scholarly journals Petrogenesis of the Jurassic Guiping Complex in the Southwestern South China Block: Insights into the Subduction Processes of the Paleo-Pacific Slab

Minerals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 807
Author(s):  
Zhao-Ying Lü ◽  
Chang-Qian Ma ◽  
Yuan-Yuan Liu ◽  
Fu-Hao Xiong ◽  
Chang-Xin Wei ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
South China ◽  
Lithospheric Mantle ◽  
Late Jurassic ◽  
Basaltic Magma ◽  
Parental Magma ◽  
Sio2 Content ◽  
Trace Element Geochemistry ◽  
Element Geochemistry

Late Jurassic NE-trending A-type granitoids are widespread in the Shihang belt, South China, though their petrogenesis and geodynamic settings remain controversial. The Guiping complex is located on the southwest margin of the Shihang belt. In this study, the petrography, major and trace element geochemistry, whole-rock Sr-Nd isotopes, and zircon U-Pb geochronology of the Guiping complex were investigated. The Guiping complex is composed of the Fenghuangling and Xishan plutons; both plutons yielded zircon U-Pb ages of ca. 160 Ma. The Fenghuangling pluton has low SiO2 content of 54.26% to 60.31%, whereas the Xishan pluton exhibits high SiO2 content of 65.19% to 71.18%. Both of them are metaluminous and belong to the high-K calc-alkaline series and are enriched in large-ion lithophile elements (LILEs) such as Rb, Th, U, and Pb. The Fenghuangling and Xishan plutons showed enrichment in light rare earth elements (LREEs) and high-field strength elements (Nb, Ta, Zr, and Hf) and depletion in heavy rare earth elements (HREEs). Marked Nb and Ta negative anomalies were not observed. Due to the high contents of Zr + Ce + Nb + Y and high Ga/Al ratios, all the samples belonged to the group of A-type granites. The Fenghuangling and Xishan plutons had low ISr (mainly in the range of 0.7046–0.7058) and high εNd(t) (−0.60 to 1.94) values, though obviously different from those of the Precambrian basement in South China. Furthermore, they lie between the ocean island basalt (OIB) of the asthenosphere and the arc basaltic rocks of the enriched lithospheric mantle. Therefore, we proposed that the basaltic parental magma of the Guiping complex originated from partial melting of the enriched lithospheric mantle, which was metasomatized by asthenosphere-related OIB-type basaltic magma. Mafic microgranular enclaves in the Xishan pluton displayed positive Nb and Ta anomalies, which is consistent with OIB-type basalts. The enclaves also had similar Sr-Nd isotopic compositions to the Xishan pluton. That indicated that the enclaves were probably formed by mixing of the OIB-type basaltic magma and the Xishan pluton. In conclusion, the formation of the Late Jurassic NE-trending A-type granite belt was attributed to back-arc extension as a result of the rollback of the Paleo-Pacific Plate.

scholarly journals Paleoproterozoic Adakitic Rocks in Qingchengzi District, Northeastern Jiao-Liao-Ji Belt: Implications for Petrogenesis and Tectonism

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 684
Author(s):  
Jian Li ◽  
Hanlun Liu ◽  
Keyong Wang ◽  
Wenyan Cai
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Biotite Granite ◽  
Granitic Rocks ◽  
Geochemical Data ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Magmatic Rocks

Herein, zircon U-Pb geochronology, Lu-Hf isotopes, and whole-rock major and trace element geochemistry are presented for two Palaeoproterozoic granitic rocks in Qingchengzi district, northeastern Jiao-Liao-Ji Belt (JLJB). These new geochronological and geochemical data provide reference clues for exploring the petrogenesis and tectonic setting of Paleoproterozoic magmatic rocks in the Qingchengzi district, which further constrain the tectonic nature of the JLJB. Our zircon U-Pb dating denotes that the Paleoproterozoic magmatic events in the Qingchengzi district were emplaced at ~2163 Ma and ~1854 Ma, represented by granite porphyry and biotite granite, respectively. Geochemically, these Palaeoproterozoic rocks are characterized by high Sr (760–842 ppm), SiO2 (69.72–70.89 wt.%), and Al2O3 (15.53–16.78 wt.%) contents, low Y (2.1–9.0 ppm) and Yb (0.25–0.80 ppm) contents, which indicate an adakite affinity. Combined with Hf isotopic composition (εHf(t) = −1.5~+4.8; TDM2 = 3109~2560 Ma), we believe that the Paleoproterozoic adakitic magma originated from partial melting of the thickened lower crust material in the Meso-Neoarchean. Moreover, these rocks are enriched in light rare earth elements and large ion lithophilic elements (e.g., K, Rb, and Cs), and depleted in heavy rare earth elements and high field strength elements (e.g., Nb and Ta). These features are similar to magmatic rocks formed in an arc environment (either island arc or active continental margin) and are not consistent with an intraplate/intracontinental environment. According to this study and previous research results, we conclude that the arc–continent collision model is conducive to the Paleoproterozoic tectonic attribute of the JLJB, and the oceanic crust subduction between the Namgrim and Longgang blocks may have induced the widespread occurrence of magmatic events in the region.

scholarly journals Petrochemical features of tholeiites from the Shaka ridge (South Atlantic)

2021 ◽  
Vol 248 ◽  
pp. 223-231
Author(s):  
Natalia Rumyantseva ◽  
Boris Vanshteyn ◽  
Sergey Skublov
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Inductively Coupled Plasma ◽  
Classical Method ◽  
Field Research ◽  
Fluorescence Analysis ◽  
Original Data ◽  
South Atlantic ◽  
Trace Element Geochemistry ◽  
Element Geochemistry

The article presents original data of chemical composition of tholeiitic basaltoids and andesites, dredged from the Shaka Ridge (South Atlantic) in the course of field research in spring 2016 on the scientific expedition vessel “Akademik Fedorov”. The analytical part of the work on estimating the contents of petrogenic, trace and rare-earth elements was carried out using the classical method (“wet chemistry”), X-ray fluorescence analysis (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). The studied samples demonstrate elevated concentrations of large-ion lithophile elements, or LILE, (Ba, Rb, Pb) and light rare earth elements, or LREE, (La, Ce, Nd, Sm) relative to high field strength elements, or HFSE, (Nb, Ta) and heavy rare earth elements, or HREE, (Dy, Yb, Lu). The specifics of trace element geochemistry suggest a significant contribution of crustal or subduction components to the magmas of the Shaka Ridge. Discrimination diagrams of basaltoids and allied rocks with fields of different geodynamic settings indicate that they were formed in the setting of the mid-ocean ridge basalt (MORB). The reason behind the appearance of subduction and crustal marks in the rocks is possibly associated with assimilation of crustal matter by magmas or lies in their inheritance from the mantle source.

Geochemistry and zircon ages of the Yushigou diabase in the Longshoushan area, Alxa Block: implications for crust–mantle interaction and tectonic evolution

2020 ◽  
pp. 1-16 ◽  
Author(s):  
Ren-Yu Zeng ◽  
Jian-Qing Lai ◽  
Xian-Cheng Mao ◽  
Jie Yan ◽  
Chen-Guang Zhang ◽  
...  
Keyword(s):  
Rare Earth ◽  
Lithospheric Mantle ◽  
Inductively Coupled Plasma ◽  
Isotope Analysis ◽  
Transitional Zone ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Inductively Coupled ◽  
The North ◽  
North Qilian

Abstract The North Qilian orogenic belt in North China has been defined as a subduction–collision zone between the Alxa Block and the Qilian Block. We present petrography, zircon U–Pb geochronology, major- and trace-element geochemistry, and Sr–Nd–Pb–Hf isotope analysis for the Yushigou diabase from the Longshoushan area, which is located SW of the Alxa Block, aiming to understand its petrogenetic link to subduction processes. The Yushigou diabase belongs to the tholeiite series, and shows enrichment in light rare earth and large-ion lithophile elements, and a depletion in heavy rare earth and high-field-strength elements. Laser ablation – inductively coupled plasma – mass spectrometry U–Pb zircon dating yielded an emplacement age of 414 ± 9 Ma, with an ϵHf(t) value in the range of −10.3 to 1.8. The whole-rock initial 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the diabase range over 16.811–17.157, 15.331–15.422 and 37.768–37.895, respectively. The (87Sr/86Sr)i ratios vary between 0.7086 and 0.7106, and ϵNd(t) values vary between −14.4 and −13.4, which are significantly higher than the ϵHf(t) value (Nd–Hf decoupling). An interpretation of the elemental and isotopic data suggests that the Yushigou diabase was derived from partial melting of an enriched mantle I (EM-I) -type lithospheric mantle in the spinel–garnet transitional zone. Based on the geochemical features and previous regional geological data, we propose that the Silurian magmatism was most likely triggered by slab break-off after the closure of the North Qilian Ocean, and ancient continental materials from the subduction slab metasomatized the overlying lithospheric mantle during exhumation.

Geochemistry of mantle-related intermediate rocks from the Tibbit Hill volcanic suite, Quebec Appalachians

1998 ◽  
Vol 62 (04) ◽  
pp. 487-500 ◽  
Author(s):  
Abdel-Fattah M. Abdel-Rahman ◽  
P. Stephen Kumarapeli
Keyword(s):  
Rare Earth ◽  
Basaltic Magma ◽  
Volcanic Rocks ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Volcanic Sequence ◽  
Wide Range ◽  
Volcanic Suite ◽  
Rift Zones ◽  
High Concentrations

Abstract We present a study on major and trace element geochemistry of some intermediate lithologies from the predominantly basaltic Tibbit Hill volcanic suite in the Humber Zone of the Quebec Appalachians. The intermediate rocks probably formed as lava flows in the volcanic sequence. Their presence shows that this rift-related, c. 554 Ma volcanic sequence is not bimodal (basaltic-comenditic) as previously thought, but consists of a spectrum of compositions ranging from mafic through intermediate to felsic lithologies. The entire volcanic sequence is poly-deformed and generally metamorphosed to greenschist facies conditions. The intermediate rocks of the Tibbit Hill Formation are trachyandesitic, trachytic and comenditic in composition, and exhibit a wide range of SiO2 content (52 to 68 wt.%). Mg is highly depleted in most samples. Variations of silica versus the alkalis show that most of the samples are alkaline in nature. The rocks display a tholeiitic trend on a standard AFM diagram. In general, the examined rocks also exhibit a wide range of Sr (15 to 174 ppm), Rb (0 to 156 ppm), Zr (155 to 899 ppm), Nb (18 to 123 ppm), and Y (18 to 94 ppm). The concentration of Hf and Ta are generally low (6.6–14.8 ppm, and 3.3–6.6 ppm, respectively), compared to those of Zr and Nb. Nevertheless, these rocks contain relatively high concentrations of the HFS elements, thus reflecting an enriched source. The suite is also relatively enriched in the rare earth elements (REE), and exhibits fractionated, subparallel REE pattems; the latter are generally uniform and conformable. Chemical features of these volcanic rocks are typical of those of anorogenic A1 type suites, related to hotspots, mantle plumes, or continental rift zones. This is consistent with earlier interpretation of volcanism associated with an Iapetan RRR triple junction, occurring shortly before the onset of seafloor spreading. At that stage of crustal evolution, alkaline to transitional basaltic magma pierced into the crust, and experienced fractionation to produce the liquids of intermediate composition. Rare earth element geochemical modelling supports the hypothesis that the most evolved composition for which REE data are available (comendite; 67.9 wt.% SiO2) was produced by 20% fractional crystallization of the least evolved trachyandesite (56.7 wt.% SiO2) of this intermediate volcanic assemblage.

scholarly journals Origin of Northeast Fujian Basalts and Limitations on the Heterogeneity of Mantle Sources for Cenozoic Alkaline Magmatism across SE China: Evidence from Zircon U-Pb Dating, Petrological, Whole-Rock Geochemical, and Isotopic Studies

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 770
Author(s):  
Guishan Zhang ◽  
Ren Peng ◽  
Hongxin Qiu ◽  
Hanjie Wen ◽  
Yonggang Feng ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Mantle Source ◽  
Trace Element Geochemistry ◽  
Alkaline Magmatism ◽  
Element Geochemistry ◽  
Alkali Basalts ◽  
Mantle Sources ◽  
Heavy Rare Earth Elements ◽  
Se China

Cenozoic alkali basalts in Southeast (SE) China generally are genetically related to intracontinental rifting. Hence, they can be used to probe the nature of their underlying mantle sources and aid studies of the tectonic background in this region. This paper focuses on the Shanhoujian alkali basalts located in Bailing County, northeastern Fujian, SE China. We herein report their petrology, whole-rock major, and trace element geochemistry, and Sr-Nd isotopic composition and provide a new zircon U-Pb age for the basalts (~40 Ma, Eocene). These data help to constrain the petrogenesis of alkali basalts, their mantle source, and tectonic settings. The basalts are characterized by high Mg# (58.21–63.52) with Na2O/K2O > 1. MgO content is weakly correlated with CaO and Cr content but shows no correlation with Ni and Fe2O3 (total). Such features suggest that fractionation of clinopyroxene rather than olivine was important. In terms of trace elements, the alkali basalts display: (1) enrichment in La, Ce, Rb, Ba, Nb, and Ta and depletion in K, Pb, Zr, Hf, and Ti and (2) notable fractionation of light rare earth elements from heavy rare earth elements. Determined (87Sr/86Sr)i is in the range of 0.7041–0.7040 and εNd (t) is between +3.2 and +3.3. The Shanhoujian alkali basalts show a notable affinity to oceanic island basalts (OIBs) with little assimilation of crustal materials. They were derived from a pyroxenite and carbonated peridotite mantle source metasomatized by sediments carried by the subduction plate at different depths. The primary magmas of these basalts were derived from partial melting of this metasomatized mantle source during upwelling of the asthenospheric mantle as an intracontinental rift formed through extension in this part of SE China.

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