發(fā)布時(shí)間：2018-05-22 12:15

  本文選題：揚(yáng)子地塊 + 米倉山��； 參考：《西北大學(xué)》2017年碩士論文

【摘要】：揚(yáng)子地塊北緣新元古代經(jīng)歷了復(fù)雜地質(zhì)過程,并發(fā)育大量的鎂鐵質(zhì)-酸性-堿性侵入巖體。米倉山位于揚(yáng)子地塊北緣,關(guān)于該區(qū)的新元古代堿性雜巖的成因機(jī)制及深部動力學(xué)背景目前仍存在極大爭議。本論文通過對揚(yáng)子地塊北緣米倉山地區(qū)堿性雜巖體展開詳細(xì)的巖石學(xué)、全巖主微量、Sr-Nd同位素及鋯石U-Pb年代學(xué)的研究,基本厘清了該區(qū)新元古代侵入雜巖體的時(shí)空格架,并結(jié)合地球化學(xué)探討該區(qū)堿性雜巖的成因機(jī)制、構(gòu)造環(huán)境及深部動力學(xué)過程。論文的研究工作取得如下成果和認(rèn)識:1、堿性巖(磷霞巖和正長巖)和閃長巖都形成于新元古代早期(～865Ma),是同一構(gòu)造背景下不同部位的巖漿產(chǎn)物。其中磷霞巖(高鎂和低鎂)具有較低的硅含量,并且Na_2OK_2O,高堿,屬于鈉質(zhì)堿性巖。稀土元素含量較低,富集大離子親石元素,虧損高場強(qiáng)元素。初始鍶比值變化范圍較大,正εNd(t)值(+0.8～-+3.27);水磨正長巖(富鈉和富鉀)具有高SiO_2、(Na_2O + K_2O)和里特曼指數(shù)(σ),低TiO_2、MgO、Al_2O_3,屬于堿性準(zhǔn)鋁質(zhì)巖系。稀土元素含量相對較低,其中輕稀土元素相對富集,重稀土元素相對虧損,弱負(fù)Eu異常,富集大離子親石元素,虧損高場強(qiáng)元素。較低初始鍶比值,正εNd(t)值(+0.89～+1.29)。二者起源于虧損地幔源,經(jīng)結(jié)晶分異演化,在后續(xù)巖漿上升過程中可能遭受了地殼的同化混染,并且正長巖演化過程不同于磷霞巖,可能是超基性-堿性巖漿演化期間不同階段的產(chǎn)物,形成于陸緣弧內(nèi)裂谷的構(gòu)造環(huán)境。石英閃長巖具有高SiO_2、Al_2O_3、TFe_2O_3和Na_2O,低K_2O、CaO和A/CNK,屬于鈉質(zhì)堿性準(zhǔn)鋁質(zhì)巖系。較低稀土元素,負(fù)Eu異常,富集Rb、Ba、Pb等,虧損Nb、Ta等,中等初始鍶比值,正εNd(t)值(+2.92～+3.66),是新生玄武質(zhì)下地殼部分熔融的產(chǎn)物,在其上升演化的過程中明顯遭受了上地殼的同化混染,形成于大陸邊緣弧的構(gòu)造環(huán)境。2、輝長巖和花崗巖形成于新元古代中期(～745Ma),其中中子園輝長巖具有低SiO_2和Na_2O,且Na_2OK_2O,高Al_2O_3、TFe_2O_3和CaO,屬于鈣堿性基性巖系。較低稀土元素總量,富集大離子親石元素,虧損高場強(qiáng)元素,無明顯Eu異常,具有低初始鍶值,正εNd(t)值(+1.6～+4.5),其起源于石榴石二輝橄欖巖虧損地幔源,其熔融程度大于15%,在巖漿上升演化階段遭受了地殼混染作用,是弧后盆地構(gòu)造環(huán)境下的產(chǎn)物。二長花崗巖具有高硅,低TiO_2、MgO、CaO、P2O5和Mg#值。稀土元素含量較低,輕重稀土元素分餾明顯,富集輕稀土元素及Rb、U和Th,虧損Ba、Nb和P,負(fù)Eu異常,屬于高分異Ⅰ型花崗巖類。正εNd(t)值(+3.6～+5.2),二階段模式年齡值為0.96～1.07Ga,是新生玄武質(zhì)下地殼部分熔融的產(chǎn)物,在其上升演化的過程中明顯遭受了上地殼的同化混染,形成于弧后伸展的構(gòu)造環(huán)境。3、綜合相關(guān)區(qū)域地質(zhì)構(gòu)造熱時(shí)間,揚(yáng)子北緣在新元古代時(shí)期(900Ma～700Ma)總體上可能處于俯沖相關(guān)的構(gòu)造背景,米倉山地區(qū)新元古代時(shí)期的巖漿活動可以大致劃分為三個(gè)階段,經(jīng)歷了從早期陸緣弧(裂谷)(～860Ma)到火山弧(～830Ma)再到弧后伸展(～750Ma)的構(gòu)造演化。揚(yáng)子北緣米倉山地區(qū)堿性侵入雜巖是俯沖相關(guān)構(gòu)造環(huán)境,是米倉山地區(qū)新元古代時(shí)期兩階段的巖漿事件,為進(jìn)一步探討揚(yáng)子北緣新元古代期間巖漿作用的成因機(jī)制和深部動力學(xué)提供重要的巖石學(xué)約束。
[Abstract]:The Neoproterozoic Era of the northern margin of the Yangtze block has experienced complex geological processes and developed a large number of mafic acid alkaline intrusive rocks. M Cangshan is located in the northern margin of the Yangtze block. The genetic mechanism and deep dynamic background of the Neoproterozoic alkaline complex in this area are still very controversial. This paper has passed to the northern margin of the Yangtze massif, Cangshan. The detailed petrology of the regional alkaline complex, the main trace of the whole rock, the Sr-Nd isotopes and the zircon U-Pb chronology have basically clarified the space-time framework of the Neoproterozoic intrusive complex in this area, and discussed the genetic mechanism, the tectonic environment and the deep dynamic process of the alkaline complex in this area with the geochemistry. The research work of this paper has been obtained. The following achievements and understandings are as follows: 1, the alkaline rocks (Lin Xiayan and zenyan) and diorite are formed in the early Neoproterozoic (~ 865Ma) and are the magma products of different parts of the same tectonic setting. Among them, the Phosphorite (high magnesium and low magnesium) has lower silicon content and Na_2OK_2O, high alkali, and sodium alkaline rock. The rare earth element is low and rich in enrichment. The initial strontium ratio has a high variation range, the initial strontium ratio has a larger variation range, the positive epsilon Nd (T) value (+0.8 ~ -+3.27), the high SiO_2, (Na_2O + K_2O) and Litman index (Na_2O + K_2O), and the low TiO_2, MgO, Al_2O_3, and low rare earth elements in the water mill. The rare-earth elements are relative loss, weak negative Eu anomaly, enrichment of large ion stone elements, high field strong elements, low initial strontium ratio and positive epsilon Nd (T) value (+0.89 to +1.29). The two originates from the source of the depleted mantle, and the evolution of crystallization differentiation may suffer from the assimilation and mixed dyeing of the crust during the subsequent magma ascending process, and the evolution process of the syenite is not. The same to the phosphorite, may be the product of the different stages of the ultrabasic basic magma evolution, which formed in the tectonic environment of the continental margin rift. The quartz diorite has high SiO_2, Al_2O_3, TFe_2O_3 and Na_2O, low K_2O, CaO and A/CNK, which belongs to the alkaline alkaline aluminous rock system of sodium, and the lower rare earth elements, negative Eu anomalies, enrichment Rb, Ba, Pb, etc. The medium initial strontium ratio and positive epsilon Nd (T) value (+2.92 ~ +3.66) are the products of partial melting of the new basaltic lower crust. In the process of its ascending and evolution, the upper crust was obviously subjected to assimilation and contamination of the upper crust and formed in the tectonic environment of the continental margin arc, and the gabbro and granite formed in the middle Neoproterozoic (to 745Ma), of which the gabbro of the neutron orchards is in the middle of the Neoproterozoic. Low SiO_2 and Na_2O, and Na_2OK_2O, high Al_2O_3, TFe_2O_3 and CaO, belong to the basic Calc basic rock series. The total amount of low rare-earth elements, rich in large ion stone elements, loss of high field and strong elements, no obvious Eu anomalies, low initial strontium, and positive e Nd (+1.6 to +4.5) value (+1.6 to +4.5), originated from the source of the garnet peridotite depleted mantle, which has a large melting degree. 15%, in the stage of the magma rising and evolution, the crustal contamination is the product of the crustal contamination, which is the product of the tectonic environment in the back arc basin. The two granites have high silicon, low TiO_2, MgO, CaO, P2O5 and Mg# values. The REE content is low, the heavy rare earth elements are fractionated, the light rare earth elements and Rb, U and Th are enriched, and the loss Ba, Nb and P, negative Eu anomalies, belong to high fractionated I. The type granitoids, the positive epsilon Nd (T) value (+3.6 ~ +5.2), the two stage model age value of 0.96 to 1.07Ga, are the products of the partial melting of the new basaltic lower crust. In the process of its ascending and evolution, the assimilation and contamination of the upper crust was obviously affected, and formed in the tectonic setting of.3 in the post arc extension. The Neoproterozoic Era (900Ma ~ 700Ma), in general, may be in the subduction related tectonic setting. The magmatic activity of the Neoproterozoic Era in Cangshan area can be roughly divided into three stages, which experienced the tectonic evolution from early continental margin arc (rift) to 860Ma to volcanic arc (to 830Ma) and then to post arc extension (to 750Ma). The alkaline intrusive complex is a subduction related tectonic environment, which is the two stage of the Neoproterozoic magma event in the Cangshan area, which provides important petrological constraints for further exploration of the genesis and deep dynamics of the Neoproterozoic magmatism during the northern margin of the Yangtze River.
【學(xué)位授予單位】：西北大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P588.15
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本文編號：1922019