Zoned quartz and feldspar phenocrysts of the Upper Carboniferous eastern Erzgebirge volcano-plutonic complex were studied by cathodoluminescence and minor and trace element profiling. The results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends, magma mixing and recharge events, and suggest that much heterogeneity in plutonic systems may be overlooked on a whole-rock scale. Multiple resorption surfaces and zones, element concentration steps in zoned quartz (Ti) and feldspar phenocrysts (anorthite content, Ba, Sr), and plagioclase-mantled K-feldspars etc. indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern Erzgebirge volcano-plutonic complex. Generally, feldspar appears to be sensitive to the physicochemical changes of the melt, whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas. The regional distribution of mixing-compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late-Variscan granites and associated volcanic rocks.
Quartz phenocrysts from 14 magmatic phases of the eastern Erzgebirge volcano-plutonic complex provide information on the relative timing of different mixing processes, storage and recharge, allowing a model for the distribution of magma reservoirs in space and time. At least two levels of magma storage are envisioned: deep reservoirs between 24 and 17 km (the crystallisation level of quartz phenocrysts) and subvolcanic reservoirs between 13 and 6 km. Deflation of the shallow reservoirs during the extrusion of the Teplice rhyolites triggered the formation of the Altenberg-Teplice caldera above the eastern Erzgebirge volcano-plutonic complex. The deep magma reservoir of the Teplice rhyolite also has a genetic relationship to the younger mineralised A-type granites, as indicated by quartz phenocryst populations. The pre-caldera biotite granites and the rhyodacitic Schönfeld volcanic rocks represent temporally and spatially separate magma sources. However, the deep magma reservoir of both is assumed to have been at a depth of 24–17 km. The drastic chemical contrast between the pre-caldera Schönfeld (Westfalian B–C) and the syn-caldera Teplice (Westfalian C–D) volcanic rocks is related to the change from late-orogenic geotectonic environment to post-orogenic faulting, and is considered an important chronostratigraphic marker. 相似文献
The Ejina Oasis (EO), located in arid northwest China, is a typical arid area in the world. The ecosystem in the oasis has
become worse since the 1990s. However, it began to improve after the Chinese government took the mandatory measure to redistribute
the water in Heihe in 2000. To understand this change, the remote sensing images in 1990, 2000 and 2006 were selected, and
exertion related Land Use/Cover Change (LUCC) model was employed. Results showed that: (1) non-vegetation cover was the main
body of the vegetation cover in oasis, showing a trend of increase at the beginning and diminution later, while low, medium
and high vegetation cover was the other way around; (2) the area of low, medium and high vegetation cover in 2006 was less
than that in 1990; the status and trend index Pt of oasis vegetation cover was 0.62 in 1990–2000, which means that the oasis ecosystem of Ejina was getting worse and was
under an unbalanced status; Pt was 0.27 in 2000–2006 indicating that the oasis ecosystem was restored obviously and the whole system tended to be balanced;
(3) all of these changes should be attributed to the water resources redistribution in Heihe River, which played a leading
role, as well as the measures and relevant policies taken by the local government, which promoted the rapid recovery of the
medium and high vegetation. 相似文献