scholarly journals Identification and Geological Significance of Early Jurassic Adakitic Volcanic Rocks in Xintaimen Area, Western Liaoning

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 331
Author(s):  
Zhi-Wei Song ◽  
Chang-Qing Zheng ◽  
Chen-Yue Liang ◽  
Bo Lin ◽  
Xue-Chun Xu ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
North China Craton ◽  
Lower Crust ◽  
North China ◽  
Basaltic Magma ◽  
Volcanic Rocks ◽  
Early Jurassic ◽  
Magma Source ◽  
Western Liaoning

The Western Liaoning area, where a large number of Jurassic-Cretaceous volcanic rocks are exposed, is one of the typical areas for studying the Mesozoic Paleo-Pacific and Mongolia-Okhotsk subduction process, and lithospheric destruction of North China Craton. The identification and investigation of Early Jurassic adakitic volcanic rocks in the Xintaimen area of Western Liaoning is of particular significance for exploring the volcanic magma source and its composition evolution, tracking the crust-mantle interaction, and revealing the craton destruction and the subduction of oceanic plates. Detailed petrography, zircon U–Pb dating, geochemistry, and zircon Hf isotope studies indicate that the Early Jurassic intermediate-acidic volcanic rocks are mainly composed of trachydacites and a few rhyolites with the formation ages of 178.6–181.9 Ma. Geochemical characteristics show that they have a high content of SiO2, MgO, Al2O3, and total-alkali, typical of the high-K calc-alkaline series. They also show enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs), depletion of heavy rare earth elements (HREEs) and high field strength elements (HFSEs), and have a high content of Sr and low content of Y and Yb, suggesting that they were derived from the partial melting of the lower crust. The εHf(t) values of dated zircons and two-stage model ages (TDM2) vary from −11.6 to −7.4 and from 1692 to 1958 Ma, respectively. During the Early Jurassic, the study area was under long-range tectonic effects with the closure of the Mongolia-Okhotsk Ocean and the subduction of the Paleo-Pacific plate, which caused the basaltic magma to invade the lower crust of the North China Craton. The mantle-derived magma was separated and crystallized while heating the Proterozoic lower crust, and part of the thickened crust melted to form these intermediate-acidic adakitic volcanic rocks.

Metasomatic Processes in the Lithospheric Mantle Beneath the No. 30 Kimberlite (Wafangdian Region, North China Craton)

2019 ◽  
Vol 57 (4) ◽  
pp. 499-517 ◽  
Author(s):  
Ren Z. Zhu ◽  
Pei Ni ◽  
Jun Y. Ding ◽  
Guo G. Wang ◽  
Ming S. Fan ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Trace Element ◽  
North China Craton ◽  
Lithospheric Mantle ◽  
North China ◽  
Compositional Data ◽  
Early Stage ◽  
Mantle Metasomatism ◽  
Element Data

AbstractThis paper presents the first major and trace element compositions of mantle-derived garnet xenocrysts from the diamondiferous No. 30 kimberlite pipe in the Wafangdian region, and these are used to constrain the nature and evolution of mantle metasomatism beneath the North China Craton (NCC). The major element data were acquired using an electron probe micro-analyzer and the trace element data were obtained using laser ablation inductively coupled plasma-mass spectrometry. Based on Ni-in-garnet thermometry, equilibrium temperatures of 1107–1365 °C were estimated for peridotitic garnets xenocrysts from the No. 30 kimberlite, with an average temperature of 1258 °C, and pressures calculated to be between 5.0 and 7.4 GPa. In a CaO versus Cr2O3 diagram, 52% of the garnets fall in the lherzolite field and 28% in the harzburgite field; a few of the garnets are eclogitic. Based on rare earth element patterns, the lherzolitic garnets are further divided into three groups. The compositional variations in garnet xenocrysts reflect two stages of metasomatism: early carbonatite melt/fluid metasomatism and late kimberlite metasomatism. The carbonatite melt/fluids are effective at introducing Sr and the light rare earth elements, but ineffective at transporting much Zr, Ti, Y, or heavy rare earth elements. The kimberlite metasomatic agent is highly effective at element transport, introducing, e.g., Ti, Zr, Y, and the rare earth elements. Combined with compositional data for garnet inclusions in diamonds and megacrysts from the Mengyin and Wafangdian kimberlites, we suggest that these signatures reflect a two-stage evolution of the sub-continental lithospheric mantle (SCLM) beneath the NCC: (1) early-stage carbonatite melt/fluid metasomatism resulting in metasomatic modification of the SCLM and likely associated with diamond crystallization; (2) late-stage kimberlite metasomatism related to the eruption of the 465 Ma kimberlite.

scholarly journals Geochemistry and Petrogenesis of Basic Paleogene Volcanic Rocks in Alamut Region

2021 ◽  
Vol 25 (2) ◽  
pp. 237-245
Author(s):  
Mehdi Nazari Sarem ◽  
Mansour Vosoghi Abedini ◽  
Rahim Dabiri ◽  
Mohammad Reza Ansari
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Basaltic Magma ◽  
Volcanic Rocks ◽  
Geochemical Properties ◽  
Deep Faults ◽  
Microscopic Studies ◽  
Rift Zones ◽  
Geochemical Studies ◽  
Low K

Structurally, the study area belongs to the tectonic range of the Central Alborz. The rocks were analyzed to detect main elements as well as rare and rare earth elements. Based on microscopic studies, the rocks in the region include basalt, trachyandesite and basaltic andesite with alkaline geochemical properties. According to geochemical studies, the early magma was affected by Nb, Ti, Ta, Eu negative anomalies, the enrichment of Rhizosphere rocks of rare earth elements (LRRE), high LREE/HREE ratio and low K/Nb ratio and high ratios of Th/Nb, La/Nb, Ba/Nb, Zr/ Nb magmatic contamination. The early basaltic magma has been formed of a garnet lherzolite mantle with phlogopite/pargasite by metasomatism at a pressure of 2.5-5.3 GPa at depths of more than 80-150 km. Structural evidence suggests the formation of these volcanic rocks in intercontinental rift zones. The formation of these rocks can be attributed to the effects of intercontinental extensional phases in deep faults during Eocene Alpine orogeny phases.

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.

Fraction characteristics of rare earth elements in the surface sediment of Bohai Bay, North China

2012 ◽  
Vol 184 (12) ◽  
pp. 7275-7292 ◽  
Author(s):  
Yayan Xu ◽  
Jinming Song ◽  
Liqin Duan ◽  
Xuegang Li ◽  
Huamao Yuan ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Surface Sediment ◽  
North China ◽  
Bohai Bay
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