利用石榴橄榄岩重建大陆俯冲带的古动力学环境及其演化过程  

Using garnet peridotite to reconstruct the paleo-geodynamic settings and evolution processes of the continental subduction zone

作　　者：张聪[1] 黄杰[1,2] 陈梅[1,2] 杨经绥[1] 

机构地区：[1]中国地质科学院地质研究所、大陆构造与动力学国家重点实验室,北京100037 [2]中国地质大学地球科学与资源学院,北京100871

出　　处：《岩石学报》2015年第12期3743-3754,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41202034、41572051);中国地质科学院地质研究所基本科研业务费(J1518);中国地质调查项目(12120115026801)联合资助

摘　　要：本文提出一种对于造山带石榴橄榄岩的简单概念分类模型。该模型将造山带石榴橄榄岩划分为地幔楔型和俯冲带型两种类型,根据所记录温压条件及P-T轨迹的差异,地幔楔型石榴橄榄岩进而被划分为A-D四个亚类,分别对应不同厚度的克拉通型岩石圈地幔及普通大陆岩石圈地幔环境中冷的/古老的/稳定的地幔环境及与之对应的相对热的/年轻的/活动地幔环境。我们选择研究程度较高的斯堪的纳维亚加里东期造山带及我国柴北缘造山带中出露的石榴橄榄岩来检验该模型的适用性。出露于挪威西片麻岩地区的Mg-Cr型及Fe-Ti型石榴橄榄岩分别属于地幔楔型的A亚类(来自于古老的/冷的/厚的/亏损的克拉通岩石圈地幔)及壳源俯冲带石榴橄榄岩,而来自Seve,Troms和Linds地体的石榴橄榄岩则属于地幔楔型的C亚类(来自于古老的/冷的/薄的/亏损的大陆岩石圈地幔)后经历俯冲过程变为俯冲带石榴橄榄岩。对我国柴北缘超高压带绿梁山石榴橄榄岩的检验结果相对复杂。前人的研究表明绿梁山石榴橄榄岩存在三种不同的成因方式,对应分类模型中的:1)D亚类橄榄岩(阿拉斯加型岩浆岩堆晶体);2)壳源俯冲带型石榴橄榄岩;3)A亚类来自克拉通岩石圈地幔的太古代石榴橄榄岩。检验结果表明,该分类模型能较好的解释斯堪的纳维亚加里东期造山带中的石榴橄榄岩的出露规律,岩石学及矿物学特征及不同期次矿物之间的年代学关系,但对于我国绿梁山石榴橄榄岩的成因分类仍需进一步研究。假设该分类模型能适用于大多研究程度较高的造山带石榴橄榄岩,起到决定性作用的两个分类参数为地幔楔形成初期的平均温度(T)及造山带岩石圈地幔的厚度(P)。熔融作用发生的时间及深度同样是区分不同类型石榴橄榄岩的重要因素。A simplified conceptual model that can be used to classify orogenic garnet peridotites has been proposed,allowing a more systematic way to investigate such variables in nature. In addition to the ‘classic ＇ mantle wedge-versus subduction zone garnet peridotites,the model subdivides mantle wedge garnet peridotites into four subtypes,called type A,B,C and D,equivalent to young /hot / dynamic- versus cold / old / static mantle in thick or thin garnet-olivine bearing mantle wedges. Two well-studied orogenic belts in Scandinavia and China have been chosen to illustrate the applicability of the model. For garnet peridotite of the Scandinavian Caledonides,the model fit well with geological observations and petrological,mineral-chemical and isotope characteristics. Different types of mantle wedge garnet peridotite can be recognized when garnet peridotites of the Western Gneiss Region（ type A = old,cold,thick,depleted mantle wedge- and / or crustal type overprinted by subduction zone garnet peridotite） are compared to those in the Seve-,Troms- and Linds Nappes（ type C = old,cold,thin,depleted mantle wedge- and / or crustal type overprinted by subduction zone garnet peridotite）. Similar investigations on the orogenic garnet peridotites from the North Qaidam orogen appear to be more complicated. There are two contrasting interpretations for the origin of the Lüliangshan garnet peridotite in the North Qaidam orogenic belt： 1） type D = thin,hot,young and dynamic（ Alaskan type magmatic cumulate）; 2） subduction zone garnet peridotite of crustal origin; 3） type A = Archean fragments underneath a subcratonic lithosphere. Assuming universal applicability of our model,we conclude that the most important discriminative parameters are： 1） The mean bulk temperature（ T） that is operative in the mantle wedge at the onset of continental collision / subduction; and 2） the thickness（ P） of the lithosphere underneath the overriding plate during collision. Finally,it needs to be emphasized that bo

关 键 词：造山带石榴橄榄岩分类 地幔楔 俯冲带 超高压变质作用 

分 类 号：P541[天文地球—构造地质学] P588.34[天文地球—地质学]