The Wanghaigang pluton, lithologically consisting mainly of quartz syenite, is a typical Late Mesozoic central stock intruded in a caldera in the coastal area of Zhejiang Province. Zircon LA-ICP-MS U-Pb dating for two representative samples yields ages of 98. 3 ± 1. 2Ma and 98. 5 ±1. 3Ma, respectively, indicating that they were generated during the initial stage of Late Cretaceous. The quartz syenites consist mainly of alkali-feldspar (35% - 60% ) , plagioclase (15% ～ 20% , An = 13 - 20 ) , quartz (15% - 18% ), amphibole (3% -5% ) and minor biotite ( < 1% ) , with accessory titanite, zircon and apatite. Micrographic intergrowth9 of quartz and alkali feldspar (granophyric texture) are fairly common in most samples and mafic enclaves have been observed in some parts of this pluton. Geochemically, the quartz syenites show metaluminous, sub-alkaline and K-rich features, and are enriched in Rb, Th, Ba, Zr, Hf and LREEs, and depleted in Sr, P, Ti, Nb, Ta, and display weakly to moderately negative europium anomalies (5Eu = 0. 64 ～ 0. 76 ) in the chondrite-normalized REE distribution patterns. The rocks have homogeneous Sr, Nd isotopic compositions with /srvalues of 0. 7089 -0. 7090 and εNd(t) values of -6. 16～ -7. 12. However, their zircon Hf isotopic compositions are highly variablewith εHf(t) values ranging from - 12.2 to -2.9. Using the zircon saturation geothermometer proposed by Watson and Harrison (1983) , and the Al-in-hornblende geobarometer of Johnson and Rutherford (1989) , the rock-forming temperature and pressure have been estimated. The results have shown that the pluton was crystallized in a high temperature (826 ～ 846℃) and hypabyasal (emplacement depth of about 2 ～3km) environment The integrated petrology, elemental and isotopic compositions suggest that the pluton was most likely generated under a back-arc extensional setting, and via a process including formation of parental magma by mixing of a underplated mantle-derived magma and an induced crustal-melted magma in the deep crust, then suffered differentiation during magma ascent and at last emplaced at a hypabyssal environment%望海岗岩体是浙江沿海晚中生代一个典型的破火口中央岩株侵入体,其主体岩性为石英正长岩.锆石LA-ICP-MS定年测得两件代表性样品的U-Pb年龄分别为98.3±1.2Ma和98.5±1.3Ma,表明该岩体属晚白垩世初期岩浆活动的产物.岩体的组成矿物主要为碱性长石(35％～60％)、斜长石(15 ～ 20％,An= 13 ～20)、石英(15％～18％)、角闪石(3％～5％)和少量黑云母(＜1％),副矿物有榍石、锆石、磷灰石等.岩石普遍发育花斑结构,岩体中可见深色闪长质包体.地球化学特征上,该岩体具有准铝、亚碱性和富钾特点,并富 Rb、Th、Ba、Zr、Hf,贫Sr、P、Ti、Nb、Ta,岩石的稀土总量较高,富轻稀土,具中-弱的铕负异常(δEu =0.64 ～0.76).其Sr、Nd同位素组成较均一[1st=0.7089～0.7090,εNd(t)=-6.16～-7.12],但锆石 Hf同位素组成变化范围大[εHf(t)= -12.2～-2.9].温压计算结果表明该岩体具有高温(826 ～ 846℃)浅成特点,定位深度约在2 ～3km.岩石学及元素与Sr-Nd-Hf同位素组成特征综合指示该岩体是在弧后伸展引张背景下,由底侵的幔源岩浆与其诱发熔融的深部壳源岩浆经混合后,并经一定程度的分异演化,最后在浅成环境定位的产物.
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