大兴安岭东北部早白垩世秀山火山—侵入杂岩体特征及成因

Characteristics and petrogenesis of Early Cretaceous Xiushan volcanic—intrusive complex in northeastern Da Hinggan Mt.

大兴安岭东北部秀山林场一带的早白垩世花岗质火山--侵入杂岩体由喷发旋回期的流纹岩、流纹质熔结凝灰岩--粗面英安岩、粗安岩和浅成侵入期的二长花岗斑岩--晶洞正长花岗岩--文象碱长正长花岗岩构成。晚期侵入岩体充填于火山喷发形成的塌陷破火山口中央,岩石具文象结构、晶洞构造等特征,未见碱性暗色矿物。流纹岩(118.20±1.90Ma)与侵入岩形成时代(116.86～118.3Ma)相近。杂岩体岩石大多数属碱性系列,具高硅、富碱、铝、Ga和高场强元素(HFSE)的特征,各岩石微量元素蛛网图上曲线形态基本一致,均出现Sr、Ba谷,稀土配分曲线也相似,呈轻稀土富集的不对称右倾"海鸥"型,δEu中等亏损。流纹岩与石英正长岩的86Sr/87Sr初始值(0.708734～0.711488)、143Nd/144Nd初始值(0.512485～0.512503)相近。杂岩体具时、空、源的一致性,为铝质A1型火山--侵入杂岩体,形成于岩石圈伸展机制下的非造山板内拉张构造环境。

Early Cretaceous granitic volcanic-intrusive complex in Xiushanlinchang of northeastern Da Hinggan Mt. consists mainly of rhyolite, rhyolite ignimbrite-trachytic dacite, traehyandesite formed in eruptive cycle stage and adamellite porphyrygeode syenogranite-graphic alkali feldspar syenogranite formed in hypabyssal invasion stage. Later intrusive body filling in the center of collapse caldera formed by volcanic eruption, and the rocks have graphic texture and geode structure without dark alkaline minerals. The age of rhyolite （ 118.20 ± 1.90 Ma） is similar to the intrusive rocks （116. 86 ± 118.3 Ma）. Most rocks of the complex belong to alkaline series with high silicon, alkali, aluminum, Ga and HFSEs. The spider diagrams of trace elements of these rocks are close, with Sr, Ba low valley. The rare-earth distribution patterns are similar too, and present slightly LREE enrichment asymmetric right-wing ＂seagull＂ type and medium Eu negative anomaly. The ^86Sr/^87 Sr and ^143 Nd/^144 Nd initial values of rhyolite and quartz syenite are also similar. The time-space-source consistency indicates that the complex is aluminum Al-type granite and formed in non-orogenic intraplate extensional tectonic setting under the extension mechanism of lithosphere.