Volcanism from fissure zones and the Caldeira central volcano of Faial Island, Azores archipelago: geochemical processes in multiple feeding systems

2013 ◽  
Vol 150 (3) ◽  
pp. 536-555 ◽  
Author(s):  
VITTORIO ZANON ◽  
ULRICH KUEPPERS ◽  
JOSÉ MANUEL PACHECO ◽  
INÊS CRUZ
Keyword(s):  
Fractional Crystallization ◽  
Central Volcano ◽  
Geochemical Processes ◽  
Magma Reservoirs ◽  
Incompatible Elements ◽  
Mantle Sources ◽  
Mafic Magmas ◽  
Multiple Feeding ◽  
Atlantic Area ◽  
Feeding Systems

AbstractMagmas in Faial Island, Azores (Portugal), were mostly erupted from two fissure zones and the Caldeira central volcano during overlapping periods. The fissure zones follow extensional trends oriented WNW and ESE and erupted nepheline- to hypersthene-normative basalts and hawaiites. The Caldeira central volcano builds the central part of the island, which is cut by the fissure zones. Ne-normative basalts show similar high-field-strength element (HFSE) concentrations but higher large ion lithophile element (LILE) concentrations than hy-normative equivalents. Primitive melts were generated by small (3–5%) degrees of partial melting of garnet-bearing peridotite, variably enriched in incompatible elements. Overall, basalts from Faial show relatively higher LILE abundances and LILE/HFSE ratios than those of the other islands of the Azores and of many other volcanoes in the Atlantic area. This feature indicates the existence of chemical heterogeneities in the mantle sources characterized by variable degrees of metasomatism, both at local and regional scales. Hawaiites evolved from basalts through 30–40% fractional crystallization of mafic phases plus some plagioclase, in deep reservoirs, at about 430–425 MPa (~ 15 km). The Caldeira central volcano rocks range from basalts to trachytes. Basalts, produced under similar conditions as fissure basalts, evolved to trachytes through large degrees of polybaric fractional crystallization (100–760 MPa; i.e. ~ 3.6–26 km), involving olivine, clinopyroxene, feldspar and minor quantities of amphibole, biotite, apatite and oxides. In contrast, mafic magmas from the fissure zones were erupted directly onto the surface from magma reservoirs mainly located at the crust–mantle boundary.

Le terrane de Slide Mountain (Cordillères canadiennes) : une lithosphère océanique marquée par des points chauds

2003 ◽  
Vol 40 (6) ◽  
pp. 833-852 ◽  
Author(s):  
M Tardy ◽  
H Lapierre ◽  
D Bosch ◽  
A Cadoux ◽  
A Narros ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Island ◽  
Light Rare Earth ◽  
Isotopic Compositions ◽  
Incompatible Elements ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
British Colombia ◽  
Ultramafic Cumulates ◽  
Back Arc

The Slide Mountain Terrane consists of Devonian to Permian siliceous and detrital sediments in which are interbedded basalts and dolerites. Locally, ultramafic cumulates intrude these sediments. The Slide Mountain Terrane is considered to represent a back-arc basin related to the Quesnellia Paleozoic arc-terrane. However, the Slide Mountain mafic volcanic rocks exposed in central British Colombia do not exhibit features of back-arc basin basalts (BABB) but those of mid-oceanic ridge (MORB) and oceanic island (OIB) basalts. The N-MORB-type volcanic rocks are characterized by light rare-earth element (LREE)-depleted patterns, La/Nb ratios ranging between 1 and 2. Moreover, their Nd and Pb isotopic compositions suggest that they derived from a depleted mantle source. The within-plate basalts differ from those of MORB affinity by LREE-enriched patterns; higher TiO2, Nb, Ta, and Th abundances; lower εNd values; and correlatively higher isotopic Pb ratios. The Nd and Pb isotopic compositions of the ultramafic cumulates are similar to those of MORB-type volcanic rocks. The correlations between εNd and incompatible elements suggest that part of the Slide Mountain volcanic rocks derive from the mixing of two mantle sources: a depleted N-MORB type and an enriched OIB type. This indicates that some volcanic rocks of the Slide Mountain basin likely developed from a ridge-centered or near-ridge hotspot. The activity of this hotspot is probably related to the worldwide important mantle plume activity that occurred at the end of Permian times, notably in Siberia.

scholarly journals Feldspar megacrysts and anorthosite xenolith-bearing dykes in the Narssarssuaq area, South Greenland

1992 ◽  
Vol 154 ◽  
pp. 49-59
Author(s):  
T Winther
Keyword(s):  
Open Systems ◽  
Early Stage ◽  
Rift System ◽  
Magma Chambers ◽  
Degree Of Contamination ◽  
Magma Reservoirs ◽  
Incompatible Elements ◽  
Low Degree ◽  
Alkaline Magmas ◽  
Compositional Gradients

Numerous dyke intrusions are found in the Narssarssuaq area of the Gardar province, a Mid-Proterozoic intracontinental rift system. Ten to fifteen percent of these dykes, which range in composition from trachybasalt to phonolite and rhyolite, contain significant proportions of feldspar megacrysts and occasionally anorthosite xenoliths. Two groups of dykes are distinguished; the older group is more alkaline, richer in incompatible elements and contains more anorthosite xenoliths than the younger. It is probable that the main reason for the differences is variation in magma production through time and from one area to another. Chemical zonation in the dykes reflects compositional gradients in the feeding magma reservoirs; the magma reservoirs acting as open systems in which crystal fractionation was an important controlling process. The anorthosite xenoliths are not strictly cognate with their hosts, but were derived from comparable alkaline magmas with a composition roughly corresponding to the most primitive of the dykes. The plagioclase megacrysts were presumably formed at an early stage of the development of the magma chambers. Rb-Sr dating of one of the dykes from the older group of dykes gives an age of 1206 ± 20 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0001 supporting a low degree of contamination with upper crustal Sr.

scholarly journals Geochemistry of Garga-Sarali intrusive granitoids (central domain of the central African fold belt in Cameroon): petrological implication

2020 ◽  
Vol 8 (1) ◽  
pp. 33
Author(s):  
Daama Isaac ◽  
Mbowou Gbambie Isaac Bertrand ◽  
Yamgouot Ngounouno Fadimatou ◽  
Ntoumbe Mama ◽  
Ngounouno Ismaïla
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Partial Melting ◽  
Fractional Crystallization ◽  
Coarse Grained ◽  
Geochemical Analysis ◽  
Fold Belt ◽  
Volcanic Arcs ◽  
Fine Grained ◽  
Incompatible Elements

The Garga-Sarali granitoids outcrop in form of large slabs and undistorted large blocks, into a schisto-gneissic basement. These rocks contain mainly muscovite and microcline, followed by K-feldspar, quartz, biotite, pyroxene, zircon and oxides, with coarse-grained to fine-grained textures. Geochemical analysis show that it belongs to differentiated rocks group (granodiorite-granite) with high SiO2 (up to 72 wt%) contents. Their genesis was made from a process of partial melting and fractional crystallization. These rocks are classified as belonging to I- and S-Type, meta-peraluminous, shoshonitic granites; belonging to the domain of volcanic arcs. The rare earth elements patterns suggest a source enriched of incompatible elements. The Nb-Ta and Ti negative anomalies from the multi-element patterns are characteristics of the subduction domains.  

Magma oxygen fugacity of mafic-ultramafic intrusions in convergent margin settings: Insights for the role of magma oxidation states on magmatic Ni-Cu sulfide mineralization

2020 ◽  
Vol 105 (12) ◽  
pp. 1841-1856 ◽  
Author(s):  
Yonghua Cao ◽  
Christina Yan Wang ◽  
Bo Wei
Keyword(s):  
Key Factors ◽  
Convergent Margin ◽  
Sulfide Deposits ◽  
Central Asian ◽  
Mantle Sources ◽  
Oxygen Buffer ◽  
Mafic Magmas ◽  
Orogenic Belts ◽  
Ocean Ridge ◽  
Metasomatized Mantle

Abstract Oxygen fugacities (fO2) of mantle-derived mafic magmas have important controls on the sulfur status and solubility of the magmas, which are key factors to the formation of magmatic Ni-Cu sulfide deposits, particularly those in convergent margin settings. To investigate the fO2 of mafic magmas related to Ni-Cu sulfide deposits in convergent margin settings, we obtained the magma fO2 of several Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the Central Asian Orogenic Belt (CAOB), North China, based on the olivine-spinel oxygen barometer and the modeling of V partitioning between olivine and melt. We also calculated the mantle fO2 on the basis of V/Sc ratios of primary magmas of these intrusions. Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the CAOB include arc-related Silurian-Carboniferous ones and post-collisional Permian-Triassic ones. Arc-related intrusions formed before the closure of the paleo-Asian ocean and include the Jinbulake, Heishan, Kuwei, and Erbutu intrusions. Post-collisional intrusions were emplaced in extensional settings after the closure of the paleo-Asian ocean and include the Kalatongke, Baixintan, Huangshandong, Huangshan, Poyi, Poshi, Tulaergen, and Hongqiling No. 7 intrusions. It is clear that the magma fO2 values of all these intrusions in both settings range mostly from FMQ+0.5 (FMQ means fayalite-magnetite-quartz oxygen buffer) to FMQ+3 and are generally elevated with the fractionation of magmas, much higher than that of MORBs (FMQ-1 to FMQ+0.5). However, the mantle fO2 values of these intrusions vary from ~FMQ to ~FMQ+1.0, just slightly higher than that of mid-ocean ridge basalts (MORBs) (≤FMQ). This slight difference is interpreted as the intrusions in the CAOB may have been derived from the metasomatized mantle wedges where only minor slab-derived, oxidized components were involved. Therefore, the high-magma fO2 values of most Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the CAOB were attributed to the fractionation of magmas derived from the slightly oxidized metasomatized mantle. In addition, the intrusions that host economic Ni-Cu sulfide deposits in the CAOB usually have magma fO2 of >FMQ+1.0 and sulfides with mantle-like δ34S values (–1.0 to +1.1‰), indicating that the oxidized mafic magmas may be able to dissolve enough mantle-derived sulfur to form economic Ni-Cu sulfide deposits. Oxidized mafic magmas derived from metasomatized mantle sources may be an important feature of major orogenic belts.

The magmatic evolution of the late Miocene laccolith–pluton–dyke granitic complex of Elba Island, Italy

2002 ◽  
Vol 139 (3) ◽  
pp. 257-279 ◽  
Author(s):  
A. DINI ◽  
F. INNOCENTI ◽  
S. ROCCHI ◽  
S. TONARINI ◽  
D. S. WESTERMAN
Keyword(s):  
Late Miocene ◽  
Dyke Swarm ◽  
Short Time Span ◽  
Variable Nature ◽  
Mantle Sources ◽  
Magma Sources ◽  
Igneous Activity ◽  
Mafic Magmas ◽  
Elba Island ◽  
Short Time

Since late Miocene time, post-collisional extension of the internal parts of the Apennine orogenic belt has led to the opening of the Tyrrhenian basin. Extensive, mainly acidic peraluminous magmatism affected the Tuscan Archipelago and the Italian mainland during this time, building up the Tuscan Magmatic Province as the fold belt was progressively thinned, heated and intruded by mafic magmas. An intrusive complex was progressively built on western Elba Island by emplacement, within a stack of nappes, of multiple, shallow-level porphyritic laccoliths, a major pluton, and a final dyke swarm, all within the span from about 8 to 6.8 Ma. New geochemical and Sr–Nd isotopic investigations constrain the compositions of materials involved in the genesis of the magmas of Elba Island compared to the whole Tuscan Magmatic Province. Several distinct magma sources, in both the crust and mantle, have been identified as contributing to the Elba magmatism as it evolved from crust-, to hybrid-, to mantle-dominated. However, a restricted number of components, geochemically similar to mafic K-andesites of the Island of Capraia and crustal melts like the Cotoncello dyke at Elba, are sufficient to account for the generation by melt hybridization of the most voluminous magmas (c. εNd(t) −8.5, 87Sr/86Sr 0.715). Unusual magmas were emplaced at the beginning and end of the igneous activity, without contributing to the generation of these hybrid magmas. These are represented by early peraluminous melts of a different crustal origin (εNd(t) between −9.5 and −10.0, 87Sr/86Sr variable between 0.7115 and 0.7146), and late mantle-derived magma strongly enriched in incompatible elements (εNd(t) = −7.0, 87Sr/86Sr = 0.7114) with geochemical–isotopic characteristics intermediate between contemporaneous Capraia K-andesites and later lamproites from the Tuscan Magmatic Province. Magmas not involved in the generation of the main hybrid products are not volumetrically significant, but their occurrence emphasizes the highly variable nature of crust and mantle sources that can be activated in a short time span during post-collisional magmatism.

Variation in the geochemistry of mantle sources for tholeiitic and calc-alkaline mafic magmas, Western Sunda volcanic arc, Indonesia

1980 ◽  
Vol 30 (3) ◽  
pp. 177-199 ◽  
Author(s):  
I.A. Nicholls ◽  
D.J. Whitford ◽  
K.L. Harris ◽  
S.R. Taylor
Keyword(s):  
Calc Alkaline ◽  
Volcanic Arc ◽  
Mantle Sources ◽  
Mafic Magmas

Possible crustal contamination of Midcontinent Rift igneous rocks: examples from the Mineral Lake intrusions, Wisconsin

1992 ◽  
Vol 29 (6) ◽  
pp. 1140-1153 ◽  
Author(s):  
Karl E. Seifert ◽  
Zell E. Peterman ◽  
Scott E. Thieben
Keyword(s):  
Fractional Crystallization ◽  
Crustal Contamination ◽  
Flood Basalt ◽  
Igneous Rocks ◽  
Midcontinent Rift ◽  
Mafic Intrusions ◽  
Enriched Mantle ◽  
Mantle Sources ◽  
Geochemical Variations ◽  
Compositional Pattern

Interlayered mafic–telsic intrusions from the Mineral Lake intrusive complex in northwest Wisconsin reflect the typical bimodal basalt–rhyolite compositional pattern of the Midcontinent Rift flood basalt province in the Lake Superior region. The later felsic intrusions were emplaced between the mafic intrusions and overlying basalt flows, and postemplacement fractional crystallization produced gradational mineralogical and geochemical variations. Isotopic and trace-element data for the Mineral Lake intrusions are consistent with mantle sources for both mafic and felsic intrusions, with compositional differences explained by the extent of fractional crystallization and crustal contamination or mantle source characteristics.εNd–εSr plots of analyzed Midcontinent Rift igneous rocks define three largely separate isotopic fields that suggest separate sources. However, the spread in isotopic data and a spider diagram plot of mafic samples from the εNd = εSr = 0 field suggest a crustal component and derivation from depleted rather than chondritic mantle. Evolved felsic rocks plotting in two negative εNd – positive εSr fields can be explained by derivation from separate enriched mantle sources or crustal contamination or both.

Petrological Mixing ­ A Regression Approach

2000 ◽  
Vol 50 (1-2) ◽  
pp. 79-94
Author(s):  
Aditya Chatterjee ◽  
Subho Sankar Sarkar ◽  
Suvas Nandi
Keyword(s):  
Regression Model ◽  
Fractional Crystallization ◽  
Geochemical Processes ◽  
Mixing Process ◽  
Eastern India ◽  
Constrained Least Squares ◽  
Primary 62J05 ◽  
Partial Fusion ◽  
Regression Approach ◽  
Log Ratio

The geochemical processes of fractional crystallization of a magma, partial fusion of a rock and assimilation or hybridization of rock(s) and/or magma(s) are generally termed as petrological mixing process. In the present paper a unified attempt has been made to describe the three processes under the purview of regression model. As the data involved are essentially compositional in nature, their suitable log-ratio transforms have been utilized and the constrained least squares principle has been applied to reach a meaningful solution. A highly accommodative procedure is suggested so as to describe any specified d~gree of fractional crystallization of magma or of partial fusion of a rock. The paper concludes with applications of the proposed method on data available from i) Rajmahal Trap, Eastern India (fractional crystallization) ii) Bihar Mica Belt, Eastern India (partial fusion) and iii) Kilauea Volcano, Hawai (formation of hybrid magma). AMS (2000} Subject Classification: Primary: 62J05, 62P99; Secondary: 90C20.

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