大兴安岭北段东坡小莫尔可地区中生代火山岩成因及其地质意义:元素、Hf同位素地球化学与锆石U-Pb同位素定年
发布时间：2019-06-20 18:00
【摘要】：大兴安岭是中国东北部陆相火山岩发育的地区之一,其不仅分布广泛,而且空间岩相组合变化较大、成因复杂。笔者对大杨树火山盆地西缘喷发就位在花岗岩带的小莫尔可地区中生代火山岩的地质、岩相学、年代学、元素和Hf同位素地球化学进行了研究。结果表明,该区出露火山岩可划分3个阶段,第一阶段主要为英安质火山碎屑岩夹英安岩组合,呈爆发式火山喷发特征;第二阶段为玄武质粗面安山岩、粗面安山岩组合,呈溢流式火山喷发特征;第三阶段是玄武粗面安山质熔结火山碎屑岩(部分含角砾)。各阶段代表性火山熔岩以及熔结火山碎屑岩的元素地球化学特征揭示:均为富碱(w(Na_2O+K_2O)=4.88%~7.12%),属高钾钙碱性系列;具有相似的痕量元素地球化学分馏特征,即明显富集Ba、K、LRRE等大离子亲石元素,亏损Nb、Ta、Ti、HREE等高场强元素;稀土元素分馏程度中等(LREE/HREE=8.4~8.5)、Eu负异常不明显(δEu为0.91~1.02)。这些特征表明它们是同源岩浆房结晶分异演化的产物,岩浆源区性质呈现地幔与壳幔混合过渡类型的属性,或呈现E-MORB性质的源区或交代洋壳性质的源区。鉴于获得的英安质岩屑晶屑凝灰岩(HSY-1)和玄武粗面安山质岩屑晶屑熔结凝灰岩(P2121)单颗粒锆石U-Pb同位素定年分别为(124.8±1.0)、(123.3±1.3)Ma,ε_(Hf)(t)为1.7~9.7、T_(DM)=705~407 Ma、T_(DM)~C=1 464~748Ma,并结合区域地球动力学研究进展,可进一步得出:火山作用背景应属于中生代古太平洋板块向中国东部大陆俯冲的大陆边缘岩浆弧环境,适值东北地区大规模岩浆底侵、岩石圈拆沉作用的峰期(约120 Ma),初始岩浆应是古太平洋板块深俯冲作用过程形成的埃达克质岩浆,而呈现埃达克质岩浆与岛弧性质的过渡岩石学、地球化学特征,可能是在岩浆底侵、岩石圈拆沉过程与地壳物质发生一定程度的混染作用;并从成矿元素的相容性角度确认该期岩浆作用具有提供Mo、Cu和Ag成矿流体的可能。
[Abstract]:Daxinganling is one of the areas where continental volcanic rocks are developed in northeast China. It is not only widely distributed, but also has great changes in spatial lithofacies assemblages and complex Genesis. The geological, petrographic, chronological, element and Hf isotopic geochemistry of the Mesozoic volcanic rocks in Xiaomoke area, which is located in the granite belt, is studied in this paper. The results show that the exposed volcanic rocks in this area can be divided into three stages, the first stage is mainly Yingan pyroclastic rock assemblage, showing explosive volcanic eruption characteristics, the second stage is basaltic rough andesite assemblage, showing overflow volcanic eruption characteristics, and the third stage is Black Tortoise rough andesite molten pyroclastic rock (part containing breccia). The element geochemistry characteristics of representative volcanic lava and molten pyroclastic rock in each stage show that they are alkali-rich (w (Na_2O K 鈮，
本文编号：2503414
[Abstract]:Daxinganling is one of the areas where continental volcanic rocks are developed in northeast China. It is not only widely distributed, but also has great changes in spatial lithofacies assemblages and complex Genesis. The geological, petrographic, chronological, element and Hf isotopic geochemistry of the Mesozoic volcanic rocks in Xiaomoke area, which is located in the granite belt, is studied in this paper. The results show that the exposed volcanic rocks in this area can be divided into three stages, the first stage is mainly Yingan pyroclastic rock assemblage, showing explosive volcanic eruption characteristics, the second stage is basaltic rough andesite assemblage, showing overflow volcanic eruption characteristics, and the third stage is Black Tortoise rough andesite molten pyroclastic rock (part containing breccia). The element geochemistry characteristics of representative volcanic lava and molten pyroclastic rock in each stage show that they are alkali-rich (w (Na_2O K 鈮，
本文编号：2503414
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