scholarly journals Iron Isotope Compositions of Ultrapotassic Volcanic Rocks from Northeastern China and the Implication on Deep Oxygen Cycle

2020 ◽  
Author(s):  
Yongsheng He ◽  
Qianqian Yan ◽  
Shan Ke
Keyword(s):  
Volcanic Rocks ◽  
Northeastern China ◽  
Iron Isotope ◽  
Oxygen Cycle

A method to estimate the pre-eruptive water content of basalts: Application to the Wudalianchi–Erkeshan–Keluo volcanic field, Northeastern China

2020 ◽  
Vol 105 (2) ◽  
pp. 149-161 ◽  
Author(s):  
Yankun Di ◽  
Wei Tian ◽  
Mimi Chen ◽  
Zefeng Li ◽  
Zhuyin Chu ◽  
...  
Keyword(s):  
Water Content ◽  
Volcanic Rocks ◽  
High Water ◽  
Volcanic Field ◽  
Northeastern China ◽  
Magma Ascent ◽  
High Water Content ◽  
Silica Activity ◽  
Igneous Provinces ◽  
The Difference

Abstract Water plays an important role in the generation and evolution of volcanic systems. However, the direct measurement of the pre-eruption water content of subaerial volcanic rocks is difficult, because of the degassing during magma ascent. In this study, we developed a method to calculate the pre-eruption water content of the basalts from the Cenozoic Wudalianchi–Erkeshan–Keluo (WEK) potassic volcanic field, Northeastern China, and investigated their mantle source. A water-insensitive clinopyroxene–melt thermobarometer and a water-sensitive silica activity thermobarometer were applied to these basalts. Two pressure-temperature (P-T) paths of the ascending magma were calculated using these two independent thermobarometers, with a similar P-T slope but clear offset. By adjusting the water content used in the calculation, the difference between the two P-T paths was minimized, and the water content of the WEK melts was estimated to be 4.5 ± 1.2 wt% at a pressure range of 10.1–13.5 kbar, corresponding to depths of 37–47 km. Degassing modeling shows that during the magma ascent from below the Moho to near the surface, CO2 was predominantly degassed, while the melt H2O content kept stable. Significant H2O degassing occurred until the magma ascended to 5–2 kbar. The silica activity P–T estimates of the most primary WEK samples suggest that the magmas were generated by the melting of convective mantle, which was probably facilitated by a wet upwelling plume from the mantle transition zone. The high water content found in the WEK basalts is similar to the recent reports on Phanerozoic intraplate large igneous provinces (LIPs) and supports the presence of hydrated deep mantle reservoirs as one possible source of the LIPs.

Geochronology of the Mesozoic volcanic rocks in the Great Xing'an Range, northeastern China: Implications for subduction-induced delamination

2010 ◽  
Vol 276 (3-4) ◽  
pp. 144-165 ◽  
Author(s):  
Ji-Heng Zhang ◽  
Shan Gao ◽  
Wen-Chun Ge ◽  
Fu-Yuan Wu ◽  
Jin-Hui Yang ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Northeastern China ◽  
Great Xing’An Range

TEM/AEM characterization of fine-grained clay minerals in very-low-grade rocks: Evaluation of contamination by empa involving celadonite family minerals

1996 ◽  
Vol 54 ◽  
pp. 694-695
Author(s):  
Gejing Li ◽  
D. R. Peacor ◽  
D. S. Coombs ◽  
Y. Kawachi
Keyword(s):  
Electron Microscopy ◽  
Volcanic Rocks ◽  
Analytical Electron Microscopy ◽  
Metamorphic Rocks ◽  
New Mineral ◽  
Chemical Compositions ◽  
Low Grade ◽  
Fine Grained ◽  
Depth Analysis ◽  
Mineral Aggregates

Recent advances in transmission electron microscopy (TEM) and analytical electron microscopy (AEM) have led to many new insights into the structural and chemical characteristics of very finegrained, optically homogeneous mineral aggregates in sedimentary and very low-grade metamorphic rocks. Chemical compositions obtained by electron microprobe analysis (EMPA) on such materials have been shown by TEM/AEM to result from beam overlap on contaminant phases on a scale below resolution of EMPA, which in turn can lead to errors in interpretation and determination of formation conditions. Here we present an in-depth analysis of the relation between AEM and EMPA data, which leads also to the definition of new mineral phases, and demonstrate the resolution power of AEM relative to EMPA in investigations of very fine-grained mineral aggregates in sedimentary and very low-grade metamorphic rocks.Celadonite, having end-member composition KMgFe3+Si4O10(OH)2, and with minor substitution of Fe2+ for Mg and Al for Fe3+ on octahedral sites, is a fine-grained mica widespread in volcanic rocks and volcaniclastic sediments which have undergone low-temperature alteration in the oceanic crust and in burial metamorphic sequences.

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