Petrology and geochemistry of Carboniferous volcanic rocks from the Awulale Iron Metallogenetic Belt in the West Tianshan Orogen (NW China): Constraints on petrogenesis and tectonic setting

Volcanic rocks of Early Cretaceous Yixian Formation were widely distributed in western Liaoning. The Yixian Formation in the Chaoyang basin can be divided into two subcycles from bottom to top. The first subcycle is composed of basalt, basalt andesite and andesite. The second subcycle is composed of trachyandensite and trachyte. The volcanic rocks are characterized by high SiO2, Al2O3, K2O and Na2O, and comparatively low TiO2 components. The volcanic rocks are obviously enriched in incompatible elements (K, Rb, Sr, Zr, Ba, Pb, Li etc.), and depleted in compatible elements (Co, Ni, Cr, V etc.). The volcanic rocks are rich in LREE. There is a slight low Eu negative abnormality and low Ce negative abnormality. Based on t he studies of petrology and geochemistry, volcanic rocks of Yixian Formation belong to the high-K calc-alkaline magmatic serious. Comprehensive study of regional structures and geochemistry of volcanic rocks, the volcanic rocks of Yixian Formation were generated in the environment of lithosphere inhomogeneous extension, as a product of the intraplate orogeny of Yanshan Mountains.

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Detrital zircon constraints on the tectonic evolution of the Gravina belt, southeastern Alaska

Canadian Journal of Earth Sciences ◽

10.1139/e97-110 ◽

1998 ◽

Vol 35 (3) ◽

pp. 253-268 ◽

Cited By ~ 33

Author(s):

Paul A Kapp ◽

George E Gehrels

Keyword(s):

Detrital Zircon ◽

Tectonic Setting ◽

Volcanic Rocks ◽

Upper Jurassic ◽

Ocean Basin ◽

Detrital Zircons ◽

Plate Motion ◽

The West ◽

Gravina Belt ◽

Cordilleran Margin

Upper Jurassic - Lower Cretaceous marine clastic strata and mafic to intermediate volcanic rocks of the Gravina belt are part of a complex suture zone separating the Alexander and Wrangellia terranes on the west from the Yukon-Tanana and Stikine terranes to the east. U-Pb ages have been determined on 118 single detrital zircon grains from Gravina strata in an effort to determine the tectonic setting of the Gravina belt and the paleoposition of outboard terranes prior to their Late Cretaceous juxtaposition against inboard terranes. Samples from five stratigraphic units yield ages of 105-120 (n = 5), 140-165 (n = 56), 310-380 (n = 17), 400-450 (n = 19), 520-560 (n = 5), 920-1310 (n = 5), and 1755-1955 Ma (n = 5). The 105-120 and 140-165 Ma grains were shed primarily from arc-related plutons that lie outboard of the Gravina belt. The lack of 120-140 Ma ages coincides with a lull in magmatism in the outboard arc and in the western United States, which suggests that Gravina strata accumulated during major changes in plate motion along the Cordilleran margin. The 400-560 Ma zircons were derived from rocks of the Alexander terrane which also lie to the west. In contrast, the 310-380 and >900 Ma grains were apparently shed from inboard regions. Likely sources include the Yukon-Tanana and Stikine terranes in the northern Cordillera and assemblages in the northern California region which contain igneous rocks and detrital zircons of the appropriate ages. Our data accordingly support models in which the Gravina basin formed in narrow rift or transtensional basins, whereas the outboard Alexander and Wrangellia terranes were located along the California - Oregon - Washington - British Columbia - Alaska margin. Our data are less supportive of models in which the Gravina strata and underlying Alexander and Wrangellia terranes were separated from western North America by a large ocean basin, or were located along the coast of Mexico.

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