earlier workers (e.g. Steiner, 1958; Clark, 1960). The apparent geochemical 'gap' or discontinuity between about 68% and 71.5% SiO2 noted by Steiner (1958) is further substantiated by the new geochemical data presented here. It is considered likely that basalt, andesite and rhyolite are all primary magmas in the Taupo Volcanic Zone. Their possible origins, and the origins of Taupo Zone dacites are discussed.</p>

scholarly journals The Petrology and Petrochemistry of Andesite and Dacite Volcanoes in Eastern Bay of Plenty, New Zealand

2021 ◽  
Author(s):  
◽  
Andrew Rae Duncan
Keyword(s):  
Volcanic Rocks ◽  
Taupo Volcanic Zone ◽  
Geochemical Data ◽  
Crustal Material ◽  
Volcanic Zone ◽  
Element Abundances ◽  
Three Samples ◽  
Chemical Trends ◽  
Variation Trends ◽  
White Island

<p>The volcanic rocks of Edgecumbe, Whale Island, White Island and Manawahe are andesites and dacites, which are collectively termed the Bay of Plenty volcanics. Edgecumbe is a comparatively young volcano, being active between 1700 and 8000 years B.P.; Whale Island has probably been inactive for at least the last 36,000 years; White Island has probably been active for much of the late Pleistocene, and is still in a stage of solfataric activity with intermittent tephra eruptions; and Manawahe is probably of the order of 750,000 year old (K-Ar date by J.J. Stipp). The geology of Edgecumbe, Whale Island and White Island is discussed, and the petrography and mineralogy of the Bay of plenty volcanics is discussed and compared. The rocks of Edgecumbe and Whale Island are extremely similar petrographically, but the rocks of White Island and Manawahe are sufficiently different that they can be distinguished both from one another and from Edgecumbe and Whale Island rocks. Most of the Bay of Plenty volcanics are plagioclase andesites or plagioclase dacites. New total rock analyses for 28 elements in 44 samples of the Bay of Plenty volcanics are presented, together with analyses of 4 samples from elsewhere in the Taupo Volcanic Zone. Three samples were analysed for an additional 17 elements. The Bay of Plenty volcanics are calc-alkaline and are predominantly dacites (greater than or equal to 63% SiO2) by Taylor et al.'s (1969) definition, but there is chemical continuity from samples with about 61% SiO2 to samples with about 66% SiO2. Major and trace element variation trends cannot be explained entirely by a crystal fractionation hypothesis, and assimilation of upper crustal material of rhyolitic composition best explains the variation trends for Edgecumbe and Whale Island. The variation trends and certain element abundances in White Island rocks suggest the assimilation of marine sediments, and introduction of seawater into the magma. Taken as a whole, the Bay of Plenty volcanics fit the chemical trends which have been established for the Taupo Zone by earlier workers (e.g. Steiner, 1958; Clark, 1960). The apparent geochemical 'gap' or discontinuity between about 68% and 71.5% SiO2 noted by Steiner (1958) is further substantiated by the new geochemical data presented here. It is considered likely that basalt, andesite and rhyolite are all primary magmas in the Taupo Volcanic Zone. Their possible origins, and the origins of Taupo Zone dacites are discussed.</p>

Superposed Neoproterozoic and Silurian magmatic arcs in central Cape Breton Island, Canada: geochemical and geochronological constraints

2000 ◽  
Vol 137 (2) ◽  
pp. 137-153 ◽  
Author(s):  
J. D. KEPPIE ◽  
J. DOSTAL ◽  
R. D. DALLMEYER ◽  
R. DOIG
Keyword(s):  
New Brunswick ◽  
New England ◽  
Volcanic Rocks ◽  
Geochemical Data ◽  
Zircon Age ◽  
Cape Breton Island ◽  
Northern Margin ◽  
Element Abundances ◽  
Southern New England ◽  
Cape Breton

Isotopic and geochemical data indicate that intrusions in the eastern Creignish Hills of central Cape Breton Island, Canada represent the roots of arcs active at ∼ 540–585 Ma and ∼ 440 Ma. Times of intrusion are closely dated by (1) a nearly concordant U–Pb zircon age of 553±2 Ma in diorites of the Creignish Hills pluton; (2) a lower intercept U–Pb zircon age of 540±3 Ma that is within analytical error of 40Ar/39 Ar hornblende plateau isotope-correlation ages of 545 and 550±7 Ma in the River Denys diorite; and (3) an upper intercept U–Pb zircon age of 586±2 Ma in the Melford granitic stock. On the other hand, ∼ 441–455 Ma 40Ar/39 Ar muscovite plateau ages in the host rock adjacent to the Skye Mountain granite provide the best estimate of the time of intrusion, and are consistent with the presence of granitic dykes cutting the Skye Mountain gabbro–diorite previously dated at 438±2 Ma. All the intrusions are calc-alkaline; the Skye Mountain granite is peraluminous. Trace element abundances and Nb and Ti depletions of the intrusive rocks are characteristic of subduction-related rocks. The ∼ 540–585 Ma intrusions form part of an extensive belt running across central Cape Breton Island, and represent the youngest Neoproterozoic arc magmas in this part of Avalonia. Nearby, they are overlain by Middle Cambrian units containing rift-related volcanic rocks, which bracket the transition from convergence to extension between ∼ 540 and 505/520 Ma. This transition varies along the Avalon arc: 590 Ma in southern New England, 560–538 Ma in southern New Brunswick, and 570 Ma in eastern Newfoundland. The bi-directional diachronism in this transition is attributed to northwestward subduction of two mid-ocean ridges bordering an oceanic plate, and the migration of two ridge–trench–transform triple points. Following complete subduction of the ridges, remnant mantle upwelling along the subducted ridges produced uplift, gravitational collapse and the high-temperature/low-pressure metamorphism in the arc in both southern New Brunswick and central Cape Breton Island. The ∼ 440 Ma arc magmatism in the Creignish Hills extends through the Cape Breton Highlands and into southern Newfoundland, and has recently been attributed to northwesterly subduction along the northern margin of the Rheic Ocean.

Petrology and petrogenesis of volcanic rocks from the Taupo Volcanic Zone: a review

1995 ◽  
Vol 68 (1-3) ◽  
pp. 59-87 ◽  
Author(s):  
I.J. Graham ◽  
J.W. Cole ◽  
R.M. Briggs ◽  
J.A. Gamble ◽  
I.E.M. Smith
Keyword(s):  
Volcanic Rocks ◽  
Taupo Volcanic Zone ◽  
Volcanic Zone

Sr-Nd-Pb-Hf-Mg isotope geochemistry of volcanic rocks from Oldoinyo Lengai, Tanzania

2020 ◽  
Author(s):  
Sung Hi Choi ◽  
Seung Gi Jung ◽  
Kang Hyeun Ji
Keyword(s):  
Rift Valley ◽  
Source Region ◽  
Regression Line ◽  
Volcanic Rocks ◽  
Primitive Mantle ◽  
Geochemical Data ◽  
Stability Field ◽  
Crustal Material ◽  
Oldoinyo Lengai ◽  
Isotopic Compositions

&lt;p&gt;Oldoinyo Lengai is the only active carbonatite volcano within the East African Rift Valley in northern Tanzania. The volcano is dominated by peralkaline silicate rocks with natrocarbonatites. This study presents new mineralogical and geochemical data, including Sr&amp;#8211;Nd&amp;#8211;Pb&amp;#8211;Hf&amp;#8211;Mg isotopic compositions, for volcanic rocks at Oldoinyo Lengai and lavas from the nearby Gregory Rift Valley. The samples analyzed in this study include olivine melilitite, melanephelinite, wollastonite nephelinite, and phonolite. The olivine melilitites and melanephelinites have highly fractionated REE patterns with (La/Yb)&lt;sub&gt;N&lt;/sub&gt; values of 26.4&amp;#8211;64.9, suggesting that they formed from magmas generated by low-degree (up to ~7%) of partial melting within the garnet stability field. The wollastonite nephelinites have much higher (La/Sm)&lt;sub&gt;N&lt;/sub&gt; values but lower (Sm/Yb)&lt;sub&gt;N&lt;/sub&gt; values relative to typical OIB, with flat HREE patterns [(La/Yb)&lt;sub&gt;N&lt;/sub&gt; = ~22]. The phonolites have elevated REE abundances but with patterns intermediate between the other two sample groups [(La/Yb)&lt;sub&gt;N&lt;/sub&gt; = ~41]. All samples have primitive-mantle-normalized incompatible element patterns that are characterized by negative K and Rb anomalies but no significant Eu anomalies. They also have elevated Yb contents relative to the compositions of modeled garnet peridotite-derived melts, suggesting that they were derived from a sublithospheric source containing enriched HIMU-like recycled oceanic crustal material. However, the wollastonite nephelinites have significantly positive Ba, U, Sr, and Pb anomalies similar to those found within the Oldoinyo Lengai natrocarbonatites. The wollastonite nephelinites might have been sourced from a region of sub-continental lithospheric mantle (SCLM) that was previously metasomatized by interaction with carbonatite melts. The phonolites in the study area have also weakly positive Pb and Sr anomalies indicative of some interaction with the SCLM. All samples have d&lt;sup&gt;26&lt;/sup&gt;Mg values (&amp;#8211;0.39&amp;#8240; &amp;#177; 0.07&amp;#8240;) lighter than the composition of normal mantle material (&amp;#8211;0.25&amp;#8240; &amp;#177; 0.04&amp;#8240;). In addition, a negative correlation between d&lt;sup&gt;26&lt;/sup&gt;Mg values and MgO concentrations suggests derivation from a source region containing recycled carbonate. The samples from the study area define a mixing array between HIMU- and EM1-type OIB in Sr&amp;#8211;Nd and Pb&amp;#8211;Pb isotopic correlation diagrams, and have pronounced Nd&amp;#8211;Hf isotopic decoupling, plotting below the mantle regression line in Nd&amp;#8211;Hf isotopic space. The negative deviation from the Nd&amp;#8211;Hf isotopic mantle array and the presence of an EM1-type mantle component in the Sr&amp;#8211;Nd isotopic compositions of the Oldoinyo Lengai volcanic rocks can be generated by recycling of E-MORB-type oceanic crustal material with an age of 1.5&amp;#8211;1.0 Ga.&lt;/p&gt;

The Chengwatana Volcanics, Wisconsin and Minnesota: petrogenesis of the southernmost volcanic rocks exposed in the Midcontinent rift

1997 ◽  
Vol 34 (4) ◽  
pp. 536-548 ◽  
Author(s):  
Karl R. Wirth ◽  
Zachary J. Naiman ◽  
Jeffrey D. Vervoort
Keyword(s):  
Trace Element ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Geothermal Gradient ◽  
Limited Range ◽  
Geochemical Data ◽  
Rift System ◽  
Midcontinent Rift ◽  
Element Abundances ◽  
Isotopic Compositions

The southernmost exposed rocks of the North American Midcontinent rift system (1100 Ma) consist of 3000 m of mafic volcanic flows and minor interflow sediment exposed along the St. Croix River in Minnesota and Wisconsin. The flows are mostly high-Fe tholeiitic basalt with plagioclase phenocrysts and ophitic to subophitic clinopyroxene. Abundant secondary chlorite, epidote, and actinolite indicate the group was metamorphosed to greenschist facies (~350 °C). Low sodium (M4 site) and tetrahedral aluminum (AlIV) contents of actinolite indicate low-pressure metamorphism (0.25 GPa) and imply a geothermal gradient of 45 – 50 °C/km. Low magnesium (Mg# = 0.37–0.58) and Ni contents (36–185 ppm) indicate the basalts have undergone significant fractionation and are not primary mantle melts. Incompatible element abundances are inversely correlated with Mg#, and most samples plot within either high or low trace element groups (e.g., Ti, P, Zr). The basalts are enriched in the light rare earth elements and Th, and are variably depleted in Ta and Nb relative to La and Th. Initial 143Nd/144Nd compositions of the group range from 0.51099 to 0.51122 (initial εNd = −4.5 to +0.1). Most flows have isotopic compositions within a relatively limited range (initial εNd = −2.5 to −1.6), but exhibit variable trace element abundances. Flows with the highest and lowest initial 143Nd/144Nd ratios have isotopic compositions that are inversely correlated with trace element abundances and ratios (e.g., La/Yb, Th/La, Th/Ta). The combined geochemical data suggest that the Chengwatana basalts originated from plume-derived melts and underwent variable fractional crystallization and crustal contamination. These melts may have interacted with lithospheric mantle enriched during Penokean subduction.

The tectonic evolution of the Abitibi greenstone belt of Canada

1986 ◽  
Vol 123 (2) ◽  
pp. 153-166 ◽  
Author(s):  
John Ludden ◽  
Claude Hubert ◽  
Clement Gariépy
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Taupo Volcanic Zone ◽  
Rift Basins ◽  
Volcanic Zone ◽  
Tectonic Model ◽  
Abitibi Greenstone Belt ◽  
Southern Volcanic Zone ◽  
The Difference ◽  
Felsic Volcanic

AbstractBased on structural, geochemical, sedimentological and geochronological studies, we have formulated a model for the evolution of the late Archaean Abitibi greenstone belt of the Superior Province of Canada. The southern volcanic zone (SVZ) of the belt is dominated by komatiitic to tholeiitic volcanic plateaux and large, bimodal, mafic-felsic volcanic centres. These volcanic rocks were erupted between approximately 2710 Ma and 2700 Ma in a series of rift basins formed as a result of wrench-fault tectonics.The SVZ superimposes an older volcanic terrane which is characterized in the northern volcanic zone (NVZ) of the Abitibi belt and is approximately 2720 Ma or older. The NVZ comprises basaltic to andesitic and dacitic subaqueous massive volcanics which are cored by comagmatic sill complexes and layered mafic-anorthositic plutonic complexes. These volcanics are overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 ±2 Ma.The tectonic model envisages the SVZ to have formed in a series of rift basins which dissected an earlier formed volcanic arc (the NVZ). Analogous rift environments have been postulated for the Hokuroko basin of Japan, the Taupo volcanic zone of New Zealand and the Sumatra and Nicaragua arcs. The difference between rift related ‘submergent’ volcanism in the SVZ and ‘emergent’ volcanism in the NVZ resulted in the contrasting metallogenic styles, the former being characterized by syngenetic massive sulphide deposits, whilst the latter was dominated by epigenetic ‘porphyry-type’ Cu(Au) deposits.

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