A型岩套的分类、判别标志和成因

A型岩套的分类、判别标志和成因

刘昌实, 陈小明, 陈培荣, 王汝成, 胡欢

南京大学地球科学系及成矿作用研究国家重点实验室，南京 210093

收稿日期:2003-12-20 修回日期:2003-12-20 出版日期:2003-12-20 发布日期:2003-12-20

Subdivision，Discrimination Criteria and Genesis for A Type Rock Suites

LIU Chang-shi, CHEN Xiao-ming, CHEN Pei-rong, WANG Ru-cheng, HU Huan

Department of Earth Sciences, State Key Laboratory for Mineral Deposits Research, Nanjing University, 210093, China

Received:2003-12-20 Revised:2003-12-20 Online:2003-12-20 Published:2003-12-20

摘要/Abstract

摘要： 以新近在粤北开展A型岩套研究所获得的新数据，结合国内外文献中已发表的数据(17个岩体，124件样品)，讨论了A型岩套亚类型划分的必要性和亚类型之间的判别方法。将A型岩套分为两亚类型三组。A1类型主要以似长石正长岩、碱性正长岩和响岩为主(AS组)，SiO2不饱和、准铝、过碱-碱性岩石，通常含似长石，如方钠石、霞石、白榴石和钠沸石等为特征。A2亚类型为SiO2过饱和、碱质-亚碱质岩石。该亚类型又包括铝质A型花岗岩(AU她组)(弱过铝质、亚碱质岩石)和碱性花岗岩(AAG组)(准铝质、碱质-亚碱质岩石)；后者通常含少量钠钙质和钠质辉石和角闪石。在地球化学特征上，A1亚型具低SiO2，高ALK和NK／A值，相对富氯低氟，低R1和高R2，低Y／Nb比(具OIB源区特征)，高Nb／Ta，Zr／Hf，Eu／Eu*，LREE／HREE和锆石饱和温度等。A2亚型中，以AAG组为例，其许多地球化学特征与Al亚型相悖，如高SiO2，较低ALK，相对贫氯富氟，高R1和低R2，高10^4Ga／Al和Y／Nb(具IAB源区特征)，低Nb／Ta，Eu／Eu*和LREE／HREE，以及高的锆石饱和温度等。A2亚型中ALAG组除铝过饱和外，其他地球化学特征很相似于．AAG组。利用R1-R2，Yb／Nb-Yb／Ta，Nb-Y-Ce，Nb／Ta-Nb等图解可有效地区分和判别A型岩套中Al和A2两种亚型。利用A1和A2亚型Sr，Nd同位素组成，以亏损地幔-全壳两端员混合模拟计算A2亚型花岗岩物质来源得出结论，其源区物质主要是以地幔端员占优势，地幔组分占68％～78％(7个岩体)，只有Namibia的碱流岩为下地壳成因，其地幔组分仅占30%。A1亚型碱性正长岩(3个岩体)以亏损地幔-富集地幔两端员混合模拟计算表明，其源区物质中富集地幔端员所占比例较低，为4％～17％，表明A型岩套两亚型其源区物质组成有明显不同。

Abstract: This paper discusses the necessity for subdivision of A type suites into A1 and A2 subtypes and the judging criteria to distinguish them，based on new data obtained in study on A type suites in north Guangdong province and the data published in Chinese and overseas literature． The A type suites can be divided into two subtypes and three groups(A1 subtype：AS group；A2 subtype：ALAG group and AAG group)．The A1 subtype(AS group)is usually SiO2-undersaturated，metaluminous，and peralkaline-alkaline rocks，which include feldspathide syenites, a1kaline syenites and phonolites ．They are essentially characterized by existence of more or lass amount of feldspathide minerals such as Sodalite，nepheline，leucite etc．The A2 subtype is usually Si02-oversaturated，alkaline-subalkaline granitic rocks，which include the peraluminous，subalka1ine A type granites (ALAG group)，and the metaluminous，alkaline A type granites (AAG group)．Distinguishable from the ALAG group，the AAG group generally contains more or less amount of Ca-Na-or Na-pyroxenes and amphiboles ．Geochemically，the A1 subtype has relatively lower Si02(54.13％～61.29％)，higher ALK (12.65％～ 13.50％)，NK／A (0.85～1.03)，chlorine(50×10-6 ～9600×10-6)，R2(623，average，the same below)，Nb/Ta (15.69)，Zr／Hf(36.17)，Eu/Eu* (0.60)，LREE/HREE (15.18) and zircon．saturation temperature(833℃ )，and relatively lower R1(-263)，10^4 Ga/A1(2.4)，Y/Nb(0.34，similar to OIB source materials)and relatively lower fluorine(50×10-6～3523×10-6)．In contrast to A1 subtype，the AAG group of A2 subtype has relatively higher SiO2(71.93％-76.28％)，lower ALK(7.81％～9.80％)，chlorine(26×10-6～500×10I6)，R2 (318，in average，the same below)，Nb／Ta(13.09)，Eu／Eu* (0.29)and LREE/HREE (7.57)，and higher R1(2295)，10^4 Ga/A1 (3.93)，Y (1.64，similar to IAB source materials)，higher fluorine(6OO×10-6 ～1900×10-6)and zircon-saturation temperature(883℃ )．The ALAG group of A2 subtype is similar in geochemical properties to the AAG group，but is peraluminous．Using a series of diagrams of R1-R2，Y/Nb-Yb/Ta, Nb-Y - Ce and Nb/Ta-Nb，the A type suites can be readily distinguished into A1 and A2 subtype ．Based on the Nd，Sr isotopic data and using the mixing model of depleted mantle endmember and bulk crust endmember, it is calculated that the source materials for most A2 subtype granites of seven rock bodies are dominated by depleted mantle endmember component(68％～78％)．The mixing model of depleted mantle endmember and enriched mantle endmember shows that the source material components for A1 type rock suites are composed of EM4DM96-EM17DM83，and the enriched mantle endmember comprises only a minor proportion．

刘昌实, 陈小明, 陈培荣, 王汝成, 胡欢. A型岩套的分类、判别标志和成因[J]. J4.

LIU Chang-shi, CHEN Xiao-ming, CHEN Pei-rong, WANG Ru-cheng, HU Huan. Subdivision，Discrimination Criteria and Genesis for A Type Rock Suites[J]. J4.