A bimodal volcanic–plutonic system: the Zarembo Island extrusive suite and the Burnett Inlet intrusive complex

2004 ◽  
Vol 41 (4) ◽  
pp. 355-375 ◽  
Author(s):  
Jennifer Lindline ◽  
William A Crawford ◽  
Maria Luisa Crawford
Keyword(s):  
Volcanic Rocks ◽  
Intrusive Complex ◽  
Crustal Extension ◽  
Mafic Enclaves ◽  
Volcanic Suite ◽  
Silica Concentration ◽  
Plutonic Complex ◽  
Igneous Activity ◽  
Tectonic Motion ◽  
Igneous Layering

The Zarembo Island volcanic rocks and the Burnett Inlet plutonic complex in central southeastern Alaska were investigated to determine if they are genetically related. The Zarembo Island volcanic suite consists of basalt, andesite, and rhyolite lava flows, which exhibit features that suggest simultaneous eruptions of mafic and felsic lavas. Five kilometres to the southeast, the broadly layered Burnett Inlet plutonic complex consists of gabbro–diorite and granite plutons that also show characteristics of contemporaneous mafic and felsic magmatism. These bimodal volcanic and plutonic rocks are similar in age, ranging from 18.5 to 21.5 Ma. Both suites show a gap in silica concentration between 60 and 65 wt.% and have similar major, trace, and rare-earth element composition. Both suites also show igneous layering, either as interlayered basalt and rhyolite flows or as alternating gabbro and granite sheets. Additionally, both groups contain magma mingling and mixing textures, including mafic enclaves in felsic members and quartz xenocrysts rimmed by clinopyroxene in enclaves. These characteristics suggest that the Burnett Inlet intrusive complex and the Zarembo Island volcanic suite represent an eroded, shallow-level plutonic center and its eruptive cover. The style of volcanism and the bimodal nature of magmatism suggest that igneous activity occurred during crustal extension and thinning that accompanied strike-slip tectonic motion in southeastern Alaska during the Tertiary. The volcanic–plutonic rock associations now exposed at the surface indicate that at least 7° of post-20 Ma crustal tilting has affected the region and can help to explain aberrant paleomagnetic poles in mid-Cretaceous intrusions of the Cordillera Coast belt.

Upper Paleozoic to lower Mesozoic strata and their conodonts, western Coast Plutonic Complex, British Columbia

1985 ◽  
Vol 22 (9) ◽  
pp. 1329-1344 ◽  
Author(s):  
G. J. Woodsworth ◽  
M. J. Orchard
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Late Triassic ◽  
Western Coast ◽  
Upper Paleozoic ◽  
Facies Metamorphism ◽  
Volcanic Suite ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Greenschist Facies Metamorphism

Six lithologic units, including two newly named formations, were mapped on Randall, Dunira, and nearby islands. The islands are characterized by greenschist-facies metamorphism and westerly directed thrusting. The oldest unit is a Late Mississippian, massive limestone on Ducie Island. The Dunira Formation, composed of thin-bedded limestone and siltstone, is Early and Middle Pennsylvanian in age. It is unconformably overlain by limestone and dolomite of the Upper Triassic Randall Formation. The Randall Formation grades upwards into a green phyllitic unit of Late Triassic(?) age. Rhyolitic and more mafic volcanic rocks may represent a bimodal volcanic suite of Early Jurassic age, based on a U–Pb date of 188 Ma on zircons. These five units correlate with rocks in the Alexander Terrane in southeastern Alaska. The sixth and presumed youngest unit consists of flysch-like sedimentary rocks of probable Middle Jurassic to Early Cretaceous age that may correlate with rocks of the Gravina–Nutzotin belt. The three older units yielded 15 conodont genera from 29 localities. The 13 Paleozoic genera are described and illustrated.

The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland

1999 ◽  
pp. 103-112
Author(s):  
Feiko Kalsbeek ◽  
Lilian Skjernaa
Keyword(s):  
Intrusive Complex ◽  
The South ◽  
Original Series ◽  
Early Proterozoic ◽  
West Greenland ◽  
North East ◽  
The North ◽  
Southern Border ◽  
Area North ◽  
Igneous Layering

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Kalsbeek, F., & Skjernaa, L. (1999). The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 103-112. https://doi.org/10.34194/ggub.v181.5118 _______________ The 2800 Ma Atâ intrusive complex (elsewhere referred to as ‘Atâ granite’ or ‘Atâ tonalite’), which occupies an area of c. 400 km2 in the area north-east of Disko Bugt, was emplaced into grey migmatitic gneisses and supracrustal rocks. At its southern border the Atâ complex is cut by younger granites. The complex is divided by a belt of supracrustal rocks into a western, mainly tonalitic part, and an eastern part consisting mainly of granodiorite and trondhjemite. The ‘eastern complex’ is a classical pluton. It is little deformed in its central part, displaying well-preserved igneous layering and local orbicular textures. Near its intrusive contact with the overlying supracrustal rocks the rocks become foliated, with foliation parallel to the contact. The Atâ intrusive complex has escaped much of the later Archaean and early Proterozoic deformation and metamorphism that characterises the gneisses to the north and to the south; it belongs to the best-preserved Archaean tonalite-trondhjemite-granodiorite intrusions in Greenland.

Age, chemistry, and tectonic setting of Miramichi terrane (Early Paleozoic) volcanic rocks, eastern and east-central Maine, USA

2021 ◽  
Vol 57 ◽  
pp. 239-273
Author(s):  
Allan Ludman ◽  
Christopher McFarlane ◽  
Amber T.H. Whittaker
Keyword(s):  
New Brunswick ◽  
Subduction Zone ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Calc Alkaline ◽  
East Central ◽  
Arc Volcanism ◽  
Middle Ordovician ◽  
Volcanic Suite ◽  
Back Arc

Volcanic rocks in the Miramichi inlier in Maine occur in two areas separated by the Bottle Lake plutonic complex: the Danforth segment (Stetson Mountain Formation) north of the complex and Greenfield segment to the south (Olamon Stream Formation). Both suites are dominantly pyroclastic, with abundant andesite, dacite, and rhyolite tuffs and subordinate lavas, breccias, and agglomerates. Rare basaltic tuffs and a small area of basaltic tuffs, agglomerates, and lavas are restricted to the Greenfield segment. U–Pb zircon geochronology dates Greenfield segment volcanism at ca. 469 Ma, the Floian–Dapingian boundary between the Lower and Middle Ordovician. Chemical analyses reveal a calc-alkaline suite erupted in a continental volcanic arc, either the Meductic or earliest Balmoral phase of Popelogan arc activity. The Maine Miramichi volcanic rocks are most likely correlative with the Meductic Group volcanic suite in west-central New Brunswick. Orogen-parallel lithologic and chemical variations from New Brunswick to east-central Maine may result from eruptions at different volcanic centers. The bimodal Poplar Mountain volcanic suite at the Maine–New Brunswick border is 10–20 myr younger than the Miramichi volcanic rocks and more likely an early phase of back-arc basin rifting than a late-stage Meductic phase event. Coeval calc-alkaline arc volcanism in the Miramichi, Weeksboro–Lunksoos Lake, and Munsungun Cambrian–Ordovician inliers in Maine is not consistent with tectonic models involving northwestward migration of arc volcanism. This >150 km span cannot be explained by a single east-facing subduction zone, suggesting more than one subduction zone/arc complex in the region.

scholarly journals Vulcânicas potássicas intemperizadas como protólitos dos filitos hematíticos da Serra do Espinhaço Meridional (Minas Gerais)

2020 ◽  
Vol 34 (2) ◽  
pp. 183-194
Author(s):  
Alexandre Chaves ◽  
Luiz Knauer
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Volcanic Rocks ◽  
Alkaline Rock ◽  
Major Elements ◽  
Volcanic Origin ◽  
Espinhaço Range ◽  
Weathering Processes ◽  
Igneous Layering ◽  
Hematitic Phyllite

The hematitic phyllite is a rock that occurs in the São João da Chapada and Sopa-Brumadinho formations of the southern Espinhaço range. Its origin is widely discussed in papers on Espinhaço, but there is no consensus on its protolith due to certain characteristics of the lithotype, such as its chemical composition and textural features. The pattern of rare earth elements strongly enriched [(La/Yb)N 6.80-17.68], with light rare earth elements [(La/Sm)N 2.54-4.83] richer than heavy ones [(Gd/Yb)N 1.28-3,32], suggests that the protolith was an alkaline volcanic rock formed during the rift that generated the Espinhaço basin. The major elements indicate that the alkaline rock met weathering processes, becoming a regolith. During the Brasiliano metamorphism, it finally became hematitic phyllite. Other characteristics of the lithotype, such as the presence of sericite-bearing rounded parts (possibly formed by alteration and deformation of leucite crystals) and the preservation of igneous layering, suggest a potassic volcanic origin for hematitic phyllite. In diagram that allows identifying altered and metamorphic volcanic rocks, the investigated samples have composition similar to a feldspathoid-rich alkali-basalt, probably a leucite tephrite, a leucitite or even a lamproite, rocks from mantle source.

scholarly journals “Trachytes” from Sardinia: Geoheritage and Current Use

2019 ◽  
Vol 11 (13) ◽  
pp. 3706 ◽  
Author(s):  
Nicola Careddu ◽  
Silvana Maria Grillo
Keyword(s):  
Volcanic Rocks ◽  
Mineralogical Composition ◽  
Building Stone ◽  
Step Method ◽  
Public And Private ◽  
Current State ◽  
Igneous Activity ◽  
Mineral Components ◽  
Granitoid Rocks ◽  
The Aesthetic

Sardinia was affected by an intense igneous activity which generated calc-alkaline products during the Oligo-Miocene period. The volcanic substance shows large variations, ranging from pyroclastic flow deposits, lava flows and domes. By composition, the deposits are all primarily dacites and rhyolites, with subordinate andesites and very scarce basalts. The rhyolite lavas show porphyritic and ash-flow tuffs. Ignimbrite structures are found in the dacitic domes and rhyolitic lavas. These rocks—commercially known as “Trachytes of Sardinia”—used to be quarried in all historical provinces, mainly in the central part of the island to be used as ornamental and building stone. They continue to be commonly used nowadays, but their use dates back to the prehistoric age. They are easily found in many nuraghi, “domus de janas”, holy wells, Roman works (mosaics, paving, roads, bridges), many churches built in Sardinia and practically in all kinds of structural elements in public and private buildings, such as walls, houses, and bridges. Contrary to the granitoid rocks, whose appearance is largely influenced by the mineralogical composition, the aesthetic feature of volcanic rocks is rather affected by the widest range of colors, structure and texture, i.e., shape, size and distribution of mineral components, porphyric index, etc. “Trachyte” is quarried opencast with the “single low step” method, with descending development, with prevalent use of double-disc sawing machines. Whenever the stone deposit allows higher steps, the chain cutting machine, in combination with diamond wire, becomes the preferred extraction solution. This study aims to at look Sardinian “trachytes” from a geoheritage perspective. After a geological-petrographic framework, the paper discusses the historical uses of “trachyte” in Sardinia. The current state of the art of “trachyte” quarrying, processing and usage in the Island is also described. An analysis of the “trachyte” production has been carried out. Finally, a consideration about how to enhance geotourism in the area is suggested.

Copper-Gold Fertility of Arc Volcanic Rocks: A Case Study from the Early Permian Lizzie Creek Volcanic Group, NE Queensland, Australia

2020 ◽  
Author(s):  
Helge Behnsen ◽  
Carl Spandler ◽  
Isaac Corral ◽  
Zhaoshan Chang ◽  
Paul H.G.M. Dirks
Keyword(s):  
Major Element ◽  
Regional Scale ◽  
Volcanic Rocks ◽  
Early Permian ◽  
Magma Evolution ◽  
High Sulfidation ◽  
Volcanic Group ◽  
Volcanic Suite ◽  
Copper Gold

Abstract The Early Permian Lizzie Creek Volcanic Group of the northern Bowen Basin, NE Queensland, Australia, has compositions that range from basalt through andesite to rhyolite with geochemical signatures (e.g., enrichment in Cs, Rb, Ba, U, Th, and Pb, depletion in Nb and Ta) that are typical of arc lavas. In the Mount Carlton district the Lizzie Creek Volcanic Group is host to high-sulfidation epithermal Cu-Au-Ag mineralization, whereas farther to the south near Collinsville (~50 km from Mount Carlton) these volcanic sequences are barren of magmatic-related mineralization. Here, we assess whether geochemical indicators of magma fertility (e.g., Sr/Y, La/Yb, V/Sc) can be applied to volcanic rocks through study of coeval volcanic sequences from these two locations. The two volcanic suites share similar petrographic and major element geochemical characteristics, and both have undergone appreciable hydrothermal alteration during, or after, emplacement. Nevertheless, the two suites have distinct differences in alteration-immobile trace element (V, Sc, Zr, Ti, REE, Y) concentrations. The unmineralized suite has relatively low V/Sc and La/Yb, particularly in the high SiO2 rocks, which is related to magma evolution dominated by fractionation of clinopyroxene, plagioclase, and magnetite. By contrast, the mineralized suite has relatively high V/Sc but includes high SiO2 rocks with depleted HREE and Y contents, and hence high La/Yb. These trends are interpreted to reflect magma evolution under high magmatic H2O conditions leading to enhanced amphibole crystallization and suppressed plagioclase and magnetite crystallization. These rocks have somewhat elevated Sr/Y compared to the unmineralized suite, but as Sr is likely affected by hydrothermal mobility, Sr/Y is not considered to be a reliable indicator of magmatic conditions. Our data show that geochemical proxies such as V/Sc and La/Yb that are used to assess Cu-Au fertility of porphyry intrusions can also be applied to cogenetic volcanic sequences, provided elemental trends with fractionation can be assessed for a volcanic suite. These geochemical tools may aid regional-scale exploration for Cu-Au mineralization in convergent margin terranes, especially in areas that have undergone limited exhumation or where epithermal and porphyry mineralization may be buried beneath cogenetic volcanic successions.

scholarly journals Supplemental Material: Heterogenous late Miocene extension in the northern Walker Lane (California-Nevada, USA) demonstrates vertically decoupled crustal extension

2021 ◽  
Author(s):  
M.C. Say ◽  
A.V. Zuza
Keyword(s):  
Late Miocene ◽  
Volcanic Rocks ◽  
Crustal Extension ◽  
Study Region ◽  
Walker Lane ◽  
Argon Dating ◽  
Geochemical Analyses

Figures S1–S3: Geochemical plots, photomicrographs of representative volcanic rocks dated in this study, and field photographs of alteration in the study region. Table S1: Geochemical analyses. Table S2: Argon dating analyses.

scholarly journals Supplemental Material: Heterogenous late Miocene extension in the northern Walker Lane (California-Nevada, USA) demonstrates vertically decoupled crustal extension

2021 ◽  
Author(s):  
M.C. Say ◽  
A.V. Zuza
Keyword(s):  
Late Miocene ◽  
Volcanic Rocks ◽  
Crustal Extension ◽  
Study Region ◽  
Walker Lane ◽  
Argon Dating ◽  
Geochemical Analyses

Figures S1–S3: Geochemical plots, photomicrographs of representative volcanic rocks dated in this study, and field photographs of alteration in the study region. Table S1: Geochemical analyses. Table S2: Argon dating analyses.

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