新疆西准噶尔地区加尔路阿甫花岗斑岩岩石成因及地质意义:元素和锆石Hf同位素地球化学制约

加尔路阿甫花岗斑岩体出露于西准噶尔北部萨吾尔地区,侵入于上石炭统巴塔玛依内山组二段地层之中,主要矿物组成为斜长石、石英、钾长石、黑云母等。该岩体SiO₂为69.54%~71.25%, Al₂O₃为13.92%~14.93%, K₂O/Na₂O为1.04~1.07,富钾贫钠, FeO^t/MgO为12.31~22.60,铁高而镁低。在原始地幔标准化的微量元素配分图中,大离子亲石元素(LILE)Rb、Ba、Th等富集,高场强元素(HFSE)Nb、Ta、Sr、P、Ti等相对亏损。稀土元素总量较高(ΣREE=122.75×10^-6~172.39×10^-6),稀土元素球粒陨石标准化配分型式表现为轻稀土强烈富集、重稀土相对亏损的右倾型,且Eu负异常非常明显(LREE/HREE为6.56~9.28,(La/Yb)_N为4.58~10.58, δEu为0.29~0.47),轻重稀土之间分异明显。LA-ICP-MS锆石U-Pb测年表明其形成年龄为305±2 Ma,属于晚石炭世。锆石Lu-Hf同位素分析表明, ε_Hf(t)值变化于12.2~14.9,平均值为13.54,均具有较高的正值, T_DM1变化于462~345 Ma之间, T_DM2变化于638~393 Ma之间。结合前人研究和本次的工作分析认为,加尔路阿甫花岗斑岩体形成于后碰撞的构造环境,该岩体是新生地壳物质源区在晚石炭世部分熔融的最终产物,加入到大陆地壳中的新生组分可能主要为来自亏损地幔的玄武质岩浆。

Petrogenesis and tectonic implication for Jiaerluafu granitic porphyry pluton in western Junggar,Xinjiang: Constraints from the element and zircon Hf isotope geochemistry

The Jiaerluafu granite-porphyry pluton intruding the Haerjiawu Formation outcrops in the northern of western Junggar, Sara area, and consists mainly of monzonitic granite mineralogically containing plagioclase, quartz, potassium feldspar and biotie. SiO₂ values between 69.54% and 71.25%, Al₂O₃ values between 13.92% and 14.93%, K₂O/Na₂O values between 1.04 and 1.07, and FeO^t/MgO values between 12.31 and 22.60. Primitive mantle normalized trace elements patterns reveal that large ion lithophile elements(LILE)Rb, Ba, Th are enriched, and strength element(HFSE)Nb, Ta, Sr, P, Ti are depleted. Total REE content are high with ΣREE=122.75×10^-6~172.39×10^-6. Chondrite-normalized REE distribution pattern show strong enrichment in LREE and relative depletion in HREE, with obviously Eu negative anomaly(LREE/HREE=6.56~9.28,(La/Yb)_N=4.58~10.58, δEu=0.29~0.47). The zircon Lu-Hf isotope analysis indicates that most ε_Hf(t)values of the granites are big positive. ε_Hf(t)values between 12.21 and 14.90. T_DM1 values between 462~345 Ma. T_DM2 values between 638~393 Ma. LA-ICP-MS isotopic dating show a zircon U-Pb isotopic age of 305±2 Ma for the pluton, indicating it belongs to Late Carboniferous. Previous studies and this study reveal that the Jiaerluafu granitic pluton formed in a post-collision tectonic environment. The pluton is partial melting product of new crustal material source area in Late Carboniferous. To join the new components of continental crust may mainly come from depleted mantle basaltic magma.