scholarly journals Petrology, Geochronology and Geochemistry of Late Triassic Alkaline Rocks of the Bailinchuan District in Liaodong Peninsula, Northeast China

Minerals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 528
Author(s):  
Xihui Cheng ◽  
Jiuhua Xu ◽  
Hao Wei ◽  
Fuquan Yang ◽  
Hui Zhang ◽  
...  
Keyword(s):  
Mantle Source ◽  
Lithospheric Mantle ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Late Triassic ◽  
Geochemical Data ◽  
Geodynamic Setting ◽  
Growth Zoning ◽  
Geochemical Studies ◽  
Alkaline Complexes

The Bailinchuan alkaline syenite (BAS) is located in the easternmost part of the Triassic alkaline magmatic belt along the northern North China Craton (NCC). Based on a detailed study of the zircon U–Pb age, petrological, and geochemical data of the complex, the characteristics of the magmas system, petrogenesis and the nature of mantle source provide new constraints on the origin and tectonic setting of the Triassic alkaline belt. The BAS is composed of alkaline syenite and/or aegirine-nepheline syenite, with zircon U–Pb age of 226–229 Ma. Aegirine, Na-rich augite, biotite, orthoclase, and nepheline are the major minerals. Most of the zircons selected for the analysis show fine-scale to weak oscillatory growth zoning in CL images, suggesting a magmatic origin. Mineralogy, petrology and geochemical studies show that the parental magma of the BAS is SiO2-undersaturated, potassic, and is characterized by high contents of CaO, Fe2O3, K2O, Na2O. The BAS originated from a phlogopite-rich, enriched lithospheric mantle source in a garnet-stable area. The occurrence of the BAS, together with many other alkaline complexes of similar ages (235–209 Ma) in the northern NCC during the Late Triassic implies that the lithospheric mantle beneath the northern NCC was previously metasomatized by melts/fluids. Bailinchuan Late Triassic syenites were formed in a post-collisional extensional setting, which provides time constraints on the major geodynamic setting at the northern NCC.

Mineral ages and zircon Hf isotopic composition of the Andong ultramafic complex: implications for the evolution of Mesozoic subduction system and subcontinental lithospheric mantle beneath SE Korea

2013 ◽  
Vol 151 (5) ◽  
pp. 765-776 ◽  
Author(s):  
GI YOUNG JEONG ◽  
CHANG-SIK CHEONG ◽  
KEEWOOK YI ◽  
JEONGMIN KIM ◽  
NAMHOON KIM ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Tectonic Setting ◽  
Eastern China ◽  
Mantle Xenoliths ◽  
Late Triassic ◽  
Magmatic Differentiation ◽  
Suprasubduction Zone ◽  
Ultramafic Complex ◽  
Yeongnam Massif ◽  
Subduction System

AbstractThe Phanerozoic subduction system of the Korean peninsula is considered to have been activated by at least Middle Permian time. The geochemically arc-like Andong ultramafic complex (AUC) occurring along the border between the Precambrian Yeongnam massif and the Cretaceous Gyeongsang back-arc basin provides a rare opportunity for direct study of the pre-Cretaceous mantle wedge lying above the subduction zone. The tightly constrained SHRIMP U–Pb age of zircons extracted from orthopyroxenite specimens (222.1±1.0 Ma) is indistinguishable from the Ar/Ar age of coexisting phlogopite (220±6 Ma). These ages represent the timing of suprasubduction zone magmatism likely in response to the sinking of cold and dense oceanic lithosphere and the resultant extensional strain regime in a nascent arc environment. The nearly coeval occurrence of a syenite-gabbro-monzonite suite in the SW Yeongnam massif also suggests an extensional tectonic setting along the continental margin side during Late Triassic time. The relatively enriched ɛHf range of dated zircons (+6.2 to −0.6 at 222 Ma) is in contrast to previously reported primitive Sr–Nd–Hf isotopic features of Cenozoic mantle xenoliths from Korea and eastern China. This enrichment is not ascribed to contamination by the hypothetical Palaeozoic crust beneath SE Korea, but is instead attributable to metasomatism of the lithospheric mantle during the earlier subduction of the palaeo-Pacific plate. Most AUC zircons show a restricted core-to-rim spread of ɛHf values, but some grains testify to the operation of open-system processes during magmatic differentiation.

Neoproterozoic Amdo and Jiayuqiao microblocks in the Tibetan Plateau: Implications for Rodinia reconstruction

2020 ◽  
Author(s):  
Yiming Liu ◽  
Yuhua Wang ◽  
Sanzhong Li ◽  
M. Santosh ◽  
Runhua Guo ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
South China ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Tibet Plateau ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
South China Craton ◽  
Neoproterozoic Magmatism ◽  
T Values

The Tibetan Plateau is composed of several microblocks, the tectonic affinity and paleogeographic correlations of which remain enigmatic. We investigated the Amdo and Jiayuqiao microblocks in central Tibet Plateau with a view to understand their tectonic setting and paleogeographic position within the Neoproterozoic supercontinent Rodinia. We present zircon U-Pb and Lu-Hf isotope, and whole-rock geochemical data on Neoproterozoic granitic gneisses from these microblocks. Zircon grains from the Jiayuqiao granitic gneiss yielded an age of 857 ± 9 Ma with variable εHf(t) values (−8.9 to 4.0). The Amdo granitic gneisses yielded ages of 893 ± 5 Ma, 807 ± 5 Ma, and 767 ± 11 Ma, with εHf(t) values in the range of −4.9 to 3.5. Geochemically, the granitoids belong to high-K calc-alkaline series, with the protolith derived from partial melting of ancient crustal components. The ascending parental magma of the Amdo granitoids experienced significant mantle contamination as compared to the less contaminated magmas that generated the Jiayuqiao intrusions. In contrast to the Lhasa, Himalaya, South China, and Tarim blocks, we suggest that the Amdo and Jiayuqiao microblocks probably formed a unified block during the Neoproterozoic and were located adjacent to the southwestern part of South China craton. The Neoproterozoic magmatism was probably associated with the subduction of the peripheral ocean under the South China craton and the delamination of lithospheric mantle beneath the Jiangnan orogen.

A ~1.4 Ga alkaline mafic sill from the Carletonville area: connection to the Pilanesberg Alkaline Province?

2020 ◽  
Vol 123 (4) ◽  
pp. 597-614
Author(s):  
F. Humbert ◽  
M.A. Elburg ◽  
A. Agangi ◽  
G. Belyanin ◽  
J. Akoh ◽  
...  
Keyword(s):  
Basaltic Andesite ◽  
Lithospheric Mantle ◽  
Crustal Contamination ◽  
Dyke Swarm ◽  
Geochemical Data ◽  
Magma Source ◽  
Geochemical Study ◽  
Mantle Reservoir ◽  
Alkaline Complexes ◽  
Emplacement Depth

Abstract Numerous Mesoproterozoic alkaline intrusions belonging to the Pilanesberg Alkaline Province are present within the Transvaal sub-basin of the Kaapvaal Craton. The Pilanesberg Complex is the best-known example; it represents one of the world’s largest alkaline complexes, and is associated with a northwest-southeast trending dyke swarm that extends from Botswana to the southwest of Johannesburg. This paper documents the results of a petrological and geochemical study of a thin mafic sill (here referred to as an alkaline igneous body, AIB), which intrudes the ca. 2 200 Ma Silverton Formation close to the southernmost part of the Pilanesberg dyke swarm. The AIB has only been observed in cores from a borehole drilled close to Carletonville. It is hypocrystalline, containing randomly oriented elongated skeletal kaersutite crystals and 6 to 8 mm varioles mainly composed of radially oriented acicular plagioclase. These two textures are related to undercooling, probably linked to the limited thickness (70 cm) of the AIB coupled with a probable shallow emplacement depth. Ar-Ar dating of the kaersutite gives an age of ca. 1 400 Ma, similar to the age of Pilanesberg Complex. However, the AIB is an alkaline basaltic andesite and is thus notably less differentiated than the Pilanesberg Complex and some of its associated dykes, such as the Maanhaarrand dyke, for which we provide whole-rock geochemical data. Literature data indicate that the Pilanesberg dyke swarm also contains mafic hypabyssal rocks suggesting a link between the dyke swarm and the AIB. The AIB is characterized by strongly negative εNd and εHf, that cannot be related to crustal contamination, as shown by positive Ti and P anomalies, and the absence of negative Nb-Ta anomalies in mantle-normalised trace element diagrams. The AIB magma is interpreted to have been derived from a long-lived enriched, probably lithospheric mantle reservoir. The AIB thus provides important information on the magma source of the Pilanesberg Alkaline Province.

Geochemical and Sr-Nd isotopic characteristics of the lamprophyre in the Tethyan Himalaya, South Tibet

2020 ◽  
Author(s):  
Zhi-Chao Liu ◽  
Jian-Gang Wang ◽  
Xiao-Chi Liu
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Lithospheric Mantle ◽  
Indian Plate ◽  
Late Triassic ◽  
Geochemical Data ◽  
Low Grade ◽  
Northern Margin ◽  
Two Samples ◽  
Tethyan Himalaya

<p>A lamprophyre dyke has been found in Ramba area within the Tethyan Himalaya. It intruded into the Late Triassic low-grade metasedimentary rocks (Langjiexue Group) and show typical porphyritic textures, with phlogopite as the dominant phenocrysts. In this study, we performed phlogopite 40Ar/39Ar dating and whole-rock major and trace element as well as Sr and Nd isotope geochemical analyses on the lamprophyre. The <sup>40</sup>Ar/<sup>39</sup>Ar plateau ages (13.1 ± 0.2 Ma and 13.5 ± 0.2 Ma) of the phlogopites from two samples are both in excellent agreement with the inverse isochron ages of 13.1 ±0.3 Ma and 13.6 ± 0.3 Ma, recording the times at which the lamprophyre dyke has cooled below ~300 °C. The lamprophyre has low contents of SiO<sub>2</sub> (51.43–55.15 wt%) and Al<sub>2</sub>O<sub>3</sub> (11.10–11.85 wt%), high Fe<sub>2</sub>O<sub>3T</sub> (8.57–9.27 wt%) and MgO (9.14–9.49 wt %) contents with Mg<sup>#</sup> of 66–69, higher content of K<sub>2</sub>O (3.26–5.57 wt%) relative to Na<sub>2</sub>O (0.50–1.39 wt%) with K<sub>2</sub>O/Na<sub>2</sub>O of 2.3–11.1. Furthermore, the lamprophyre has high abundances of large ion lithophile elements (e.g., Rb, Ba, Sr), shows depletions in high field strength elements (e.g., Nb, Ta, Ti), and displays enrichment in light rare-earth elements over heavy rare earth elements with (La/Yb)<sub>N</sub> of 42.3~47.0. Besides, the lamprophyre is characterized by high initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios of 0.7196~0.7204 and negative ε<sub>Nd</sub>(t) values of -10.7~-10.8. Geochemical data suggest that the Ramba lamprophyre was likely generated by partial melting of a metasomatized, phlogopite-bearing harzburgite lithospheric mantle source, followed by crystal fractionation and varying degree of crustal assimilation. The studied lamprophyre provides a window into the composition of the subcontinental lithospheric mantle (SCLM) in the northern margin of the Indian plate. We suggest that the northern Indian plate might be involved in the Andean-type orogeny from the subduction of the Proto-Tethys Ocean during Cambrian to Early Ordovician.</p>

scholarly journals Early Cambrian syenite and monzonite magmatism in the southeast of the East European Platform: petrogenesis and tectonic setting

2019 ◽  
Vol 27 (4) ◽  
pp. 357-400
Author(s):  
A. A. Nosova ◽  
A. A. Voznyak ◽  
S. V. Bogdanova ◽  
K. A. Savko ◽  
N. M. Lebedeva ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
East European Platform ◽  
Tectonic Setting ◽  
Geochemical Data ◽  
Early Cambrian ◽  
Southeastern Part ◽  
East European ◽  
Isotopic Compositions ◽  
Time Period ◽  
Feature Negative

The paper reports new geochronological, petrological, and isotope-geochemical data on the syenites and alkali syenites of the Artyushki massif, and the monzonites of the Gusikha massif. These massifs are located along the southwestern and northeastern margins of the Pachelma aulacogen, in the southeastern part of the East European Platform (EEP). They have Early Cambrian ages of 524 ± 3 (Artyushki) and 514 ± 2 Ma (Gusikha) obtained by the U-Pb zircon method and similar ages of amphibole and K-feldspar by the 40Ar/39Ar method. This time period has previously been regarded as amagmatic in the EEP evolution. The Artyushki massif is made up of Amp-Cpx syenite porphyries and Grt-Cpx alkali syenite porphyries and their fenitized varieties. As compared to the Amp-Cpx varieties the Grt-Cpx rocks are more peralkaline (A/NK > 0.9) and have higher LREE and HFSE, and fractionated HREE patterns. The metasomatized (fenitized) varieties are more potassic and bear geochemical evidence of fluid reworking (high Y/Ho ratios, significant Zn variations, and etc.). Bulk samples have weakly radiogenic Sr isotopic compositions: (87Sr/86Sr)520 are within 0.703066–0.703615. The values of εNd(520) vary from –0.69 to +1.64. The Grt-Cpx syenite porphyries have the positive εNd(520), while the Amp-Cpx and fenitized syenite porphyries feature negative εNd. The Gusikha massif consists of biotite-amphibole and biotite monzonites. Similar to the Artyushki syenites in SiO2 contents, the Gusikha monzonites have higher Mg# (0.22–0.54 and 0.34–0.71 for the Artyushki and Gusikha massifs, respectively). They are also characterized by a negative Nb-Ta anomaly (Nb/Nb* = 0.5), high Ва/Sr ratio, and highly radiogenic (87Sr/86Sr)520 = 0.705204 and 0.705320. Their Nd-isotopic compositions correspond to εNd(520) = –6.7 and –7.0. Two melts contributed to the formation of the Artyushki massif. One was a strongly contaminated melt (Amp-Cpx syenite porphyries, the other was weakly contaminated (Grt-Cpx syenite porphyries). The main contribution was phonolitic melt derived from the melting of a moderately metasomatized (carbonate- and amphibole-bearing) shallow lithospheric mantle. The earliest and deepest melt portions were carbonate-silicate in composition. The geochemical, as well as the Sr and Nd isotopic compositions of the Gusikha monzonites indicate a predominant crustal contribution and pervasive reworking of the lithospheric mantle beneath southeastern Volgo-Uralia of the EEP in the Mesoproterozoic. Both massifs feature the geochemistry of within-plate and supra-subduction derivatives, which suggests a postorogenic tectonic setting of the magmatism. The presence of the Early Cambrian postorogenic magmatism within the East European Platform/Baltica is direct evidence for the involvement of Baltica in the collisional and/or accretionary events during the terminal Neoproterozoic – the beginning of the Paleozoic. This suggests reworking of the lithospheric mantle of Baltica during its collision with Timanian and East Avalonian/Cadomian terranes, including Scythia.

scholarly journals Mineralogical features and petrogenetic significance of the clinopyroxene and hornblende of the Wuhaolai mafic complex in northern North China Craton, Inner Mongolia

2019 ◽  
Vol 23 (2) ◽  
pp. 133-146
Author(s):  
Chen Wang ◽  
Liu Jianchao ◽  
Zhang Haidong ◽  
Ge Jiakun ◽  
Xi Zhixuan ◽  
...  
Keyword(s):  
North China Craton ◽  
Lithospheric Mantle ◽  
Inner Mongolia ◽  
North China ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Magma Source ◽  
Alkaline Basalt ◽  
The North ◽  
Mafic Complex

The Wuhaolai mafic complex is located in the north margin of the North China Craton (NCC), Inner Mongolia. To discuss the mineralogical features, magma evolution process, and tectonic setting of the complex, we analyzed the geochemical compositions of clinopyroxene and hornblende using an electron probe. The results revealed that the parental magma of this complex belonged to the intraplate alkaline basalt series. The normal zoning texture and the relation between Mg# and FeO, Al2O3, CaO, Na2O, SiO2 and Cr2O3 suggested that the clinopyroxenes of pyroxenite and gabbro crystallized from the same parental magma. The similar CaO content of clinopyroxenes indicated that the parental magma of the Wuhaolai complex may have suffered crustal contamination. Furthermore, the characteristics of hornblende demonstrated that the magma source was modified by fluids derived from subducted slab. Based on the value of Kdcpx (0.23–0.27), the equilibrium melt with clinopyroxene exhibited a relatively low Mg# (43–53), indicating that the parental magma was derived from the lithospheric mantle and underwent crystal fractionation. The gabbro crystallization temperature and pressure was found to be lower than that of pyroxenite, indicating that gabbro was formed at a lower depth than that of pyroxenite. Combining the tectonic setting discrimination diagram of clinopyroxene with the results of previous studies on the late Paleozoic intrusions near the research area, we proposed that the Wuhaolai complex was formed in an intraplate environment. The magma source was modified by fluids derived from the subducted slab during the subduction of the Paleo-Asian Ocean (PAO). After the PAO closure, the parental magma of the Wuhaolai complex was produced by the partial melting of the enriched lithospheric mantle

Triassic magmatism in the European Southern Alps as an early phase of Pangea break-up

2020 ◽  
Vol 157 (11) ◽  
pp. 1800-1822 ◽  
Author(s):  
Angelo De Min ◽  
Matteo Velicogna ◽  
Luca Ziberna ◽  
Massimo Chiaradia ◽  
Antonio Alberti ◽  
...  
Keyword(s):  
Mantle Source ◽  
Crustal Contamination ◽  
Mineral Chemistry ◽  
Western Mediterranean ◽  
Southern Alps ◽  
Late Triassic ◽  
Geodynamic Setting ◽  
Isotopic Data ◽  
Geological Evidence ◽  
Break Up

AbstractMagmatic rocks from the Dolomites, Carnic and Julian Alps, Italy, have been sampled to investigate the origin and geodynamic setting of Triassic magmatism in the Southern Alps. Basaltic, gabbroic and lamprophyric samples have been characterized for their petrography, mineral chemistry, whole-rock major and trace elements, and Sr, Nd and Pb isotopic compositions. Geothermobarometric estimates suggest that the basaltic magmas crystallized mostly at depths of 14–20 km. Isotopic data show variable degrees of crustal contamination decreasing westwards, probably reflecting a progressively more restitic nature of the crust, which has been variably affected by melting during the Permian period. Geochemical and isotopic data suggest that the mantle source was metasomatized by slab-derived fluids. In agreement with previous studies and based on geological evidence, we argue that this metasomatism was not contemporaneous with the Ladinian–Carnian magmatism but was related to previous subduction episodes. The lamprophyres, which likely originated some 20 Ma later by lower degrees of melting and at higher pressures with respect to the basaltic suite, suggest that the mantle source regions of Triassic magmatism in the Dolomites was both laterally and vertically heterogeneous. We conclude that the orogenic signatures of the magmas do not imply any coeval subduction in the surrounding of Adria. We rather suggest that this magmatism is related to the Triassic rifting episodes that affected the western Mediterranean region and that were ultimately connected to the rifting events that caused the break-up of Pangea during the Late Triassic – Early Jurassic period.

Mineral chemistry, petrogenesis, and tectonic setting of the Wateranga layered intrusion, southeast Queensland, Australia

2005 ◽  
Vol 42 (11) ◽  
pp. 1967-1985 ◽  
Author(s):  
Reddy VR Talusani ◽  
Warwick J Sivell ◽  
Paul M Ashley
Keyword(s):  
Tectonic Setting ◽  
Parental Magma ◽  
Layered Intrusion ◽  
Mafic Magma ◽  
Mineral Chemistry ◽  
Geochemical Data ◽  
Magma Source ◽  
Olivine Gabbro ◽  
Layered Mafic Intrusion ◽  
Southeast Queensland

The Wateranga layered mafic intrusion (28 km2 in area, > 500 m thick) is a tholeiitic, undeformed, unmetamorphosed, Permo-Triassic layered gabbroic pluton intruded into the late Carboniferous Goodnight beds of the Goodnight Block in southeast Queensland. The intrusion mainly consists of gabbro and norite, associated with subordinate amounts of troctolite, anorthosite, and orthopyroxenite, and rare picrite. Olivine gabbro is the dominant rock type of the intrusion. Fractionation followed a tholeiitic trend with iron enrichment in the liquid. Petrographic, mineral chemical, and whole-rock geochemical data have been used to divide the intrusion into Lower, Middle, and Upper zones, which are interpreted as reflecting magma chamber replenishment. The observed changes in the crystallization order between the zones reveal that a single parental magma is inadequate to explain the data. The common differentiation indices, such as An content of plagioclase, Mg#s of olivine, clinopyroxene, orthopyroxene and whole-rocks, and the whole-rock concentrations of various incompatible trace elements (Zr, Y, Nb, La Ba, Rb, Sr, and Nd), all vary widely with stratigraphic depth and display abrupt shifts at the zone boundaries, indicating open system addition of new mafic magma. Temperatures estimated from two-pyroxene geothermometer vary from 1057 to 927 °C. During the course of crystallization, pressure probably was > 2 and < 4 kbar (1 kbar = 100 MPa). The variation trend of anorthite content of plagioclase versus the forsterite content of olivine precludes an arc-related magma source. The composition and geological setting of the intrusion are consistent with emplacement in a post-subduction extensional tectonic environment.

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