Petrographic Characteristics and Geochemistry of Volcanic Rocks in the Kyaukmyet Prospect, Monywa District, Central Myanmar

The Kyaukmyet prospect lies approximately 5 km ENE of the highsulfidation Kyisintaung copper-gold deposit, Monywa district, central Myanmar. Geologically, the research area is remarked by magmatic extrusion that occurred during the Late Oligocene to Middle Miocene of Magyigon Formation which led to the outcrops of volcanic rocks. Study detailed on petrographical and geochemical of the Kyaukmyet volcanic rocks has not been performed before the present work. The principal aim of this paper is to document the petrographical and geochemical characteristics of volcanic suite rocks exposed in the Kyaukmyet prospect. The results of this data have provided insight into the origin of the rocks and petrogenetic processes during evolution. Petrographically, all the studied volcanic rocks in the research area show that trachytic and porphyritic textures with phenocrysts of quartz, plagioclase, and K-feldspar which are embedded in a fine to medium grained groundmass. The accessory minerals of this rock consist of biotite, chlorite and opaque mineral.Geochemically, these volcanic rocks having calc-alkaline nature and classified as volcanic field (rhyolite) as well as volcanic arc setting. Based on the chondrite normalized spider diagram, LREE has enriched to HREE in this area which indicated negative Eu anomaly and subduction tectonic setting.

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

Atlantic Geology ◽

10.4138/atlgeol.2021.012 ◽

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.

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Tectonic setting and regional correlation of Ordovician–Silurian rocks of the Aspy terrane, Cape Breton Island, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e91-158 ◽

1991 ◽

Vol 28 (11) ◽

pp. 1769-1779 ◽

Cited By ~ 15

Author(s):

Sandra M. Barr ◽

Rebecca A. Jamieson

Keyword(s):

Tectonic Setting ◽

Volcanic Rocks ◽

Volcanic Arc ◽

Cape Breton Island ◽

Metasedimentary Rocks ◽

Tectonic History ◽

Cape Breton ◽

Metavolcanic Rocks ◽

High Grade Metamorphism ◽

Arc Setting

Interlayered mafic and felsic metavolcanic rocks and metasedimentary rocks of Ordovician to Silurian age are characteristic of the Aspy terrane of northwestern Cape Breton Island. These rocks were affected by medium- to high-grade metamorphism and were intruded by synkinematic granitoid orthogneisses during Late Silurian to Early Devonian times. They were intruded by posttectonic Devonian granitic plutons and experienced rapid Devonian decompression and cooling. The chemical characteristics of the mafic metavolcanic rocks indicate that they are tholeiites formed in a volcanic-arc setting. The volcanic rocks of the Aspy terrane differ from many other Silurian and Silurian–Devonian successions in Atlantic Canada, which have chemical and stratigraphic characteristics of volcanic rocks formed in extensional within-plate settings, and are somewhat younger than the Aspy terrane sequences. Aspy terrane units are most similar to Ordovician–Silurian volcanic and metamorphic units in southwestern Newfoundland, including the La Poile Group and the Port aux Basques gneiss. Together with other occurrences of Late Ordovician to Early Silurian volcanic-arc units, they indicate that subduction-related compressional tectonics continued into the Silurian in parts of the northern Appalachian Orogen. The complex Late Silurian – Devonian tectonic history of the Aspy terrane may reflect collision with the southeastern edge of a Grenvillian crustal promentory.

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

Economic Geology ◽

10.5382/econgeo.4806 ◽

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.

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Geochemical, mineralogical, and isotopic data relating to the origin and tectonic setting of the Rossland volcanic rocks, southern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e81-083 ◽

1981 ◽

Vol 18 (5) ◽

pp. 858-868 ◽

Cited By ~ 6

Author(s):

B. Beddoe-Stephens ◽

R. St J. Lambert

Keyword(s):

British Columbia ◽

Tectonic Setting ◽

Volcanic Rocks ◽

Major And Trace Elements ◽

Lower Jurassic ◽

Island Arcs ◽

Rock Types ◽

Tectonic Environment ◽

Isotopic Analyses ◽

Arc Setting

Bulk-rock and mineral chemical and isotopic analyses of Rossland volcanic rocks are used to infer the nature of the magma extruded in the Nelson–Rossland area of southern British Columbia during the Early Jurassic. Metamorphism of the volcanic rocks to subgreenschist and greenschist facies precludes use of mobile major and trace elements (e.g., Na, K, and Rb) as petrogenetic indicators. Data on immobile elements (Ti, Zr, and Y) and pyroxene compositions indicate that the volcanic rocks formed in a destructive-margin plate tectonic environment. Present-day 87Sr/86Sr ratios range from 0.70372 to 0.70480 but do not define an isochron. Corrected to Jurassic time, the initial ratios range from 0.70328 to 0.70404. Whole-rock δO18 values range from 7.9 to 11.6%, correlating inversely with metamorphic grade. Clinopyroxene δO18 of 4.8–6.5 is comparable with fresh clinopyroxenes from mafic rocks of mantle origin. In view of the preponderance of basaltic rather than andesitic rock types, and because of the nature of the lithologies within the volcanic rocks and associated sediments, an island-arc setting is indicated. The appearance of primary amphibole in basaltic members of the Rossland suite, and the occurrence of ankaramitic rocks, are thought to indicate a mildly alkalic rather than a subalkalic parent magma. Comparison of the Rossland volcanic rocks with those of recent island arcs, and consideration of the Upper Triassic – Lower Jurassic paleogeography in the Cordillera, suggest the rocks may be related to a localized oceanic basin, their extrusion being associated with faults bounding its western edge.

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Chapter 29: Grasberg Copper-Gold-(Molybdenum) Deposit: Product of Two Overlapping Porphyry Systems

10.5382/sp.23.29 ◽

2020 ◽

pp. 599-620

Author(s):

Clyde Leys ◽

Adam Schwarz ◽

Mark Cloos ◽

Sugeng Widodo ◽

J. Richard Kyle ◽

...

Keyword(s):

Tectonic Setting ◽

Volcanic Rocks ◽

Parental Magma ◽

Strike Slip ◽

Igneous Complex ◽

Steep Temperature Gradient ◽

Copper Gold ◽

Sulfide Melt ◽

Porphyry System ◽

Porphyry Systems

Abstract The supergiant Grasberg porphyry deposit in Papua, Indonesia (5.26 Gt @ 0.61% Cu and 0.57 g/t Au, with no cutoff applied) is hosted by the Grasberg Igneous Complex that fills an upward-flared diatreme ~1,800 m wide at the 4,250-m surface elevation. The Grasberg Igneous Complex is emplaced into folded and strike-slip faulted Tertiary and older sediments and comprises 3.6 to 3.3 Ma Dalam monzodiorite intrusions and subordinate volcanic rocks occupying much of the pipe, the central 3.2 Ma Main Grasberg intrusion, and the NW-SE-trending 3.2 to 3.0 Ma Kali dikes. The Grasberg Igneous Complex contains two porphyry systems: Gajah Tidur copper-(molybdenum) and Main Grasberg copper-gold. The Gajah Tidur intrusion belongs to the Dalam igneous group and is a 3.4 Ma porphyritic monzonite with its top at a 2,750-m elevation; it is overprinted by an extensive, domal, quartz stockwork, with a low-grade and intensely phyllic-altered core, surrounded by molybdenite-bearing veins, with a pre-Main Grasberg Re-Os age, as well as chalcopyrite and overprinting pyrite-covellite veins. The strongly potassic-altered, Main Grasberg monzodiorite porphyry extends from surface to the 2,700-m elevation and is overprinted by a cylindrical, ~1-km-diameter, intense quartz-magnetite stockwork cut by abundant chalcopyrite-bornite veins with rare molybdenite dated at 3.09 Ma. A 700-m-wide annulus of chalcopyrite overprinted by pyrite-covellite-mineralized phyllic alteration surrounds the stockwork. Altered and mineralized Main Grasberg and surrounding Dalam rocks were subsequently wedged apart by the largely unmineralized Kali dikes. Gold is predominantly associated with the Main Grasberg porphyry system where it occurs as 1- to 150-µm (avg ~15 µm) native gold inclusions within chalcopyrite and bornite. Melt and fluid inclusions from Main Grasberg stockwork quartz veins, which exhibit crack-seal textures, comprise K-feldspar-rich silicate melt, sulfide melt, virtually water-free salt melt, and coexisting hypersaline and vapor-rich fluids. Factors important in forming the Grasberg deposit include the following: (1) generation of highly oxidized fertile magma in a postsubduction tectonic setting; (2) efficient extraction of metals from the parental magma chamber; (3) prolonged maintenance of a fluid-accumulating cupola in a strike-slip structural setting that delivered multiple overlapping discharges of metal-rich fluid; (4) highly focused fluid flow into a narrow, permeable stockwork zone in which a steep temperature gradient enabled highly efficient copper and gold precipitation and led to high ore grades; (5) limited dilution by postmineral intrusions; (6) the youthfulness of the deposit minimized erosion and resulted in preservation of nearly all the high-grade Main Grasberg porphyry orebody; and (7) the proximity of the two porphyry centers enables them to be mined as a single, large deposit. The Gajah Tidur copper-(molybdenum) and Main Grasberg copper-gold porphyry centers overlap in space and formed within ~250,000 years of one another. However, their distinct metal endowment, depth of emplacement, and geometry indicate that they formed under different magmatic, hydrothermal, and structural conditions, which are the subject of ongoing research.

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From subduction to strike slip-related volcanism: insights from Sr, Nd, and Pb isotopes and geochronology of lavas from Sivas–Malatya region, Central Eastern Anatolia

International Journal of Earth Sciences ◽

10.1007/s00531-021-01995-0 ◽

2021 ◽

Author(s):

Paolo Di Giuseppe ◽

Samuele Agostini ◽

Gianfranco Di Vincenzo ◽

Piero Manetti ◽

Mehmet Yilmaz Savaşçın ◽

...

Keyword(s):

Middle Miocene ◽

Mantle Wedge ◽

Volcanic Rocks ◽

Volcanic Field ◽

Igneous Rocks ◽

Eastern Anatolia ◽

Calc Alkaline ◽

Alkaline Rocks ◽

Alkaline Magmas ◽

Central Eastern

AbstractAnatolia is characterised by a complex geodynamic evolution, mirrored by a wide spectrum of magmatism. Here, we investigated the timing and the geochemical/isotopic characters of the Miocene to Pliocene volcanism of Sivas–Malatya Region (Central Eastern Anatolia), and its relationships with local and regional tectonics. Na-alkaline basaltic lavas were emplaced during middle Miocene at Sivas (16.7–13.1 Ma), in the North, whilst transition from calc-alkaline to Na-alkaline rocks is observed at Yamadağ and Kepez Dağ volcanic complexes. Calc-alkaline products erupted during early to middle Miocene, and more precisely from 19.5 to 13.6 Ma at Yamadağ and from 16.4 to 13.5 Ma at Kepez Dağ, with final Na-alkaline activity of the Arguvan volcanic field lasting till late Miocene (15.7–10.6 Ma). Volcanism renewed during the Pliocene in the Kangal (5.9–4.0 Ma) volcanic field with the emission of K-alkaline igneous rocks. Mafic calc-alkaline and Na-alkaline rocks partially overlap in age but can be easily distinguished by their petrochemical characters. Mafic calc-alkaline igneous rocks show typical subduction-related petrological and geochemical affinities. They are both two-pyroxene or clinopyroxene and amphibole-bearing rocks, characterised by high LILE/HFSE values, with variable 87Sr/86Sri (0.70396–0.70539) and 143Nd/144Ndi (0.51260–0.51287). Mafic Na-alkaline igneous rocks are characterised by big olivine phenocrysts and show intraplate geochemical flavours, although some LILE depletion with respect to HFSE as well as variable 87Sr/86Sri (0.70347–0.70553) and 143Nd/144Ndi (0.51261–0.51291) isotopic compositions are present. These characteristics are suggestive for the occurrence, at some stage of their genesis, of a possible interaction with subduction-related reservoirs. The Kangal K-alkali basalts still show intraplate-like petrological and geochemical affinities with LILE/HFSE ratios similar to those of the Miocene Na-alkaline rocks, and largely variable 87Sr/86Sri (0.70425–0.70520) and 143Nd/144Ndi (0.51262–0.51277) isotopic compositions, overlapping the arrays observed in the earlier stages of volcanism. A general transition from calc-alkaline to Na-alkaline volcanic rocks is observed with time, according to the evolution of the geodynamics of the Anatolia region. Early to middle Miocene calc-alkaline magmas were derived by partial melting of the mantle wedge delimited by the subduction of the last oceanic branch of Neotethys. The Na-alkaline magmas, on the other hand, were generated within the asthenospheric mantle beneath the slab and migrated through slab tears into the mantle wedge where they mixed with subduction-related components. The subduction-related component decreased with time and transitional magmas are found in the youngest activity of Yamadağ and Kepez Dağ, shortly followed by clear within-plate lavas formed in the Arguvan volcanic field. The appearance of the youngest K-alkaline volcanic rocks in the Kangal basin represents an abrupt change in the magma supply at depth, although continental crustal contamination en-route to the surface played an important role in their genesis.

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Stratigraphic evolution of the Paleozoic Stikine assemblage in the Stikine and Iskut rivers area, northwestern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e91-087 ◽

1991 ◽

Vol 28 (6) ◽

pp. 958-972 ◽

Cited By ~ 14

Author(s):

Derek A. Brown ◽

James M. Logan ◽

Michael H. Gunning ◽

Michael J. Orchard ◽

Wayne E. Bamber

Keyword(s):

Middle Devonian ◽

Tectonic Setting ◽

Volcanic Rocks ◽

Upper Permian ◽

Lower Permian ◽

Early Permian ◽

Lower Carboniferous ◽

Modern Analogue ◽

Arc Setting ◽

Coralline Limestone

The Stikine assemblage, the "basement" of Stikinia, extends 500 km along the western flank of the Intermontane Belt, east of younger Coast Belt plutons. Four different stratigraphic successions are characteristic of Lower to Middle Devonian, Carboniferous and Permian rocks in the Stikine and Iskut rivers area. West of Forrest Kerr Creek are penetratively deformed Lower to Middle Devonian island-arc volcaniclastic rocks, coralline limestone, and felsic tuff. Fringing carbonate buildups in an arc setting are best illustrated in the sequence at Round Lake where Lower Carboniferous mafic-dominated, bimodal submarine volcanic rocks grade upward into two distinctive coarse echinoderm limestone units and medial siliceous siltstone and limestone conglomerate. Conodont colour alteration indices for Lower Carboniferous rocks near Newmont Lake indicate an anomalously low-temperature thermal history. Upper Carboniferous–Permian polymictic volcanic conglomerate and Lower Permian limestone overlie these strata there. The Scud River sequence is distinguished by subgreenschist- to greenschist-grade Carboniferous(?) volcanic and sedimentary rocks overlain by a structurally thickened package (greater than 1000 m) of Lower Permian limestone. Local calcalkaline pyroclastic rocks interfinger with limestone near the top of the Scud River sequence. Basinal, shelf, and shallow-water carbonate facies developed in the Early Permian, giving way to calcalkaline volcanism in Late Permian followed by deposition of deep-water chert and argillite.The tectonic setting during the Devonian and Carboniferous is comparable with modern Pacific volcanic arcs and atolls, but there is no modern analogue for the shelf-carbonate accumulation during the Early Permian which characterizes the Stikine assemblage and permits Cordilleran-scale correlations. Permian fusulinid and coral species have very close affinity to those of the McCloud Limestone of the eastern Klamath Mountains, California. Other geologic events common to both Stikinia and the Eastern Klamath terrane are Devonian limestone breccia deposition, Lower Permian limestone accumulation with McCloud faunal affinity, Carboniferous and Permian calcalkaline volcanism, and Upper Permian tuffaceous limestone. Stratigraphic differences include the absence of quartz detritus in Devonian strata and lack of thick Upper Permian volcanic rocks in the Stikine River area.

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