Decoding whole rock, plagioclase, zircon and apatite isotopic and geochemical signatures from variably contaminated dioritic magmas
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Io-ages obtained for glass-zircon pairs which were not consistent with expected ages were discussed on the basis of uranium and thorium distribution between zircon and glass. Uranium and thorium distribution between zircon and host rocks from dacites and granites were also discussed. Discordant Io-ages obtained for glass-zircon pairs with normal (Th/U)zircon/(Th/U)glass ratio are explained by early stage crysallization of the zircon in the magma. Discordant Io-ages with abnormal (Th/U)zircon/(Th/U)glass ratios suggest that the zircon was captured in the magma as xenoryst. The discrepancy between (Th/U)zircon/(Th/U)glass ratios (about 0.19) for dacites and (Th/U)zircon/(Th/U)whole rock ratios (about 0.12) for granites could be explained by crystallization of granitic zircon from liquid having chemical composition different from that of the whole rock of granite.
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The intrusive rocks in El Sela area can be arranged from the oldest to the youngest into: two-mica granite and postgranitic dikes which include microgranite, dolerite and bostonite dikes. Zircon is the most abundant accessory mineral. Zircon morphology and geochemical features are good indicators for evolution of rocks. The aim of the work is to determine the morphology, internal structure and chemical composition of zircon to identify the difference of zircon in various intrusive rocks. Results show that morphologically, zircon in the two-mica granite is euhedral coarse- grained with zonation. It is represented by crystals up to 125 µm and corresponds to S10 and P2. Zircon in post-granitic dikes exhibit irregular forms. Geochemically, zircon crystals have higher ZrO2 values in the core whereas HfO2 , UO2 , ThO2 increase at the peripheries of zoned crystals of the two-mica granite. Zircon of two-mica granite contains high HfO2 , UO2 , ThO2 and CaO contents but low Sc2 O3 content. HfO2 is not detected in zircon of microgranite. TiO2 in zircon of two-mica granite and bostonite dikes is under detection limits. REEs are not recorded in zircon of the studied intrusive rocks
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Abstract Major, trace, and isotopic compositions of plagioclase megacrysts from plagioclase ultraphyric basalts (PUB) from multiple mid‐ocean ridges were determined to characterize the liquid compositions from which they were derived. Large (up to 2 cm) plagioclase megacrysts exhibit homogeneous major element compositions, with variable degrees of trace element and isotopic heterogeneity. The pattern and degree of heterogeneity is itself variable between megacrysts, with some being homogenous and others exhibiting a wide range of trace element and isotopic zoning. Liquids calculated to be in equilibrium with the plagioclase megacrysts exhibit a range equivalent to lavas erupted from entire ridge segments. Many of the megacrysts may be considered to be cognate xenocrysts in that they are related to the same mantle material as the host lavas in which they were carried to the surface. The observed trace element patterns together with the isotopic diversity suggest a complex set of processes are active, that include mixing of distinct primitive melts, fractional crystallization, and diffusive reequilibration. The degree to which each process influences the megacrysts varies between individual crystals in each sample. Equally important is the range of composition we see within individual crystals. For example, Ba concentrations vary by as much as a factor of 5 but not systematically from core to rim.
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Table S1: Location information for new detrital zircon samples. Table S2: New zircon U-Pb and trace element data. Table S3: Compiled zircon U-Pb and trace element data. Figure S1: Comparison of Ce anomaly (A) and Eu anomaly (B) of zircons calculated using the method of Onuma et al. (1968) and traditional methods. Figure S2: Summary figures from zircon trace element compilation.
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In this article we present a compilation of U-Pb zircon ages of the whole Xolapa terrane in coastal southern Mexico (dataset 1) as a curved line, obtained from plotting individual zircon grains versus its corresponding age. We identified five low-slope segments of the curved line, each one assigned to a high zircon-production (or preservation) event (HZE). Crystallization temperatures (CT) from Ti-in-zircon geothermometer data on Xolapa rocks were estimated separately from individual zircon grains (dataset 2), in order to compare CT ranges corresponding to each HZE identified. Datasets 1 and 2 are discussed for tectonic implications in the research article "The opening and closure of the Jurassic-Cretaceous Xolapa basin, southern Mexico" Peña-Alonso et al., 2017.
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