【作者】 魏巍；

【导师】 姜常义； 赵东宏；

【作者基本信息】 长安大学 ， 矿物学、岩石学、矿床学， 2008， 硕士

【摘要】 阿奇山组位于准噶尔板块的觉罗塔格-红旗山晚古生代沟弧带中的雅满苏岛弧带上,位于项目工作区的东南部。虽然前人对于东天山觉罗塔格地区有较深入的研究,但是就阿奇山组来说,研究程度还很低。因此,本文通过对阿奇山组火山岩进行岩相学、稀土元素、微量元素地球化学的系统研究,科学论证了该组火山岩的岩浆过程、岩浆性质、地幔源区等特征。通过研究取得了以下几点初步认识:1、阿奇山组火山岩的岩石类型主要有英安质火山尘凝灰岩、英安质玻屑凝灰岩、英安质玻屑岩屑凝灰岩、英安质晶屑玻屑凝灰岩、英安质晶屑凝灰岩、英安质晶屑岩屑凝灰岩、英安质岩屑凝灰岩、英安质复屑凝灰岩、英安质含角砾玻屑凝灰岩、英安质含角砾晶屑凝灰岩、英安质含角砾复屑凝灰岩、英安质角砾凝灰岩、安山质晶屑岩屑凝灰岩、安山质岩屑凝灰岩、安山质复屑凝灰岩、安山岩、玄武粗面安山岩。主体岩性为英安质火山碎屑岩、安山岩和粗面安山玄武质熔岩。主要的造岩矿物为单斜辉石和斜长石。2、在阿奇山组火山岩的粗面英安岩区采集的岩石样品,经过北京离子探针中心SHRIMP锆石U-Pb法测定其形成年龄为341.7±2.7Ma,属于早石炭世维宪阶早期。3、阿奇山组火山岩的稀土元素表现为轻稀土元素富集型,有明显的正铕异常,富集大离子亲石元素,相对亏损高场强元素。其中Nb、Ta、Ti明显亏损,表现具有岛弧火山岩的岩石学和地球化学标志,反映了B型俯冲环境中火山岩的典型特征(Gill,1981)。4、阿奇山组火山岩属于同源岩浆,在岩浆上侵的过程中受到同化混染的程度较低,而岩浆分离结晶的主要矿物为单斜辉石和斜长石。5、通过地球化学分析,阿奇山组火山岩表现出典型的洋壳俯冲型埃达克岩的特征,也从另一个角度证明了阿奇山组火山岩的岛弧火山环境,而且根据俯冲型埃达克岩的定义,可以推论出,阿奇山组火山岩的岩浆源区应是洋壳板片的俯冲熔融形成的。更多还原

【Abstract】 Aqishan Formation lies in the Yamansu island-arc belt of Late Paleozoic ditch-arc belt of Jueluotage-Hongqishan in Junggar plate, located in the southeast of this work area. While predecessors have in-depth researched for Jueluotage area of eastern Tianshan, the study for the Aqishan Formation is still in very low-level. Therefore, this paper according to systematically research the petrography, rare earth elements, trace elements geochemistry of the volcanics of Aqishan Formation, scientifically demonstrates the formation of volcanic magmatic process, magma nature and mantle source district features. Based on these researches we get some initial understanding as follows:1. The main volcanic rock types of Aqishan Formation are dacite dust tuff, dacite glass tuff, dacite glass debris tuff, dacite crystal glass tuff, dacitic crystal tuff, dacite crystal debris tuff, dacite debris tuff, dacite complex tuff, dacite breccia tuff, dacite breccia-bearing glass tuff, dacite breccia-bearing crystal tuff, dacite breccia-bearing complex tuff, dacite breccia tuff ,andesite crystal debris tuff , andesite debris tuff, andesite complex tuff, andesite and basatic trachyte andesite. The main lithologies are dacite pyroclastic rock, andesite and trachyte andesite basaltic lava. The main rock-forming minerals are clinopyroxene and plagioclase.2. Dacite samples are collected from Aqishan Formation volcanics, its formation age is 341.7±2.7Ma by SHRIMP U-Pb zircon determination in the centre of Beijing ion probe, belonging to early Viseen stage of Early Carboniferous.3.The rare earth elements pattern of Aqishan Formation volcanics is enriched in light-REE, obvious positive Eu anomaly, and enriches LILE and correspondingly depletes high-field strength elements, Nb, Ta and Ti are obvious depleted. These are of the petrology and geochemical indication of island arc volcanics, and reflect the volcanic rocks character of B-type subduction environment (Gill, 1981).4.Aqishan Formation volcanics belongs to comagmatic region. when the magma is rising, it should be hybridized a little by the crust substance, and the fractional crystallization of the main mineral are olivine and clinopyroxene. 5.Through geochemical analysis, Aqishan Formation volcanics show characteristics of typical oceanic crust subduction type adakite, and it also proves that Aqishan Formation volcanics are of the island arc volcanic environment from another perspective. Furthermore, according to the definition of adakite, it can be inferred that the magma source of Aqishan Formation volcanics is formed by the oceanic crust plate subduction melting.更多还原