铝质A型花岗岩与碱性岩的成因联系：以辽东半岛赛马-柏林川岩体为例

Although A-type granites have attracted much attention due to their important tectonic significance, the sources and petrogenesis of these rocks, especially for the peraluminous A-type granites, are still in debate. The peraluminous A-type granites are mainly derived from a felsic infracrustal source and thus associated minor mantle-derived rocks. However, Triassic peraluminous A-type granites that are associated intimately with contemporaneous alkaline rocks were found in the north Liaodong Peninsula, and their genetic relationship is still not well established. This project will carry out detailed field and petrographic observations for the Triassic peraluminous A-type granites and associated alkaline rocks located in Saima-bolinchuan region of the north Liaodong Peninsula. Based on this, an integrated study of geochronology, whole-rock geochemistry, mineral chemistry, in-situ trace element and Sr-Nd-Hf-O isotopic analysis of accessory minerals (e.g., zircon, titanite and apatite) will be performed for these rocks with aims to reveal ages and petrogenesis of the peraluminous A-type granites and their genetic relationship with the associated alkaline rocks, and, on this basis, to constrain the contribution of mantle-derived alkaline magmatism to the peraluminous A-type granites.

A型花岗岩因蕴含伸展动力学信息而广受关注，但A型花岗岩源区及其成因却一直存在较大争议，尤其是铝质A型花岗岩。通常认为铝质A型花岗岩是壳源岩浆作用的产物，但辽东半岛北部赛马-柏林川地区三叠纪铝质A型花岗岩却与同期的幔源碱性岩密切伴生，至今缺乏二者间的成因关系研究。本项目拟选择赛马-柏林川地区的铝质A型花岗岩和伴生碱性岩为研究对象，在详细的野外岩性填图和室内岩相学观察基础之上，对铝质A型花岗岩开展副矿物（锆石、榍石和磷灰石）原位微区U-Pb年代学、原位微区微量元素和Sr-Nd-Hf-O同位素研究，结合全岩主微量元素、同位素数据和矿物成分分析，查明铝质A型花岗岩的侵位时代、岩浆源区及成岩过程，对比已有碱性岩研究成果，揭示铝质A型花岗岩与碱性岩之间的成因联系，探讨幔源碱性岩浆在铝质A型花岗岩形成过程中的作用。

铝质A型花岗岩很少与较大规模幔源岩石共生，通常认为其岩浆源区为地壳，地幔在其成岩过程中主要提供热源。但是辽东赛马-柏林川地区的三叠纪铝质A型花岗岩却与同期的幔源碱性岩密切伴生，其岩浆源区和成岩过程以及与碱性岩的关系缺少研究。本项目选择该地区出露的腰牌、小石门、大石湖庙和天桥沟四个花岗岩岩体以及侵入其中的基性岩脉为研究对象，通过对这些岩石开展详细的岩石学，矿物学，全岩地球化学，锆石U-Pb年代学以及副矿物Sr-Nd-Hf-O同位素分析，示踪其岩浆源区和成岩过程，并与伴生赛马碱性岩进行对比，探讨二者之间的成因联系。研究发现，这些花岗岩与基性岩脉形成于223-230Ma，与伴生赛马碱性岩属于同期岩浆活动产物。花岗岩具有高碱，高FeOt/MgO、Ga/Al和高Nb、Zr等特征，属于铝质A型花岗岩。基性岩脉为碱性富钾系列岩石。基性岩脉形成于富集岩石圈地幔的低程度部分熔融，与伴生碱性岩的特征与成因一致。铝质A型花岗岩与基性岩脉以及伴生的碱性岩有着相同的全岩和副矿物同位素组成。矿物学和地球化学证据表明它们的形成与伴生硅饱和碱性岩发生辉石+角闪石+碱性长石+磷灰石的结晶分异有关，是幔源碱性岩浆结晶分异的产物。该研究揭示出铝质A型花岗岩可以由幔源碱性岩经结晶分异作用产生，地幔不仅可以为铝质A型花岗岩的形成提供热量，也可以是其主要物质来源。