Twin magma source geneses of bimodal volcanic rocks in continental rifts, Se China: Constraints on elemental and Nd-Pb-isotopic studies

1998 ◽  
Vol 43 (S1) ◽  
pp. 39-39
Author(s):  
Z. Fang ◽  
X. C. Tao ◽  
H. M. Li ◽  
J. H. Yu ◽  
H. B. Lu
Keyword(s):  
Volcanic Rocks ◽  
Magma Source ◽  
Isotopic Studies ◽  
Continental Rifts ◽  
Se China

Magmatic evidence for Late Carboniferous-Early Permian slab breakoff and extension of the southern Mongolia collage system in Central Asia

2021 ◽  
Author(s):  
Hai Zhou ◽  
Guochun Zhao ◽  
Donghai Zhang
Keyword(s):  
Subduction Zones ◽  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Ocean Basin ◽  
Magma Source ◽  
Central Asian ◽  
Slab Rollback ◽  
Slab Breakoff ◽  
Subduction Fluids ◽  
Arc Setting

<p>Oceanic subduction and its last underthrusted part can both triggers arc-like magmatism. As the existence of multi-subduction zones in the Central Asian Orogenic Belt, controversy still surrounds on when and especially how the subduction of the (Paleo-Asian Ocean) PAO terminated. We present geochronological, geochemical, and Lu-Hf isotopic data for a suite of basalt-andesites, dacite-rhyolites and later trachyandesite-mugearitic dykes from the Khan-Bogd area in the Gobi Tianshan Zone (GTZ) of the southern Mongolia. U-Pb dating of zircons indicate the basalt-andesites and dacite-rhyolites were formed at ~334-338 Ma, and the dykes at ~300 Ma. These Early Carboniferous volcanic rocks display high U/Th, Ba/Th, low La/Sm and variable Zr/Nb ratios, implying the involvement of subduction fluids or sediment melt. They display arc geochemical features such as calc-alkaline and metaluminous nature and positive Ba and U and negative Nb, Ta and Ti anomalies. Moreover, their continental geochemical signals (e.g. positive Pb, K anomalies) and some old captured zircons implying a continental arc setting. Comparatively, the ~300 Ma dykes are characterized by high alkaline contents, which are common for coeval (~320-290 Ma) and widespread post-subductional granites there. Given a mainly crust-derived magma source for those granites, these dykes likely reflect a mantle disturbance due to: (1) their relative low SiO<sub>2 </sub>(51.71-55.85 wt. %) and high Mg# (40.3-67.3) values, and (2) positive zircon Ɛ<sub>Hf</sub>(t) (most > 12). Considering a slab rollback model during the Carboniferous and Triassic, the mantle disturbance was possibly induced by the oceanic slab breakoff. Combined with previous work, this ~320-290 Ma slab breakoff-induced extension marks the closure of a wide secondary ocean (North Tianshan-Hegenshan ocean) north of the main ocean basin of the PAO. This research was financially supported by NSFC Projects (41730213, 42072264, 41902229, 41972237) and Hong Kong RGC GRF (17307918).</p>

Geochemistry of Sainte-Marguerite volcanic rocks: implications for the evolution of Silurian–Devonian volcanism in the Gaspé Peninsula

2008 ◽  
Vol 45 (1) ◽  
pp. 15-29 ◽  
Author(s):  
Alan D’hulst ◽  
Georges Beaudoin ◽  
Michel Malo ◽  
Marc Constantin ◽  
Pierre Pilote
Keyword(s):  
Lower Devonian ◽  
Volcanic Rocks ◽  
Magma Source ◽  
Volcanic Arc ◽  
Lower Silurian ◽  
Trace Element Signature ◽  
Arc Setting ◽  
Back Arc ◽  
Gaspe Peninsula ◽  
Gaspé Peninsula

The Lower Devonian Sainte-Marguerite volcanic rocks are part of a Silurian–Devonian volcanic sequence deposited between the Taconian and Acadian orogenies in the Gaspé Peninsula, Quebec, Canada. The Sainte-Marguerite unit includes basaltic and dacitic lava flows with calc-alkaline and volcanic-arc affinities. Such affinities are also recorded by the trace-element signature in Lower Silurian and most Lower Devonian volcanic units of the Gaspé Peninsula. However, most of the other Silurian–Devonian volcanic rocks occurring in the Gaspé Peninsula have been previously interpreted to have erupted in an intracontinental setting. A back-arc setting for the Gaspé Peninsula between the Taconian and Acadian orogenies could account for these subduction volcanic-arc signatures, though a metasomatized lithospheric mantle magma source, unrelated to subduction, cannot be excluded. Lower Silurian and Lower Devonian volcanic rocks in the central part of the Gaspé Peninsula show an arc affinity, whereas Upper Silurian and Lower to Middle Devonian volcanic rocks, located in the south and north of the Gaspé Peninsula, respectively, show a within-plate affinity. The Lower Devonian Archibald Settlement and Boutet volcanic rocks of the southern and northern Gaspé Peninsula, respectively, show a trend toward a within-plate affinity. This suggests that within-plate volcanism migrated from south to north through time in an evolving back-arc environment and that the subduction signature of Lower Silurian and Lower Devonian rocks results from a source that melted only under the central part of the Gaspé Peninsula.

scholarly journals Genesis of Volcanic Rocks in the Zijinshan Ore District, SE China: Implications for Porphyry-Epithermal Mineralization

Minerals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 200 ◽  
Author(s):  
Zheng-Zheng Feng ◽  
Zhong-Jie Bai ◽  
Hong Zhong ◽  
Wei-Guang Zhu ◽  
Shi-Ji Zheng
Keyword(s):  
Oxygen Fugacity ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Parental Magma ◽  
High Oxygen ◽  
Magma Source ◽  
High Water Content ◽  
High Oxygen Fugacity ◽  
Epithermal Mineralization ◽  
T Values

Volcanic rocks, as the extrusive counterparts of the mineralized intrusions, can provide important information on the magma source, petrogenesis, and metallogenic conditions of the coeval porphyry-epithermal system. Shanghang Basin volcanic rocks are spatially and temporally related to a series of adjacent porphyry-epithermal Cu–Au deposits, and they can be used as a window to study the related deposits. Two laser-ablation–inductively coupled plasma–mass spectrometry zircon U–Pb analyses of the volcanic rocks yield weighted mean ages of ~105 Ma, identical to the age of the coeval porphyry-epithermal mineralization. Rocks have SiO2 contents of 55.4 to 74.8 wt % and belong to the high-K to shoshonitic series, characterized by strong differentiation of light rare-earth elements (REEs) relative to heavy REEs (mean LaN/YbN = 16.88); enrichment in light REEs, Rb, Th, and U; and depletion in Nb, Ta, Zr, Hf, and Ti. The volcanic rocks display (87Sr/86Sr)i values of 0.709341 to 0.711610, εNd(t) values of −6.9 to −3.3 εHf(t) values of −3.95 to −0.30, and δ18O values of 6.07‰–6.79‰, suggesting that the parental magmas were derived from a mantle source enriched by subduction-related progress. SiO2 content shows a strong negative correlation with the contents of some major and trace elements, indicating that fractional crystallization played an important role in the generation of these rocks. A binary mixing model of Hf–O isotopes gives an estimated degree of crustal contamination of 30%. In addition, magnetite crystallized early, and the samples showed high zircon EuN/EuN* values (0.48–0.68), indicating that the parental magma had a high oxygen fugacity. The inferred suppression of plagioclase crystallization and increasing hornblende crystallization during magma evolution suggest that the magma was water rich. The high-water content and high oxygen fugacity of the magma promoted the dissolving of sulfides containing Cu and Au in the source area and contributed to the migration of ore-forming elements.

Andesite Geochemistry Features of Late Triassic Tumugou Formation, in Zhongdian, Yunnan Province

2012 ◽  
Vol 524-527 ◽  
pp. 16-23
Author(s):  
Jian Guo Huang ◽  
Run Sheng Han ◽  
Ren Tao ◽  
Zhi Qiang Li
Keyword(s):  
Trace Element ◽  
Volcanic Rock ◽  
Continental Margin ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Distribution Patterns ◽  
Island Arc ◽  
Late Triassic ◽  
Magma Source ◽  
Volcanic Arc

The Late Triassic Tumugou Formation volcanic rocks which belongs to typical island arc volcanic rocks in southern end of Yidun island arc belt is located at the eastern of the Zhongdian ,NW Yunnan, SW China. The volcanic rocks can be divided into three categories:andesitic basalt, andesite, quartz andesite, etc. Through geochemical analysis the major elements, rare earth ele and trace element in volcanic rocks, SiO255.18-57.59×10-2,TiO21.16-1.45×10-2,Na2O+K2O5.11-8.05×10-2.consider it is calc-alkaline- alkaline Series of high-K andesite, volcanic may be controlled by the crystal fractionation of magma.Rb31.50-101×10-6,Ba1310-12300×10-6,Nb/Ta11.4-15.5,REE166.07-240.78×10-6,δEu0.74-1.00,REE distribution patterns show oblique to the HREE side and enrichment in LREE .Eu anomaly is not obvious. It is can see from the relevant figure about trace element, it is very similar in magmatic distribution patterns between volcanic rock and Volcanic-arc rock, indicating that the volcanic in this area may be formed in volcanic-arc environment. From east to west, Magma source depth have regular change with the really thickness of mainland shell. Explain that Tumugou Formation volcanic rock is subduction by Ganzi- Litang Ocean basin from east to west. Hongshan-Ousaila region of eastern edge of Zhongdian is the volcanic island arc system during the passive continental margin into an active continental margin.

Sr isotopic studies of volcanic rocks from island arcs in the western pacific

1977 ◽  
Vol 37 (1-3) ◽  
pp. 141-151 ◽  
Author(s):  
Jun-Ichi Matsuda ◽  
Shigeo Zashu ◽  
Minoru Ozima
Keyword(s):  
Volcanic Rocks ◽  
Western Pacific ◽  
Island Arcs ◽  
Isotopic Studies ◽  
The Western Pacific
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