大别-苏鲁造山带南北两侧晚中生代富钾火山岩的成因:微量元素及Sr-Nd-Pb同位素制约  

Petrogenesis of K-rich Volcanic Rocks on the Northern and Southern Sides of the Dabie-Sulu Orogenic Belt,Eastern China:Constraints from Trace Elements and Sr-Nd-Pb Isotopes

作　　者：邱检生[1] 蒋少涌[1] 张晓琳[1] 胡建[1] 

机构地区：[1]南京大学地球科学系及成矿作用国家重点实验室,江苏南京210093

出　　处：《地球学报》2004年第2期255-262,共8页Acta Geoscientica Sinica

基　　金：国家自然科学基金项目 (编号 :40 2 72 0 3 5 );国家创新研究群体科学基金项目 (编号 :40 2 2 13 0 1)资助

摘　　要：大别 苏鲁造山带南、北两侧广泛发育晚中生代富钾火山岩 ,主要岩石组合为粗面玄武岩 玄武粗安岩 粗安岩 安粗岩 粗面岩 ,这套岩石总体具有富碱、富钾、富轻稀土和大离子亲石元素 (如Rb、Th等 ) ,贫高场强元素 (如Nb、Ti等 ) ,(87Sr/ 86Sr) i值偏高 ,εNd(t)值偏低等特点 ,但南、北两侧富钾火山岩的地球化学特征存在较显著的差异 ,主要表现在造山带北侧富钾火山岩稀土总量更高 ,轻、重稀土分异更明显 ,且 (87Sr/ 86Sr) i 值更高 ,εNd(t)值和2 0 6Pb/ 2 0 4Pb值显著偏低。元素 同位素综合示踪显示 ,区内富钾火山岩均起源于富集地幔的部分熔融 ,但南、北两侧源区地幔的富集机制存在差异 ,南侧富集地幔的形成主要与俯冲洋壳析出流体的交代作用有关 ,而北侧富集地幔的形成除受到俯冲洋壳析出流体的交代作用外 ,在更大程度上主要起因于俯冲的扬子陆壳析出流体的交代作用 ,即其源区遭受了多次富集事件的影响 ,后者是导致南、北两侧富钾火山岩地球化学特征差异的主要原因。Late Mesozoic K-rich volcanic rocks,mainly of the trachybasalt-basaltic trachyandesite-trachyandesite-latite-trachyte association,are widely developed on the northern and southern sides of the Dabie-Sulu Orogenic Belt (DSCB). These rocks generally have abundant alkali-and potassium-rich LILE and LREE like Rb and Th,and are depleted in HFSE such as Nb and Ti. They also have high ( 87 Sr/ 86 Sr)_ i ratios and low ε_ Nd ( t ) values. Compared with those on the southern side of DSCB,the K-rich volcanic rocks on the northern side of DSCB have higher total REE contents and higher LREE/HREE and ( 87 Sr/ 86 Sr)_ i ratios but much lower ε_ Nd ( t ) and 206 Pb/ 204 Pb values. Combined element-isotope tracing demonstrates that the studied K-rich volcanic rocks all originated from partial melting of the enriched mantle. However,the mantle source on the northern side of DSCB may be quite different from that on the southern side in the enrichment process. The formation of the enriched mantle on the southern side of DSCB is mainly related to metasomatism by fluids from dehydration of subducted oceanic crust materials,whereas the mantle source on the northern side of DSCB was subjected to the involvement of subducted Yangtze continental crust materials besides the influence of subducted oceanic crust materials. The involvement of continental crust materials in the mantle source is considered to be the main factor responsible for the geochemical differences of the K-rich volcanic rocks between the northern side and the southern side of DSCB.

关 键 词：大别-苏鲁造山带 晚中生代 富钾火山岩 地球化学 岩石成因 

分 类 号：P588.14[天文地球—岩石学]