溧水火山构造洼地火山活动及与锶成矿作用关系研究

发布时间：2018-03-30 16:16

本文选题：溧水盆地　切入点：中生代火山岩　出处：《中国地质科学院》2015年硕士论文

【摘要】：由于强烈的中生代火山活动,溧水火山构造洼地中该期陆相火山岩系广泛分布。溧水火山构造洼地是长江中下游多金属成矿带中众多火山构造洼地之一,也是长江中下游中生代沿江火山岩带的重要组成部分。但由于该区植被和第四系覆盖极其严重,制约了相关研究工作的深入开展。因此,长期以来,溧水火山构造洼地缺乏系统的年代学、地球化学及火山岩岩浆成因学研究。这一方面制约了对该火山构造洼地中生代火山活动的期限、火山岩成因及其岩浆演化过程的认识；另一方面也制约了对其龙王山旋回晶屑凝灰岩中的锶矿床的研究。因此,本文选取了溧水火山构造洼地中生代各旋回代表性火山岩地层进行了详细的野外调查及路线地质剖面观察,进行了系统的锆石U-Pb年代学、岩相学、地球化学等研究,并在此基础上建立了该火山构造洼地火山活动的年代学格架,探讨了火山岩的成因及岩浆演化过程。另外对该火山构造洼地中最大的锶矿床爱景山锶矿进行了重砂、矿物原位微区分析、包裹体成分、温度、盐度等研究,从而初步探讨了该区锶矿床的物质来源及锶富集机制。锆石LA-ICPMS U-Pb定年分析测得溧水火山构造洼地龙王山旋回火山岩形成于135～132Ma：大王山旋回火山岩形成于132-125Ma,姚家边旋回火山岩形成于130～128Ma之后该区大规模的火山活动基本终止并进入长期沉寂期,最晚期甲山旋回火山岩形成于110Ma,火山活动结束。火山岩锆石年代学研究结果表明溧水火山构造洼地中生代火山岩均形成于早白垩世,其主体火山活动时间与长江中下游其它火山构造洼地火山岩的形成时代一致(135～124Ma)。溧水火山构造洼地火山岩含一套具有正常演化序列的基性-中酸性-酸性火山岩及其火山碎屑岩,其中以基性-中酸性为主。岩石普遍具有富碱、富钾、富集轻稀土元素及大离子亲石元素K、Rb、 Ba、Th、U,明显亏损高场强元素Nb、Ta、Ti的特征。并具有高87Sr/86Sr初始比值(0.705604-0.707080)、负εNd(t)(-2～-9)、负εNd(t)(-4--13)的同位素特征。综上分析,笔者认为溧水火山岩岩浆来源于壳源熔体/流体交代的岩石圈富集地幔,并在岩浆上升过程中有地壳物质的混染及单斜辉石、角闪石、磷灰石等矿物的分离结晶,其中中基性岩浆遭遇地壳物质混染及分异作用程度较低。爱景山锶矿天青石中锆石年龄复杂,包含了太古代、元古代、印支期及加里东期多组年龄,显示基底地层对锶矿成矿物质具有一定的贡献。溧水地区龙王山旋回火山岩具有较高的锶含量(平均为965×10-6),其它旋回火山岩的锶含量较低(512×10-6、164×10-6～315×10-6、和338×10-6～389×10-6)。结合前人测得的锶矿区基底地层及富矿围岩锶含量及硫同位素数据,笔者认为锶来源于龙王山旋回晶屑凝灰岩,同时,安山玢岩也可能是其源岩之一；硫主要来源于该盆地基底地层周冲村组膏岩层。龙王山组火山岩具有较下地壳和地幔稍高的Rb/Sr比值(0.21-0.31)和高的Sr含量(609×10-6～1140×10-6))以及富矿晶屑凝灰岩中大量斜长石(含量达60%)的存在,笔者分析认为地壳的混染不是锶富集的主导原因,斜长石的分离结晶作用可能是导致锶元素富集的主要原因。通过天青石流体包裹体的成分、温度、盐度分析结果显示流体包裹体的成分以CO2、CO、H2、 N2成分为主,并含有少量的H2S、CH4等,液相以H20为主。天青石流体包裹体温度变化于240-360℃之间,盐度多变化于0.5-6.5%之间。结合锶矿体的地质特征,初步分析认为初步分析认为溧水爱景山锶矿锶的富集机制为火山热液,同时不排除地下热泉对锶的富集作用。
[Abstract]:Due to the strong Mesozoic volcano activity, the continental volcano rocks of Lishui volcano tectonic depression are widely distributed in Lishui. The volcano tectonic depression of Yangtze River is a polymetallic metallogenic belt in one of the many volcano tectonic depression is a Mesozoic volcano rocks along the Yangtze River, the Yangtze River with the important part. But because of the vegetation and Quaternary Cover extremely seriously, restricted the related research work carried out in-depth. Therefore, for a long time, the Lishui volcano tectonic depression and lack of systematic study on geochronology, geochemistry and volcano magma origin. This restricts the volcano tectonic depression Mesozoic volcano activity period, volcano rock formation and understanding of magma evolution; on the other hand also restricted the research of the Longwangshan strontium deposit cycles in crystal tuff. Therefore, this paper selects the Lishui volcano tectonic depression during every rotation Back to the representative of the volcano rock formation were observed and detailed field investigation and geological profile, the zircon U-Pb chronology, the petrography, geochemistry, and established the geochronological framework of the volcano tectonic depression volcano activity, discusses the origin and evolution of magma and volcano rock. In addition to the the volcano tectonic depression in strontium deposit, the greatest love of Jingshan Hill strontium ore placer, in-situ analysis of mineral inclusions, body composition, temperature, salinity and so on, so as to investigate the strontium deposit in this area of the material source and strontium enrichment mechanism.
Zircon LA-ICPMS U-Pb dating of measured Lishui volcano tectonic depression Longwangshan cycle volcano rocks formed in 135 ~ 132Ma: dawangshan cycle volcano rocks formed in the 132-125Ma, Yao Jia Bian cycled volcano rocks formed in 130 ~ 128Ma after the massive volcano activities cease to long period of silence, the most advanced cycle of a mountain volcano rock formed in the 110Ma end of the event. The volcano volcano rock zircon geochronology indicates that the Lishui volcano tectonic depression Mesozoic volcano rocks were formed in the early Cretaceous, the volcano activity time and the lower reaches of other volcano structure formation, consistent with the age of fire made wa rock (135 ~ 124Ma). A set of basic and normal evolution sequence in the intermediate acidic volcano rock and volcano clastic rocks containing Lishui volcano tectonic depression volcano rock, in which basic to intermediate acid rock. Generally with alkali, potassium rich, rich in Light rare earth elements and large ion lithophile elements K, Rb, Ba, Th, U, significantly depleted in high field strength elements Nb, Ta, Ti and 87Sr/86Sr. Features with high initial ratio (0.705604-0.707080), negative epsilon Nd (T) (-2 ~ -9), epsilon negative (T) Nd (-4--13). Isotope analysis. To sum up, the author believes that the Lishui volcano magma derived from crust derived melt / fluid metasomatic lithosphere mantle enrichment, and the contamination during magma ascent and clinopyroxene, crustal amphibole, apatite mineral separation and crystallization, which in the magma crust material contamination and encounter differentiation degree is relatively low.
Love the Jingshan Hill of Strontium in celestite zircon age complex contains Archean, Proterozoic, Caledonian and Indosinian age group, indicates that the basal formation has some contribution to strontium ore forming materials. Strontium content Longwangshan cycle volcano rocks in the Lishui area has high (the average is 965 x 10-6), strontium content of other cycles volcano rock is low (512 * 10-6164 * 10-6 ~ 315 * 10-6 and 338 * 10-6 ~ 389 * 10-6). Combined with previous measured strontium mine basement strata and ore rock and sulfur content of strontium isotope data, the author thinks that the strontium from Longwangshan cycle crystal tuff, and andesitic porphyrite may is one of the main sources of sulfur source rocks; the basin basement strata of Zhou Chong village. Gypsum rocks volcano rock mountain dragon group has a lower Rb/Sr ratio of crust and mantle slightly higher (0.21-0.31) and high Sr content (609 * 10-6 ~ 1140 * 10-6)) and rich crystal coagulation The existence of massive plagioclase (content 60%) in limestone indicates that the mixing of the crust is not the leading cause of strontium enrichment. The separation and crystallization of plagioclase may be the main reason for the enrichment of strontium.
The celestite fluid inclusion composition, temperature, salinity analysis results showed that the fluid inclusion composition by CO2, CO, H2, N2 components, and contains a small amount of H2S, CH4, H20 in liquid phase. Celestite fluid inclusions temperature change to 240-360 DEG, salinity changes between 0.5-6.5% with multi. The geological characteristics of strontium ore, preliminary analysis that the preliminary analysis that the enrichment mechanism of Lishui love Jingshan Hill for strontium strontium ore volcano hydrothermal, and does not exclude the enrichment of underground hot springs of strontium.

【学位授予单位】：中国地质科学院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P317;P618.78

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