本文選題：柴北緣 + 石英閃長寄主巖�。� 參考：《合肥工業(yè)大學(xué)》2017年碩士論文

【摘要】：柴達(dá)木盆地北緣果可山地區(qū)石英閃長巖中發(fā)育大量的暗色微粒包體,石英閃長寄主巖及其暗色微粒包體鋯石U-Pb定年結(jié)果分別為247 Ma和250 Ma,在誤差范圍內(nèi)二者形成時(shí)代一致,均為柴北緣三疊紀(jì)早期(早、中三疊世)巖漿活動(dòng)產(chǎn)物。石英閃長寄主巖屬準(zhǔn)鋁質(zhì)-弱過鋁質(zhì)系列(A/CNK=0.95~1.02),具有I型花崗巖特征。寄主巖富集輕稀土元素和大離子親石元素,相對(duì)虧損重稀土元素和高場(chǎng)強(qiáng)元素,顯示出弧巖漿巖特征。寄主巖具有平坦的重稀土元素配分曲線,暗示角閃巖可能為主要的源區(qū)殘留相礦物。巖石學(xué)實(shí)驗(yàn)表明其可能由低鉀的玄武質(zhì)巖石(角閃巖)部分熔融形成,而不是中-高鉀玄武巖、英云閃長巖、變硬砂巖部分熔融形成。寄主巖MgO含量(2.04%~2.44%)和Mg#值(48.9~51.9)均高于變玄武巖/變泥巖在1~4 GPa壓力下部分熔融形成的熔體,暗示其形成過程中有幔源物質(zhì)的加入。寄主巖鋯石低的Ti溫度和高的Ce4+/Ce3+比值,反映其結(jié)晶自低溫、高氧逸度巖漿,暗示巖漿形成過程中可能有富水熔體/流體的加入;另外,寄主巖La/Nb比值(2.27~2.64)與活動(dòng)大陸邊緣區(qū)高La/Nb比值(2.0)特征相吻合,并在花崗巖構(gòu)造環(huán)境判別圖解上均落在火山弧環(huán)境區(qū)域,表明寄主巖可能是活動(dòng)大陸邊緣環(huán)境下,由下地殼角閃巖部分熔融產(chǎn)生的巖漿和幔源巖漿混合而成。暗色微粒包體巖性為閃長質(zhì)巖石;呈橢圓狀、透鏡狀和不規(guī)則狀產(chǎn)出,與寄主巖石界限截然,部分暗色微粒包體具有弱的拉長現(xiàn)象或發(fā)育反向脈。暗色微粒包體具有巖漿結(jié)構(gòu),礦物顆粒明顯小于寄主巖,發(fā)育礦物不平衡結(jié)構(gòu)(斜長石包含有早期結(jié)晶形成的角閃石微晶)和短柱狀-針狀磷灰石。另外,暗色微粒包體其Nb/Ta比值(9.50~10.33)和Zr/Hf比值(27.65~36.92)接近于大陸地殼(Nb/Ta=11,Zr/Hf=33)。綜合以上表明,閃長質(zhì)暗色微粒包體為基性巖漿注入酸性巖漿與之發(fā)生不徹底混合的產(chǎn)物。結(jié)合區(qū)域地質(zhì)背景分析,認(rèn)為柴北緣果可山地區(qū)石英閃長寄主巖及其暗色微粒包體形成于古特提斯洋向北俯沖的活動(dòng)大陸邊緣弧環(huán)境。
[Abstract]:A large number of dark particle inclusions have been developed in quartz diorites in the northern margin of Qaidam Basin. The U-Pb dating results of quartz diorite and its dark grain-inclusion zircon are 247Ma and 250Ma, respectively. The age of their formation is the same within the error range. They are the products of early Triassic (early and Middle Triassic) magmatic activity in the northern margin of Qaihai. Quartz diorite is a kind of quasialuminum-weak peraluminous series (A / CNK _ (0.95N) 1.02), which is characterized by I-type granite. The host rocks are enriched in light rare earth elements and large ion lithophile elements, and are relatively depleted of heavy rare earth elements and high field strength elements, showing the characteristics of arc magmatic rocks. The host rock has a flat distribution curve of heavy rare earth elements, suggesting that amphibolite may be a major source of residual facies minerals. The petrological experiments indicate that it may be formed by partial melting of low potassium Black Tortoise rocks (amphibolite), rather than medium-high potassium basalt, dolomite diorite, and hardened sandstone. The MgO content and Mg# value of host rock are higher than that of melts formed by partial melting of metamorphic rocks / metamorphic rocks under 1 GPa pressure, indicating that there are mantle source materials in the formation process of the host rocks. The low Ti temperature and high Ce4 / ce _ 3 ratio of zircon from host rock indicate that the crystallization of the host rock is from low temperature and high oxygen fugacity magma, suggesting that there may be water-rich melt / fluid in magma formation. The La/Nb ratio of host rock (2.27 / 2.64) coincides with that of high La/Nb ratio (2.0) in active continental margin, and falls in volcanic arc environment on the distinguishing diagram of granite tectonic environment, indicating that the host rock may be active continental margin environment. Magma derived from partial melting of amphibolite in the lower crust is mixed with mantle magma. The diorite rocks are ellipsoidal, lenticular and irregular, and have a distinct boundary with host rocks. Some of the inclusions have weak elongations or develop reverse veins. The dark particle inclusions have magmatic structure, and the mineral particles are obviously smaller than the host rocks. The mineral disequilibrium structure (plagioclase contains hornblende microcrystals formed in early crystallization) and short columnar acicular apatite. In addition, the Nb/Ta ratio of dark particle inclusions is 9.50 ~ 10.33) and the Zr/Hf ratio is 27.65 ~ 36.92), which is close to that of NB / Ta _ (11) Zr / HF ~ (33) in continental crust. The above results indicate that the diorite dark color inclusions are the product of incomplete mixing of basic magma injected with acid magma. Based on the analysis of the regional geological background, it is considered that the quartz diorite host rock and its dark particle inclusions were formed in the active continental margin arc environment of the PaleoTethys ocean subducting northward in the Guokeshan area of the northern margin of Qaidam.
【學(xué)位授予單位】：合肥工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P597.3;P588.12

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