1. Zircon U-Pb chronology, geochemistry, and petrogenesis of the high Nb-Ta alkaline rhyolites at the Tuohe Tree Farm, northern Volcanic Belt, Great Xing'an Range, China
- Author
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Sun, Guosheng, Zhao, Tianxue, Jin, Ruixiang, and Wang, Qinghai
- Subjects
Volcanoes -- Canada -- China -- Australia -- Chronologies ,Rare earth metals -- Chronologies ,Petrogenesis -- Chronologies ,Tectonics (Geology) -- Chronologies ,Zirconium -- Chronologies ,Basalt -- Chronologies ,Earth -- Mantle ,Earth sciences - Abstract
We studied newly found high Nb-Ta alkaline rhyolites in the northern volcanic belt of the Great Xing'an Range, China. The LA-ICP-MS U-Pb weighted mean age is 114.07 [+ or -] 0.55 Ma, indicating that the rocks formed during the late Early Cretaceous and were the product of the late eruption of a Mesozoic volcano. The major element contents are characterized by high Si, rich K, low Fe, and poor Ca and Mg. In the total alkaline--silicon diagram, the sample points are in the alkaline rhyolite region. Meanwhile, rare earth elements show obvious Ce/Ce* positive anomalies and Eu/Eu* negative anomalies. In addition, trace elements are characterized by high Nb, Ta, and Yb, and low Sr. The two-stage Nd isotopic model age [T.sub.2]DM of the depleted mantle is between 799-813 Ma, indicating that the diagenetic material originated from the depleted mantle or partial melting of newly formed young crustal materials. The source rocks melted at a relative shallow depth ( Key words: Xingan block, high Nb-Ta, alkaline rhyolite, zircon U-Pb chronology, geochemistry, petrogenesis. Nous avons etudie des rhyolites alcalines riches en Nb-Ta decouvertes recemment dans la ceinture volcanique septentrionale de la chaine du Grand Xing'an (Chine). L'age U-Pb pondere moyen obtenu par LA-ICP-MS est de 114,07 [+ or -] 0,55 Ma, ce qui indique que les roches se sont formees vers la fin du Cretace precoce et sont le produit de l'eruption tardive d'un volcan mesozoique. La signature des elements majeurs est riche en Si et K et pauvre en Fe, Ca et Mg. Dans le diagramme alcalis totaux-silice, les echantillons tombent dans la region des rhyolites alcalines. Les terres rares presentent pour leur part des anomalies positives du rapport Ce/Ce* et negatives du rapport Eu/Eu*; la signature des elements traces est en outre riche en Nb, Ta et Yb et pauvre en Sr. L'age [T.sub.2]DM obtenu des isotopes de Nb pour un modele a deux etapes du manteau appauvri est de 799-813 Ma, indiquant que le materiau source provient du manteau appauvri ou de la fusion partielle de jeunes materiaux crustaux nouvellement formes. La fusion des roches sources s'est produite a relativement faible profondeur ( Mots-cles : bloc de Xing'an, Nb-Ta eleves, rhyolite alcaline, geochronologie U-Pb sur zircon, geochimie, petrogenese., Introduction The northern volcanic belt of the Great Xing'an Range is the superimposed portion of the ancient Asian oceanic tectonic domain, the Pacific domain, and the Mongolia--Okhotsk oceanic domain (Wu [...]
- Published
- 2019
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