南黄海千里岩岛榴辉岩的岩石学、矿物学、年代学特征及其地质意义

发布时间：2018-07-02 22:22

本文选题：苏鲁大别超高压变质带 + 榴辉岩　；参考：《山东科技大学》2017年硕士论文

【摘要】：大别苏鲁超高压变质带是三叠纪由中朝板块和杨子板块俯冲碰撞的产物,为全球规模最大的超高压变质带之一,是近二十年,全世界地质专家研究的重点课题。我国地质科学家通过岩石学、矿物学、地球化学、年代学等其他研究手段取得了丰硕的成果,使我国对超高压变质带的认知有很大的提升。南黄海北部千里岩隆起区属于苏鲁高压-超高压变质带(许志琴,2006),千里岩岛是千里岩隆起的海上出露区,是苏鲁造山带的重要组成部分,由于千里岩岛位于苏鲁-大别造山带与朝鲜半岛之间这样的特殊的地理位置,并且在千里岩岛发现榴辉岩,其可能为大别-苏鲁造山带延伸至朝鲜半岛的重要线索。论文取得以下主要认识:(1)根据岩石学特征,千里岩岛榴辉岩矿物世代可划分为:第一世代矿物组合:石榴石中的绿辉石、金红石及绿帘石包体,代表了深俯冲进变质的阶段。第二世代矿物组合:有石榴石、多硅白云母、绿辉石、及其金红石,代表高压榴辉岩相峰期变质组合。第三世代矿物组合:主要由透辉石、钠长石、石英、角闪石等石榴石退变边及绿辉石的后成合晶构成,说明了角闪岩相退变质阶段的矿物组合。第四世代矿物组合:主要由矿物边缘及裂隙中的绿泥石、石英及黑云母构成,说明了绿片岩相退变质阶段矿物组合。(2)矿物学特征表明,石榴石总体上富Alm,贫Spe组分,五个端元组分含量分别为:Alm (42.07～52.72%),Spe (0.57～1.21), And (0.61 ～3.47), Pyr(18.22～29.82), Gro (21.19～28.26)。根据石榴石的成分剖面(图4-2)可以看出,从核部到边部,XMg先上升,然后下降,XMg的变化反映了温度先升高后降低的过程,XFe总体上轻微下降,XCa则表现为逐渐上升,单斜辉石大多数为绿辉石,部分为后成合晶中的透辉石。绿辉石内部基本没有包体,早期的绿辉石包体中的硬玉组分(35%)到基质中绿辉石的硬玉组分(40%-45%),再到后成合晶中透辉石的硬玉含量(10—14%)。角闪石主要是钠-钙质和钙质角闪石,以变斑晶存在于基质当中的主要是韭闪石,以后成合晶以及退变边存在的主要是镁普通角闪石,阳起石则主要存在于裂隙当中。多硅白云母只存在于基质当中,内部不见任何包体,在BSE图中不存在不均匀的分区现象,成分大体上均匀,多硅白云母由核部向边部,Si4+有轻微的增加。(3)本文通过采用地质温压计,榴辉岩的峰期温度应用Ravna(2000)的Grt-Cpx温度计,榴辉岩的峰期压力采用Waters and Martin( 1993 )的Grt-Omp-Phe压力计,并进行联合求解,峰期温度为755-759℃,压力为2.69-2.76GPa。本文采用 Waters and Matrin (2001) Amp-Di-Pl 压力计和 Holland and Blundy (1994)的Amp-Pl温度计,得到了角闪岩相退变质阶段温度为580-605℃,压力为1.1-1.3Gpa。通过矿物边缘及裂隙中的绿泥石、石英、黑云母矿物组合,笔者推断其处于绿片岩相变质,其温压条件应当为:T450℃, P0.3Gpa。(4)年代学数据表明,继承锆石的加权平均年龄以及表面年龄可以确定,千里岩榴辉岩的原岩形成时代为新元古代,两组样品(Q3、QⅢ)的变质成因锆石的加权平均年龄(231.4±3.3Ma,231.3±4.3Ma)和其下交点年龄(228.0±7.5,231.0±4.2)基本一致,应代表千里岩榴辉岩的峰期变质年龄。
[Abstract]:The Dabie Sulu ultrahigh pressure metamorphic belt is the product of the Triassic subduction and collision of the Sino Korean plate and the Yang Zi plate. It is one of the largest ultrahigh pressure metamorphic belts in the world. It is the key topic of the geological experts all over the world in the past twenty years. In the northern part of the South Yellow Sea, the thousand li rock uplift area belongs to the Su Lu high pressure superhigh pressure metamorphic zone (Xu Zhiqin, 2006), the thousand li Rock Island is an outcropping area of the thousand li rock uplift, an important part of the Su Lu orogenic belt, and the thousand li Rock Island is located in the Su Lu Dabie orogenic belt. Such special geographical location with the Korean Peninsula, and the discovery of Eclogite in the thousand li Rock Island, may be an important clue to the Dabie Su Lu orogenic belt extending to the Korean Peninsula. The following main understanding: (1) according to the petrological characteristics, the garnet mineral assemblage of the first generation can be divided into the first generation mineral assemblage: garnet The diopside, rutile and epidote xenoliths represent the stage of deep dive into the metamorphic stage. The second generation mineral assemblage: garnet, polysilicon muscovite, oroxene, and rutile, representing the peak metamorphic combination of the high pressure eclogite facies. The third generation mineral assemblage: mainly from diopside, sodium feldspar, quartz, hornblende and other garnet edge and green. The retroxectic composition of the pyroxene illustrates the mineral assemblage of the phase of the amphibolite phase retrograde metamorphism. The fourth generation mineral assemblage is composed mainly of chlorite, quartz and biotite in the mineral edge and fissure, indicating the mineral assemblage in the phase of the phase retrogression of the green schist. (2) the mineralogical characteristics indicate that the garnet is generally rich in Alm, poor Spe component and five ends. The components of the tuples are as follows: Alm (42.07 ~ 52.72%), Spe (0.57 ~ 1.21), And (0.61 ~ 3.47), Pyr (18.22 to 29.82) and Gro (21.19 to 28.26). According to the composition profile of garnet (Fig. 4-2), it can be seen that XMg rises first and then decreases from the nucleus to the edge, and the change of XMg reflects the process that the temperature rises first and then decreases, and XFe is generally slightly lower. Descending, XCa is gradually rising, and most of the monoclinopyroxene is diopside, part of the Diopside in the posterior diopyroxene. There are basically no inclusions inside the diopyroxene, the early jadeite component in the early omroxene inclusion (35%) to the jadeite component (40%-45%) in the matrix, and then the diopside content of the diopside (10 - 14%). If sodium calcium and calcareous amphibole, the main part of the matrix in the matrix is leek amphibole, and then the main form of eutectic and degenerative edge is magnesium common amphibole, and the allimite mainly exists in the crack. The polysilicon Muscovite exists only in the matrix and does not have any inclusions in the interior, and there is no inhomogeneous distribution in the BSE diagram. The composition of the region is generally uniform, and the polysilicon Muscovite is slightly increased from the nucleus to the edge. (3) by using the geological thermometer, the peak temperature of the eclogite is applied to the Grt-Cpx thermometer of Ravna (2000), the peak pressure of the eclogite adopts the Grt-Omp-Phe pressure meter of Waters and Martin (1993), and the peak temperature of the peak period is solved jointly. The degree is 755-759 degrees C, the pressure is 2.69-2.76GPa., the Amp-Pl thermometer of Waters and Matrin (2001) Amp-Di-Pl pressure meter and Holland and Blundy (1994) is used. The temperature of the phase of amphibolite phase retrograde metamorphism is 580-605 C, the pressure is a combination of chlorite, quartz and black mica mineral in the mineral edge and fissure of 1.1-1.3Gpa.. It is inferred that the temperature and pressure conditions should be: T450 C, P0.3Gpa. (4) geochronological data show that the weighted average age of the inherited zircon and the surface age can be determined, the age of the Proterozoic era of the garnet eclogite is Neoproterozoic, and the weighted average age of the metamorphic zircons of the two groups of samples (Q3, Q III) is 231.4 + 3.3Ma, 23 1.3 + 4.3Ma) is basically consistent with the age of the lower internode (228 + 7.5231.0 + 4.2). It should represent the peak age of the Eclogite in the thousand li rock.
【学位授予单位】：山东科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.3

【参考文献】