【作者】 刘善丽；

【导师】 孙国胜；

【作者基本信息】 吉林大学 ， 地球化学， 2012， 硕士

【摘要】 华北地台努鲁尔虎隆起东北部闫家杖子紫苏麻粒岩和卢家地石榴斜长辉岩是本次工作中新发现的建平群高压麻粒岩相变质岩出露点,对全面认识建平群高压麻粒岩相带甚至华北高压麻粒岩相带的分布具有重要意义；同时对其开展变质作用等方面的研究,可以进一步揭示华北地台的形成与演化机制。本文在充分收集前人资料的基础上,通过野外地质调查及室内综合研究工作,对华北地台北缘努鲁尔虎隆起东北部建平群麻粒岩相变质岩,进行了野外地质产状特征观察,对采集的样品进行了岩相学、矿物和岩石地球化学、变质作用以及原岩恢复等研究工作通过野外地质调查,麻粒岩相变质岩赋存于太古代片麻杂岩的表壳岩包体中,表壳岩包体主要由斜长角闪岩组成,麻粒岩相变质岩在其中呈条带状、透镜状和似层状产出。室内岩相学的研究表明：紫苏麻粒岩的矿物组合为紫苏辉石+斜长石+云母+石英；石榴黑云角闪斜长辉岩主要矿物成分为石榴石+单斜辉石+斜长石+角闪石+黑云母+石英。可见弱片麻状构造、块状构造；粒状变晶结构、包含变晶结构、变余似斑状结构和退变质结构等。麻粒岩的岩石化学、岩石地球化学研究表明,麻粒岩相变质岩主成分特征位于世界范围内地体麻粒岩的分布范围内,与华北地台下地壳的化学成分接近。紫苏麻粒岩稀土元素总量较低,轻重稀土分馏较为明显,为δ Eu正异常,曲线向右缓倾。石榴斜长辉岩稀土元素总量较高,轻重稀土分馏较为弱,为δ Eu弱的负异常,曲线右倾较缓。微量元素中,亲铁元素、高场强元素亏损,而大离子亲石元素相对富集。在麻粒岩微量元素蛛网图上显示出明显的富Ba,U、Th亏损特征,可能也反映了华北克拉通太古宙下地壳的原始组成特征；与世界上其它地区同类麻粒岩平均值相比,麻粒岩具有较高的Sm/Nd比值和较低的LaN/YbN比值,反映华北克拉通麻粒岩的REE分异程度总体较低,也说明太古宙下地壳组成具有较低的分异程度。通过对单矿物主量、稀土微量元素的研究表明：斜方辉石为变质成因的紫苏辉石,单矿物紫苏辉石的∑REE很低,特别富集重稀土,均有强烈的δEu负异常,稀土元素配分曲线为向左陡倾；紫苏辉石中大离子亲石元素和高场强元素明显亏损,亲铁元素V、Co富集而Ni、Cr含量相对亏损。单斜辉石主要为变质成因的透辉石。石榴石具有较弱的生长环带,石榴石的∑REE较低,富集重稀土,以δEu负异常为主,稀土元素配分曲线为向左缓倾、具弱δEu负异常的重稀土富集型曲线；石榴石中微量元素含量总体较低,与原始地幔相比,以亏损为主,大离子亲石元素Sr亏损强烈。角闪石为变质成因的钙镁闪石,∑REE较高,富集轻稀土,轻重稀土分馏明显,为δEu负异常；大离子亲石元素和高场强元素Nb、Ta在角闪石中富集最为显著。斜长石为更长石,相对富集轻稀土,轻重稀土分馏明显,具有强的δEu正异常；大离子亲石元素均为明显的富集,Sr、Pb富集尤其明显,高场强元素、亲铁元素均以亏损为主。黑云母为高铁镁云母,∑REE很低,具有中等强度的δEu正异常,富集轻稀土,轻重稀土分馏不十分明显；富集大离子亲石元素,特别是Rb、Ba富集十分明显,而Sr则亏损,高场强元素Nb、Ta显著富集。石榴斜长辉岩中单斜辉石、石榴石、与单斜辉石和石榴石共生的角闪石和黑云母的矿物变质相均达到了麻粒岩相,石榴斜长辉岩应为麻粒岩相变质岩。紫苏麻粒岩的峰期变质温度较高,为800-868℃；石榴角闪斜长辉岩的温度有两期,第一期变质温度650-750℃,压力为0.86-1.2Gpa;第二期退变质温度500℃左右。温度计算表明,石榴角闪辉岩形成的温度,达到了麻粒岩相变质的温压条件。具有的近等温减压(ITD)顺时针P-T-t演化特征。紫苏麻粒岩、石榴斜长辉岩的原岩恢复及构造环境的研究表明,其原岩为生成于大洋岛弧构造环境的中性火山岩-安山质岩石,并在陆-陆碰撞过程中,形成高压中性麻粒岩。更多还原

【Abstract】 It is important for comprehensive understanding the distribution of the Jianpi-ng group high-pressure granulitic metamorphic rock zone and North China Platform high-pressure granulitic metamorphic rock zone,that Yanjiazhangzi hypersthene gran-ulite and Lujiadi garnet-plagioclase pyroxenite in the north-east of Nuluerhu uplift in North China Platform as new places are found in this study,which outcropes Jianping group high-pressure granulitic metamorphic rock.With studying of metam-orphism to reveal the forming and the Evolution Mechanism.On bases of collecting sufficient previous material, and taking field surveys and c-omprehensive laboratory test, this paper states the observation for field geological chara-cterist-ics for granulitic metamorphic rock of Jianping group in Nuluerhu uplift of n-orthernmargin of the north China platform, and the study of petrography, mineral, lith-ogeoch-emistry, metamorphism and recovering original rock for collected samples.By field survey, granulitic metamorphic rock occurrences in supracrustal encla-ves of archean gneiss complexes. Supracrustal enclaves are composed of amphibo-lite, in which granulitic metamorphic rock presents banted-like structure, lenticular structure and stratoid structure. The research of indoor petrographical shows that mineral association of hypersthene granulite is composed of hypersthene+plagio-clase+biotite+quartz; and major ingredient of garnet-biotite-amphibol-plagioclasep-yroxenite are garnet+clinopyroxene+plagioclase+hornblende+biotite+quartz Thus, it can been seen that weakly-gneissose strucrure,massive structure; granuloblast-ic texture,poikilitic blastic texture,blastoporphyritic texture and retrograde metamor-phism texture etc.The research of petrochemistry and petrological geochemistry of granulite sh-ows that major ingredient feature of granulitic metamorphic rock is located in dist-ribution range of terrain granulites of the world, which is similar to chemical co-mposition of lower crust in North China Platform.The totel REE of hypersthene granulite are lower, light and heavy REE show obvious fractionation and δEu is positive anomaly, slightly right-oblique REE distribution patterns.The totel REE of garnet-plagioclase-pyroxenite are high, light and heavy REE fractionation is not cl-ear and δEu is negative anomaly, slightly right-oblique REE distribution patterns. Siderophile elements,high field strength elements lost and lithophile element richm-ent. In the spider diagram of trace element of granulite, it shows the obvious fea-tures of riching in Ba and lost of U and Th.This maybe also presents original c-omposition feature of the Archean lower crust of north China craton; Comparing with the average of similar granulites in other parts of world, the granulite has a high ratio of Sm/Nd and low ratio of LaN/YbN. That shows that differentiation degree of granulite of north China craton are generally low, also presents that co-mposition of the Archean lower crust have low differential degree.By studying major elements and rare earth lelment and trace element of the si-ngle mineral, it is concluded that orthorhombic pyroxene is metamorphogenetic hypers-thene, which is monomineral with low REE, but very rich tombar thite, both have stron-g negative anomaly of δEu, tombar thite distribution curve incline steeply to left.Lithop-hile element and high field strength elements in hypersthene lost obviously,siderophi-le elements such as V and Co are rich and Ni and Cr comparingly lost.Orthopyroxen-e are mainly composed of metamorphogenetic diopsite.Garnet has relatively weak growi-ng zone, with low REE, but riches tombar thite, main for negative anomaly of δEu. Dis-tribution curve of tombar thite inclines to left slowly, and curve of rich tombar thite wit-h weak8Eu negative anomaly.The total of garnet of trace elements is low, compare-ng with primitive mantle, major for lost, and strong lost for lithophile element Sr. Am-phibole is composed of metamorphogenetic tschermakitic hornblende, with high REE a-nd rich tombar thite and light and heavy REE fractionation is clear, with negative anomaly of δEu.It is significant that Lithophile element and high field strength elem-ents Nb and Ta in Amphibole are very rich.Plagioclase is oligoclase, comparing ha-ving rich tombar thite, with obvious fractionafion and strong δEu positive anomaly. Lithophile element are rich obviously, especially Sr and Pb, high field strength el-ements,siderophile elements are main for lost.Biotite is iron-rich magnesia mica, with low REE and medium positive anomaly positive anomaly of δEu, light REE enrichment that is not obvious fractionafion. It is rich with lithophile element,esp-ecially Rb and Ba, but Sr lost, high field strength elements Nb and Ta obviously rich.The Orthopyroxene and garnet in garnet-plagioclase pyroxenite and Amphibole and biotite which is coexistence with them are attained granulitic.so, garnet-plagio-clase pyroxenite should be granulitic metamorphic rock.The peak metamorphic temp-erature higher in hypersthene granulite that is800-868℃; There are2period of the metamorphic temperature in garnet-plagioclase pyroxenite.The first metamorphic te-mperature could reach650-750℃, the pressure ranged from0.86to1.2Gpa and then, the retrometamorphism could be about500℃.Through the calculation of forming te-mperature of the garnet-plagioclase pyroxenite,it could reach the temperature-Pressure condition in granulitic metamorphic,with a clockwise nearly isothermal decompressi-onal evolvement trend of P-T-t.The research in the protolith recovery and the tectonic setting of hypersthene granulite and garnet-plagioclase pyroxenite shows,the Protolith restoration is interm-ediate volcanic rocks-andesite which is formd in oceanic island arc tectonic setting, and transformed into High pressure neutral granuliet during continent-continent coll-ision.更多还原