【摘要】：位于湘中盆地周緣的紫云山巖體主要由似斑狀石英二長巖(主體)和二云母花崗巖(補體)組成,前者分布于該巖體的周邊,后者分布于其內(nèi)部,巖體內(nèi)可見有大量巖漿結(jié)構(gòu)的鎂鐵質(zhì)暗色包體。利用高精度SIMS鋯石U-Pb定年方法得到主體巖體的年齡為225.2±1.7Ma和225.6±1.4Ma,補體巖體的年齡為227.0±2.2Ma,兩者均形成于印支晚期,基本上是同時形成的。該區(qū)兩類巖石均具有富SiO_2、Na_2O和K_2O,貧Ca O、Mg O和Al2O3的特征,A/CNK比值為0.85~1.05,固結(jié)指數(shù)較高,主體巖石為3.61~5.05,補體巖石為4.13~14.06;其微量元素均表現(xiàn)出富集Rb、U、La、Nd和Zr,虧損Ba、Nb、Ta、Sr、P和Ti的特征;稀土元素配分模式均呈明顯的右傾"V"字型,輕重稀土分餾明顯((La/Yb)N=7.35~11.7),Eu負異常較顯著(δEu=0.32~0.70);該區(qū)花崗巖的主體和補體的鋯石Hf-O同位素組成非常相似,εHf(t)值為-10.0~-1.6,δ18O值為7.8~11.4,兩階段模式年齡tDM2為1.22~1.79Ga;各類巖石主要氧化物之間表現(xiàn)出良好的線性協(xié)變關(guān)系,且明顯沿I型花崗巖演化趨勢線分布,反映主體和補體巖石具有密切的親緣關(guān)系,均應(yīng)歸屬于高分異的I型花崗巖。各類巖石樣品沿巖漿混合趨勢線分布、而遠離結(jié)晶分異趨勢線,結(jié)合Hf-O同位素分析,認為該巖體來源于揚子地塊中元古代下地殼變質(zhì)雜砂巖重熔,與部分幔源巖漿形成的殼�；旌蠋r漿源區(qū)。該巖體形成于碰撞后構(gòu)造背景,暗示華南地塊受太平洋板塊及印支地塊的雙重影響,在印支晚期處于伸展-減薄的構(gòu)造環(huán)境。通過與華南地塊其它印支期花崗巖對比分析,提出揚子地塊與華夏地塊的拼合帶在湖南境內(nèi)應(yīng)沿"攸縣-雙牌"一線展布。
[Abstract]:The Ziyunshan rock mass located around Xiangzhong Basin is mainly composed of macular quartz monzonitic feldspar (main body) and dicalite granite (complement). The former is distributed around the rock mass, the latter is distributed in its interior, and a large number of mafic dark inclusions with magmatic structure can be seen in the rock mass. By using the high precision SIMS zircon U-Pb dating method, the ages of the main rock mass are 225.2 鹵1.7Ma and 225.6 鹵1.4 Ma, and the age of the complement rock mass is 227.0 鹵2.2 Ma. both of them were formed in the late Indosinian period and were basically formed at the same time. Both rocks in this area are rich in SiO_2,Na_2O and K 鈮，

本文編號：2500098