發(fā)布時(shí)間：2018-06-29 05:05

  本文選題：六合 + 石榴石角閃巖　； 參考：《巖石學(xué)報(bào)》2017年07期

【摘要】：六合地區(qū)地處揚(yáng)子克拉通的西緣,前人對該地區(qū)下地殼的成分與形成機(jī)制尚無系統(tǒng)認(rèn)識。本文通過研究新生代幔源侵入巖中所攜帶的深源捕虜體為認(rèn)識該地區(qū)下地殼的成分和形成機(jī)制提供了直接證據(jù)。該捕虜體為高級正變質(zhì)巖(麻粒巖相),巖性分別為石榴石透輝巖、石榴石角閃透輝巖、石榴石角閃巖。三者全巖Si O2=43.85%~50.82%,MgO=6.83%~14.77%,Mg#=0.50~0.64,Cr=87.1×10~(-6)~616×10~(-6),Ni=19.7×10~(-6)~143×10~(-6),皆屬于低鎂石榴石堆晶巖。通過石榴石-單斜輝石Mg-Fe交換地質(zhì)溫度計(jì)計(jì)算得知石榴石角閃巖的形成溫度721~774℃,形成深度為45~47km,石榴石角閃透輝巖和石榴石透輝巖的形成溫度803~829℃,形成深度為48~51km,說明三者皆形成于下地殼。捕虜體鋯石多為變質(zhì)鋯石,鋯石U-Pb年齡分別為259±9Ma和773±23Ma。捕虜體的全巖Sm-Nd等時(shí)線年齡分別為251±4Ma和809±64Ma。259Ma的鋯石εHf(t)=-5.69~10.3,773Ma的鋯石εHf(t)=5.87~17.7。年代學(xué)數(shù)據(jù)和鋯石Hf同位素?cái)?shù)據(jù)表明六合地區(qū)下地殼受到新元古代和晚二疊世巖漿底侵作用,同時(shí)發(fā)生變質(zhì)作用。新元古代捕虜體富集大離子親石元素(LILE),如Rb、Ba、Sr。高度虧損高場強(qiáng)元素(HFSE),如Nb、Ta、Ti。εNd(t)=4.36~5.28。表明在新元古代時(shí)期,六合地區(qū)的地殼受到俯沖弧巖漿底侵,經(jīng)過批式熔融計(jì)算得知底侵巖漿源自地幔石榴石-尖晶石橄欖巖10%~30%部分熔融。晚二疊世捕虜體富集大離子親石元素(LILE),如Rb、Ba、Sr。輕度虧損高場強(qiáng)元素(HFSE),如Nb、Ta、Ti。εNd(t)=-5.68~2.33。表明在晚二疊世時(shí)期,六合地區(qū)的地殼受到地幔柱-巖石圈地幔相互作用產(chǎn)生的巖漿底侵,經(jīng)過批式熔融計(jì)算得知底侵巖漿由地幔石榴石-尖晶石橄欖巖10%~20%部分熔融而成。綜上所述,在新元古代板塊俯沖和晚二疊世地幔柱的分別作用下,六合地區(qū)的地殼受到地幔物質(zhì)的加入形成鎂鐵質(zhì)的新生下地殼。
[Abstract]:The Liuhe area is located in the western margin of the Yangtze craton. There is no systematic understanding of the composition and formation mechanism of the lower crust in this area. In this paper, the study of deep-source xenoliths carried in Cenozoic mantle intrusive rocks provides direct evidence for understanding the composition and formation mechanism of the lower crust in this area. The xenoliths are advanced orthomorphic rocks (granulite facies), which are garnet diopherite and garnet amphibolite. The whole rock Sio _ 2 ~ (43.85) consists of 50.82% MgO ~ (6.83), including 14.77 mg #0.50 ~ (0.50) ~ (0.64) Cr ~ (67.1) 脳 10 ~ (-6) ~ (-6) ~ (616 脳 10 ~ (-6) Ni ~ (19. 7) 脳 10 ~ (-6) ~ (6) ~ (143 脳 10 ~ (-6), all of them belong to low-magnesium garnet heap. Through the calculation of garnet and clinopyroxene Mg-Fe exchange geothermometer, the formation temperature of garnet amphibolite is 721 ~ 774 鈩，

本文編號：2080973