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In the southern Great Xing'an Range, the Xishala area exposes a substantial amount of Mesozoic strata of Xinmin Formation (J2x) and Manketouebo Formation (J3m). However, due to the presence of rhyolite in the rock association, it is easy to confuse the stratigraphic division and lead to disputes of the stratigraphic attribution of rhyolite. Therefore, zircon U-Pb dating and geochemical characteristic analysis of the rhyolites were conducted, and stratigraphic sections of the Xinmin and Manketouebo Formations were compared to explore the formation age, tectonic setting, and stratigraphic attribution of the rhyolites. The results indicate that the geochemical characteristics of the riolites in Xishala area are high SiO2 content (The value of mean is 75.74%.), rich alkali content [mean(Na2O+K2O)=7.69%] and low Mg and Ca content, belonging to peraluminous and high-K calc-alkaline series. The Chondrite-normalized REE pattern is right-dip type, with relative enrichment of LREE and relative depletion of HREE, the value of (La/Yb)Nis between 10.61~14.21 and strong negative Eu anomaly (The value of δEu is between 0.44~0.53.). LILE(large ion lithophilic elements) such as Rb, Ba and K are relatively enriched, while HFSE(high field strength elements) such as Nb, Ta and Ti are relatively depleted, indicating that the magma originated from crustal materials. The LA-ICP-MS zircon U-Pb dating results show that the age of the rhyolite is (167.7±2.6) Ma, belonging to the Middle Jurassic, and it formes in the extensional tectonic action after the closure of the Mongolian-Okhotsk ocean. Based on the comparative study of regional geology and sectional rock assemblage types, the rhyolite belongs to the Manketouebo Formation.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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