Magmatic evidence for Late Carboniferous-Early Permian slab breakoff and extension of the southern Mongolia collage system in Central Asia

2021 ◽  
Author(s):  
Hai Zhou ◽  
Guochun Zhao ◽  
Donghai Zhang
Keyword(s):  
Subduction Zones ◽  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Ocean Basin ◽  
Magma Source ◽  
Central Asian ◽  
Slab Rollback ◽  
Slab Breakoff ◽  
Subduction Fluids ◽  
Arc Setting

<p>Oceanic subduction and its last underthrusted part can both triggers arc-like magmatism. As the existence of multi-subduction zones in the Central Asian Orogenic Belt, controversy still surrounds on when and especially how the subduction of the (Paleo-Asian Ocean) PAO terminated. We present geochronological, geochemical, and Lu-Hf isotopic data for a suite of basalt-andesites, dacite-rhyolites and later trachyandesite-mugearitic dykes from the Khan-Bogd area in the Gobi Tianshan Zone (GTZ) of the southern Mongolia. U-Pb dating of zircons indicate the basalt-andesites and dacite-rhyolites were formed at ~334-338 Ma, and the dykes at ~300 Ma. These Early Carboniferous volcanic rocks display high U/Th, Ba/Th, low La/Sm and variable Zr/Nb ratios, implying the involvement of subduction fluids or sediment melt. They display arc geochemical features such as calc-alkaline and metaluminous nature and positive Ba and U and negative Nb, Ta and Ti anomalies. Moreover, their continental geochemical signals (e.g. positive Pb, K anomalies) and some old captured zircons implying a continental arc setting. Comparatively, the ~300 Ma dykes are characterized by high alkaline contents, which are common for coeval (~320-290 Ma) and widespread post-subductional granites there. Given a mainly crust-derived magma source for those granites, these dykes likely reflect a mantle disturbance due to: (1) their relative low SiO<sub>2 </sub>(51.71-55.85 wt. %) and high Mg# (40.3-67.3) values, and (2) positive zircon Ɛ<sub>Hf</sub>(t) (most > 12). Considering a slab rollback model during the Carboniferous and Triassic, the mantle disturbance was possibly induced by the oceanic slab breakoff. Combined with previous work, this ~320-290 Ma slab breakoff-induced extension marks the closure of a wide secondary ocean (North Tianshan-Hegenshan ocean) north of the main ocean basin of the PAO. This research was financially supported by NSFC Projects (41730213, 42072264, 41902229, 41972237) and Hong Kong RGC GRF (17307918).</p>

Geochemistry of Sainte-Marguerite volcanic rocks: implications for the evolution of Silurian–Devonian volcanism in the Gaspé Peninsula

2008 ◽  
Vol 45 (1) ◽  
pp. 15-29 ◽  
Author(s):  
Alan D’hulst ◽  
Georges Beaudoin ◽  
Michel Malo ◽  
Marc Constantin ◽  
Pierre Pilote
Keyword(s):  
Lower Devonian ◽  
Volcanic Rocks ◽  
Magma Source ◽  
Volcanic Arc ◽  
Lower Silurian ◽  
Trace Element Signature ◽  
Arc Setting ◽  
Back Arc ◽  
Gaspe Peninsula ◽  
Gaspé Peninsula

The Lower Devonian Sainte-Marguerite volcanic rocks are part of a Silurian–Devonian volcanic sequence deposited between the Taconian and Acadian orogenies in the Gaspé Peninsula, Quebec, Canada. The Sainte-Marguerite unit includes basaltic and dacitic lava flows with calc-alkaline and volcanic-arc affinities. Such affinities are also recorded by the trace-element signature in Lower Silurian and most Lower Devonian volcanic units of the Gaspé Peninsula. However, most of the other Silurian–Devonian volcanic rocks occurring in the Gaspé Peninsula have been previously interpreted to have erupted in an intracontinental setting. A back-arc setting for the Gaspé Peninsula between the Taconian and Acadian orogenies could account for these subduction volcanic-arc signatures, though a metasomatized lithospheric mantle magma source, unrelated to subduction, cannot be excluded. Lower Silurian and Lower Devonian volcanic rocks in the central part of the Gaspé Peninsula show an arc affinity, whereas Upper Silurian and Lower to Middle Devonian volcanic rocks, located in the south and north of the Gaspé Peninsula, respectively, show a within-plate affinity. The Lower Devonian Archibald Settlement and Boutet volcanic rocks of the southern and northern Gaspé Peninsula, respectively, show a trend toward a within-plate affinity. This suggests that within-plate volcanism migrated from south to north through time in an evolving back-arc environment and that the subduction signature of Lower Silurian and Lower Devonian rocks results from a source that melted only under the central part of the Gaspé Peninsula.

Early Carboniferous volcanic rocks of West Junggar in the western Central Asian Orogenic Belt: implications for a supra-subduction system

2014 ◽  
Vol 56 (7) ◽  
pp. 823-844 ◽  
Author(s):  
Gaoxue Yang ◽  
Yongjun Li ◽  
Inna Safonova ◽  
Shanxin Yi ◽  
Lili Tong ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Central Asian ◽  
West Junggar ◽  
Subduction System

scholarly journals Petrology and Geochemical Features of Semporna Volcanic Rocks, South-east Sabah, Malaysia

2021 ◽  
Vol 50 (1) ◽  
pp. 9-21
Author(s):  
Elvaene James ◽  
Azman Abdul Ghani ◽  
Oluwatoyin O. Akinola ◽  
Junaidi Asis
Keyword(s):  
Volcanic Rocks ◽  
Geochemical Data ◽  
Magma Source ◽  
Light Rare Earth ◽  
Calc Alkaline ◽  
Ce Anomaly ◽  
Arc Setting ◽  
A Minor ◽  
Light Rare Earth Elements

The volcanic rocks in Semporna Peninsula, Sabah, Malaysia forms parts of the Miocene subjected slab during the Miocene-Pliocene orogeny. This study presents new petrographic and geochemical data of volcanic rocks in Semporna area. The volcanic rocks range in composition from basaltic andesite, andesite, dacite to rhyolite, with most of the volcanic shows calc-alkaline affinity with a minor tholeiitic feature. The trace elements shows enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE) suggesting that the volcanic rocks have similar geochemical patterns and might come from similar magma source. The petrochemical data suggests that volcanic rocks of Semporna shows characteristic of subduction zone (negative Nb, Ta, and Ti). Decreasing magnitude of Europium anomalies from intermediate to acid lavas suggests an important role of plagioclase in the fractional crystallization. Negative Ce anomaly in part of Semporna volcanic rocks suggest that those volcanic rocks may related with emergence of oxygenated deep-sea environment. Tectonic diagrams showed that the Semporna volcanic rocks were formed in an island arc setting.

A Late Miocene magmatic flare-up in West Sulawesi triggered by Banda slab rollback

2020 ◽  
Vol 132 (11-12) ◽  
pp. 2517-2528
Author(s):  
Xiaoran Zhang ◽  
Chia-Yu Tien ◽  
Sun-Lin Chung ◽  
Adi Maulana ◽  
Musri Mawaleda ◽  
...  
Keyword(s):  
Late Miocene ◽  
Source Region ◽  
River Sediments ◽  
Volcanic Rocks ◽  
Detrital Zircons ◽  
Magma Source ◽  
Magmatic Rocks ◽  
High K ◽  
Slab Rollback ◽  
T Values

Abstract Cenozoic magmatism occurs throughout West Sulawesi, Indonesia, yet its detailed evolution remains enigmatic due mainly to the scarcity of precise dating. Here, we report new whole-rock geochemical and zircon U-Pb-Hf isotopic data of plutonic/volcanic rocks and river sediments from West Sulawesi to constrain the petrogenesis and magmatic tempo. The magmatic rocks are intermediate to felsic (SiO2 = 58.1–68.0 wt%), high-K calc-alkaline to shoshonitic (K2O = 2.2–6.0 wt%), metaluminous to weakly peraluminous, and I-type in composition. Trace element concentrations and ratios (e.g., Nb/U = 1.7–4.3 and Ti/Zr < 28), along with negative zircon εHf(t) values (–17.0 to –0.4) and old crustal model ages (TDMC = 2.1–1.1 Ga), indicate a dominant magma source region from the underlying continental crystalline basement. U-Pb dating on zircons from ten magmatic rocks yielded weighted mean 206Pb/238U ages of 7.2–6.1 Ma, best representing the crystallization ages of host magmas, further consistent with the prominent age peaks (7.3–6.3 Ma) defined by detrital zircons from four sedimentary samples. Our new data, combined with available results, allow the identification of a noticeable climax of magmatism (flare-up) at ca. 7–6 Ma, forming a continuous magmatic belt throughout West Sulawesi. Given the absence of contemporaneous subduction and the coincidence of incipient opening of the South Banda Basin during ca. 7.15–6.5 Ma, the Late Miocene magmatic flare-up in West Sulawesi and coeval regional extension in eastern Indonesia are attributed to a resumed episode of Banda slab rollback.

Petrochronology resolves the multi-Myr crustal scale magmatic evolution of an arc segment resulting in porphyry copper formation

2020 ◽  
Author(s):  
Simon Large ◽  
Yannick Buret ◽  
Tom Knott ◽  
Jamie Wilkinson
Keyword(s):  
San Francisco ◽  
Subduction Zones ◽  
Porphyry Copper ◽  
Empirical Studies ◽  
Volcanic Rocks ◽  
Geochemical Evolution ◽  
Magma Source ◽  
Magmatic Evolution ◽  
Ore Formation ◽  
The North

<p>The crustal-scale magmatic systems of Andean-style subduction zones produce thick volcanic deposits and abundant plutons emplaced into the upper crust. They can also result in the formation of spatially- and temporally-restricted, economically-important porphyry Cu deposits. Understanding the magmatic and tectonic processes acting within an arc segment, including changes in the fractionating assemblage, subduction angle, chemistry of slab-derived melts or water content, is essential to develop and refine quantitative models for the formation of these deposits. Specific geochemical signatures (e.g. elevated Sr/Y) are associated with magmas that source the metals and volatiles to form porphyry deposits based on empirical studies. However, it is unclear whether this geochemical signature is the result of geologically rapid processes resulting in sudden shifts in magma chemistry or whether they are the result of protracted changes within the crustal-scale magmatic system over extended timescales.</p><p>In this study we examine the magmatic evolution of the Rio Blanco-Los Bronces district, ~30 km northeast of Santiago, Chile, which is host to the Earth’s largest resource of Cu. Eocene to Early Miocene volcanic rocks were intruded by the Miocene San Francisco Batholith that, in turn, partially hosts intrusions related to the Late Miocene to Early Pliocene Rio Blanco-Los Bronces porphyry deposit cluster. We apply a combination of whole-rock and zircon geochemistry, isotopic tracing and LA-ICP-MS U-Pb geochronology to the intrusive rock suite of the district to provide temporally- constrained geochemical information over the entire duration of batholith assembly and ore formation.</p><p>U-Pb geochronology reveals incremental assembly of the San Francisco Batholith by individual magma batches over >13Myr (~17 – 4 Ma), with ore formation occurring in discrete pulses in the last 3 Myr before cessation of intrusive activity within the district. Temporally-resolved whole-rock major element chemistry shows that the progressively-emplaced magmas were not sourced from a common, continuously differentiating, lower crustal magma reservoir. Evolving trace element signatures over the recorded timescale indicate that magmas were sourced from progressively deeper fractional crystallisation reservoir(s) that exhibited increasing water contents. The geochemical evolution recorded over the entire investigated 13 Myr timescale could reflect geodynamic changes linked to the ingression of the subducting Juan Fernandez ridge from the north. However, within this continuous evolution, the most prominent geochemical shifts occur over a much shorter timescale of a few Myr, directly preceding economic ore-formation, implicating an additional mechanism for controlling the metallogenic potential of the magma source.</p><p> </p><p> </p><p> </p>

Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996

1997 ◽  
pp. 66-74
Author(s):  
Henrik Stendal ◽  
Wulf Mueller ◽  
Nicolai Birkedal ◽  
Esben I. Hansen ◽  
Claus Østergaard
Keyword(s):  
Mineral Exploration ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Field Work ◽  
Igneous Rocks ◽  
Border Zone ◽  
The South ◽  
East Greenland ◽  
North West ◽  
Arc Setting

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Stendal, H., Mueller, W., Birkedal, N., Hansen, E. I., & Østergaard, C. (1997). Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996. Geology of Greenland Survey Bulletin, 176, 66-74. https://doi.org/10.34194/ggub.v176.5064 _______________ The multidisciplinary SUPRASYD project (1992–96) focused on a regional investigation of the Palaeoproterozoic Ketilidian orogenic belt which crosses the southern tip of Greenland. Apart from a broad range of geological and structural studies (Nielsen et al., 1993; Garde & Schønwandt, 1994, 1995; Garde et al., 1997), the project included a mineral resource evaluation of the supracrustal sequences associated with the Ketilidian orogen (e.g. Mosher, 1995). The Ketilidian orogen of southern Greenland can be divided from north-west to south-east into: (1) a border zone in which the crystalline rocks of the Archaean craton are unconformably overlain by Ketilidian supracrustal rocks; (2) a major polyphase pluton, referred to as the Julianehåb batholith; and (3) extensive areas of Ketilidian supracrustal rocks, divided into psammitic and pelitic rocks with subordinate interstratified mafic volcanic rocks (Fig. 1). The Julianehåb batholith is viewed as emplaced in a magmatic arc setting; the supracrustal sequences south of the batholith have been interpreted as either (1) deposited in an intra-arc and fore-arc basin (Chadwick & Garde, 1996), or (2) deposited in a back-arc or intra-arc setting (Stendal & Swager, 1995; Swager, 1995). Both possibilities are plausible and infer subduction-related processes. Regional compilations of geological, geochemical and geophysical data for southern Greenland have been presented by Thorning et al. (1994). Mosher (1995) has recently reviewed the mineral exploration potential of the region. The commercial company Nunaoil A/S has been engaged in gold prospecting in South Greenland since 1990 (e.g. Gowen et al., 1993). A principal goal of the SUPRASYD project was to test the mineral potential of the Ketilidian supracrustal sequences and define the gold potential in the shear zones in the Julianehåb batholith. Previous work has substantiated a gold potential in amphibolitic rocks in the south-west coastal areas (Gowen et al., 1993.), and in the amphibolitic rocks of the Kutseq area (Swager et al., 1995). Field work in 1996 was focused on prospective gold-bearing sites in mafic rocks in South-East Greenland. Three M.Sc. students mapped showings under the supervision of the H. S., while an area on the south side of Kangerluluk fjord was mapped by H. S. and W. M. (Fig. 4).

Supplemental Material: Tectonic origin of the Bainaimiao arc terrane in the southern Central Asian orogenic belt: Evidence from sedimentary and magmatic rocks in the Damao region

2020 ◽  
Author(s):  
Hai Zhou ◽  
Guochun Zhao ◽  
et al.
Keyword(s):  
Volcanic Rocks ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Isotopic Data ◽  
Magmatic Rocks ◽  
Central Asian ◽  
Southern Central ◽  
Samples And Sampling ◽  
Tectonic Origin

Table S1: Summary of the samples and sampling positions in this study (sampling sites are marked in Fig. 3); Table S2: U-Pb age data for zircons of (meta-)sedimentary and volcanic rocks in this study; Table S3: Lu-Hf isotopic data for zircons of (meta-)sedimentary and volcanic rocks in this study.

scholarly journals Gold in Mineralized Volcanic Systems from the Lesser Khingan Range (Russian Far East): Textural Types, Composition and Possible Origins

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 103
Author(s):  
Nikolai Berdnikov ◽  
Victor Nevstruev ◽  
Pavel Kepezhinskas ◽  
Ivan Astapov ◽  
Natalia Konovalova
Keyword(s):  
Iron Oxide ◽  
Subduction Zones ◽  
Gold Mineralization ◽  
Russian Far East ◽  
Far East ◽  
Volcanic Rocks ◽  
Liquid Immiscibility ◽  
Explosive Volcanism ◽  
Deep Roots ◽  
Scientific Debate

While gold partitioning into hydrothermal fluids responsible for the formation of porphyry and epithermal deposits is currently well understood, its behavior during the differentiation of metal-rich silicate melts is still subject of an intense scientific debate. Typically, gold is scavenged into sulfides during crustal fractionation of sulfur-rich mafic to intermediate magmas and development of native forms and alloys of this important precious metal in igneous rocks and associated ores are still poorly documented. We present new data on gold (Cu-Ag-Au, Ni-Cu-Zn-Ag-Au, Ti-Cu-Ag-Au, Ag-Au) alloys from iron oxide deposits in the Lesser Khingan Range (LKR) of the Russian Far East. Gold alloy particles are from 10 to 100 µm in size and irregular to spherical in shape. Gold spherules were formed through silicate-metal liquid immiscibility and then injected into fissures surrounding the ascending melt column, or emplaced through a volcanic eruption. Presence of globular (occasionally with meniscus-like textures) Cu-O micro-inclusions in Cu-Ag-Au spherules confirms their crystallization from a metal melt via extremely fast cooling. Irregularly shaped Cu-Ag-Au particles were formed through hydrothermal alteration of gold-bearing volcanic rocks and ores. Association of primarily liquid Cu-Ag-Au spherules with iron-oxide mineralization in the LKR indicates possible involvement of silicate-metallic immiscibility and explosive volcanism in the formation of the Andean-type iron oxide gold-copper (IOCG) and related copper-gold porphyry deposits in the deeper parts of sub-volcanic epithermal systems. Thus, formation of gold alloys in deep roots of arc volcanoes may serve as a precursor and an exploration guide for high-grade epithermal gold mineralization at shallow structural levels of hydrothermal-volcanic environments in subduction zones.

Constraints on the formation of the giant Daheishan porphyry Mo deposit (NE China) from whole-rock and accessory mineral geochemistry

2021 ◽  
Author(s):  
Kai Xing ◽  
Qihai Shu ◽  
David R Lentz
Keyword(s):  
High Water ◽  
Accessory Mineral ◽  
Ne China ◽  
Accessory Minerals ◽  
Slab Rollback ◽  
Continental Arc ◽  
Arc Setting ◽  
Porphyry Mo Deposit ◽  
T Values ◽  
Water Contents

Abstract There are more than 90 porphyry (or skarn) Mo deposits in northeastern China with Jurassic or Cretaceous ages. These are thought to have formed mainly in a continental arc setting related to the subduction of the Paleo-Pacific oceanic plate in the Jurassic and subsequent slab rollback in the early Cretaceous. The Jurassic Daheishan porphyry Mo deposit is one of the largest Mo deposits in NE China, which contains 1.09 Mt Mo with an average Mo grade of 0.07%. To better understand the factors that could have controlled Mo mineralization at Daheishan, and potentially in other similar porphyry Mo deposits in NE China, the geochemical and isotopic compositions of the ore-related granite porphyry and biotite granodiorite, and the magmatic accessory minerals apatite, titanite and zircon from the Daheishan intrusions, were investigated so as to evaluate the potential roles that magma oxidation states, water contents, sulfur and metal concentrations could have played in the formation of the deposit. Magmatic apatite and titanite from the causative intrusions show similar εNd(t) values from -1.1 to 1.4, corresponding to TDM2 ages ranging from 1040 to 840 Ma, which could be accounted for by a mixing model through the interaction of mantle-derived basaltic melts with the Precambrian lower crust. The Ce and Eu anomalies of the magmatic accessory minerals have been used as proxies for magma redox state, and the results suggest that the ore-forming magmas are highly oxidized, with an estimated ΔFMQ range of + 1.8 to + 4.1 (+2.7 in average). This is also consistent with the high whole-rock Fe2O3/FeO ratios (1.3–26.4). The Daheishan intrusions display negligible Eu anomalies (Eu/Eu* = 0.7–1.1) and have relatively high Sr/Y ratios (40–94) with adakitic signatures; they also have relatively high Sr/Y ratios in apatite and titanite. These suggest that the fractionation of amphibole rather than plagioclase is dominant during the crystallization of the ore-related magmas, which further indicates a high magmatic water content (e.g., >5 wt%). The magmatic sulfur concentrations were calculated using available partitioning models for apatite from granitoids, and the results (9–125 ppm) are indistinguishable from other mineralized, subeconomic and barren intrusions. Furthermore, Monte Carlo modelling has been conducted to simulate the magmatic processes associated with the formation of the Daheishan Mo deposit, and the result reveals that a magma volume of ∼280 km3 with ∼10 ppm Mo was required to form the Mo ores containing 1.09 Mt Mo in Daheishan. The present study suggests that a relatively large volume of parental magmas with high oxygen fugacities and high water contents is essential for the generation of a giant porphyry Mo deposit like Daheishan, whereas a specific magma composition (e.g., with unusually high Mo and/or S concentrations), might be less critical.

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