Contrasting arc magma fertilities in the Gangdese belt, Southern Tibet: Evidence from geochemical variations of Jurassic volcanic rocks

Lithos ◽  
2019 ◽  
Vol 324-325 ◽  
pp. 789-802 ◽  
Author(s):  
Xilian Chen ◽  
Jeremy P. Richards ◽  
Huaying Liang ◽  
Yinqiao Zou ◽  
Jian Zhang ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Southern Tibet ◽  
Geochemical Variations ◽  
Arc Magma

scholarly journals Petrogenesis and Geodynamic Implications of Miocene Felsic Magmatic Rocks in the Wuyu Basin, Southern Gangdese Belt, Qinghai-Tibet Plateau

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 655
Author(s):  
Hanzhi Chen ◽  
Mingcai Hou ◽  
Fuhao Xiong ◽  
Hongwei Tang ◽  
Gangqiang Shao
Keyword(s):  
Lower Crust ◽  
Volcanic Rocks ◽  
Tibet Plateau ◽  
Southern Tibet ◽  
Mixed Product ◽  
Good Opportunity ◽  
Magmatic Rocks ◽  
Adakitic Rocks ◽  
Felsic Volcanic ◽  
Qinghai Tibet Plateau

Miocene felsic magmatic rocks with high Sr/Y ratios are widely distributed throughout the Gangdese belt of southern Tibet. These provide a good opportunity to explore the magmatic process and deep dynamic mechanisms that occurred after collision between the Indo and the Asian plates. In this paper, felsic volcanic rocks from the Zongdangcun Formation in the Wuyu Basin in the central part of the southern Gangdese belt are used to disclose their origin. Zircon U-Pb geochronology analysis shows that the felsic magmatism occurred at ca. 10.3 ± 0.2 Ma, indicating that the Zongdangcun Formation formed during the Miocene. Most of these felsic magmatic rocks plot in the rhyolite area in the TAS diagram. The rhyolite specimens from the Zongdangcun Formation have the characteristics of high SiO2 (>64%), K2O, SiO2, and Sr contents, a low Y content and a high Sr/Y ratio, and the rocks are rich in LREE and depleted in HREE, showing geochemical affinity to adakitic rocks. The rocks have an enriched Sr-Nd isotopic composition (εNd(t) = −6.76 to −6.68, (87Sr/86Sr)i = 0.7082–0.7088), which is similar to the mixed product of the juvenile Lhasa lower continental crust and the ancient Indian crust. The Hf isotopes of zircon define a wide compositional range (εHf(t) = −4.19 to 6.72) with predominant enriched signatures. The Miocene-aged crustal thickness in southern Tibet, calculated on the basis of the Sr/Y and (La/Yb)N ratios was approximately 60–80 km, which is consistent with the thickening of the Qinghai-Tibet Plateau. The origin of Miocene felsic magmatic rocks with high Sr/Y ratios in the middle section of the Gangdese belt likely involved a partial melting of the thickened lower crust, essentially formed by the lower crust of the Lhasa block, with minor contribution from the ancient Indian crust. After comprehensively analyzing the post-collisional high Sr/Y magmatic rocks (33–8 Ma) collected from the southern margin of the Gangdese belt, we propose that the front edge tearing and segmented subduction of the Indian continental slab may be the major factor driving the east-west trending compositional changes of the Miocene adakitic rocks in southern Tibet.

scholarly journals Multi-stage arc magma evolution recorded by apatite in volcanic rocks

Geology ◽  
2020 ◽  
Vol 48 (4) ◽  
pp. 323-327 ◽  
Author(s):  
Chetan L. Nathwani ◽  
Matthew A. Loader ◽  
Jamie J. Wilkinson ◽  
Yannick Buret ◽  
Robert H. Sievwright ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Explosive Volcanism ◽  
Ore Deposits ◽  
Magma Evolution ◽  
Arc Magmas ◽  
Deep Crust ◽  
Multi Stage ◽  
Novel Approach ◽  
Arc Magma

Abstract Protracted magma storage in the deep crust is a key stage in the formation of evolved, hydrous arc magmas that can result in explosive volcanism and the formation of economically valuable magmatic-hydrothermal ore deposits. High magmatic water content in the deep crust results in extensive amphibole ± garnet fractionation and the suppression of plagioclase crystallization as recorded by elevated Sr/Y ratios and high Eu (high Eu/Eu*) in the melt. Here, we use a novel approach to track the petrogenesis of arc magmas using apatite trace element chemistry in volcanic formations from the Cenozoic arc of central Chile. These rocks formed in a magmatic cycle that culminated in high-Sr/Y magmatism and porphyry ore deposit formation in the Miocene. We use Sr/Y, Eu/Eu*, and Mg in apatite to track discrete stages of arc magma evolution. We apply fractional crystallization modeling to show that early-crystallizing apatite can inherit a high-Sr/Y and high-Eu/Eu* melt chemistry signature that is predetermined by amphibole-dominated fractional crystallization in the lower crust. Our modeling shows that crystallization of the in situ host-rock mineral assemblage in the shallow crust causes competition for trace elements in the melt that leads to apatite compositions diverging from bulk-magma chemistry. Understanding this decoupling behavior is important for the use of apatite as an indicator of metallogenic fertility in arcs and for interpretation of provenance in detrital studies.

scholarly journals LATE OLIGOCENE THOLEIITIC LAVA FROM KENANGA RIVER, TEGALOMBO PACITAN, EAST JAVA

2009 ◽  
Vol 1 (1) ◽  
Author(s):  
Dian Novia Sartika ◽  
I Wayan Warmada ◽  
Bhakti H. Harahap ◽  
Widiasmoro Soewondo
Keyword(s):  
Volcanic Rocks ◽  
Parental Magma ◽  
Volcanic Glass ◽  
Island Arc ◽  
Petrographic Analysis ◽  
Late Oligocene ◽  
Basaltic Composition ◽  
Regional Tectonic ◽  
Opaque Minerals ◽  
Arc Magma

Watupatok Formation in Pacitan area consists of lava with basaltic composition and pillow structure. Kenanga river is only 5 km to southeast Watupatok village as type locality of this formation. Kenanga river’s lava were varying from diabasic with paving surface and columnar joint structure to basaltic composition with pillow structure. Lava were found as effusive flow and dike with sandstone inclusion. In field observation, lava exhibits strong porphiritic to aphyric texture, with vesicular to amygdaloidal structure. Plagioclase as phenocryst has mediumsized (2-4 mm) surrounded by volcanic glass as groundmass. Petrographic analysis shows intersertal to hyalophilitic texture, consist of plagioclase, pyroxene and opaque minerals as phenocryst and also groundmass together with volcanic glass. Seconday minerals are quartz, zeolite and calcite. Geochemichal analysis results indicate a low TiO2 (0.8– 0.9 wt.%), medium to high Al2O3 (14–17 wt.%), high Fe2O3 (10–12 wt.%) and low Mg value (Mg#) (39–42). According to TAS and AFM diagram, the rocks is apparently to be basalt and tholeiitic island arc magma. While spidergram pattern of the trace elements shows relatively flat fo HREE and enriched pattern on LREE. Niobium element displays a depleted anomaly, indicated that the crust influences in parental magma, which is another characteristic of magmatic island arc. Based on regional tectonic, the volcanic rocks from Late Oligocene in the area has relationship with subduction processes between Indo-Australia plate and Eurasian plate.Keywords: Pillow structure, tholeiitic, lava, subduction

Geochemical variations in Middle Ordovician volcanic rocks of the northern Miramichi Highlands and their tectonic significance

1991 ◽  
Vol 28 (7) ◽  
pp. 1031-1049 ◽  
Author(s):  
C. R. Van Staal ◽  
J. A. Winchester ◽  
J. H. Bédard
Keyword(s):  
Volcanic Rocks ◽  
Structural Data ◽  
Middle Ordovician ◽  
Chemical Signatures ◽  
Geochemical Study ◽  
Lower Ordovician ◽  
Geochemical Variations ◽  
Thrust Zone ◽  
Arc Setting ◽  
Back Arc

A detailed geochemical study of Middle Ordovician volcanic rocks, undertaken in the northern Miramichi Highlands of New Brunswick, shows that 10 basaltic suites can be distinguished. These suites are assigned to the Tetagouche and Fournier groups. The contact between these two groups is a major thrust zone, marked for over 70 km by a prominent blueschist zone. All the Tetagouche Group volcanic rocks have chemistries consistent with extrusion in a continental rift, but most Fournier Group basalts in the Miramichi Highlands have chemistries suggestive of an oceanic back-arc setting. The chemical signatures, stratigraphic variations, and structural data indicate that the northern Miramichi Highlands preserve a section across a telescoped Middle Ordovician back-arc basin that initially opened as a result of asthenospheric injection near the rear part of a Lower Ordovician ensialic arc.

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