【作者】 葛小月；

【导师】 李献华； 周汉文；

【作者基本信息】 中国科学院研究生院（广州地球化学研究所） ， 地球化学， 2003， 博士

【摘要】 琼中和儋县花岗岩主要为具定向构造的斑状黑云母二长花岗岩，属于准铝质Ⅰ型花岗岩。花岗岩的主量元素和部分微量元素成分与SiO₂呈良好的相关关系，显示出明显的斜长石、角闪石、磷灰石和Ti-Fe氧化物等的分离结晶作用，总体上它们与大陆岛弧花岗岩的微量元素丰度和分布特征相似，系统地亏损Ba、Nb、Sr、P和Ti等元素。琼中花岗岩大部分样品具有一致的⁸⁷Sr／⁸⁶Sr初始值（0.7079～0.7112）和ε_Nd（t）值（-8.9～-5.8），儋县岩基样品具有相对较高的⁸⁷Sr／⁸⁶Sr初始值（0.7119～0.7194）和较低的ε_Nd（t）值（-10.6～-8.1），两阶段钕模式年龄计算结果(T_2DM=1.6～1.8Ga)表明它们均源自于地壳存留年龄为早中元古代的地壳源区。高精度SHRIMP锆石U-Pb定年显示琼中岩基形成于印支期（237±3Ma），而儋县岩基形成于燕山早期（186±3Ma），修正了前人将海南岛具有定向构造的变形花岗岩等同于海西—印支期花岗岩的认识。 ⁴⁰Ar_<sup>39Ar及K-Ar定年结果显示海南岛基性岩脉的形成时代主要为～135Ma、105～117Ma和81～96Ma，其中琼南基性岩脉富碱、富钾，属钾玄质系列岩石；琼中基性岩脉的K₂O、Na₂O含量稍低，属于高钾钙碱性系列岩石。海南岛基性岩脉具有与“岛弧”特征相似的微量元素组成特征以及高Sr、低Nd的同位素特征，表明其源自具有EMⅡ特征的富集地幔。琼南基性岩脉强烈富K₂O等LILE和具有较高Nb／Ta比值，其地幔源区应受到了古俯冲板片部分熔融形成的硅质熔体的改造；而琼中基性岩脉的Nb／Ta比值接近于球粒陨石和MORB值，应为古俯冲带含水流体交代的地幔源区的产物。 根据Barbarin（1999）分类，琼中和儋县岩基花岗岩属于高K及含钾长石斑晶的钙碱性花岗岩，同时它们具有原生定向构造，是挤压—松弛—挤压的构造演化过程的产物，表明海南岛从二叠纪末期开始已经是华南大陆的一部分，主要受到了特提斯构造域的影响。琼中岩基可能形成于“印支期”碰撞造山运动峰期后的松弛阶段，而儋县岩基则可能形成于造山运动的结束阶段。白垩纪基性岩脉（81～135Ma）形成于板内拉张环境，与粤北、福建沿海地区的白垩纪基性岩脉共同指示了中国东南部白垩纪时期处于拉张的构造环境。更多还原

【Abstract】 The Qiongzhong and Danxian batholiths, as the largest early Mesozoic syntectonic granite intrusions in Hainan Island, are mainly composed of porphyritic biotite two-feldspars granitoids, in which alkali-feldspar phenocrysts and dark minerals are foliated mostly in WE-direction. The granites are of metaluminous I-type. Major and trace elements show co-variations with SiO2, suggesting the fractional crystallization of plagioclase, hornblende, apatite and Ti-Fe oxides in the evolution of the granites. With systematic depletions of Ba, Nb, Sr, P and Ti, the granites display geochemical similarities to most granitoid rocks formed in the subduction-related environments. Both the Qiongzhong and Danxian granites are relatively high in initial 87Sr/86Sr ratios (0.7079 ~ 0.71 12 and 0.71 19 - 0.7194, respectively) and low in Nd(t) (- 8.9 ~ - 5.8 and -10.6 ~ -8.1, respectively). Their two-stage depleted mantle model ages (T2DM) range from 1.6 Ga to 1.8 Ga, implying a derivation from crustal sources with average crustal residence ages of early Mesoproterozoic. The zircon SHRIMP U-Pb dating results suggest that the Qiongzhong and Danxian granites were emplaced at 237 3 Ma and 186 3 Ma, respectively, which argued against the previous thoughts that all the foliated granites with orientated structure in Hainan Island formed duing the Hercynian - Indosinian episode.40Ar-39Ar and K-Ar age data indicate that the mafic dykes in Hainan Island were emplaced in three major episodes during -135 Ma, 105 ~ 117 Ma and 81-96 Ma. Mafic dykes from the southern Hainan are rich in Alkali and K and belong to shoshonitic, while those from the northern Hainan belong to high-K calc-alkaline series with lower K2O and Na2O. The mafic dykes are characterized by arc-like trace elements, high initial 87Sr/86Sr ratios and low eNd(t) values, and show somefamiliarities with the EMII-mantle source. The southern Hainan mafic dykes arestrongly enriched in LILE with high Nb/Ta ratios, indicating a magma source reconstructed by silicic-melt through partial melting of ancient subducted slides. However, the northern Hainan mafic dykes with chondritic Nb/Ta ratio should be derived from the fiuid-metasomatized mantle related to ancient subduction zone.The Qiongzhong and Danxian granites are belong to the KCG-type (K-rich calc-alkaline) granitoids according to the tectonic nomenclature by Barbarin (1999). These foliated KCG-type granites with original orientated structure are the results generated in a changing geodynamic orogenic environment with alternating compressional to extensional stress field. This suggests that Hainan island has been a part of South China since latest Permian, and been major in extrusion environment of the Tethys tectonic system. The Qiongzhong granite should have been formed at orogenic relaxing stage after the peak of Indosinian orogeny, and the Danxian granite were formed at the latest orogenic phase. In addition, the mafic dykes of Hainan island were formed in an intraplate extensional environment, similar to the mafic dykes in North Guangdong and Fujian coastal areas, all suggesting an extension regime tectonic in southeastern China during Cretaceous.更多还原