| 王飞飞,韩宗珠,张勇,来志庆,艾丽娜.栖霞牙山花岗岩及其暗色包体地球化学特征及成因研究[J].地质找矿论丛,2019,34(3):393-405 |
| 栖霞牙山花岗岩及其暗色包体地球化学特征及成因研究 |
| Geochemical and petrogenesis of the Yashan granite and its enclaves,Qixia |
| 投稿时间：2019-04-10 |
| DOI：10.6053/j.issn.1001-1412.2019.03.009 |
| 中文关键词: 花岗岩 Sr-Nd-Pb同位素 暗色包体 岩石成因 山东省 |
| 英文关键词:granite Sr-Nd-Pb isotopes mafic enclave petrogenesis Shandong province |
| 基金项目:国家自然科学基金项目（编号：41376053）、山东省自然科学基金项目（编号：ZR2017PD002）联合资助。 |
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| 中文摘要: |
| 栖霞牙山花岗岩体形成于中生代早白垩世（118 Ma），其岩石类型以花岗岩和花岗闪长岩为主，岩体中发育大量的暗色闪长质微粒包体。通过对牙山花岗岩及其暗色包体地球化学特征研究表明，包体围岩w（SiO2）=65.5%~68.82%，铝饱和度（A/CNK）为0.89~1.03<1.1，为准铝质钙碱性Ⅰ型花岗岩；暗色包体具有较低w（SiO2）值（54.82%~60.89%）、高w（TFe2O3）值（6.11%~8.15%）、高w（MgO）值（3.57%~5.19%）的特征。稀土元素配分模式图显示二者皆为轻稀土富集的右倾型曲线，微量元素蛛网图中二者均表现为富集Ba、K等大离子亲石元素，亏损Ta、Nb、Ti等高场强元素，具有大陆地壳的特征。暗色包体与寄主岩石的Sr同位素初始比值（87Sr/86Sr）i分别为0.709 29~0.709 58和0.709 21~0.709 71，应为同源岩浆的产物。两阶段Nd模式年龄（T2DM）分为2 291 Ma-2 391 Ma和2 208 Ma-2 353 Ma，表明可能是古元古界陆壳物质部分熔融的产物。Pb同位素特征显示牙山岩体的原始岩浆以下地壳为主，w（Nb）/w（Ta）值介于下地壳与原始地幔之间，表明可能受到幔源物质的影响，包体中大量磷灰石呈针状结晶状态，进一步暗示存在岩浆混合作用。综上并结合区域构造背景认为，牙山岩体为早白垩世中晚期起源于火山弧环境的壳源特征花岗岩，形成过程中存在幔源物质的加入，它的形成与太平洋板块的俯冲作用密切相关。 |
| 英文摘要: |
| Yashan granitic body is formed in Mesozoic Early Cretaceous Epoch(118 Ma) and composed mainly of granite and granodiorite. Dioritic melan enclusions are well developed in the granitic body. w(SiO2)=65.5% to 68.82%, A/CNK=0.89 to 1.03<1.1 of host rock of the enclusions show that they are calc-mantle metaluminous I-type granite. The melan enclusion is characterized by lower SiO2 (54.82% to 60.89%), and higher TFe2O3 (6.11% to 8.15%) and MgO (3.57% to 5.19%). REE pattern of the enclusion snd host show LREE enrichment and their trace element spider diagrams show large lithophile ion element (Ba, K) enrichment and high field strenth element (Ta, Nb, Ti) depletion which is charateristic of continental crust. The enclusion and host rock have initial 87Sr/86Sr ratios of 0.709 21 to 0.709 71 and 0.709 29 to 0.709 58 suggesting that hey are of the same source. The two stage Rb model age (T2DM) is respectively 2 291 Ma-2 391 Ma and 2 208 Ma-2 353 Ma suggesting that they are the product of partial melting of the crustal materials. Pb isotope characteristics show dominance of lower crustal material of primitive magma of Yashan granite body. The value of w(Nb)/w(Ta) is between those of crust and primitive mantle that is the indication of influence of primitive mantle. The needle-like apatite crystal in the enclusion implies the magma mingle. Therefore, Yashan rock body is a crust-derived granite closely related to subduction of the Pacific ocean plate and incorporated with mantle materials and formed under volcanic arc environment in middle-late Early Cretaceous Epoch. |
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