The Petrochemistry on Intermediated-Basic Plutons at the Otanri Area of Kyeonggi Massif, Korea
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The Otanri area in the central part of Kyeonggi massif, Korea, is composed of Precambrian gneisses that have been intruded by Jurassic to Cretaceous, felsic to mafic batholiths and stocks. U-Pb zircon ages for plutons in the Kyeonggi massif reported unpublished data. These ages are: Gongju migmatitic gneiss- 2413±21 Ma, Seongnam-Koyang migmatitic gneiss- 2417±39 Ma, Banded gneiss- 2163 Ma, Otanri gabbro- 166±1 Ma, Porphyritic granite- 165±2 Ma. On the basis of normative Qz-Or-Pl and Or-Ab-An diagrams, Gabbro plots monzogabbro region while the diorite plots in a diorite to a quartz diorite field. On the A-M-F diagram, the gabbro and diorite are a calc alkali rock series. The gabbro has high lithopile, HFS, zinc and low ferromagnesian and REE. On the the other hand diorite has high ferromagnesian, copper, REE and low lithophile. For the gabbro-diorite complex the REE characteristics of ΣREE, Eu/Sm and are 104.76 ppm to 139.59 ppm, 0.31 to 0.29 and 8.52 and 5.65 with no Eu(-) anomaly and thus indicate alkali basalt to andesitic composition. On silica diagram the plutons plot in subalkaline field. But on the alkalinity-silica diagram all plutonic rocks plot in the calc alkaline region. Based on the silica vs. trace element diagrams gabbro-diorite complex could have formed near volcanic arc or plate collision environments.Keywords:
Diorite
Porphyritic
Felsic
Massif
Quartz monzonite
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Acid and intermediate-acid intrusive rocks are widely distributed in Tamusu, northern Alxa massif. These rocks are mainly biotite granite, granodiorite, adamellite and tonalite, with the last three forming the main body of the intrusive rocks in Tamsag area. The massif, unconformably covered by Cretaceous and Jurassic strata, was intruded into Late Carboniferous-Early Permian Amushan Formation, and its regional distribution shows sub-latitudinal feature. The LA-ICP-MS zircon U-Pb ages of the monzonitic granite and tonalite in this region are respectively 264.2±3.3Ma and 273.0±3.3Ma. The granodiorite, monzonitic granite and tonalite are of calc-alkalic to high potassium calc-alkalic suite, characterized by A/CNK ratios of 0.874~1.01, 1.06~1.54, and 0.91~1.03, and ∑REE values of 156.99×10-6~212.87×10-6, 126.92×10-6~212.98×10-6and 128.13×10-6~214.5×10-6, respectively. These intrusive rocks show a close affinity to island-arc granites in Rb-(Yb+Nb) and Rb-(Yb+Ta) diagrams, with enrichment of Ba, Rb,Th, K and other large ion lithophile elements, and depletion of Nb, Ta, P, Ti and other high field strength elements. It is considered that the northern margin of Alxa might still have had some arc-related magmatic activities during the Permian period.
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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 ± 2.0 Ma, 124.8 ± 1.3 Ma, and 124.1 ± 0.9 Ma, 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.
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Aegirine
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The characteristics,formation,and evolution of the porphyritic granitic gneiss in Taili area of western Liaoning Province was studied in detail based on petrology,geochemistry and zircon U-Pb dating.This study provides new petrological evidence for investigating the geological evolution of the North China Craton.The granitoid rocks are mainly composed of granitic gneiss,porphyritic granitic gneiss,and biotite adamellite in the study area.The porphyritic granitic gneiss intruded into and was formed later than granitic gneiss.The porphyritic texture is well-developed with different amount of alkali feldspar and quartz depending on the distance relative to the deformation zone.Phenocrysts are much bigger in the areas far away from the deformation zone,while the porphyritic granitic gneiss with eye-like structures has been highly deformed and mylonitized in the deformaltion zone.The SiO 2 and K 2 O contents of the porphyritic granitic gneiss range from 67.54% to 75.64% and from 2.89% to 4.67%,respectively.It is enriched in light rare earth elements as well as in Ba and Sr;while depleted in heavy rare earth elements Ti,Nb,Ta and P.Chondrite-normalized REE distribution patterns of granitic rocks show weak negative Eu anomalies.Therefore we speculate that the residual phase of the source has more garnets.Geochronological studies have shown that zircons,which are characterized by growth bands and high Th/U ratios(0.28~1.20),are attributed to magmatic origin.The LA-ICP-MS zircon U-Pb weighted average ages of two samples are(224.6±2.5) Ma and(216.44±0.50) Ma,respectively.In conclusion,we find that the protolith of porphyritic granitic gneiss belongs to I-type granite with source rocks of meso-basic volcanic rocks from the lower crust,and was formed in the late Triassic as evidenced by lithospheric thinning of the North China Craton in the Mesozoic.
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Located in Lapeiquan area,northern Altun Mountains of Xinjiang,the Qilesayi pluton consisting mainly of gabbro and diorite intruded into the Lapeiquan Group.This paper has studied petrographic,geochemical and zircon U-Pb chronological characteristics of gabbro and diorite from Qilesayi pluton as well as their tectonic significance.Geochemical analyses suggest that the gabbro has high Al2O3(13.47%~15.34%),FeOT(10.77%~16.89%) and moderate MgO(5.15%~7.49%) values,whereas the diorite samples are characterized by low SiO2 content(52.06%~54.23%) and high Mg# values(58.63~62.45),belonging to the calc-alkaline series.The gabbro and diorite samples have features of low ΣREE content with low fractionation of LREE/LREE and no or slightly negative Eu anomalies,depletion of HFSE(Nb,Ta,Zr,Hf) and enrichment of LILE(Rb,Ba).These geochemical features imply an origin similar to that of the subduction-related tectonic setting.Zircon U-Pb ages obtained by LA-ICP-MS analyses from the gabbro and diorite samples are 477.5±3.3 Ma and 469.7±3.4 Ma,respectively,implying that these rocks were emplaced in the Early-Middle Ordovician period.Their petrogenic ages are similar to rock-forming ages of the adjacent Bashenkaogong gigantic phenocryst granitoid(474 Ma),Bashenkaogong-Xiemierbulake quartz diorite(481.6±5.6 Ma) and Jinyanshan granodiorite intrusive bodies(467.1±6 Ma),suggesting that they may be products of the same magmatism and constitute the basic-intermediate-acidic magmatic evolution series.Integrated with geochemistry,trace elements discrimination,geochronology and regional background,it is inferred that that the gabbro and diorite were formed in a subduction-related active continental margin arc.Meanwhile,this study proposes that the gabbro and diorite from Qilesayi pluton were derived from the southward subduction of an oceanic crust to Milanhe-Jinyanshan active continental margin during the Early Paleozoic period,and this provides the corroborating evidence for the further ascertaining of the existence of the Early-Middle Ordovician continental margin arc and subduction polarity of Hongliugou-Lapeiquan ophiolite melange zone in the North Altun Mountains.
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Hornblende
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Located in Hengshan of Hunan Province, Nanyue complex pluton intruded in the Neoproterozoic Lengjiaxi Group. The LA-ICP MS zircon U-Pb ages indicate that the main pluton was formed in the Triassic with a weighted mean age of 215.5 ±1.5 Ma. However, some small granitic plutons were formed in the early Cretaceous with a206Pb/238U age of 140.6 ±0.8 Ma. The late Triassic granites are composed of three individual rock units, being mainly fine- and medium-grained porphyritic hornblende biotite monzonitic granite and surbordinately two-mica monzonitic granite. The early Cretaceous granite is two-mica monzonitic granite. The major and trace element analyses show that the late Triassic granites are of the peraluminous high-K calc-alkaline series, while the early Cretaceous granite is of the high-peraluminous high-K calc-alkaline series. The rocks are enriched in large-ion lithophile elements and depleted in high field-strength elements, with the data ∑REE= 92.88-296.56 and weak negative Eu anomaly(δEu=0.28-0.87). The Sr-Nd isotope analyses indicate high ISr values(0.7093-0.7189), low eNd values(-8.04--11.38) and high T2DM values(1.63 Ga-1.90 Ga). The results obtained by the authors show that the Nanyue muscovite-bearing peraluminous granitoids were derived from remelting of Precambrian basement, the magma source of late Triassic granites had the mixed mantle and lower crust materials, and the lithogenesis was related to the lithospheric extension after the orogenesis.
Lithophile
Hornblende
Porphyritic
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Diachronous
Dike
Sill
Continental arc
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Diorite
Hornblende
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Allanite
Felsic
Amphibole
Geochronology
Lile
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Diorite
Quartz monzonite
Felsic
Fractional crystallization (geology)
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The Kungeyite plutons,outcropped in Qingeli River in Qinghe County of southern margin of Altay orogenic belt are mainly hornblende biotite tonalite,which were determined for LA-ICP-MS zircon U-Pb ages. The result shows that the zircon206Pb /238U weighted average age is( 403. 4 ± 7. 4) Ma( MSWD = 1. 07),indicating the plutons were formed at Early Devonian. The SiO2contents range from 52. 39% to 71. 89% and σ from 0. 68 to 1. 53,A / CNK from 0. 76 to 1. 06,indicating that the plutons are mid-K calc-alkaline,metaluminous-weakly peraluminous rocks. In addition,the plutons are enrichment in LILE( Cs,Rb,Th,U) and LREE,obvious negative anomaly in HFSE( Nb,Ta,Hf,Ti),HREE and Eu( δEu = 0. 56-0. 86),thus resembling granitoid rocks formed in island-arc. Combined with the data of southern margin of Altay,the Kungeyite plutons were generated by partial melting of the lower crust underplayed by mafic magma of the mantle in a continental arc setting of active continental margin,and occurred magma mixing and differentiation.
Lile
Continental arc
Geochronology
Continental Margin
Petrogenesis
Devonian
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