陕西省洛南长岭正长岩矿物学及地球化学研究
发布时间：2018-12-16 22:11
【摘要】：北秦岭出露北西-南东向展布的碱性岩带,经历了长期而复杂的地质演化过程,受到了诸多研究学者的关注。但对于岩石成因及形成环境,迄今为止仍存有诸多不同观点。本文以陕西省洛南县长岭正长岩体为研究对象,通过野外地质观察,偏光显微镜,电子探针,ICP-OES,ICP-MS,LA-ICP-MS,U-Th-Pb等分析手段,对其矿物学、岩石学、岩石地球化学及锆石年代学等方面进行了较为详细的研究工作,并对其成因、年代归属和构造环境有了较为科学的认识。研究结果表明:1.长岭正长岩主要包括石英正长岩和霓辉正长岩,中细粒结构,块状构造。霓辉正长岩中造岩矿物为钾长石(70%),霓辉石(10%),钠长石(3%)、石英(3%),钠铁闪石(2%)和黑云母(1%),石英正长岩中主要造岩矿物为钾长石(80%),石英(10%),钠长石(4%),霓辉石(3%)、钠铁闪石(2%)和黑云母(1%)。副矿物为磷钇矿、独居石、重晶石、磷灰石、钛铁矿、磁铁矿、金红石、榍石、锆石、方解石、钙铁榴石。2.石英正长岩和霓辉正长岩为同源演化的产物,且演化由石英正长岩向霓辉正长岩变化。岩石有稀土总量低,稀土亏损、轻稀土富集重,轻重稀土分异明显的右倾配分模式;Th、U、Ba和大离子亲石元素Rb、K富集,P、Ti等元素亏损的特征。3.锆石U-Pb年龄为265Ma,指示正长岩形成于海西期,但规模较小。4.长岭正长岩中,钾长石中Ba的含量较高,且环带现象明显;黑云母是具有壳源特征的铁质黑云母;副矿物独居石中铈的含量较高;金红石富铌;锆石为岩浆成因。岩石中副矿物种类繁杂,普遍富Ba、K等壳源元素,暗示源区为下地壳。5.长岭正长岩成岩过程中,钾长石环带在岩浆贫钙、动荡环境中形成,岩浆温度变化范围为693℃~713℃,分离结晶作用起决定作用,形成于局部拉张的环境。6.该区碱性岩是由于局部拉张作用使地壳裂解,压力减小,部分地幔物质上涌,使下地壳物质发生部分熔融,并沿次级断裂上升而形成的。
[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，
本文编号：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，
本文编号：2383122
本文链接：https://www.wllwen.com/kejilunwen/diqiudizhi/2383122.html
