大兴安岭中生代花岗岩类的地球化学

大兴安岭中生代花岗岩根据微量元素地球化学特征划分为高锶花岗岩类和低锶花岗岩类,前者富集Ba、Sr、Ti,而后者强烈亏损这些元素而富集大离子亲石元素和高场强元素。高锶花岗岩类主要由石英闪长岩、英云闪长岩和花岗闪长岩组成,属于Ⅰ型花岗岩;低锶花岗岩类由二长花岗岩、正长花岗岩、碱长花岗岩和碱性花岗岩组成,二长花岗岩一正长花岗岩一碱长花岗岩也属于Ⅰ型花岗岩,碱性花岗岩为A1型花岗岩。这两类花岗岩均显示εNd(t)正值^87Sr／^86Sr低值以及较低的Nd模式年龄。高锶与低锶花岗岩类地球化学差异性表明,高锶花岗岩起源于相对亏损的幔源岩浆的分异作用,而低锶花岗岩类的源区与显生宙地壳增生时期起源于地幔的年轻地壳物质有关,即起源于富集型幔源基性岩石的部分熔融。大兴安岭中生代花岗岩与流纹岩之间地球化学相似性以及与玄武岩类的相关性表明,它们是统一的构造一岩浆体系的产物,共同制约于古亚洲洋闭合后的大陆伸展的构造环境和闭合期间壳幔相互作用形成的地幔源区。     

Nummulitic banks in the upper Lutetian ‘Buil level’, Ainsa Basin,South Central Pyrenean Zone: the impact of internal waves

Nummulites, a particularly abundant and diverse genus of larger benthonic foraminifera, formed huge accumulations (banks) during the Eocene, which are often good hydrocarbon reservoirs, especially in North Africa. Despite their economical interest, these accumulations are not well‐understood and their origin is still under discussion. Reasons for this debate are the absence of living Nummulites accumulations and the high‐variability of facies, including the size, shape and extension of the banks, which reflect the array of processes controlling sediment production and accumulation. The nummulitic banks near Santa María de Buil, in the Ainsa Basin (South Pyrenean Foreland Basin) are composed of recurrent facies associations within mappable bed units bounded by physical surfaces. The depositional processes that produced the Nummulites deshayesi accumulations are interpreted considering the shape of the banks, the type of bounding surfaces, the distribution of sedimentary textures, Nummulites test shapes and the associated skeletal components within the banks. This integrative analysis indicates that nummulitic banks accumulated from mass flows, with very poor sediment sorting. Textural and compositional differences among banks suggest that globose Nummulites thrived in the shallower part of the mesophotic zone with abundant nummulithoclasts, whereas flat nummulitic forms thrived in deeper mesophotic, clay‐dominated settings. Interbedded with nummulitic banks, coral biostromes and coral mounds bearing Operculina, Discocyclina and Asterocyclina, represent in situ accumulation near the base of the photic zone. Internal waves (waves that propagate along the pycnocline) are thought to be the triggering mechanism for the density flows. Internal waves and induced bottom currents are sporadic but strong enough to bring sediments into suspension. In contrast to surface waves (both fair‐weather and storm), whose impact is strongest near the sea surface and decreases with bathymetry, the impact of internal waves is usually strongest in the mid‐shelf region and weaker in shallow water. This explains the compositional character of the nummulitic banks.     

北阿尔金巴什考供盆地南缘花岗杂岩体特征及锆石SHRIMP定年

北阿尔金巴什考供盆地南缘花岗杂岩体呈近东西向分布,长约49公里,出露面积约90平方公里,与围岩之间为明显的侵入接触关系,接触界线为不规则的渡状、锯齿状。围岩为前寒武纪砂岩、片岩、泥岩及凝灰质砂岩。该杂岩体主要由巨斑花岗岩、红色花岗岩、灰白色似斑状花岗岩和粉红色似斑状花岗岩组成。杂岩体的主元素含量变化不大,SiO2为65．14％- 75．66％,全碱含量为7．49-8．96％,K2O／Na2O比值为1．12-2．68,岩石的里特曼指数平均为2．34,CIPW标准矿物计算均出现刚玉(AC)(平均为1．78),说明岩石铝过饱和;杂岩体的稀土总量变化于89．44×10-6-335．28×10-6之间,不同岩石类型均有负铕异常,且从巨斑花岗岩→灰白色似斑状花岗岩→红色似斑状花岗岩→红色花岗岩,负铕异常越来越明显,表现在Eu／ Eu+值由0．65→0．51→0．48→0．30。在微量元素蛛网图上,所有样品的微量元素丰度均高于原始地幔值,并具有相似的配分模式,即在Ba、Nb、Sr、P、Ti处呈明显的低谷,显示出S型花岗岩的特征。锆石SHRIMP U-Pb定年得出,巨斑花岗岩、红色中细粒花岗岩、灰白色和粉红色似斑状花岗岩的年龄分别为474．3±6．8Ma、446．6±5．2Ma、434．5±3．8Ma和431．1±3．8Ma。结合区域地质特征,我们认为,该杂岩体形成于同碰撞-碰撞后的构造环境。     

南菲律宾地区类埃达克岩和富铌玄武质熔岩的成因

埃达克岩（adakite)最初 是指由消减板片玄武岩物质熔融形成的富硅、富钠、高Sr/Y和La/Yb比值的弧火山熔岩。它通常产在会聚带，这个部位的年轻的、因而仍然是热的大洋板片正在发生俯冲消减。富铌的岛弦玄武央进则是吕等到高碱的镁铁质熔岩，它们相对于正常的岛弦玄武岩含有较多的高场强元素（HFSE）。这些玄武岩通常与埃达克央共生， 这一组合是直被用于论证他们的高HFSE含量是因为他们的地幔源区受到板片来源的熔体的交代。先前的区域研究结果表明，南菲律宾是埃达克岩和富铌岛孤玄武岩的一个典型产地。然而最近的详细研究显示，尽管该地区的一些岛弧火山岩是类埃达克岩的，但是它们很可能是来自地幔楔的母岩浆的分异作用的产物，而这里的地幔楔主要是受沉积来源的成分交代的，此外，菲律宾南部最典型的富铌熔岩中HFSE的富集，也很有可能是起因于似乎是西太平洋边缘特有的富集地幔组分的熔融。这些结果提出了如下问题：南菲律宾是否存在真正的板片来源的熔体？这里的富铌岛弧 熔岩是否起因于地幔楔被这种熔体交代？