陜西洋縣城山輝長巖體地球化學及鋯石U-Pb年代學研究
發(fā)布時間：2018-09-05 06:03
【摘要】：新元古代是揚子板塊巖漿活動極為發(fā)育的時期之一,其北緣漢南隆起區(qū)出露大面積的760-830Ma的各類火成巖,這一時期揚子板塊北緣的成巖構造環(huán)境存在地幔柱源巖漿作用和島弧巖漿作用兩種不同的認識,差異主要由基性雜巖體的地球化學數據解釋和認識不同而造成。漢南基性雜巖區(qū)西北部的畢機溝-城山巖帶,東部畢機溝一帶,輝長巖體上部層位發(fā)現有大型含釩鈦磁鐵礦床,研究程度較高,西部城山輝長巖體研究程度低,本文通過對城山輝長巖體的野外地質、元素地球化學特征、巖石類項和礦物組合特征、鋯石U-Pb同位素年齡、鋯石氧同位素組成研究,深入討論該輝長巖體成因類型及漢南基性雜巖動力學機制。取得的主要研究工作進展包括:(1)城山巖體由紫蘇輝長巖、輝長巖、含云母輝長巖組成,見少量含橄欖石輝長巖。與畢機溝巖區(qū)相比,巖石類型相對穩(wěn)定,成分韻律層構造不發(fā)育,紫蘇輝石、黑云母等暗色礦物呈現出弱定向排列,可見有由礦物粒度變化顯示的韻律層構造,巖石學研究指示斜長石早于輝石結晶,指示其成巖巖漿為干熔漿。巖體周邊發(fā)育有與其密切伴生的花崗閃長巖,淺、暗色礦物成略定向排列,呈條帶狀構造,主要有斜長石、單斜輝石和角閃石組成。(2)礦物學研究揭示,城山輝長巖體中斜長石的Ca含量變化較大,An:38-70,中長石為主,其次為鈉長石和倍長石;單斜輝石主要為普通輝石;斜方輝石多為紫蘇輝石。與含釩鈦磁鐵礦畢機溝巖體礦物成分的對比研究表明,造巖礦物類型一致,成分特征反映城山輝長巖體相當于結晶分異完善的畢機溝輝長巖體所揭示的堆晶層位的橄欖輝長巖帶,或反映,城山輝長巖區(qū)距巖漿補給區(qū)遠,靠近巖漿房邊緣,結晶分異不甚發(fā)育。(3)巖石地球化學研究揭示,微量元素蛛網圖中顯示城山巖體富集Ba、K、Sr等大離子親石元素(LILE),部分樣品呈現不同程度虧損Nb、Ta、Zr、Hf和Th等高場強元素(HFSE),輝長巖中顯示出弱的Ti負異常;城山輝長巖體中各類巖石均顯示具LREE富集的右傾配分模式,部分巖石呈現出Eu正異常,顯示成巖過程中伴有分離結晶和斜長石的堆晶,且Eu的異常與Zr、Hf的異常呈現正相關,即Eu越富集,Zr、Hf的虧損程度就越弱;結合常量元素成分主體沿拉斑玄武巖趨勢線演化的特征,顯現其成巖母巖漿為堿性玄武質熔漿。(4)城山輝長巖體三件樣品進行LA-ICP-MS鋯石U-Pb測年分析,結果顯示城山輝長巖體輝長巖(15BJ-119)和紫蘇輝長巖(15BJ-125)的成巖年齡分別為為781.5±4.0 Ma和783.1±3.7 Ma,揭示城山輝長巖體的成巖年齡約為782 Ma。與城山輝長巖體密切伴生的花崗閃長巖(15BJ-120)中成巖年齡780.4±6.0 Ma,并捕獲有820.2±3.8 Ma的捕獲鋯石,指示其可能是研究區(qū)~820 Ma基性玄武質巖漿活動侵入結晶后,隨后期構造運動發(fā)生部分熔融的產物。(5)對紫蘇輝長巖(15BJ-125)中鋯石氧同位素組成進行了初步研究,表明,城山輝長巖體礦物的氧同位素值δ18O(‰)介于4.52-7.14之間平均值δ18O(‰)為5.53,指示了成巖母巖漿沒有受到地殼物質混染,由幔源玄武質溶漿上升侵位至下地殼后,在相對穩(wěn)定和封閉環(huán)境下結晶成巖。(6)綜合研究揭示城山輝長巖體是揚子北緣~820Ma玄武質巖漿大規(guī)模侵入之后又一次幔源巖漿活動產物,侵位年齡~782 Ma,該期巖漿成分具有鈣堿性巖特征,含有相對高的K2O+Na2O,和LREE及大離子親石元素,反映城山輝長巖是伴隨Rodinia超大陸裂解,在揚子北緣發(fā)生進一步裂解,形成有~782Ma的大陸玄武巖漿侵入和早期結晶巖石部分熔融產生的中酸性巖漿活動。
[Abstract]:The Neoproterozoic is one of the most developed periods of the Yangtze plate magmatism. The Hannan uplift in the northern margin of the Yangtze plate exposed a large area of 760-830 Ma igneous rocks. During this period, there were two different understandings of mantle plume-derived magmatism and island-arc magmatism in the diagenetic tectonic environment of the northern margin of the Yangtze plate. The difference was mainly due to the geology of the basic complex. In the Bijigou-Chengshan rock belt in the northwest of Hannan basic complex area and in the Bijigou area in the east, a large-scale vanadium-bearing titanomagnetite deposit has been found in the upper stratum of gabbro-intrusive body. The study of Chengshan gabbro-intrusive body in the west is relatively low. In this paper, the field geology and elements of Chengshan gabbro-intrusive body have been studied. Geochemical characteristics, rock types and mineral assemblages, zircon U-Pb isotope age, zircon oxygen isotope composition, and in-depth discussion of the genetic types of the gabbro and the dynamics of the basic complex in Hannan have been carried out. The main research progresses achieved include: (1) Chengshan pluton is composed of purple peridotite gabbro, gabbro and mica-bearing gabbro. A small amount of olivine-bearing gabbro is found. Compared with Bijigou area, the rock type is relatively stable, the composition rhythm layer structure is not developed, dark minerals such as perilla pyroxene and biotite show a weak directional arrangement. It can be seen that there are rhythm layer structures indicated by mineral grain size changes. Petrological studies indicate that plagioclase crystallizes earlier than pyroxene, indicating that the magma is magmatic. Dry magma. There are granodiorites closely associated with the granodiorite, light and dark minerals aligned slightly in a directional direction, with strip-like structure, mainly plagioclase, monoclinopyroxene and amphibole. (2) Mineralogical study reveals that the Ca content of plagioclase in the Chengshan gabbro varies greatly, with A:38-70 being the dominant medium feldspar, followed by albite and amphibole. The comparative study of mineralogical compositions between the Chengshan gabbro and the Bijigou pluton of vanadium-bearing titanomagnetite shows that the type of rock-forming minerals is the same, and the composition characteristics reflect that the Chengshan gabbro is equivalent to the olivine gabbro of the accumulative horizon revealed by the well-differentiated Bijigou gabbro. (3) Petrogeochemical study reveals that the Chengshan gabbro is rich in Ba, K, Sr and other heavy ion lithophilic elements (LILE), and some samples show different depletion of Nb, Ta, Zr, Hf and Th high field strength elements (HFSE). All kinds of rocks in Chengshan gabbro body show LREE enrichment right-dip distribution pattern, and some rocks show positive Eu anomaly, indicating separation crystallization and plagioclase accumulation during diagenesis, and Eu anomaly is positively correlated with Zr and Hf anomalies, that is, the more Eu enrichment, the more Zr and Hf are depleted. (4) LA-ICP-MS zircon U-Pb dating of three samples of Chengshan gabbro shows that the diagenetic ages of Chengshan gabbro gabbro (15BJ-119) and purple peridotite gabbro (15BJ-125) are respectively. The diagenetic age of the Chengshan gabbro is about 782 Ma. The diagenetic age of the granodiorite (15BJ-120) closely associated with the Chengshan gabbro is 780.4+6.0 Ma, and the trapped zircon with 820.2+3.8 Ma is captured, indicating that it may be the result of intrusion and crystallization of ~820 Ma basic basaltic magma. The oxygen isotope composition of zircon in the Zisu gabbro (15BJ-125) has been preliminarily studied. The results show that the oxygen isotope value of the Chengshan gabbro is between 4.52-7.14 and the average value of 8240 (6) The Chengshan gabbro is the product of mantle-derived magma activity after the large-scale intrusion of basaltic magma from the northern margin of Yangtze to 820 Ma. The emplacement age is ~782 Ma. The magma composition of this period is characterized by calc-alkaline rocks with relatively high K2 content. O+Na2O, LREE and large-ion lithophilic elements indicate that the Chengshan gabbro was accompanied by the Rodinia supercontinent cracking and further cracking occurred in the northern margin of Yangtze, resulting in the formation of intermediate-acid magmatism resulting from the continental basalt magma intrusion of ~782Ma and the partial melting of early crystalline rocks.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P59;P588.124
本文編號：2223413
[Abstract]:The Neoproterozoic is one of the most developed periods of the Yangtze plate magmatism. The Hannan uplift in the northern margin of the Yangtze plate exposed a large area of 760-830 Ma igneous rocks. During this period, there were two different understandings of mantle plume-derived magmatism and island-arc magmatism in the diagenetic tectonic environment of the northern margin of the Yangtze plate. The difference was mainly due to the geology of the basic complex. In the Bijigou-Chengshan rock belt in the northwest of Hannan basic complex area and in the Bijigou area in the east, a large-scale vanadium-bearing titanomagnetite deposit has been found in the upper stratum of gabbro-intrusive body. The study of Chengshan gabbro-intrusive body in the west is relatively low. In this paper, the field geology and elements of Chengshan gabbro-intrusive body have been studied. Geochemical characteristics, rock types and mineral assemblages, zircon U-Pb isotope age, zircon oxygen isotope composition, and in-depth discussion of the genetic types of the gabbro and the dynamics of the basic complex in Hannan have been carried out. The main research progresses achieved include: (1) Chengshan pluton is composed of purple peridotite gabbro, gabbro and mica-bearing gabbro. A small amount of olivine-bearing gabbro is found. Compared with Bijigou area, the rock type is relatively stable, the composition rhythm layer structure is not developed, dark minerals such as perilla pyroxene and biotite show a weak directional arrangement. It can be seen that there are rhythm layer structures indicated by mineral grain size changes. Petrological studies indicate that plagioclase crystallizes earlier than pyroxene, indicating that the magma is magmatic. Dry magma. There are granodiorites closely associated with the granodiorite, light and dark minerals aligned slightly in a directional direction, with strip-like structure, mainly plagioclase, monoclinopyroxene and amphibole. (2) Mineralogical study reveals that the Ca content of plagioclase in the Chengshan gabbro varies greatly, with A:38-70 being the dominant medium feldspar, followed by albite and amphibole. The comparative study of mineralogical compositions between the Chengshan gabbro and the Bijigou pluton of vanadium-bearing titanomagnetite shows that the type of rock-forming minerals is the same, and the composition characteristics reflect that the Chengshan gabbro is equivalent to the olivine gabbro of the accumulative horizon revealed by the well-differentiated Bijigou gabbro. (3) Petrogeochemical study reveals that the Chengshan gabbro is rich in Ba, K, Sr and other heavy ion lithophilic elements (LILE), and some samples show different depletion of Nb, Ta, Zr, Hf and Th high field strength elements (HFSE). All kinds of rocks in Chengshan gabbro body show LREE enrichment right-dip distribution pattern, and some rocks show positive Eu anomaly, indicating separation crystallization and plagioclase accumulation during diagenesis, and Eu anomaly is positively correlated with Zr and Hf anomalies, that is, the more Eu enrichment, the more Zr and Hf are depleted. (4) LA-ICP-MS zircon U-Pb dating of three samples of Chengshan gabbro shows that the diagenetic ages of Chengshan gabbro gabbro (15BJ-119) and purple peridotite gabbro (15BJ-125) are respectively. The diagenetic age of the Chengshan gabbro is about 782 Ma. The diagenetic age of the granodiorite (15BJ-120) closely associated with the Chengshan gabbro is 780.4+6.0 Ma, and the trapped zircon with 820.2+3.8 Ma is captured, indicating that it may be the result of intrusion and crystallization of ~820 Ma basic basaltic magma. The oxygen isotope composition of zircon in the Zisu gabbro (15BJ-125) has been preliminarily studied. The results show that the oxygen isotope value of the Chengshan gabbro is between 4.52-7.14 and the average value of 8240 (6) The Chengshan gabbro is the product of mantle-derived magma activity after the large-scale intrusion of basaltic magma from the northern margin of Yangtze to 820 Ma. The emplacement age is ~782 Ma. The magma composition of this period is characterized by calc-alkaline rocks with relatively high K2 content. O+Na2O, LREE and large-ion lithophilic elements indicate that the Chengshan gabbro was accompanied by the Rodinia supercontinent cracking and further cracking occurred in the northern margin of Yangtze, resulting in the formation of intermediate-acid magmatism resulting from the continental basalt magma intrusion of ~782Ma and the partial melting of early crystalline rocks.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P59;P588.124
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