海南岛早三叠世超钾质强过铝花岗岩地球化学特征及成因

发布时间：2018-07-10 02:51

本文选题：超钾强过铝花岗质侵入岩 + 锆石SHRIMP　；参考：《东华理工大学》2017年硕士论文

【摘要】：目前,对华南地区(含海南岛)三叠纪(印支期)构造演化的认识还存在较多争论。而三叠纪超钾质岩正是用于界定三叠纪构造环境的关键性证据,由于其比较罕见,因此,研究海南岛三叠纪超钾质岩对探讨分析该时期的构造演化有着十分重要的地质意义。近期在海南岛琼海市迈州岭地区,在野外地质调查的过程中发现了三叠纪超钾质强过铝侵入岩,由于其具有独特的岩石地球化学性质,在壳幔间的相互作用及对构造环境的指示意义,因此选取海南岛迈州岭地区超钾质强过铝花岗岩作为研究对象,通过对其进行系统的岩石学、地球化学等研究,探讨其岩石成因及形成的构造环境。它们的高精度锆石SHRIMP U-Pb年龄分别是247.5±6.1 Ma和248.43±5.9 Ma,指示其形成于早三叠世,为海西-印支期岩浆活动的产物。海南岛超钾质强过铝侵入岩主要由花岗斑岩组成,其SiO_2含量较高,为73.41%~75.04%,富碱,全碱(Na_2O+K_2O)含量为7.41%~10.44%,K_2O含量超高,为7.31%~10.20%(平均含量为9.24%),K_2O/Na_2O平均值大于403,属超钾质岩;A/CNK1.1,属强过铝质;Harker图显示,SiO_2与多数氧化物存在相关性,SiO_2与TiO_2、MnO、FeOT、Na_2O存在良好的负相关关系,Al_2O_3与SiO_2存在良好的正相关关系,显示黑云母、Ti-Fe氧化物和斜长石等物质可能发生了分离结晶作用;稀土元素含量普遍较高且变化较大,其含量为281.86×10~（-6）~519.05×10~（-6）,ω(LREE)/ω(HREE)为12.28~20.32,稀土配分曲线显著向右陡倾,轻重稀土分异明显;δEu多数介于0.275~0.498之间(平均值为0.31),负铕异常明显,Eu的亏损指示着斜长石的结晶分离;在微量元素蛛网图上,大离子亲石元素(LILE)Rb、Th、U、K明显富集,Ta、Nb、Ti、P相对亏损,说明有磷灰石和钛铁矿存在一定程度的结晶分离,尤其Ti显著亏损,暗示其与俯冲带有亲缘性;由于Rb/Sr比值过高(平均值为20),造成初始锶比值(I_(Sr))过低(平均值为0.646,低于原始地幔值),致使初始锶比值不可用,ε_(Nd(t))值为-7.4~-6.4,T_(2DM)为1542~1626 Ma,同位素地球化学显示其源岩物质不太均一,并且岩浆未得到充分均一化,暗示其壳源熔融混染地幔的特点。
[Abstract]:At present, there are still many controversies about the Triassic (Indosinian) tectonic evolution in South China (including Hainan Island). The Triassic ultrakalitic rocks are the key evidence for defining the Triassic tectonic environment. Therefore, the study of the Triassic ultrapotash rocks in Hainan Island is of great geological significance for the analysis of the tectonic evolution of the period. In the Meizhou Ridge area of Qionghai City, Hainan Island recently, the Triassic ultrapotash strong peraluminous intrusive rocks were discovered in the course of field geological survey, due to their unique petrogeochemical properties. The interaction between crust and mantle and its indicative significance to the tectonic environment. Therefore, ultrapotash peraluminous granite in Meizhou Ridge area, Hainan Island, is selected as the research object, and its systematic petrology and geochemistry are studied. The petrogenesis and tectonic environment of its formation are discussed. Their high precision shrimp U-Pb ages are 247.5 卤6.1 Ma and 248.43 卤5.9 Ma, respectively, indicating that they were formed in the early Triassic and were the product of the Hercynian-Indosinian magmatism. The ultrapotash strong peraluminite intrusive rocks in Hainan Island are mainly composed of granitic porphyry rocks. The SiOSP _ 2 content is 73.41% and 75.040.The content of Na _ 2O -rich K _ 2O is 7.41% and 10.44% K _ 2O is very high. 7.31% 10.20% (average content 9.24%) the average value of K _ 2O / Na _ 2O is greater than 403, belong to the ultrapotash rock Ar / CNK 1.1, belong to the Harker chart of strong peraluminite, and show that there is a good negative correlation between SiO2 and TiO2MnOFeOTNa2O; Al2O3 and SiO2O2 have a good positive correlation with SiO2.The results show that there is a good positive correlation between SiO2 and TiO2MnOFeOTNa2O, and there is a good positive correlation between SiO2O3 and SiO2.There is a good positive correlation between SiO2 and SiO2MnOFeOTNa2O. The results show that the biotite Ti-Fe oxide and plagioclase may be separated and crystallized, the content of rare earth elements is generally high and varies greatly, its contents are 281.86 脳 10 ~ (-6) (519.05 脳 10 ~ (-6), 蠅 (LREE) / 蠅 (hree) is 12.28 ~ (20.32), the rare earth partition curve is steeply and steeply to the right. Most of 未 EU is between 0.275 and 0.498 (mean value is 0.31), and the depletion of negative EU indicates the crystallization separation of plagioclase, and on the trace element cobweb diagram, the large ion lithophile element (Lile) RbP- ThUU K is obviously enriched in TaNbTiP, and the relative depletion of TaNbTiP is also found in the trace element cobweb diagram. It is suggested that there is a certain degree of crystallization separation between apatite and ilmenite, especially the significant depletion of Ti, which suggests that there is affinity between apatite and subduction. The initial Sr ratio (I _ (Sr) is too low (the average value is 0.646, lower than the original mantle value) due to the high RB / Sr ratio (average 20), which makes the initial Sr ratio unusable, 蔚 _ (ND (t) = -7.4 ~ -6.4) T2DM = 15421626 Ma.The isotopic geochemistry shows that the source rocks are not homogeneous. And the magma has not been sufficiently homogenized, implying the characteristics of the mantle mixed by melting of its crust source.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.121;P534.51

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