本文選題：火山作用　切入點(diǎn)：深成巖漿活動(dòng)　出處：《成都理工大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：赤城地區(qū)火山巖主要包括火山熔巖和火山碎屑巖,其中以火山熔巖為主,其次為火山碎屑巖,主要分布于該地區(qū)北部、東部及南部的一部分巖石。本文通過巖相學(xué)、礦物學(xué)、地球化學(xué)、LA-ICP-MS鋯石U-Pb測(cè)年等方法,對(duì)該地區(qū)火山巖進(jìn)行了巖石類型劃分、地球化學(xué)特征、巖漿物質(zhì)來源、形成的構(gòu)造環(huán)境以及形成時(shí)代的確定等研究,在此基礎(chǔ)上,與該地區(qū)花崗巖漿作用進(jìn)行對(duì)比,推斷赤城地區(qū)構(gòu)造演化過程。根據(jù)巖石主量元素?cái)?shù)據(jù),利用火山巖巖石類型圖解,對(duì)所采的火山巖樣品進(jìn)行巖石類型的劃分,主要為流紋巖、粗面巖、粗安巖。根據(jù)A/CNK值劃分,赤城地區(qū)火山巖屬于過鋁質(zhì),與同時(shí)期的花崗巖屬于同一系列的巖石。微量元素采用原始地幔標(biāo)準(zhǔn)化蛛網(wǎng)圖和稀土元素球粒隕石標(biāo)準(zhǔn)作圖,流紋巖具有輕稀土富集而重稀土虧損,巖漿分異程度較高的特征;具有鈣堿性演化趨勢(shì)。對(duì)火山巖進(jìn)行成因類型的劃分,由于巖石中的SiO2、Na2O和K2O含量較高,而且CaO、MgO、TiO和P2O5值較低,Sr、Rb值較低,Zr、Nb、Ce值較高,比較符合A型花崗巖的特征,并且在K2O-Na2O圖中也證明了這一推斷。對(duì)構(gòu)造環(huán)境投圖發(fā)現(xiàn),赤城地區(qū)火山巖全部形成于碰撞后構(gòu)造環(huán)境中。對(duì)火山巖εHf(t)值進(jìn)行計(jì)算并投圖發(fā)現(xiàn),其εHf(t)值全部為負(fù)值,表明赤城地區(qū)火山巖巖漿的物質(zhì)源區(qū)來自于下地殼。根據(jù)火山巖的二階段模式年齡分析赤城地區(qū)火山巖巖漿的形成年齡為1896Ma和1763Ma,即形成于古元古代。而造成源巖年齡的不一致,可能是由于形成火山巖巖漿的物源不同。LA-ICP-MS鋯石U-Pb技術(shù)獲得的火山巖年齡為(137.91±0.95)Ma和(141.03±0.95)Ma,屬于燕山期。本文通過對(duì)赤城地區(qū)燕山期火山巖與燕山期花崗巖的對(duì)比,發(fā)現(xiàn)兩者之間存在一些聯(lián)系與差異。燕山期花崗巖主要為I型花崗巖類型,與火山巖呈現(xiàn)的A型花崗巖特征有所區(qū)別�；鹕綆r與花崗巖的εHf(t)值全部為負(fù)值,說明兩者均為殼源,兩者的二階段模式年齡(tDM2)平均值為1838Ma~1763Ma、1940Ma。表明兩赤城地區(qū)火山巖與花崗巖的物質(zhì)來源均為古老的下地殼。形成于同碰撞擠壓環(huán)境下的花崗巖與形成于碰撞后拉張環(huán)境下的火山巖,兩者之間存在構(gòu)造轉(zhuǎn)換事件,其時(shí)限為(143.9±2.2)Ma~(141.03±0.95)Ma,持續(xù)時(shí)間約為2.87Ma。
[Abstract]:The volcanic rocks in Chicheng area mainly include volcanic lava and pyroclastic rocks, among which volcanic lava is the main rock, followed by pyroclastic rock, mainly distributed in the northern, eastern and southern parts of the area. Geochemical LA-ICP-MS zircon U-Pb dating method has been used to study the classification of volcanic rocks, geochemical characteristics, source of magmatic material, tectonic environment of formation and determination of forming age in this area. The tectonic evolution process of Chicheng area is inferred by contrasting with granite magma in this area. According to the data of rock principal elements and the diagram of volcanic rock types, the rock types of volcanic rock samples collected are classified mainly as rhyolite. The volcanic rocks in the Chicheng area belong to peraluminous rocks and belong to the same series of rocks as the granite of the same period. Trace elements are mapped using the primitive mantle standardized spider web map and the standard rare earth element chondrites. The rhyolite is characterized by light rare earth enrichment, heavy rare earth depletion, high magma differentiation, calc-alkaline evolution trend. For the classification of volcanic rocks, the content of Sio _ 2N _ 2O and K _ 2O in the rocks is relatively high. In addition, the values of CaOO _ (MgO) _ (TIO) and P _ 2O _ (5) are lower, and the values of Sr _ 2O _ (RB) are lower than that of zirconia, which is consistent with the characteristics of A-type granite, and this inference is also proved in the K _ 2O-Na _ 2O diagram. The volcanic rocks in Chicheng area were all formed in the post-collision tectonic environment. This indicates that the source of volcanic magma in Chicheng area comes from the lower crust. According to the two-stage model age of volcanic rocks, the age of formation of volcanic magma in Chicheng area is 1896 Ma and 1763 Ma, that is, formed in ancient Gu Yuan, which results in the inconsistent age of source rocks. It may be due to the different provenance of volcanic magma. LA-ICP-MS zircon U-Pb technique has obtained volcanic rocks of 137.91 鹵0.95Ma and 141.03 鹵0.95Ma. which belong to Yanshanian period. This paper compares Yanshanian volcanic rocks with Yanshanian granites in Chicheng area. It is found that there are some relations and differences between them. The Yanshanian granites are mainly I-type granite types, which are different from the A-type granite features of volcanic rocks. The 蔚 Hftt values of volcanic rocks and granites are all negative, indicating that both of them are crust-source. The average two-stage model age (tDM2) is 1838 Ma, 1763 Ma, 1940 Ma. it shows that the material sources of volcanic rocks and granites in the two Chicheng areas are both ancient lower crust, which are formed in the same collision compression environment and the volcanic rocks formed in the post-collision extensional environment. There is a tectonic transition event between them, the time limit is 143.9 鹵2.2 Ma, 141.03 鹵0.95Ma, and the duration is about 2.87 Ma.
【學(xué)位授予單位】：成都理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P317;P588.1

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本文編號(hào)：1584896