觉罗塔格南缘石炭系火山岩地球化学特征及其对古亚洲洋南缘构造演化的指示意义

研究了觉罗塔格南缘石炭系雅满苏组与土古土布拉克组火山岩的主量元素、微量元素和Sr-Nd同位素特征。结果显示,雅满苏组(中)酸性熔岩属贫钾钙碱性岩浆系列,Mg#值介于0.49~0.51,ISr介于0.706 42~0.707 68、εNd(t)为3.28~5.49,富集轻稀土与大离子亲石元素、相对亏损重稀土与高场强元素,具中等负Eu异常(δEu=0.62~0.65),其形成可能与幔源基性岩浆结晶分异有关。土古土布拉克组中(酸)性火山岩属钙碱性-高钾钙碱性系列,Mg#值介于0.53~0.57,轻稀土相对富集,重稀土相对亏损,略具负铕异常(δEu=0.63~0.84),富集大离子亲石元素,相对亏损高场强元素,ISr介于0.703 71~0.708 47、εNd(t)为6.48~6.83,表明其母岩浆来源于受交代的富集岩石圈地幔楔。结合区域地质背景研究成果,认为它们形成于古亚洲洋壳向南俯冲的岛弧环境,并且早石炭世的雅满苏组火山岩代表不成熟的洋内岛弧的产物,而晚石炭世的土古土布拉克组火山岩是岛弧演化到相对成熟阶段的产物。这种物质成分和时空分布特征揭示的石炭纪该区壳幔岩石圈由北向南、由老到新明显增厚现象,为古亚洲洋南缘吐哈古洋壳当时在该处具有向南俯冲的极性提供了有力证据。     

中天山卡瓦布拉克地区中-基性岩脉的年代学及岩石成因

中天山卡瓦布拉克地区侵入岩类广泛发育,并多处被中-基性岩脉穿插。LA-ICP-MS锆石U-Pb测年获得闪长岩和辉长岩脉年龄分别为296.1±2.5 Ma(MSWD=1.4),299.5±2 Ma(MSWD=1.07),均侵位于早二叠世。岩石学和岩石地球化学分析结果表明该区中-基性岩脉具有富集轻稀土元素(LREE)和大离子亲石元素(Rb,U,Th)、亏损高场强元素(Nb,Ta,Ti)的地球化学特征,SREE为69.19~234.62,LREE/HREE=3.97~11.18。闪长岩脉锆石(176Hf/177Hf)值为0.280 618~0.283 329,对应的εHf(t)值为-14.57^+25.06。研究数据表明,该区中-基性岩脉可能起源于亏损岩石圈地幔,原始岩浆在侵位过程中发生了分离结晶作用,同时还受到了地壳混染作用的影响。基于卡瓦布拉克地区中-基性岩脉的野外地质特征和地球化学分析结果,并结合区域地质资料,认为它们形成于南天山洋闭合之后的后碰撞伸展构造背景。     

Geochemistry and Sr–Nd isotope composition of Carboniferous volcanic rocks of the Jueluotage Orogenic Belt: implications for the tectonic evolution of Eastern Tianshan,China

The major and trace element, and Sr–Nd isotopic compositions of the Carboniferous Qi’eshan, Wutongwozi, and Yamansu volcanic rocks from the northern and southern parts of the Jueluotage Orogenic Belt in East Tianshan, China, were analysed to understand their genesis and geodynamic implications. The early Carboniferous Qi’eshan basalts are characterized by high Al₂O₃, with La/Sm (1.38–1.79) and Ba/La (27.06–58.76) values higher than those of typical normal mid-ocean ridge basalt. They are relatively enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), and depleted in high field strength elements. Overall, their initial Nd–Sr isotopic compositions are ε_Nd(t) = (5.6–7.0) and Isr = 0.70397–0.70429, implying the magma originated from a mantle wedge source that was metasomatized by subduction-related fluids. In contrast, the late Carboniferous Wutongwozi basalts have lower Ba/La (4.86–12.82), La/Nb (0.87–2.45), and LILE concentrations. They have the isotopic characteristics of depleted asthenosphere, relatively high and heterogeneous ε_Nd(t) (9.3–9.4), and high Isr (0.70471–0.70533). Thus, the late Carboniferous Wutongwozi basalts may have been derived from the partial melting of mantle sources during asthenospheric upwelling. The early Carboniferous Yamansu acid volcanic rocks are characterized by high Mg# (46–48) and Lu/Y (~0.15), and low K₂O/Na₂O (0.01–0.20), similar to M-type granites. However, their ε_Nd(t) (5.0–5.5) and Isr (0.70642–0.70768) values are lower than those of depleted mantle, indicating they were contaminated by lower crustal material. The magma source originated from a mantle-derived magma that was contaminated by middle Tianshan massif in a continental margin arc setting. Based on the results and previous field-based studies, we conclude that the Carboniferous volcanics in the Jueluotage Orogenic Belt formed in a complex trench–arc–basin setting in the Kuguertage–Aqikuduke Suture Zone.     

Using regression model to identify and evaluate heavy metal pollution sources in an open pit coal mine area,Eastern Junggar,China

This study aims at identifying multi-source heavy metal pollution from natural and anthropogenic sources using a regression model, principal component analysis, and five different indices (geo-accumulation index (I _geo), the modified degree of contamination, pollution load index (PLI), enrichment factor, and ecological risk factor. Results revealed that: (1) although the average concentrations of soil heavy metals (Cu, Cr, Pb, Hg, As, Zn) were generally low, Hg, As, and Cr concentrations exceeded national standard values by approximately 0.91, 1.84, and 0.91 times with maximum concentrations up to 0.41, 78.6, and 175.2 μg/g, respectively; (2) PLI results showed that the industrial park and Wucaiwan open coal mining area were the most polluted (PLI of 1.98, 1.71). The potential ecological hazards index indicated that the E _i ^r of three heavy metals (Cu, Hg, As) in the soil were relatively high, presenting potential ecological risk factors of 74.89, 16.71, 4.15%, respectively; (3) stepwise regression model and principal component analysis suggest that Cu and Zn were primarily effected by the natural geological condition and atmospheric dust fall. Cr, Hg, Pb are mainly derived from anthropogenic sources, particularly coal mining activities and industrial sources. Results of this research have some significant implications for heavy metal pollution prevention and the sustainable development of the economy and ecology of arid regions in China.