【作者】 赵军红；

【导师】 胡瑞忠；

【作者基本信息】 中国科学院研究生院（地球化学研究所） ， 地球化学， 2004， 博士

【摘要】 中国东南部地处太平洋板块与欧亚板块的接合部位，其独特的地理位置和构造运动长期以来引起了地质学家的广泛关注。自印支运动以来，板内构造演化复杂而多样。最引人注目的无疑是燕山期广泛而强烈的构造-岩浆热事件。近年来随着研究的深入，逐渐凸显出两个重要的地质问题需要解决：（1） 中国东南部晚中生代构造属性的转变时间及地球动力学演化过程；（2） 多金属成矿作用与岩石圈伸展减薄及地壳拉张的关系。基于此，本文以中国东南部福建省的基性脉岩、岩体为研究对象，运用系统的矿物学、岩石学、岩石地球化学、同位素地球化学及同位素年代学证据，详细论述了晚中生代中国东南部板块俯冲、地幔演化、壳幔相互作用及岩石圈伸展减薄的地球动力学过程，探讨了地壳拉张期次在福建省区域构造上的响应。本研究主要获得以下几点认识： 1、岱前山辉长岩体沿福建长乐—南澳大断裂带分布，侵位于沿海的绿片岩相和角闪岩相的变质岩中及内陆的中生代火山岩中。岩体的微量元素特征表现为与俯冲作用有关的岛弧特点。岱前山岩体由低程度部分熔融形成（约7％），伴有角闪石、单斜辉石的分离结晶作用和斜长石的堆晶作用。时间上与古太平洋板块低角度—歪斜俯冲、晚中生代的变质事件、平潭—东山变质带抬升和长乐—南澳剪切带运动在时间上基本一致。岩体是受俯冲流体交代的上地幔，经部分熔融沿长乐—南澳断裂—应力转换带侵入。它与中国东南部出露的其它基性岩同源，但未受到地壳的混染作用。 2、闽南茅坪-晒鞍角基性侵入体具独特的地球化学属性，表现为高Al₂O₃、Ca_O、MnO，低FeO_T、MgO、TiO₂含量，富集轻稀土元素（LREE）和大离子亲石元素（LILE），并具正的Pb异常和负的Ti异常；Sr-Nd-Pb同位素结果显示，该基性岩有EM2组分的参与。模拟计算表明，该基性岩墙群是尖晶石二辉橄榄岩地幔5-15％部分熔融的产物；微量元素配分模式及理论模拟表明茅坪—晒鞍角基性岩体的地幔源区在熔融前曾受到1％俯冲沉积物熔体的源区混染和5％流体交代作用。基性岩浆在上升过程中还受到10％左右的地壳物质的混染作用，导致该区基性岩富放射成因Sr、Pb同位素。 3、福建省晚中生代基性脉岩富Al₂O₃（14.0-20.4wt％）、CaO（4.09-12.7wt％）。按地球化学特征可分为两组：第一组脉岩具较低稀土总量（53.8-145.5μg／g）和平缓的稀土配分模式[（La／Yb）_n=1.68-4.65]，而第二组脉岩的稀土总量较高（63-247μg／g），且轻稀土富集[（La／Yb）_n=4.63-19]。在原始地幔标准化图解上，第一组脉岩显示Pb的正异常 和Ti负异常，无Nb、Ta异常，而第二组脉岩显示明显的Nb一几.Ti负异常和Pb正 异常。两组脉岩经历了不同的源区混合和陆壳混染过程，第一组脉岩显示了以陆壳 混染为主的地球化学过程，不具有岛弧特点的微量元素配分模式表明该类基性岩的 地慢源区可能未受俯冲作用过程影响，第二组脉岩的岛弧地球化学特点暗示该类基 性岩地慢源区是经俯冲作用改造过的富集岩石圈地慢。第一组基性脉岩来源于石榴 石一尖晶石二辉橄榄岩地慢，而第二组脉岩来源于尖晶石或尖晶石一斜长石二辉橄 榄岩地慢。地球化学数据显示，不同类型的地慢存在不均一性，反映了不同程度的 交代作用或不同量俯冲沉积物的加入。福建省晚中生代基性脉岩产生于拉张构造背 景，与岩石圈的伸展减薄及软流圈的上涌紧密联系;4、福建省基性脉岩的同位素特征显示，第一组脉岩具较高的’43N创4的d，第二组脉岩 的’43N出，科Nd较低;ThiNd、B拢a比值及理论模拟结果表明，第二组脉岩可能受到 流体交代和俯冲沉积物的源区混合作用，而第一组脉岩基本未受俯冲组分（沉积物 +流体）的改造。地壳混染对两组脉岩可能起着重要的作用。EC一AFC理论模拟表明， 福建省基性脉岩在上升过程中受到前寒武纪变质岩的影响，这种混染作用在一定程 度上改变了同位素组成。因此，福建省晚中生代基性脉岩的地球化学特点是太平洋 板块俯冲与壳慢相互作用共同作用的结果;5、K一Ar年龄结果表明，出露于福建省的基性脉岩年龄具周期性分布，表现为五个周期: 70一75Ma士，85 Ma士，105一110Ma，125Ma士和135一140Ma。这与前人的研究结果 基本一致，表明福建省与中国东南部区域上有相似的地壳拉张期次。K一Ar年龄主要 集中分布在14OMa--65Ma之间，这表明:①140Ma限定了中国东南部岩石圈伸展 作用开始的下限，也就是说中国东南部晚中生代的岩石圈伸展至少开始于14OMa左 右，而并非90Ma;②标志着中国东南部大规模拉张作用的开始，表明构造属性由 挤压为主转变为以拉张作用为主。更多还原

【Abstract】 The southeastern China locates at the joint of the Pacific plate and Eurasian plate. The special geological location and structural movements have received considerable attention by geologists. The area has experienced complicated and various structural movements since the Indosinian stage, of which the most important thing is the massive Yanshanian structural-magmatic event. Recently, two important things need to be further addressed: (1) The time of the transition from compressional to extensional setting, and the geodynamics processes in SE China; (2) The relationship between polymetallic mineralization and lithospheric thinning and crustal extension. Thus, the paper focuses on mineralogy, petrology, petrogeochemistry, isotopic chorology, and Sr-Nd-Pb isotopes of the mafic intrusions and dikes in Fujian province, SE China. In addition, we also discussed the process of the plate subduction, mantle evolution, crust-mantle interaction, lithospheric thinning and extension, and the reaction for crustal extension in Fujian province, SE China.(1) Daiqianshan mafic intrusion is situated along the Changle-Nanao fault, which intruded in the metamorphic rocks. The metamorphic rocks are composed of biotite geniss, amphibole schist, sillmanite schist and Mesozoic volcanic rocks. This paper indicates that the island affinity of the intrusion is related to subduction. However, the age of the rock closely approximates the timing of low-angle oblique subduction of an ancient Pacific plate, high-pressure metamorphic event, uplift of the Pingtan-Dongshan metamorphic belt and movement along the Changle-Nanao shear zone. The intrusion was formed by low-degree partial melting of the upper mantle. Thus, the formation of the rock is related to lithospheric extension or collision events, which was derived from upper mantle and intruded along Changle-nanao frature zone. The Daiqianshan intrusion has the same source with other mafic rocks exposed in southeastern China, which had been experienced metasomatism before emplacement. But the former has not been subjected to significant crustal assimilation.(2) Major- and trace-element, as well as Sr-Nd-Pb isotopic data of the Mesozoic Maopin and Shaianjiao mafic intrusions, exposed in Nanjin region, Fujian province, provide an insight into the nature of their mantle source and the secular evolution of the lithospheric mantle beneath the Cathaysian Block, SE China. They are characterized by higher Al2O3, CaO and MnO contents, and lower FeOT, MgO, TiO2 and K2O+Na2O contents than those of theCenozoic basalts. Those rocks are enriched in LILE and LREE, and relatively low HFSE, with positive Pb and negative Ti anomalies. The mafic rocks have high (87Sr/86Sr )j (0.7046-0.7077) and 207Pb/204Pb (15.47-15.67), but relatively low in (143Nd/144Nd)i (0.5125-0.5127) and 206Pb/204Pb (18.26-18.52). The negative correlation between 143Nd/144Nd and 206Pb/204Pb and the positive relationship between 87Sr/86Sr-206Pb/204Pb suggest a mixing of a depleted mantle source and an EM2 component in the study area. Calculation reveals that the Maopin-Shaianjiao mafic rocks are formed by 5-15% degree of partial melting of an LREE-riched spinel Iherzolite. The high Nb and Zr contents, as well as EM2 signature, may have been resulted from addition about 1% melts derived from subducted sediments. Their island arc characteristics suggest that the fluid derived from subducted slab still played important role in the magma genesis. The degree of the crustal contamination is about 10%, which significantly influenced their Sr and Pb isotopes.(3) The mafic dikes in Fujian province are alkali to subalkali in compositions and are characterized by higher A12O3 (14.0-20.4 wt%) and moderate CaO (4.09-12.7 wt%) compared with the Cenozoic basalts in the same region. They are divided into two types based on their REE contents. Type 1 has low total REE (53.8-145.5 g/g) concentration with relatively flat chondrite-normalized patterns [(La/Yb)n=l.68-4.65], whereas type 2 has much higher total REE (63-247 g/g) concentrat更多还原