【作者】 郭春丽；

【导师】 陈毓川；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2010， 博士

【摘要】 花岗岩是大陆地壳的重要组成,是人类了解地球深部信息的有效探针,是地质学研究的重要课题。尽管花岗岩的组成矿物较其他类型岩石简单,但是关于花岗岩起源和演化的一系列问题都还没有定论。随着近年来高分辨率测试技术与先进研究方法的运用,使得地质学家对花岗岩研究有了新的和高质量的测试分析手段,推动花岗岩研究不断深化。南岭地区广泛出露多时期花岗岩类,其中中生代花岗岩类分布面积广泛,而且与稀有多金属矿产有非常密切的关系,是花岗岩与成矿作用研究的摇篮。中生代花岗岩类也具有成岩成矿作用的多阶段性,对各个阶段与不同矿化相关花岗岩类进行详细研究,是认识南岭乃至华南地区板块俯冲、壳幔相互作用、地球动力学演化过程的一个重要窗口。本论文选择赣西南地区崇义县的三叠纪柯树岭-仙鹅塘花岗岩体、晚侏罗世九龙脑花岗岩体和上犹县的中侏罗世营前花岗闪长岩体为解剖对象,通过详细的野外地质学、矿物学、岩石地球化学、同位素地球化学的研究,并对比了南岭地区中生代四个阶段(三叠纪、中侏罗世、晚侏罗世、白垩纪)相似花岗岩类特征,探讨了不同阶段花岗岩类对华南地区中生代大地构造背景及岩石圈演化过程的指示意义,在以下四个方面取得新的认识：1.证实了柯树岭-仙鹅塘花岗岩岩体为三叠纪岩浆活动的产物(251.5±6.6Ma和202±15Ma),与前人测得仙鹅塘矿区含矿石英脉中白云母40Ar/39Ar坪年龄(231.4±2.4Ma)相吻合。极低的∑REE含量表明是岩浆高度分异演化的产物；锆石Hf同位素表明该岩体来源于古老地壳物质的重熔,但花岗质锆石的核部有幔源锆石,证明在岩浆形成初期混入了幔源岩浆结晶的产物。结合区域上的研究资料,认为三叠纪花岗岩属于高钾系列过铝质花岗岩类,成岩物质主要来源于地壳,但不排除地幔物质参与成岩作用。2.通过对营前岩体及其暗色包体系统的SHRIMP锆石U-Pb年代学、岩石学、地球化学、Sr-Nd、Hf同位素研究,证实了营前两期花岗质岩(172.2±3.1Ma和168±3Ma)和暗色包体(167.6±3.3Ma)为同期生成,两期花岗质岩石源于地壳重熔,地幔底侵导致地壳熔融形成营前岩体,基性岩浆加入到未冷却的酸性岩浆中形成了目前所见到的暗色包体。结合区域上的研究资料,认为中侏罗世花岗闪长岩沿“十杭”断裂带和与之相平行的北东向断裂带分布,属于高钾钙碱系列准铝-弱过铝质花岗岩类,比较明显的特征是偏基性的组分含量较高,此类花岗岩具有壳幔混合的特征,成因上属壳幔同熔型成因的花岗质岩类。3.通过对九龙脑岩体北侧淘锡坑大型钨矿区枫林坑矿段隐伏花岗岩的SHRIMP锆石U-Pb定年(158.7±3.9Ma和157.6±3.5Ma)、含矿石英脉中流体包裹体的Rb-Sr定年(157.1±2.9Ma)、花岗岩体与围岩接触部位云英岩化花岗岩中白云母的Ar-Ar定年(坪年龄为155.0±1.4Ma、153.4±1.3Ma和152.7±1.5Ma)研究,厘定成岩成矿年龄在误差范围内是一致的。通过对九龙脑花岗岩主体及其北侧淘锡坑钨矿隐伏花岗岩、南侧天井窝钨矿隐伏花岗岩、东侧宝山矽卡岩型铅锌矿隐伏花岗岩的岩石学、地球化学、Sr-Nd、Hf同位素研究,推测前三者源于古元古宙地壳的重熔,可能有很少地幔物质的贡献,而宝山隐伏花岗岩虽然锆石U-Pb年龄(157.7±2.7Ma)与九龙脑花岗岩主体相同,但Sr-Nd、Hf同位素组成却更靠近富集地幔端元,推断宝山隐伏花岗岩形成时有较多地幔物质参与了成岩过程。结合区域上的研究资料,认为晚侏罗世花岗岩多为复式岩体,岩石类型比较复杂,且由于强烈的岩体一熔体相互作用而导致成因类型划分的困难,但矿物学、地球化学表明该期花岗岩具有I型、S型、A型三类并存的特征。根据稀土元素分布型式图可将该期花岗岩分为“海鸥式”和“倾斜式”两类,后者的地幔物质更多的参与了成岩成矿作用。根据Sr-Nd-Hf-O-Pb同位素,发现I型和A型花岗岩主要与锡的成矿作用有关,集中分布在湘南、桂北地区,成岩成矿更明显有地幔物质的参与；S型花岗岩主要与钨的成矿作用有关,集中分布在赣南地区,成岩成矿与地幔几乎没有关系,可能是“十杭”断裂带的存在控制了“东钨西锡”的空间分布形式。4.通过对南岭地区中生代上述四个阶段花岗质岩石的地质学、矿物学、年代学、地球化学、Sr-Nd同位素的总结和对比,认为它们之间存在一定差别：三叠纪和白垩纪花岗岩属高钾钙碱性系列,早中侏罗世和晚侏罗世花岗岩属钾玄质与高钾钙碱性系列；三叠纪花岗岩的∑REE远低于后三个时代花岗岩的∑REE,早-中侏罗世花岗岩的稀土元素球粒陨石标准化曲线与其它三者显著不同,为一明显向右倾斜的平滑曲线,无或有极小的Eu负异常；部分三叠纪、部分晚侏罗世、白垩纪花岗岩的稀土元素具有“四分组效应”特点；它们在构造环境判别图解中分别投影在不同的区域。暗示这四个时代的花岗质岩在形成构造环境、物质来源、岩浆-熔体-流体相互作用等方面存在着根本性的差别,即随着区域地质发展和时空框架变换,能够产生不同类型的花岗质岩浆活动。由此在前人研究成果的基础上,结合前述华南成矿与花岗岩演化的关系,提出华南地区中生代构造地质历史演化的合理模型,即三叠纪由于华南地块和印支板块的碰撞,印支期花岗岩形成于“后碰撞”的动力学环境；中侏罗世期间古太平洋板块北西向的俯冲,沿岩石圈相对薄弱的“十杭”断裂带及与其相平行的深断裂发生了板块的撕裂,这一阶段是由挤压转变成伸展的构造体制；晚侏罗世期间华南地区全面进入一个岩石圈“伸展-减薄”的地球动力学环境,推断古太平洋板块北西向全面俯冲到华南板块下部,导致下地壳拆沉,软流圈物质上涌底垫到上地壳底部；白垩纪则可以分为先俯冲挤压(伴随弧后拉张作用和板片的局部撕裂),后北东向走滑两个阶段。更多还原

【Abstract】 Granitoids are the important ingredients of the continental crust, and the effective explorer to understand the deep information of the Earth. Although granitoids are composed of more simple minerals than other types of rocks, a series of problems about origin and evolution of granitoids have not been settled. With the development of high-resolution technology and advanced theories, geologists mastered new analytical measures to make more and more progress of study on granites.There are all kinds of granites with different epochs in the Nanling region and rare metal-related Mesozoic granitoids distribute abroad, which is the cradle of study on the relationship of granite and metallogenesis. However, Mesozoic granites also have multistage pulses. In order to understand the subduction of ancient Pacific plate, interaction of crust and mantle, geodynamic evolution of the Earth, Mesozoic granites should be studied in detail.This paper detailedly studies of geology, mineralogy, litho-geochemistry, and isotope geochemistry of three granitic intrusions including Triassic Keshuling-Xian’etang granite, Mid-Jurassic Yingqian granodiorite, Late-Jurassic Jiulongnao granite in southwestern Jiangxi province. Through comparisons with four periods (Triassic, Mid-Jurassic, Late-Jurassic, and Cretaceous) similar granitoids, significance of different phases granites to tectonic background and lithosphere evolution in Mesozoic in Nanling region has been deeply discussed.1. The Keshuling-Xian’etang intrusion has been verified as a Triassic magmatic rock (251.5±6.6Ma and 202±15Ma), which are the same as the muscovite 40Ar/39Ar plateau age (231.4±2.4Ma) from ore-bearing quartz veins in Xian’etang section. From the characteristics of petrology and isotopic geochemistry, it was mainly divided from ancient crustal materials. But it was not come from single felsic magma chamber, or its source region was impacted by mantle materials according to zircon Hf isotopic values. Triassic granites should be high-K peraluminous granitoids, which mainly come from crustal materials with a few of mantle-derived magmas.2. The Yingqian intrusion consists of granitoids of two periods, mega-porphyritic granodiorites and fine-grained granites. There are a lot of melanic monzonitic enclaves in the former. Zircon SHRIMP U-Pb dating gives the ages of 172.2±3.1Ma for the earlier granodiorites,167.6±3.3Ma for enclaves, 168±3Ma for later granites, indicating that the Yingqian pluton is a Mid-Jurassic magmatic intrusion. According to petrology, geochemistry, Sr-Nd and Hf isotopic values, it was result of partial melting of ancient crustal materials, interacted with mantle-derived magmas. Mid-Jurassic granitoids along the "Shi-Hang" fault and paralleling NE-trending faults should be high-K calc-alkaline series and metaluminous-peraluminous granitoids those were formed in a continental crustal thinning setting, which is a favorable event to interaction with crustal and mantle.3. The Taoxikeng wolframite-quartz vein type tungsten deposit is located in North to Jiulongnao intrusion. SHRIMP zircon U-Pb analysis of the granite which hosts the Taoxikeng deposit has yielded ages of 158.7±3.9Ma and 157.6±3.5Ma, which are interpreted as the emplacement age of the granite. Muscovites separated from greisen between the host granite and country rocks yield 40Ar/39Ar plateau ages of 155.0±1.4Ma,153.4±1.3Ma and 152.7±1.5Ma. Fluid inclusions separated from ore-bearing quartz veins yields a Rb-Sr isochron age of 157.1±2.9Ma. These ages obtained from three independent geochronological techniques constrain the ore-forming age of the Taoxikeng tungsten deposit and link ore genesis to that of the hosting granite intrusion. Through petrology, geochemistry, Sr-Nd and Hf isotopic studies of Jiulongnao granitic intrusion, buried granite of Taoxikeng tungsten deposit, buried granite of Tianjingwo tungsten deposit and buried granite of Baoshan skarn-type Pb-Zn deposit, the three formers were derived from Pale-Proterozoic crust with few mantle. Although SHRIMP zircon U-Pb age of Baoshan buried granite is 157.7±2.7Ma that is the same as the age of Jiulongnao granite, Sr-Nd and Hf isotopic data are near to enriched mantle, so it can be inferred that more mantle-derived materials were involved in diagenetic process. Combined with regional research information, Late-Jurassic granites are mostly complex and it is difficult to divide them to various genetic classifications because of rock-melt interaction, but characteristics of geology, mineral and geochemistry indicate that I-type, S-type and A-type coexist in the Late-Jurassic granitoids. According to Chondrite-normalized REE pattern diagrams, the Late-Jurassic granitoids can be divided to two types, "sea-gull type" and "inclining type", and the latter has been included more mantle-derived materials. According to Sr-Nd-Hf-O-Pb isotopic data,Ⅰ-type and A-type granitoids concentrated in South Hunan and North Guangxi are mainly related to tin-mineralization, but S-type granitoids concentrate in South Jiangxi are mainly related to tungsten-mineralization. Maybe spatial distribution of "East tungsten and West tin" is controlled by "Shi-Hang" fault.4. Through comparing on geological, mineralogical, geochronological, geochemical, and Sr-Nd isotopic characteristics, there are obvious distinctions of four-stage granitoids including Triassic, Mid-Jurassic, Late-Jurassic and Cretaceous. Triassic and Cretaceous granitoids belong to high-K calc-alkaline series, but Mid-Jurassic and Late-Jurassic granitoids belong to shoshonitic and high-K calc-alkaline series. The total REE contents of Triassic granitoids are lower than others. The Chondrite-normalized REE pattern diagrams of Mid-Jurassic and Late-Jurassic granitoids are extraordinarily different with other two. The REE of some Triassic granitoids, some Late-Jurassic granitoids and Cretaceous granitoids have "tetrad effect". These four-stage granitoids fall into different positions in tectonic illustrated diagrams from Pearce J A et al (1984). Above characteristics show that different kinds of granitoids can be generated with the development of geological history. On the base of previous achievements, we suggest a new model. The formation mechanism of Mesozoic granitoids is as follows:Triassic granitoids were produced in post-collision setting owing to collision between the South China Block and the Indo-Chinese Block; In Mid-Jurassic the NW-trending subducing ancient Pacific plate was tore along the "Shi-Hang" fault and paralleling NE-trending deep faults; In Late-Jurassic because the ancient Pacific plate subduced wholly below the South China Block leading to delamination of lower crust and crust-mantle interaction, there was an overall "extension and thinning" dynamical setting; In Cretaceous there were two stages including NW-trending subduction and NE-trending sliding.更多还原