scholarly journals Geochemical and Sr-Nd-Pb-Hf Isotopic Characteristics of Muchen Pluton in Southeast China, Constrain the Petrogenesis of Alkaline A-Type Magma

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 80
Author(s):  
Haiyang Yan ◽  
Fangyue Wang ◽  
Hai-Ou Gu ◽  
He Sun ◽  
Can Ge
Keyword(s):  
Early Cretaceous ◽  
Lithospheric Mantle ◽  
Magma Ascent ◽  
Geodynamic Setting ◽  
Southeast China ◽  
Geochemical Properties ◽  
Arc Setting ◽  
Back Arc ◽  
T Values

We present comprehensive petrological, major-trace element, in situ zircon U-Pb dating and Sr-Nd-Pb isotopic data for Muchen granitoid (western Zhejiang Province, Southeast China), to constrain the petrogenesis of alkaline A-type granites and the geodynamic setting of Southeast China in the Early Cretaceous. The Early Cretaceous Muchen quartz monzonite yielded zircon U-Pb crystallization ages of 111.3 ± 0.7 Ma and is metaluminous to weakly peraluminous with SiO2 contents ranging from 59 to 69 wt.%, and can be classified as alkaline A-type granitoid. The quartz monzonites have low (87Sr/86Sr)i values (0.7052 to 0.7061) and high εNd(t) values (−2.6 to −2.0), similar to nearby coeval mafic rocks that have been proposed to be derived from the enriched lithospheric mantle. The high Nb/Ta ratios (16.7 to 30.1, average 21.8) and low Nb/U ratios (as low as 3.5) indicate the involvement of slab-derived melt and fluids in this mantle. These geochemical properties of the Muchen quartz monzonites indicated that they might be from a phlogopite-bearing and rutile-rich subduction-modified subcontinental lithospheric mantle, and underwent strong fractional crystallization of olivine + orthopyroxene + plagioclase during magma ascent. The low Mg# values of these alkaline rocks (<30 mostly) may indicate a low-pressure source in a back-arc setting. The early Cretaceous alkaline granitoids in Southeast China are related to the continental back-arc setting caused by deep angle subduction of the paleo-Pacific plate.

Geodynamic setting, crustal architecture, and VMS metallogeny of ca. 2720 Ma greenstone belt assemblages of the northern Wawa subprovince, Superior Province

2015 ◽  
Vol 52 (3) ◽  
pp. 196-214 ◽  
Author(s):  
Robert W.D. Lodge ◽  
Harold L. Gibson ◽  
Greg M. Stott ◽  
James M. Franklin ◽  
George J. Hudak
Keyword(s):  
Trace Element ◽  
Greenstone Belt ◽  
Tectonic Setting ◽  
Geodynamic Setting ◽  
Trace Element Geochemistry ◽  
Superior Province ◽  
Suprasubduction Zone ◽  
Greenstone Belts ◽  
Arc Setting ◽  
Back Arc

The greenstone belts along the northern margin of the Wawa subprovince of the Superior Province (Vermilion, Shebandowan, Winston Lake, Manitouwadge) formed at ca. 2720 Ma and have been interpreted to be representative of a rifted-arc to back-arc tectonic setting. Despite a common inferred tectonic setting and broad similarities, these greenstone belts have a significantly different metallogeny as evidenced by different endowments in volcanogenic massive sulphide (VMS), magmatic sulphide, and orogenic gold deposits. In this paper, we examine differences in geodynamic setting and crustal architecture as they pertain to the metallogeny of each greenstone belt by characterizing the regional-scale trace-element and isotopic (Nd and Pb) geochemistry of each belt. The trace-element geochemistry of the Vermilion greenstone belt (VGB) shows evidence for a transition from arc-like to back-arc mafic rocks in the Soudan belt to plume-driven rifted arcs in the ultramafic-bearing Newton belt. The Shebandowan greenstone belt (SGB) has a significant proportion of calc-alkalic, arc-like basalts, intermediate lithofacies, and high-Mg andesites, which are characteristic of low-angle, “hot” subduction. Extensional settings within the SGB are plume-driven and associated with komatiitic ultramafic and mid-ocean ridge basalt (MORB)-like basalts. The Winston Lake greenstone belt (WGB) is characterized by a transition from calc-alkalic, arc-like basalts to back-arc basalts upward in the strata and is capped by alkalic ocean-island basalt (OIB)-like basalts. This association is consistent with plume-driven rifting of a mature arc setting. Each of the VGB, SGB, and WGB show some isotopic evidence for the interaction with a juvenile or slightly older differentiated crust. The Manitouwadge greenstone belt (MGB) is characterized by isotopically juvenile, bimodal, tholeiitic to transitional volcanic lithofacies in a back-arc setting. The MGB is the most isotopically juvenile belt and is also the most productive in terms of VMS mineralization. The Zn-rich VMS mineralization within the WGB suggests a relatively lower-temperature hydrothermal system, possibly within a relatively shallow-water environment. The Zn-dominated and locally Au-enriched VMS mineralization, as well as mafic lithofacies and alteration assemblages, are characteristic of relatively shallower-water deposition in the VGB and SGB, and indicate that the ideal VMS-forming tectonic condition may have been compromised by a shallower-water depositional setting. However, the thickened arc crust and compressional tectonics of the SGB suprasubduction zone during hot subduction may have provided a crustal setting more favourable for the magmatic Ni–Cu sulphide and relative gold endowment of this belt.

Geochemistry, geochronology and Sr–Nd–Hf isotopes of two types of Early Cretaceous granite porphyry dykes in the Sulu orogenic belt, eastern China

2020 ◽  
Vol 57 (2) ◽  
pp. 249-266 ◽  
Author(s):  
Song-Jie Wang ◽  
Hans-Peter Schertl ◽  
Yu-Mao Pang
Keyword(s):  
Early Cretaceous ◽  
Eastern China ◽  
Orogenic Belt ◽  
Granite Porphyry ◽  
Granitic Rocks ◽  
Geodynamic Setting ◽  
Type I ◽  
Yangtze Craton ◽  
T Values ◽  
Sulu Orogenic Belt

Late Mesozoic granitic rocks are widely distributed in the Sulu orogenic belt, but the source, tectonic affinity, and associated geodynamic setting that produced the respective magmas remain controversial. To provide insights into these issues, we present field-based petrological, whole-rock major and trace element and Sr–Nd isotope geochemical, zircon U–Pb dating, and Lu–Hf isotope studies on two types of granite porphyry dykes that are newly recognized from the central Sulu belt. U–Pb dating of magmatic zircons from both types yields consistent ages that vary between 124 ± 2 and 118 ± 2 Ma, constraining the timing of intrusion as Early Cretaceous. The granitic rocks have high-K calc-alkaline peraluminous compositions with low Mg# values and are characterized by fractionated rare earth element patterns with strong depletion in high field strength elements. Compared with type I of the granite porphyry dykes, type II exhibits higher SiO2 but slightly lower Na2O and K2O abundances, contains higher Rb/Sr and 87Sr/86Sr ratios, and shows more pronounced negative Eu, Sr, and Ba anomalies. Both types I and II have high initial 87Sr/86Sr ratios of 0.709–0.711 and negative εNd(t) values of −19.8 to −18.4. The magmatic zircons possess negative εHf(t) values of −29.1 to −20.8, with mostly Neoarchean Hf model ages of 3001–2478 Ma. These features, together with the presence of Neoproterozoic inherited zircons, indicate that the two types of granite porphyries successively crystallized from a joint granite magma that derived from partial melting of the continental crust of the Yangtze Craton. Therefore, an interrelationship between the granite porphyry dykes and massive magmatic granitoids from adjacent regions in the Sulu belt may be documented, recording evidence of a joint ancient crustal reworking and recycling in a fossilized continental subduction zone during the Early Cretaceous.

Geochemistry, geochronology, and geodynamic setting of Ni–Cu ± PGE mineral prospects hosted by mafic and ultramafic intrusions in the Portneuf–Mauricie Domain, Grenville Province, QuebecGéologie Québec Contribution 8439-2008-2009-5. Geological Survey of Canada Contribution 20080511.

2009 ◽  
Vol 46 (5) ◽  
pp. 331-353 ◽  
Author(s):  
A.-A. Sappin ◽  
M. Constantin ◽  
T. Clark ◽  
O. van Breemen
Keyword(s):  
Trace Element ◽  
Crustal Contamination ◽  
Island Arc ◽  
Geodynamic Setting ◽  
Grenville Province ◽  
Magmatic Arc ◽  
Andean Type ◽  
Trace Element Signature ◽  
Arc Setting ◽  
Back Arc

The Portneuf–Mauricie Domain in the Grenville Province consists of the Montauban group rocks (1.45 Ga), intruded by the La Bostonnais complex plutons (1.40–1.37 Ga). This assemblage was formed in a magmatic arc setting. The sequence was intruded by mafic–ultramafic tholeiitic plutons, some of which host Ni–Cu ± PGE (platinum group element) prospects. U–Pb zircon ages determined from these plutons indicate that the mineralized intrusions were emplaced between 1.40 and 1.39 Ga and that they are coeval with the La Bostonnais complex plutons. The Ni–Cu ± PGE-bearing intrusions have mature island-arc trace element signatures, with strong chemical evidence for differentiation (Mg# and Cr content; MgO and TiO2 contents) and crustal contamination (enrichments in K2O, Rb, Ba, Th, and light rare-earth elements; Th/Yb and Ta/Yb ratios). However, one intrusion displays a back-arc trace element signature associated with evidence for weak crust assimilation. The evolution of the Portneuf–Mauricie Domain is interpreted as follows: (1) 1.45 Ga — Northwesterly directed Andean-type subduction beneath the Laurentian craton margin. Furthermore, northwest-dipping intraoceanic subduction offshore from the continent formed the Montauban island arc. (2) 1.45 to 1.40 Ga — Andean-type subduction led to the formation of a back-arc basin behind the Montauban arc. (3) 1.40 Ga — Emplacement of the La Bostonnais complex plutons, some hosting Ni–Cu ± PGE prospects, into the Montauban arc. (4) 1.39 Ga — Subduction beneath Laurentia led to arc–continent collision and to closure of the back-arc basin. Intrusion of the Ni–Cu ± PGE-bearing plutons ceased. (5) 1.37 Ga — Intrusion of all La Bostonnais complex plutons ceased.

scholarly journals Petrogenesis of the Early Cretaceous Hongshan Complex in the Southern Taihang Mountains: Constraints from Element Geochemistry, Zircon U-Pb Geochronology and Hf Isotopes

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1111
Author(s):  
Xiaolei Chu ◽  
Jinggui Sun ◽  
Fanting Sun ◽  
Yanxiong Mei ◽  
Yang Liu ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
North China Craton ◽  
Lithospheric Mantle ◽  
Lower Crust ◽  
North China ◽  
Coarse Grained ◽  
Geochemical Data ◽  
Fine Grained ◽  
The North ◽  
T Values

The Hongshan complex, located in the southern part of the Taihang Mountains in the central part of the North China Craton, consists of syenite stocks (including fine-grained biotite aegirine syenite, medium-grained aegirine gabbro syenite, coarse-grained aegirine gabbro syenite, syenite pegmatite, and biotite syenite porphyry), with monzo-diorite and monzo-gabbro dikes. This paper presents zircon U-Pb ages and Hf isotope data and whole-rock geochemical data from the Hongshan complex. LA–ICP-MS zircon U–Pb age from the fine-grained biotite aegirine syenite, monzo-diorite, and monzo-gabbro are 129.3 ± 2.0Ma, 124.8 ± 1.3Ma, and 124.1 ± 0.9Ma, respectively, indicating their emplacement in the Early Cretaceous when the North China Craton was extensively reactivated. The monzo-diorite and monzo-gabbro have low SiO2 contents (48.94–57.75 wt%), total alkali contents (5.2–9.4 wt%), and εHf (t) values of −22.3 to −18.4 and are enriched in MgO (4.0–8.2 wt%), Al2O3 (14.3–15.8 wt%), light rare earth elements (LREEs) and large ion lithophile elements (LILEs). Interpretation of elemental and isotopic data suggests that the magma of monzo-diorite and monzo-gabbro were derived from partial melting of the enriched lithospheric mantle metasomatized by slab-derived hydrous fluids. Syenites with high alkali (K2O + Na2O = 9.4–13.0 wt%) and Sr contents (356–1737 ppm) and low Yb contents (0.94–2.65 ppm) are enriched in Al (Al2O3 = 16.4–19.1 wt%), but depleted in MgO (0.09–2.56 w%), Cr (Avg = 7.16 ppm), Co (Avg = 6.85 ppm) and Ni (Avg = 9.79 ppm), showing the geochemical features of adakitic rocks associated with thickened lower crust. Combining zircon 176Hf/177Hf ratios of 0.282176 to 0.282359, εHf(t) values of −18.3 to −11.8 and εNd (t) values of −11.1 to −8.2, we conclude that the syenite magma was derived from the mixing of the thickened lower crust and the enriched lithospheric mantle magma. These magma processes were controlled by Paleo-Pacific plate subduction and resulted in the destruction and thinning of the central North China Craton.

Petrogenesis of Late Jurassic Qianlishan granites and mafic dykes, Southeast China: implications for a back-arc extension setting

2006 ◽  
Vol 143 (4) ◽  
pp. 457-474 ◽  
Author(s):  
YAO-HUI JIANG ◽  
SHAO-YONG JIANG ◽  
KUI-DONG ZHAO ◽  
HONG-FEI LING
Keyword(s):  
Lithospheric Mantle ◽  
Source Region ◽  
Biotite Granite ◽  
Granitic Rocks ◽  
Trace Element Geochemistry ◽  
Southeast China ◽  
Mafic Dykes ◽  
Late Mesozoic ◽  
Back Arc ◽  
Extensional Setting

A late Mesozoic belt of volcanic-intrusive complexes occurs in Southeast China. The Qianlishan granites are distributed in the northwest of the belt. The pluton is composed of porphyritic biotite granite (153 Ma) and equigranular biotite granite (151 Ma) and was intruded by granite-porphyry dykes (144 Ma) and mafic dykes such as lamprophyre and diabase (142 Ma). The granitic rocks, consisting mainly of K-feldspar, plagioclase, quartz and Fe-rich biotite, have SiO2 contents of 72.9–76.9%, and are enriched in alkalis, rare earth elements (REE), high field strength elements (HFSE) and Ga with high Ga/Al ratios, but depleted in Ba, Sr and transition metals. Trace-element geochemistry and Sr–Nd isotope systematics further imply that the Qianlishan granitic magmas were most probably derived by partial melting of Palaeo- to Mesoproterozoic metamorphic lower-crustal rocks that had been granulitized during an earlier thermal event. These features suggest an A-type affinity. The Qianlishan lamprophyre and neighbouring coeval mafic dykes (SiO2 = 47.9–53.8 wt%) have high MgO and compatible element contents. These rocks also have high K2O contents and are enriched in alkalis, light REE, large ion lithophile elements, and depleted in HFSE. They have low initial εNd values and relatively high initial 87Sr/86Sr ratios. We suggest a subduction-modified refractory lithospheric mantle (phlogopite-bearing harzburgite or lherzolite) for these high-Mg potassic magmas. The Qianlishan diabases (SiO2 = 48.4–48.7 wt%) are alkaline and have high TiO2 and total Fe2O3 contents, together with the positive initial εNd value, suggesting derivation from fertile asthenopheric mantle (phlogopite-bearing lherzolite). A back-arc extensional setting, related to subduction of the Palaeo-Pacific plate, is favoured to explain the petrogenesis of the Qianlishan granites and associated mafic dykes. Between 180 and 160 Ma, Southeast China was a continental arc, forming the 180–160 Ma plutons of the late Mesozoic volcanic-intrusive complex belt, and the lower-crust was granulitized. Since 160 Ma the northwestern belt has been in a back-arc extensional setting as a consequence of slab roll-back, resulting in the lithosphere thinning and an influx of asthenophere. The upwelling asthenosphere, on the one hand, induced the local lithospheric mantle to melt partially, forming high-Mg potassic magmas, and on the other hand it underwent decompression melting itself to form alkaline diabase magma. Pulsatory injection of such high-temperature magmas into the granulitized crustal source region induced them to partially melt and generate the A-type magmas of the Qianlishan granitic rocks.

Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland

1999 ◽  
pp. 65-78
Author(s):  
Henrik Rasmussen ◽  
Lars Frimodt Pedersen
Keyword(s):  
Tectonic Setting ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
West Greenland ◽  
North West ◽  
North East ◽  
Metavolcanic Rocks ◽  
Arc Setting ◽  
Area North ◽  
Back Arc

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Rasmussen, H., & Frimodt Pedersen, L. (1999). Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 65-78. https://doi.org/10.34194/ggub.v181.5114 _______________ Two Archaean supracrustal sequences in the area north-east of Disko Bugt, c. 1950 and c. 800 m in thickness, are dominated by pelitic and semipelitic mica schists, interlayered with basic metavolcanic rocks. A polymict conglomerate occurs locally at the base of one of the sequences. One of the supracrustal sequences has undergone four phases of deformation; the other three phases. In both sequences an early phase, now represented by isoclinal folds, was followed by north-west-directed thrusting. A penetrative deformation represented by upright to steeply inclined folds is only recognised in one of the sequences. Steep, brittle N–S and NW–SE striking faults transect all rock units including late stage dolerites and lamprophyres. Investigation of major- and trace-element geochemistry based on discrimination diagrams for tectonic setting suggests that both metasediments and metavolcanic rocks were deposited in an environment similar to a modern back-arc setting.

In-situ reaction-replacement origin of hornblendites in the Early Cretaceous Laiyuan complex, North China Craton, and implications for its tectono-magmatic evolution

2021 ◽  
Author(s):  
Jia Chang ◽  
Andreas Audétat ◽  
Jian-Wei Li
Keyword(s):  
Partial Melting ◽  
North China Craton ◽  
Lithospheric Mantle ◽  
Lower Crust ◽  
North China ◽  
Ultramafic Rocks ◽  
Magmatic Evolution ◽  
Mafic Magmas ◽  
Felsic Rocks

Abstract Two suites of amphibole-rich mafic‒ultramafic rocks associated with the voluminous intermediate to felsic rocks in the Early Cretaceous Laiyuan intrusive-volcanic complex (North China Craton) are studied here by detailed petrography, mineral- and melt inclusion chemistry, and thermobarometry to demonstrate an in-situ reaction-replacement origin of the hornblendites. Moreover, a large set of compiled and newly obtained geochronological and whole-rock elemental and Sr-Nd isotopic data are used to constrain the tectono-magmatic evolution of the Laiyuan complex. Early mafic‒ultramafic rocks occur mainly as amphibole-rich mafic‒ultramafic intrusions situated at the edge of the Laiyuan complex. These intrusions comprise complex lithologies of olivine-, pyroxene- and phlogopite-bearing hornblendites and various types of gabbroic rocks, which largely formed by in-situ crystallization of hydrous mafic magmas that experienced gravitational settling of early-crystallized olivine and clinopyroxene at low pressures of 0.10‒0.20 GPa (∼4‒8 km crustal depth); the hornblendites formed in cumulate zones by cooling-driven crystallization of 55‒75 vol% hornblende, 10‒20 vol% orthopyroxene and 3‒10 vol% phlogopite at the expense of olivine and clinopyroxene. A later suite of mafic rocks occurs as mafic lamprophyre dikes throughout the Laiyuan complex. These dikes occasionally contain some pure hornblendite xenoliths, which formed by reaction-replacement of clinopyroxene at high pressures of up to 0.97‒1.25 GPa (∼37‒47 km crustal depth). Mass balance calculations suggest that the olivine-, pyroxene- and phlogopite-bearing hornblendites in the early mafic‒ultramafic intrusions formed almost without melt extraction, whereas the pure hornblendites brought up by lamprophyre dikes required extraction of ≥ 20‒30 wt% residual andesitic to dacitic melts. The latter suggests that fractionation of amphibole in the middle to lower crust through the formation of reaction-replacement hornblendites is a viable way to produce adakite-like magmas. New age constraints suggest that the early mafic-ultramafic intrusions formed during ∼132‒138 Ma, which overlaps with the timespan of ∼126‒145 Ma recorded by the much more voluminous intermediate to felsic rocks of the Laiyuan complex. By contrast, the late mafic and intermediate lamprophyre dikes were emplaced during ∼110‒125 Ma. Therefore, the voluminous early magmatism in the Laiyuan complex was likely triggered by the retreat of the flat-subducting Paleo-Pacific slab, whereas the minor later, mafic to intermediate magmas may have formed in response to further slab sinking-induced mantle thermal perturbations. Whole-rock geochemical data suggest that the early mafic magmas formed by partial melting of subduction-related metasomatized lithospheric mantle, and that the early intermediate to felsic magmas with adakite-like signatures formed from mafic magmas through strong amphibole fractionation without plagioclase in the lower crust. The late mafic magmas seem to be derived from a slightly different metasomatized lithospheric mantle by lower degrees of partial melting.

scholarly journals Inverted Basins by Africa–Eurasia Convergence at the Southern Back-Arc Tyrrhenian Basin

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 117
Author(s):  
Maria Filomena Loreto ◽  
Camilla Palmiotto ◽  
Filippo Muccini ◽  
Valentina Ferrante ◽  
Nevio Zitellini
Keyword(s):  
Seismic Reflection ◽  
Magnetic Data ◽  
Normal Faults ◽  
Sedimentary Sequence ◽  
Initiation Zone ◽  
Arc Setting ◽  
Seismic Reflection Profiles ◽  
Back Arc ◽  
Flower Structures ◽  
Tyrrhenian Basin

The southern part of Tyrrhenian back-arc basin (NW Sicily), formed due to the rifting and spreading processes in back-arc setting, is currently undergoing contractional tectonics. The analysis of seismic reflection profiles integrated with bathymetry, magnetic data and seismicity allowed us to map a widespread contractional tectonics structures, such as positive flower structures, anticlines and inverted normal faults, which deform the sedimentary sequence of the intra-slope basins. Two main tectonic phases have been recognised: (i) a Pliocene extensional phase, active during the opening of the Vavilov Basin, which was responsible for the formation of elongated basins bounded by faulted continental blocks and controlled by the tear of subducting lithosphere; (ii) a contractional phase related to the Africa-Eurasia convergence coeval with the opening of the Marsili Basin during the Quaternary time. The lithospheric tear occurred along the Drepano paleo-STEP (Subduction-Transform-Edge-Propagator) fault, where the upwelling of mantle, intruding the continental crust, formed a ridge. Since Pliocene, most of the contractional deformation has been focused along this ridge, becoming a good candidate for a future subduction initiation zone.

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