泰宁地区中志留世辉绿岩脉成因及对陆内造山作用的制约

华南早古生代造山作用以武夷-云开造山带最为典型.然而，该次造山作用过程中岩石圈地幔性质及构造背景一直存在争议，还需要更多的基性岩证据.对武夷造山带中段泰宁地区何宝山辉绿岩脉开展了年代学、地球化学及Sr-Nd-Hf同位素研究.LA-ICP-MS锆石U-Pb年龄（430±3 Ma）表明辉绿岩脉形成于中志留世.岩石具有高Al₂O₃（15.23%~18.49%）、低Na₂O（2.82%~4.21%）和K₂O（1.63%~2.42%）含量特征，属亚碱性系列.稀土元素标准化图呈右倾，无明显Eu异常，显示富集大离子亲石元素（Rb、Ba、K、La、Sr）、不同程度亏损高场强元素（Ta、U、Hf、Ti）.岩石具有高Nb含量（5.74×10-6~8.45×10-6），其（Nb/La）_N和Nb/U值与富Nb岛弧玄武岩相似.全岩（87Sr/86Sr）_i=0.709 5~0.710 9，ε_Nd（t）=-0.8~-0.1，锆石ε_Hf（t）=-9.2~-2.7，对应二阶段模式年龄T_2DM（Hf）=1.4~1.8 Ga.地球化学、Sr-Nd及Hf同位素揭示泰宁地区基性岩浆源自富集岩石圈地幔13.3%~21.8%的熔融，但在熔融前曾受到古俯冲物质（俯冲板片熔体+5%沉积物熔体）的源区混染.武夷地区于早古生代为陆内造山环境，脉岩形成于后造山垮塌阶段，可能与冈瓦纳东缘造山作用的应力向大陆传播引起华夏地块内部俯冲有关. 

Origin of Middle Silurian Diabase Dike in the Taining District,South China: Implications for Intracontinental Orogeny

The Early Paleozoic orogen in South China is an intraplate orogen and represented by the Wuyi-Yunkai Orogenic Belt (WYOB). However,the nature of lithospheric mantle and tectonic setting during this orogenic process have been controversial. We present here,for the first time,geochronological,isotopic and geochemical data for the Hebaoshan diabase dike in Taining area,central WYOB. LA-ICP-MS dating on zircon of the Hebaoshan diabase dike yields an age of 430±3 Ma,suggesting the formation time of Middle Silurian. Seven samples possess high Al₂O₃(15.23%-18.49%) and low Na₂O(2.82%-4.21%),K₂O (1.63%-2.42%) contents,belonging to subalkaline rocks. The REE patterns show a negative slope due to LREE enrichment with insignificant Eu anomalies. Diabase is characterized by enrichment in Rb,Ba,K,La,Sr while depletion in Ta,U,Hf and Ti,relative to the primitive mantle. The high Nb(5.74×10-6-8.45×10-6) content,together with high values of (Nb/La)_N and Nb/U,coincides with those of typical Nb-rich Island Arc Basalt. The Hebaoshan diabase dike,with variable ε_Nd(t) values (-0.8—-0.1),ε_Hf(t) values (-9.2—-2.7) and two-stage Hf model ages (T_2DM(Hf)=1.4-1.8 Ga),was probably derived from the partial melting (13.3%~21.8%) of previously subduction-modified lithospheric mantle in the garnet-spinel olives facies and was likely formed in an intracontinental post-orogenic collapse regime related to a far-field effect from Eastern Gondwana orogeny.