黑河地区早白垩世火山岩特征及其意义

发布时间：2018-02-23 20:07

本文关键词： 黑龙江黑河地区早白垩世晚期弧火山岩组合金矿俯冲环境　出处：《中国地质大学(北京)》2017年博士论文　论文类型：学位论文

【摘要】：黑龙江省黑河地区广泛发育中生代火山岩,但是火山岩的岩石组合、成因、岩浆源区以及所表征的大地构造环境目前存在很大争议,区内金矿成矿作用与火山岩之间的相互联系尚且缺乏深入研究。本文对研究区火山岩开展详细的岩石学、年代学、岩石地球化学等研究,取得如下认识:1.厘定火山岩的形成年代为早白垩世晚期,是以安山岩—英安岩—流纹岩为主的,包含钾玄岩、玄武安山岩、歪长粗安岩、安粗岩、粗面英安岩、粗面岩的火山岩组合。2.火山岩地球化学特征显示其具有宽广的Si、Al、K、Na、Ca、Fe、Mg等分布范围。火山岩主要为亚碱性系列,岩石Na_2O/K_2O比值一般1.2。A/CNK在1附近,为准铝质-过铝质岩石。SiO_2-TFe O/Mg O图上既有钙碱性系列(包括低铁钙碱性系列),又有拉斑系列。SiO_2-K_2O图上主要为中钾钙碱-高钾钙碱系列。SiO_2-(Na_2O+K_2O-Ca O)图上主要为钙碱系列、碱钙系列和碱性系列,在SiO_2-Mg O图中主要落入实验玄武岩的局部熔融范围和镁安山岩系列范围。痕量元素蛛网图显示富集大离子亲石元素,K、La、Zr、Hf、Tb、Tm为峰,亏损Nb、Ta、Ti、Y、Yb等高场强元素。稀土元素球粒陨石标准化配分模式为缓右倾型的模式,轻稀土相对富集,重稀土内部分馏不明显,具有微弱负Eu异常。大部分岩石具有高Sr低Y的特征,其中一些岩石具有埃达克岩特征。3.基于火山岩组合、火山岩地球化学特征,结合构造环境判别等,认为该区早白垩世火山岩形成于与洋俯冲有关的大地构造环境,在早白垩世晚期已经发育为成熟的大陆边缘弧。推测该区早白垩世火山岩是蒙古-鄂霍次克洋向南侧俯冲的产物,岩浆可能的源区为俯冲的洋壳、上覆的地幔楔、兴安弧的下地壳。黑河地区早白垩世晚期弧火山岩的发育,指示蒙古-鄂霍次克洋在早白垩世仍在向南部俯冲,其闭合晚于早白垩世晚期(~117Ma)。4.研究表明研究区金矿床的围岩(或母岩)为早白垩世火山岩,区内北东向的韧性剪切带可能是蒙古-鄂霍次克洋俯冲带的组成部分和浅源表现,是区域控岩控矿主体构造。区内金矿床与类似TTG特征火山岩、镁安山岩系列、埃达克岩等与俯冲有关的岩类关系密切,暗示金矿床的生成与洋板片熔融密切相关。研究区内与早白垩世火山岩相关的金矿床有两种类型:与安山岩有关的火山热液型金矿床;与闪长玢岩有关的蚀变岩型金矿床。由于闪长玢岩与安山岩具有同期、同源以及相同地球化学属性,以上两种金矿类型只是因岩浆就位深度不同而导致的。推测在已经发现的中-低温火山热液型金矿床深部可能存在蚀变岩型(韧性剪切带型)金矿,在早白垩世安山质火山岩以及次火山岩(闪长玢岩)分布区具有良好的金矿找矿远景。
[Abstract]:The Mesozoic volcanic rocks are widely developed in Heihe area, Heilongjiang Province, but the rock assemblage, genesis, magmatic source region and the geotectonic environment characterized by volcanic rocks are controversial at present. The interrelation between gold mineralization and volcanic rocks in this area is still lack of in-depth study. In this paper, detailed petrology, geochronology and geochemistry of volcanic rocks in the study area have been carried out. To determine that the volcanic rocks were formed in the late early Cretaceous and were mainly composed of andesite, dolomite and rhyolite, including kaliite, Black Tortoise andesite, asparagite, andesite, trachyte and trachyte, The volcanic rock assemblage of trachyte. 2. The geochemical characteristics of the volcanic rocks show that they have a wide range of distribution, such as Si-Al-K _ (+) -Na _ (+) Ca-Fe _ (Fe) mg, etc. The volcanic rocks are mainly subalkaline series, and the Na_2O/K_2O ratio of rocks is generally 1.2.A / C ~ (-K) in the vicinity of 1. There are calc-alkaline series (including low-iron calc-alkaline series) on the quasi-aluminum-peraluminous rock. SiO2-TFeO / MgO diagram, and plaster series. SiO2-K2O graph mainly shows medium potassium calcium alkaline-high potassium calcium alkali series. SiO2-stace Na2OK2O-CaOOgraph is mainly calcium alkali series. The alkali calcium series and alkaline series mainly fall into the local melting range of experimental basalt and the range of mafic andesite series in SiO_2-Mg O diagram. The normalized partitioning model of chondrites of rare earth elements is a slow right-dip model with relatively rich light rare earths, low fractionation within heavy rare earths and weak negative EU anomalies. Most rocks are characterized by high Sr, low Y, and weak negative EU anomalies. 3. Based on volcanic assemblage, geochemical characteristics of volcanic rocks and discrimination of tectonic environment, it is considered that the early Cretaceous volcanic rocks in this area were formed in the geotectonic environment related to ocean subduction. During the late early Cretaceous, the volcanic rocks of the early Cretaceous in this area were derived from the subduction of the Mongolia-Okhotsk Ocean to the south, and the probable source of the magma was subducted oceanic crust and overlying mantle wedge. Lower crust of Xingan arc. The development of arc volcanic rocks in late early Cretaceous in Heihe area indicates that the Mongolia-Okhotsk Ocean is still subducting south in the early Cretaceous. The study shows that the surrounding rock (or parent rock) of the gold deposit in the study area is early Cretaceous volcanic rock, and the NNE ductile shear zone may be the component and shallow source of the Mongolia-Okhotsk Ocean subduction zone. The gold deposit is closely related to subduction, such as TTG volcanic rock, mafic andesite series, adakite, etc. There are two types of gold deposits related to early Cretaceous volcanic rocks in the study area: volcanic hydrothermal gold deposits related to andesite; Altered rock type gold deposits associated with diorite-porphyrite. Because diorite-porphyrite and andesite have the same synchronic, homologous and geochemical properties, The above two types of gold deposits are only caused by the different depth of magmatic emplacement. It is speculated that there may be altered rock type (ductile shear zone) gold deposits in the depth of the volcanic hydrothermal type gold deposit found in the middle and low temperature. In the early Cretaceous Anshanian volcanic rocks and subvolcanic rocks (diorite porphyrite) distribution area has a good gold prospecting prospects.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P588.14;P618.51

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