高校地质学报
高校地質學報
고교지질학보
GEOLOGICAL JOURNAL OF CHINA UNIVERSITIES
2013年
1期
123-132
,共10页
罗红玲%吴泰然*%赵磊%贺元凯%荆旭
囉紅玲%吳泰然*%趙磊%賀元凱%荊旭
라홍령%오태연*%조뢰%하원개%형욱
锆石LA-ICP-MS U-Pb定年%Hf同位素组成%后碰撞%华北板块北缘
鋯石LA-ICP-MS U-Pb定年%Hf同位素組成%後踫撞%華北闆塊北緣
고석LA-ICP-MS U-Pb정년%Hf동위소조성%후팽당%화북판괴북연
zircon LA-ICP-MS U-Pb dating%Hf isotopic compositions%post-collision%northern margin of the North China Plate
白云鄂博巴音珠日和岩体位于华北板块北缘中段的东升庙—太仆寺旗岩浆岩带上.该岩体由角闪辉长岩和石英闪长岩组成,其地球化学性质显示:低硅高铝,SiO2=49.72%~59.34%,Al2O3=15.79%~19.50%,Mg#=38~44;大离子亲石元素(LILE)富集(如Ba=829×10-6~1104×10-6,Sr=502×10-6~726×10-6)、高场强元素(HFSE,Nb,Ta等)亏损、轻稀土(LREE)富集(La/Yb)N=5.0~11.4,多数样品为弱负铕异常(δEu=0.63~1.09);低Sr/Nd(12~24)和La/Nb(1.33~2.39)比值显示了板内岩浆作用特征.两个角闪辉长岩的高Nb/Th (9.6~18.4)比值显示了非弧玄武质岩浆特征.岩体的锆石LA-ICP-MS U-Pb年龄为(265±2) Ma,代表岩体侵位年龄.锆石εHf(t)=-13.0~-17.2、t DMC=2.12~2.38 Ga,显示了较明显的下地壳基底组分的加入.巴音珠日和岩体可能为后碰撞背景下,地壳的伸展减薄造成基性下地壳的部分熔融,熔体与来自富集地幔的玄武质岩浆发生部分混合,随后经进一步分异结晶作用形成.
白雲鄂博巴音珠日和巖體位于華北闆塊北緣中段的東升廟—太僕寺旂巖漿巖帶上.該巖體由角閃輝長巖和石英閃長巖組成,其地毬化學性質顯示:低硅高鋁,SiO2=49.72%~59.34%,Al2O3=15.79%~19.50%,Mg#=38~44;大離子親石元素(LILE)富集(如Ba=829×10-6~1104×10-6,Sr=502×10-6~726×10-6)、高場彊元素(HFSE,Nb,Ta等)虧損、輕稀土(LREE)富集(La/Yb)N=5.0~11.4,多數樣品為弱負銪異常(δEu=0.63~1.09);低Sr/Nd(12~24)和La/Nb(1.33~2.39)比值顯示瞭闆內巖漿作用特徵.兩箇角閃輝長巖的高Nb/Th (9.6~18.4)比值顯示瞭非弧玄武質巖漿特徵.巖體的鋯石LA-ICP-MS U-Pb年齡為(265±2) Ma,代錶巖體侵位年齡.鋯石εHf(t)=-13.0~-17.2、t DMC=2.12~2.38 Ga,顯示瞭較明顯的下地殼基底組分的加入.巴音珠日和巖體可能為後踫撞揹景下,地殼的伸展減薄造成基性下地殼的部分鎔融,鎔體與來自富集地幔的玄武質巖漿髮生部分混閤,隨後經進一步分異結晶作用形成.
백운악박파음주일화암체위우화북판괴북연중단적동승묘—태부사기암장암대상.해암체유각섬휘장암화석영섬장암조성,기지구화학성질현시:저규고려,SiO2=49.72%~59.34%,Al2O3=15.79%~19.50%,Mg#=38~44;대리자친석원소(LILE)부집(여Ba=829×10-6~1104×10-6,Sr=502×10-6~726×10-6)、고장강원소(HFSE,Nb,Ta등)우손、경희토(LREE)부집(La/Yb)N=5.0~11.4,다수양품위약부유이상(δEu=0.63~1.09);저Sr/Nd(12~24)화La/Nb(1.33~2.39)비치현시료판내암장작용특정.량개각섬휘장암적고Nb/Th (9.6~18.4)비치현시료비호현무질암장특정.암체적고석LA-ICP-MS U-Pb년령위(265±2) Ma,대표암체침위년령.고석εHf(t)=-13.0~-17.2、t DMC=2.12~2.38 Ga,현시료교명현적하지각기저조분적가입.파음주일화암체가능위후팽당배경하,지각적신전감박조성기성하지각적부분용융,용체여래자부집지만적현무질암장발생부분혼합,수후경진일보분이결정작용형성.
The middle segment of northern margin of the North China Plate was influenced by intense tectonic and magmatic activity during the Permian. Dozens of intrusions formed an E-W trending magmatic belt that extended from the Dongshenmiao to Xianghuang Qi, Inner Mongolia, with a length of 400 km and width of 30 km. As a representative, Bayinzhurihe Pluton consists of quartz diorite and hornblende gabbro, which belong to high-potassium calc-alkaline series. They are characterized by low SiO2 (49.72%~59.34%) and high Al2O3 (15.79%~19.50%) contents, with Mg#=38~44, enrichment in large ion lithophile elements (LILE, e.g., Ba=829×10-6~1104×10-6, Sr=502×10-6~726×10-6), relative depletion in high field strength elements (HFSE, e.g., Nb, Ta) in primitive mantle-normalized spidergrams, and right-inclined rare earth element patterns, mostly with slightly negative Eu anomalies (δEu=0.63~1.09). Their low Sr/Nd ratios (12~24) and La/Nb ratios (1.33~2.39) may reflect intraplate magmatism involved. Hornblende gabbro shows non-arc-like (Nb/Th =9.6-18.4) basalt affinity compositions. LA-ICP-MS U-Pb zircon dating of the Pluton yielded an intrusive age of 265±2Ma. Its zircons haveεHf(t)=-13.0~-17.2 and t DMC=2.12~2.38 Ga, mainly show the characteristics of lower continental crust. These features lead us to conclude that Bayinzhurihe Pluton was generated by mixing of lower crustal-derived mafic melt and minor enriched mantle-derived mafic magma, followed by fractional crystallization, due to crustal extension in post-collisional setting.
