陜西省洛南長嶺正長巖礦物學及地球化學研究
發(fā)布時間：2018-12-16 22:11
【摘要】：北秦嶺出露北西-南東向展布的堿性巖帶,經歷了長期而復雜的地質演化過程,受到了諸多研究學者的關注。但對于巖石成因及形成環(huán)境,迄今為止仍存有諸多不同觀點。本文以陜西省洛南縣長嶺正長巖體為研究對象,通過野外地質觀察,偏光顯微鏡,電子探針,ICP-OES,ICP-MS,LA-ICP-MS,U-Th-Pb等分析手段,對其礦物學、巖石學、巖石地球化學及鋯石年代學等方面進行了較為詳細的研究工作,并對其成因、年代歸屬和構造環(huán)境有了較為科學的認識。研究結果表明:1.長嶺正長巖主要包括石英正長巖和霓輝正長巖,中細粒結構,塊狀構造。霓輝正長巖中造巖礦物為鉀長石(70%),霓輝石(10%),鈉長石(3%)、石英(3%),鈉鐵閃石(2%)和黑云母(1%),石英正長巖中主要造巖礦物為鉀長石(80%),石英(10%),鈉長石(4%),霓輝石(3%)、鈉鐵閃石(2%)和黑云母(1%)。副礦物為磷釔礦、獨居石、重晶石、磷灰石、鈦鐵礦、磁鐵礦、金紅石、榍石、鋯石、方解石、鈣鐵榴石。2.石英正長巖和霓輝正長巖為同源演化的產物,且演化由石英正長巖向霓輝正長巖變化。巖石有稀土總量低,稀土虧損、輕稀土富集重,輕重稀土分異明顯的右傾配分模式;Th、U、Ba和大離子親石元素Rb、K富集,P、Ti等元素虧損的特征。3.鋯石U-Pb年齡為265Ma,指示正長巖形成于海西期,但規(guī)模較小。4.長嶺正長巖中,鉀長石中Ba的含量較高,且環(huán)帶現(xiàn)象明顯;黑云母是具有殼源特征的鐵質黑云母;副礦物獨居石中鈰的含量較高;金紅石富鈮;鋯石為巖漿成因。巖石中副礦物種類繁雜,普遍富Ba、K等殼源元素,暗示源區(qū)為下地殼。5.長嶺正長巖成巖過程中,鉀長石環(huán)帶在巖漿貧鈣、動蕩環(huán)境中形成,巖漿溫度變化范圍為693℃~713℃,分離結晶作用起決定作用,形成于局部拉張的環(huán)境。6.該區(qū)堿性巖是由于局部拉張作用使地殼裂解,壓力減小,部分地幔物質上涌,使下地殼物質發(fā)生部分熔融,并沿次級斷裂上升而形成的。
[Abstract]:The alkaline rock belt in the north Qinling has undergone a long and complicated geological evolution, which has been paid much attention by many researchers. However, there are still many different views on rock genesis and formation environment. In this paper, the mineralogy and petrology of Changling syenite in Luonan County, Shaanxi Province are studied by means of field geological observation, polarizing microscope, electron probe, ICP-OES,ICP-MS,LA-ICP-MS,U-Th-Pb and so on. The geochemistry and zircon geochronology are studied in detail, and a scientific understanding of the origin, age and tectonic environment is obtained. The results show that: 1. Changling syenite mainly includes quartz syenite and aegirine syenite, medium fine grain structure and block structure. The petrogenic minerals in the aegirite syenite are potassium feldspar (70%), aegirite (10%), albite (3%), quartz (3%), sodium ferrite (2%) and biotite (1%). The main rock-forming minerals in quartz syenite are potassium feldspar (80%), quartz (10%), albite (4%), aegirite (3%), sodium ferrite (2%) and biotite (1%). The secondary minerals are yttrium phosphate, monazite, barite, apatite, ilmenite, magnetite, rutile, sphene, zircon, calcite, calcium ferrite and garnet. Quartz syenite and aegirine syenite are the products of homologous evolution, and the evolution changes from quartz syenite to neon syenite. The rock has a right-dip partition model with low total amount of rare earth, depleted rare earth, heavy enrichment of light rare earth and obvious differentiation of light and heavy rare earths, and features of enrichment of Th,U,Ba and Rb,K, and depletion of Ti and other elements. 3. The zircon U-Pb age is 265 Ma, indicating that syenite was formed in the Hercynian period, but on a relatively small scale. In Changling syenite, the content of Ba in potash feldspar is relatively high, and the phenomenon of annular zone is obvious. Biotite is a ferric biotite with crustal characteristics; the content of cerium is higher in accessory mineral monazite; rutile is rich in niobium; and zircon is magmatic origin. The subminerals in the rocks are complicated and generally rich in Ba,K and other crustal elements, implying that the source region is the lower crust. 5. In the diagenetic process of Changling syenite, the K-feldspar ring zone is formed in the magmatic poor calcium and turbulent environment, and the magma temperature varies from 693 鈩，
本文編號：2383122
[Abstract]:The alkaline rock belt in the north Qinling has undergone a long and complicated geological evolution, which has been paid much attention by many researchers. However, there are still many different views on rock genesis and formation environment. In this paper, the mineralogy and petrology of Changling syenite in Luonan County, Shaanxi Province are studied by means of field geological observation, polarizing microscope, electron probe, ICP-OES,ICP-MS,LA-ICP-MS,U-Th-Pb and so on. The geochemistry and zircon geochronology are studied in detail, and a scientific understanding of the origin, age and tectonic environment is obtained. The results show that: 1. Changling syenite mainly includes quartz syenite and aegirine syenite, medium fine grain structure and block structure. The petrogenic minerals in the aegirite syenite are potassium feldspar (70%), aegirite (10%), albite (3%), quartz (3%), sodium ferrite (2%) and biotite (1%). The main rock-forming minerals in quartz syenite are potassium feldspar (80%), quartz (10%), albite (4%), aegirite (3%), sodium ferrite (2%) and biotite (1%). The secondary minerals are yttrium phosphate, monazite, barite, apatite, ilmenite, magnetite, rutile, sphene, zircon, calcite, calcium ferrite and garnet. Quartz syenite and aegirine syenite are the products of homologous evolution, and the evolution changes from quartz syenite to neon syenite. The rock has a right-dip partition model with low total amount of rare earth, depleted rare earth, heavy enrichment of light rare earth and obvious differentiation of light and heavy rare earths, and features of enrichment of Th,U,Ba and Rb,K, and depletion of Ti and other elements. 3. The zircon U-Pb age is 265 Ma, indicating that syenite was formed in the Hercynian period, but on a relatively small scale. In Changling syenite, the content of Ba in potash feldspar is relatively high, and the phenomenon of annular zone is obvious. Biotite is a ferric biotite with crustal characteristics; the content of cerium is higher in accessory mineral monazite; rutile is rich in niobium; and zircon is magmatic origin. The subminerals in the rocks are complicated and generally rich in Ba,K and other crustal elements, implying that the source region is the lower crust. 5. In the diagenetic process of Changling syenite, the K-feldspar ring zone is formed in the magmatic poor calcium and turbulent environment, and the magma temperature varies from 693 鈩，
本文編號：2383122
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