【作者】 苟军；

【导师】 孙德有；

【作者基本信息】 吉林大学 ， 矿物学、岩石学、矿床学， 2010， 硕士

【摘要】 本文对满洲里南部地区白音高老组火山岩进行了详细的岩石学、年代学、元素地球化学及锆石Lu-Hf同位素研究,厘定了火山岩的形成时代,阐述了火山岩的成因,探讨了其形成的构造背景。满洲里南部白音高老组火山岩的岩石类型主要有流纹岩、黑云母流纹岩、球粒流纹岩、碱长流纹岩、珍珠岩和流纹质岩屑晶屑熔结凝灰岩,锆石U-Pb定年结果显示其主体形成于139~141Ma的早白垩世早期,并非是以往认为的晚侏罗世或主要形成于120-130Ma之间。白音高老组火山岩属碱性岩,元素地球化学特征与大陆裂谷碱性流纹岩和A型花岗岩相似,并相当于张吉衡(2008)所定义的大兴安岭低Ba-Sr流纹岩。借鉴花岗岩的成因分类,在Whalen et al.(1987)和Eby(1992)所提出的花岗岩成因类型相关判别图解上,白音高老组流纹岩均位于A型花岗岩区,且属A1型。锆石Lu-Hf同位素特征显示,满洲里南部地区白音高老组火山岩的εHf(t)值>0,变化于3.49~9.98之间,两阶段Hf模式年龄(TDM2)介于556~951Ma之间,属新元古代。显示出与兴蒙造山带显生宙花岗岩的Nd和Hf模式年龄相同的特征,暗示其可能与显生宙花岗岩具有相同的岩浆源区。综合研究认为,白音高老组火山岩浆的源区为新元古代时期形成的基性下地壳物质。锆石饱和温度显示该火山岩浆形成温度约为768℃~874℃之间,火山岩低Sr高Yb的特征表明其形成压力较低,源区有斜长石和角闪石矿物相残留。根据本文对白音高老组流纹岩的研究结果,结合区域相关研究资料,认为满洲里南部白音高老组火山岩形成于非造山板内张性构造环境,与蒙古-鄂霍茨克洋闭合后的伸展作用有关。更多还原

【Abstract】 Southern Manchuria located in the central Mongolia - Ergun massif in the Eastern Xingmeng orogenic belt between the North China craton and the Siberian craton. Tectonic Evolution of this area is complicated, including the Paleo-Asian Ocean tectonic domain during Paleozoic, Mongol-Okhotsk tectonic domain during Mesozoic and Pacific tectonic domain since Mesozoic-Cenozoic. Study of Mesozoic volcanic rocks in this area is lagging behind, further research of these volcanic rocks will provide solid information for deeping the spatial and temporal evolution of the late Mesozoic volcanic magmatic activities, further dissecting the petrogenesis of the volcanic rocks and investigating the tectonic setting of the volcanic rocks, and will administer to deepen the comparative study of the whole Daxinganling volcanic belt.Based on our geochronology study and previous research results, the classification and correlation of the volcanic rocks have been established. The volcanic strata in this area were divided into five formations,including Middle Jurassic Tamulangou Formation, Late Jurassic Manketouebo and Manitu formations, Early Cretaceous Baoyingaolao and Meiletu formations. The main rock type of the volcanic rocks are rhyolite, biotite rhyolite, spherulitic rhyolite, alkali feldspar rhyolite, perlite and Rhyolitic lithic crystal-chip ignimbrite according to the geological investigation and petrographic study. Zircon LA-ICPMS U-Pb dating show the volcanic rocks in Baiyingaolao Formation were mainly formed at the earliest Early Cretaceous from 139Ma to 141Ma, different from the previous thought being formed at Late Jurassic or between 120Ma and 130Ma.The geochemistry of major elements indicate that the volcanic rocks from Baiyingaolao Formation in Southern Manchuria are characteristicd by high silica and alkali, lower Aluminum, Calcium and Magnesium, which close to the average composition of the world A-type granites and alkaline rhyolite. In the TAS classification diagram of volcanic rocks, all the samples fall into the range of the rhyolite; The alkali indexs of volcanic rocks vary from 0.80 to 0.98, average 0.91, greater than the minimum value of alkaline rocks of 0.85, near to the average of World A-type granite and alkaline rhyolite, and the alkalinity rate (AR) values range between 3.94 and 6.51, belong to alkaline rocks. The average FeOT/MgO ratio of volcanic value is 6.09 (varying from 2.77 to 36.02), significantly higher than the I-type(average 2.27), S-type (average 2.38) and M-type (average 2.37) granite.The volcanic rocks from Baiyingaolao formation are characterized by relatively high total REE contents (ΣREE=103.30×10-6~488.07×10-6) and strong negative Eu anoalies (δEu=0.01~0.41); The trace element geochemistry are characterized evidently by enrichment of Rb, Th, U, K, strong depletion of Ba, Sr, P, Ti, mediate depletion of Nb, Ta. The volcanic rocks have high Rb/Sr ratios, ranging between 1.73 and 15.33 (average 7.28), significantly different from I–type(average 0.61), S-type (average 1.81) and M-type (average 0.06) granite, also higher than the A-type granites (average 3.52); The 10000Ga/Al ratio ranges vary from 2.41 to 4.07 (average 3.52) were higher than the lower limit of A-type granite(2.6)except one sample, and significantly higher than the average values of I-type (2.1) and S-type granite (2.28).The geochemical characteristics of the volcanic rocks are similar to the continental rift alkaline rhyolite, A-type granite, and equivalent with the low Ba-Sr rhyolite from Da Hinggan Mountains defined by Zhang et al.(2008). Account to the classification illustration of granite (Whalen et al., 1987 and Eby, 1992), the volcanic rocks of Baiyingaolao Formation show an affinity with the A-type granite.Lu-Hf isotope characteristics of zircon show that the volcanic rocks of Baiyingaolao Formation in Southern Manchuria have positiveεHf(t) values, varying from 3.49 to 9.98, and TDM2 ranging from 556Ma to 951Ma, belong to the Neoproterozoic, quite agree with the Nd and Hf madel age of Phanerozoic granites from Xingmeng orogen, suggest that they may ororigined from the same magma source.The characteristics above indicate that the the magma of these volcanic rocks derived from the basic lower crust accreted from depleted mantle during Neoproterozoic. The Calculation Results of Zircon saturation temperatures suggest that the volcanic rocks were formed at the temperature of 768℃to 874℃, the volcanic rocks have lower Sr and Higher Yb contents indicate they were formed under lower pressure, residual phases of source are composed of plagioclase and amphibolite. Combining with the regional researching results, we suggest that the volcanic rocks in Baiyingaolao Formation from Southern Manchuria were formed in an intra-plate anorogenic extensional setting, which is related to the extensional functiom after the closure of Mongol-Okhotsk Ocean.更多还原