貴州省大方地區(qū)峨眉山玄武巖基本特征及成因分析
發(fā)布時間：2018-08-16 10:49
【摘要】：峨眉山大火成巖省分為內帶、中帶、外帶。貴州省大方地區(qū)的峨眉山玄武巖位于峨眉山大火成巖省的外帶,作為峨眉山玄武巖的重要部分,雖受到眾多學者的密切關注,但是對大火成巖省外帶貴州境內的峨眉山玄武巖研究卻相對較少。本文以野外實地調查為基礎,通過研究大方地區(qū)峨眉山玄武巖的巖石學特征、礦物學特征和地球化學特征等,并與鄰近的水城玄武巖為主要對比,分析了大方地區(qū)的峨眉山玄武巖的巖石學、礦物學和地球化學特征,探討其巖漿源區(qū)性質、成巖溫度壓力及玄武巖形成的構造背景。通過野外地質調查和剖面測制查明了大方地區(qū)峨眉山玄武巖的時空分布、巖石類型及巖性特征,研究其噴發(fā)環(huán)境、噴發(fā)旋回及韻律。營盤、珠場兩地雖相距不遠,但火山噴發(fā)旋回、噴發(fā)韻律(次數(shù))、玄武巖累計厚度以及玄武巖間的灰?guī)r夾層和厚度等均有明顯差異,表明本區(qū)二疊紀峨眉山玄武巖不僅橫向上而且在垂向上的變化都較大,分布不是很穩(wěn)定。玄武巖以巨厚層的塊狀構造為主,未見枕狀熔巖,火山集塊角礫巖中常見有灰紅色、褐灰色火山碎屑物,且局部沉火山碎屑巖夾層中發(fā)現(xiàn)有雙殼類化石、植物化石以及大量植物莖干化石碎片產出,這些特征均表明該套玄武巖總體上應形成于水上噴發(fā)環(huán)境。從小屯鄉(xiāng)珠場剖面(PM11)和高店鄉(xiāng)營盤剖面(PM38)上玄武巖巖石類型、巖石組合以及灰?guī)r夾層的產出特征分析,研究區(qū)內二疊紀基性火山噴發(fā)作用由早到晚可劃分為三個噴發(fā)旋回,并以第三旋回為主要噴發(fā)時期。大方縣小屯鄉(xiāng)珠場玄武巖剖面上三個巖漿噴發(fā)旋回均可劃分為9個噴發(fā)韻律;而高店鄉(xiāng)營盤玄武巖剖面僅劃分出兩個巖漿噴發(fā)旋回,但形成的火山巖地層累計厚度較大,可劃分為14個噴發(fā)韻律。巖石類型主要有微晶玄武巖、隱晶玄武巖、杏仁狀玄武巖及玄武質凝灰?guī)r和火山角礫巖等。本區(qū)玄武巖造巖礦物為斜長石和單斜輝石,副礦物為磁鐵礦、鈦鐵礦、榍石等。玄武巖具間隱結構、間粒結構、玻基交織結構等,局部杏仁體構造發(fā)育。通過單礦物電子探針分析,單斜輝石主要為普通輝石,其端元組分為Wo=37.45~40.80,En=36.54~42.89,Fs=17.06~23.22;斜長石主要為拉長石,少量中長石,其端元組分為An=41.34~58.71,Ab=38.79~54.29,Or=1.55~10.06;金屬礦物主要為鈦鐵礦,其次為磁鐵礦和鈦磁鐵礦。主量元素特征顯示SiO_2=46.42%~51.28%,平均值48.70%;TiO_2=4.07%~4.66%,平均值4.34%,屬高鈦玄武巖;玄武巖的K_2O+Na_2O均值為3.33%,全堿含量并不高;大部分巖石的里特曼指數(shù)(σ)小于3.3,多介于1.02~2.93,平均值2.15,屬鈣堿性巖石;Mg~#值=37.20~51.70,平均值43.01;m/f=0.50~0.90,平均值0.64,屬于鐵質基性巖;AFM圖解中顯示其為拉班玄武巖系列。通過CIPW標準礦物計算,玄武巖標準礦物組合主要為:Q+An+Ab+Or+Di+Hy,屬于SiO_2過飽和的正常巖石類型。玄武巖具有明顯的輕稀土富集特征,輕稀土分餾程度較高,且有著與OIB相似的地球化學特征,在巖漿演化過程中,有斜長石的結晶及移出從而導致殘余熔漿中Eu的不同程度虧損;微量元素和同位素特征顯示大方地區(qū)峨眉山玄武巖的源區(qū)為與上地殼組分相關的富集地幔,巖漿在上升過程中受到了地殼物質的強烈混染。利用巖石地球化學數(shù)據和玄武巖構造環(huán)境判別圖得知大方地區(qū)玄武巖的形成背景為大陸板內拉張環(huán)境,其形成與茅口組末期的峨眉山地幔柱活動有關。與鄰近的水城地區(qū)對比表明,大方地區(qū)峨眉山玄武巖和水城玄武巖主要礦物成分都為輝石和斜長石,輝石都屬普通輝石,斜長石主要屬拉長石,但大方地區(qū)峨眉山玄武巖不含橄欖石,而水城玄武巖含少量橄欖石(5%);通過單斜輝石溫度計估算大方地區(qū)峨眉山玄武巖的形成溫度為1110~1253℃,平均為1162℃,而水城玄武巖的形成溫度范圍為1131~1231℃,說明兩個地區(qū)玄武巖形成溫度相差不大;通過地球化學特征分析可以看出大方地區(qū)峨眉山玄武巖屬拉斑玄武巖系列,而水城玄武巖屬堿性玄武巖系列。造成兩地二疊紀玄武巖化學屬性明顯不一致的原因可能主要與所處位置、巖漿源區(qū)性質、部分熔融程度、地殼混染程度以及巖漿作用過程的不同有關。
[Abstract]:Emeishan basalt in Dafang area of Guizhou province is located in the outer belt of Emeishan igneous province. As an important part of Emeishan basalt, it has been paid close attention by many scholars, but the study of Emeishan basalt in Guizhou province is relatively few. On the basis of field investigation, this paper studies the petrological, mineralogical and geochemical characteristics of Emeishan basalt in Dafang area, and compares them with the Shuicheng basalt nearby. The petrology, mineralogy and geochemical characteristics of Emeishan basalt in Dafang area are analyzed, and the magma source area properties are discussed. Temperature and pressure of rocks and the tectonic setting of basalt formation.The spatial and temporal distribution,rock types and lithologic characteristics of the Emeishan basalt in Fangfang area have been ascertained through field geological survey and section survey.The eruption environment,eruption cycle and rhythm of the basalt have been studied.Although Yingpan and Zhuchang are not far apart from each other,volcanic eruption cycle,eruption rhythm(frequency),basalt have been discovered. The accumulative thickness of the basalt and the thickness of the limestone intercalation between the basalts are obviously different, indicating that the Permian Emeishan basalt is not only transversely but also vertically variable, and its distribution is not very stable. The occurrence of bivalve fossils, plant fossils and a large number of stem fossil fragments in partially submerged volcanic clastic rock interbeds indicate that the basalt suite should have been formed in a water eruption environment in general. The basalt rocks from the Xiaotunxiang Zhuchang section (PM11) and Gaodianxiang Yingpan section (PM38) were found. The eruption of Permian basic volcanic rocks can be divided into three eruption cycles from early to late, and the third cycle is the main eruption period. There are only two magmatic eruption cycles in the Pan basalt section, but the volcanic strata formed in this area are thick enough to be divided into 14 eruption rhythms.The main rock types are microcrystalline basalt, cryptocrystalline basalt, amygdaloid basalt, basaltic tuff and volcanic breccia.The basalt-forming minerals in this area are plagioclase and monoclinic pyroxene. Basalt has intercrystalline structure, intergranular structure, glass-based interwoven structure, and local amygdaloid structure is developed. According to single mineral electron microprobe analysis, clinopyroxene is mainly common pyroxene, and its end component is Wo=37.45~40.80, En=36.54~42.89, Fs=17.06~23.22; plagioclase is mainly elongated feldspar, with a small amount of medium pyroxene. Feldspar, whose end-members are An=41.34~58.71, Ab=38.79~54.29, Or=1.55~10.06; metal minerals are mainly ilmenite, followed by magnetite and titanomagnetite. The main element characteristics show that SiO_2=46.42%~51.28%, with an average value of 48.70%; TiO_2=4.07%~4.66%, with an average value of 4.34%, belongs to high-titanium basalt; the average value of K_2O+Na_2 of basalt is 3.33%, and the total alkali content is 3.33%. Most of the rocks are calc-alkaline with a Ritmann index (_) of less than 3.3, mostly between 1.02 and 2.93, with an average value of 2.15; Mg ~# value = 37.20 to 51.70, with an average value of 43.01; m/f = 0.50 to 0.90, with an average value of 0.64, belonging to iron-based rocks; and AFM diagrams show that they are Laban basalt series. Q+An+Ab+Or+Di+Hy belongs to SiO_2 supersaturated normal rock type.The basalt has obvious characteristics of light rare earth enrichment,high fractionation of light rare earth elements and geochemical characteristics similar to OIB.During the magma evolution,plagioclase crystallization and removal lead to different depletion of Eu in remnant magma. The source area of the Emeishan basalt in Dafang area is the enriched mantle related to the upper crustal components, and the magma was strongly contaminated by the crustal materials during the ascending process. The comparison with the adjacent Shuicheng area shows that the main mineral compositions of the Emeishan basalt and Shuicheng basalt in Dafang area are pyroxene and plagioclase, pyroxene is common pyroxene, plagioclase mainly belongs to anorthite, but the Emeishan basalt in Dafang area does not contain olivine and water. The formation temperature of the Emeishan basalt in Dafang area was estimated by clinopyroxene thermometer to be 1110~1253, with an average of 1162, while the formation temperature of the Shuicheng basalt ranged from 1131 ~1231, indicating that there was little difference in the formation temperature between the two areas. The Emeishan basalt in Fang area belongs to tholeiite series, while the Shuicheng basalt belongs to alkaline basalt series. The reasons for the obvious inconsistency of chemical properties of the Permian basalts between the two areas may be related to their location, magma source area property, partial melting degree, crustal contamination degree and magmatism process.
【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】：P588.145
本文編號：2185758
[Abstract]:Emeishan basalt in Dafang area of Guizhou province is located in the outer belt of Emeishan igneous province. As an important part of Emeishan basalt, it has been paid close attention by many scholars, but the study of Emeishan basalt in Guizhou province is relatively few. On the basis of field investigation, this paper studies the petrological, mineralogical and geochemical characteristics of Emeishan basalt in Dafang area, and compares them with the Shuicheng basalt nearby. The petrology, mineralogy and geochemical characteristics of Emeishan basalt in Dafang area are analyzed, and the magma source area properties are discussed. Temperature and pressure of rocks and the tectonic setting of basalt formation.The spatial and temporal distribution,rock types and lithologic characteristics of the Emeishan basalt in Fangfang area have been ascertained through field geological survey and section survey.The eruption environment,eruption cycle and rhythm of the basalt have been studied.Although Yingpan and Zhuchang are not far apart from each other,volcanic eruption cycle,eruption rhythm(frequency),basalt have been discovered. The accumulative thickness of the basalt and the thickness of the limestone intercalation between the basalts are obviously different, indicating that the Permian Emeishan basalt is not only transversely but also vertically variable, and its distribution is not very stable. The occurrence of bivalve fossils, plant fossils and a large number of stem fossil fragments in partially submerged volcanic clastic rock interbeds indicate that the basalt suite should have been formed in a water eruption environment in general. The basalt rocks from the Xiaotunxiang Zhuchang section (PM11) and Gaodianxiang Yingpan section (PM38) were found. The eruption of Permian basic volcanic rocks can be divided into three eruption cycles from early to late, and the third cycle is the main eruption period. There are only two magmatic eruption cycles in the Pan basalt section, but the volcanic strata formed in this area are thick enough to be divided into 14 eruption rhythms.The main rock types are microcrystalline basalt, cryptocrystalline basalt, amygdaloid basalt, basaltic tuff and volcanic breccia.The basalt-forming minerals in this area are plagioclase and monoclinic pyroxene. Basalt has intercrystalline structure, intergranular structure, glass-based interwoven structure, and local amygdaloid structure is developed. According to single mineral electron microprobe analysis, clinopyroxene is mainly common pyroxene, and its end component is Wo=37.45~40.80, En=36.54~42.89, Fs=17.06~23.22; plagioclase is mainly elongated feldspar, with a small amount of medium pyroxene. Feldspar, whose end-members are An=41.34~58.71, Ab=38.79~54.29, Or=1.55~10.06; metal minerals are mainly ilmenite, followed by magnetite and titanomagnetite. The main element characteristics show that SiO_2=46.42%~51.28%, with an average value of 48.70%; TiO_2=4.07%~4.66%, with an average value of 4.34%, belongs to high-titanium basalt; the average value of K_2O+Na_2 of basalt is 3.33%, and the total alkali content is 3.33%. Most of the rocks are calc-alkaline with a Ritmann index (_) of less than 3.3, mostly between 1.02 and 2.93, with an average value of 2.15; Mg ~# value = 37.20 to 51.70, with an average value of 43.01; m/f = 0.50 to 0.90, with an average value of 0.64, belonging to iron-based rocks; and AFM diagrams show that they are Laban basalt series. Q+An+Ab+Or+Di+Hy belongs to SiO_2 supersaturated normal rock type.The basalt has obvious characteristics of light rare earth enrichment,high fractionation of light rare earth elements and geochemical characteristics similar to OIB.During the magma evolution,plagioclase crystallization and removal lead to different depletion of Eu in remnant magma. The source area of the Emeishan basalt in Dafang area is the enriched mantle related to the upper crustal components, and the magma was strongly contaminated by the crustal materials during the ascending process. The comparison with the adjacent Shuicheng area shows that the main mineral compositions of the Emeishan basalt and Shuicheng basalt in Dafang area are pyroxene and plagioclase, pyroxene is common pyroxene, plagioclase mainly belongs to anorthite, but the Emeishan basalt in Dafang area does not contain olivine and water. The formation temperature of the Emeishan basalt in Dafang area was estimated by clinopyroxene thermometer to be 1110~1253, with an average of 1162, while the formation temperature of the Shuicheng basalt ranged from 1131 ~1231, indicating that there was little difference in the formation temperature between the two areas. The Emeishan basalt in Fang area belongs to tholeiite series, while the Shuicheng basalt belongs to alkaline basalt series. The reasons for the obvious inconsistency of chemical properties of the Permian basalts between the two areas may be related to their location, magma source area property, partial melting degree, crustal contamination degree and magmatism process.
【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】：P588.145
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