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本文对出露于豫西二郎坪地区的西庄河花岗闪长岩进行了详细的岩石学、地球化学、锆石U-Pb年代学及Hf同位素研究,重点讨论其岩石成因及地质意义。西庄河花岗闪长岩主要由斜长石、石英及少量角闪石和黑云母组成。地球化学分析显示,该花岗岩具有高Si(SiO2=66.84%～71.57%)、富Al(Al2O3=14.11%～16.78%)、富Na(Na2O=3.45%～4.78%,Na2O/K2O为1.06～2.40)及低Mg(MgO=0.88%～1.0%,Mg#为0.43～0.46)的特征。微量元素方面显示高Sr(327.04×10-6～613.97×10-6)、低Y(12.30×10-6～17.17×10-6)和Yb(1.36×10-6～1.88×10-6)及高Sr/Y比值(介于24～38);稀土含量中等(∑REE=86.79×10-6～197.04×10-6),轻重稀土高度分异((La/Yb)N=12.35～23.28),无Eu异常或正Eu异常(δEu=0.97～1.34);在原始地幔标准化微量元素蛛网图上,岩石富集轻稀土和K、Rb、Ba、Th及Sr,而Nb、Ta、P及Ti具明显的负异常。锆石Hf同位素显示具有正的εHf(t)值,变化于8.37～11.13之间。以上花岗闪长岩的岩石地球化学特征及锆石Hf同位素特征与俯冲洋壳部分熔融成因的O型埃达克岩特征相似。利用锆石原位LA-ICP-MS定年方法,获得西庄河花岗闪长岩的形成年龄为461±0.9Ma。该年龄与其共生的二郎坪基性火山岩的形成年龄(460～473Ma)在误差范围内一致,结合其O型埃达克岩的地球化学特征,共同指示豫西二郎坪地区存在早古生代洋盆及洋盆的俯冲消减事件。
In this paper, detailed petrology, geochemistry, zircon U-Pb chronology and Hf isotope studies of Xizhuanghe granodiorite exposed in the Erlangping area, western Henan Province, are discussed with emphasis on the genesis and geologic significance of the rocks. West Zhuanghe granodiorite mainly by plagioclase, quartz and a small amount of amphibole and biotite composition. Geochemical analysis shows that the granite has high Si (SiO2 = 66.84% -71.57%), rich Al (Al2O3 = 14.11% ~ 16.78%), rich Na (Na2O = 3.45% ~ 4.78%, Na2O / K2O = 1.06 ~ 2.40 ) And low Mg (MgO = 0.88% ~ 1.0%, Mg # 0.43 ~ 0.46). The trace elements show high Sr (327.04 × 10-6 ~ 613.97 × 10-6), low Y (12.30 × 10-6 ~ 17.17 × 10-6) and Yb (1.36 × 10-6 ~ 1.88 × 10-6) And high Sr / Y ratios (ranged from 24 to 38). The REE content was moderate (ΣREE = 86.79 × 10-6 ~ 197.04 × 10-6), and the REE was highly (La / Yb) N = 12.35 ~ 23.28 ), No Eu anomalies or positive Eu anomalies (δEu = 0.97 ~ 1.34). On the normalized trace element cobras of the original mantle, the rocks are enriched in LREEs and K, Rb, Ba, Th and Sr, while Nb, Ta, P and Ti with obvious negative anomalies. The zircon Hf isotopes show a positive εHf (t) value, varying between 8.37 and 11.13. The petrogeochemical characteristics of the above granodiorite and the Hf isotopic characteristics of zircon are similar to those of the O-type adakite of the partial melting of the subducted oceanic crust. Using zircon in-situ LA-ICP-MS dating method, the formation age of Xizhuanghe granodiorite was 461 ± 0.9Ma. This age is consistent with that of its associated Erlangping basic volcanic rocks (460 ~ 473Ma) within the error range. Combined with its geochemical characteristics of the O-type adakite, it indicates that there are early Paleozoic ocean basins in the Erlangping area, Ocean basin subduction reduction event.