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敖尔盖铜矿位于内蒙古巴林右旗幸福之路苏木,大地构造归属大兴安岭南段晚古生代增生造山带。本次研究所采样品为矿区大面积出露的中-酸性侵入岩体。锆石SHRIMP U-Pb定年结果表明,岩体的成岩年龄为(245.4±1.8)Ma(MSWD=1.4),为该区印支早期岩浆活动的产物。岩石地球化学特征显示敖尔盖中-酸性侵入岩体具有与埃达克岩类似的地球化学特征,其SiO2≥56%(65.03%-70.11%),Al2O3≥15%(14.45%-15.49%),MgO<3%(1.18%-1.61%),Y<18×10-6(5.85×10-6-6.83×10-6),Yb≤1.9×10-6(0.416×10-6-0.637×10-6),Sr>400×10-6(380×10-6-642×10-6),LREE/HREE=11.60-12.24,δEu=1.00-1.18。说明其来源较深,形成压力较大。Sr-Nd同位素结果表明岩体的εNd(t)值(+3.9-+4.4)较高,同时(87Sr/86Sr)i值(0.70380-0.70412)较低,且Nd同位素模式年龄(TDM)较年轻,为578-657 Ma,指示源岩物质可能来源于新元古代形成的亏损地幔。结合区域构造背景综合分析认为,古亚洲洋在本区消失后,该岩体是在挤压构造背景下,由新元古代亏损地幔部分熔融形成。同时通过对比区域岩浆活动并结合大地构造研究认为,大兴安岭南段印支期岩体随着年龄由老到新,其形成构造环境从挤压转为伸展。
Aoergai copper mine is located in Inner Mongolia Balin Right Banner, a road of happiness Sumu, the earth structure belongs to the southern section of Greater Hinggan Mountains Late Paleozoic orogeny. The samples collected in this study are medium-acidic intrusive rocks exposed in a large area in the mining area. The zircon SHRIMP U-Pb dating results show that the diagenetic age of the rock mass is (245.4 ± 1.8) Ma (MSWD = 1.4), which is the product of the Indosinian magmatic activity in this area. The geochemical characteristics of the rocks show that the Aoergai medium-acidic intrusive rock has the similar geochemical characteristics as adakites, with SiO2≥56% (65.03% -70.11%), Al2O3≥15% (14.45% -15.49%), (1.18% -1.61%), Y <18 × 10-6 (5.85 × 10-6-6.83 × 10-6), Yb ≦ 1.9 × 10-6 (0.416 × 10-6-0.637 × 10-6), Sr> 400 × 10-6 (380 × 10-6-642 × 10-6), LREE / HREE = 11.60-12.24, and δEu = 1.00-1.18. It shows that its source is deep, forming pressure. The Sr-Nd isotopic results show that the εNd (t) value of rock mass is higher (+ 3.9- + 4.4) and the value of (87Sr / 86Sr) i is lower (0.70380-0.70412), and the Nd isotopic pattern age (TDM) , 578-657 Ma, indicating that the source rocks may be derived from Neoproterozoic depleted mantle. According to the comprehensive analysis of regional tectonic setting, after the disappearance of Paleo-Asian Ocean in this area, the pluton was formed by partial melting of depleted mantle in the Neoproterozoic under the compressional tectonic setting. At the same time, by comparing the regional magmatic activity with the tectonic researches, it is concluded that the Indosinian rock mass in the southern section of the Greater Xing’an Mountains turns from old to new age and the tectonic environment of the formation changed from extrusion to stretching.