皖南晚中生代花岗闪长岩地球化学:成岩成矿制约

皖南地区是铜、钼、金多金属成矿区,成矿与晚中生代花岗闪长岩类关系密切。近十年来,皖南花岗闪长岩的成因仍然存在分歧。本次报道了皖南花岗闪长岩全岩主、微量元素和锆石原位元素数据。皖南花岗闪长岩(Si O2=64.3%~70.8%)为高钾钙碱性、过铝质岩石,具有相似的埃达克岩特征:高Si O2、Sr/Y(17.1)和(La/Yb)N(14.9)比值,低Yb(1.72×10-6)和Y(18.4×10-6)含量。它们也具有较低Al2O3和Cr(3.40×10-6~10.0×10-6)含量、低Mg#(0.34~0.42)和Nb/Ta(9.6~13.3)值,高K2O和Ba(404×10-6)含量,高K2O/Na2O(0.89~1.55)、Th/La(0.27~0.51)和Th/U(2.79~7.49)比值。锆石原位地球化学特征显示其岩浆源区为低温(锆石Ti-in-zircon温度均值674℃)和高氧逸度(lgfO2集中在-21.4~-9.18,均值-16.4;锆石Ce4+/Ce3+平均值276)的陆壳。这些特征说明皖南花岗闪长岩可能起源于较年轻的加厚下地壳的部分熔融,并经历了斜长石、钾长石和铁镁矿物等结晶分异作用。它们可能形成于与古太平洋板块俯冲密切相关的大陆活动边缘弧至弧后拉张构造转换背景。本区大规模Cu、Mo、Au成矿作用与岩浆的高氧逸度密切相关,而锆石Ce4+/Ce3+可作为矿床勘探一个有效的指标。     

华北克拉通东部鲁西早白垩纪基性岩墙成因:来自锆石年龄、地球化学和Sr-Nd-Hf同位素的证据

中生代基性辉绿岩墙广泛分布于华北克拉通东部山东地区。本研究给出代表性岩墙的U-Pb锆石年龄、地球化学和Sr-Nd-Hf同位素证据,4个代表性锆石的LA-ICP-MS年龄范围处于121.9±0.6Ma和124.3±0.5Ma之间(早白垩纪)。岩石的主量元素组成变化较小,岩石富集轻稀土元素和大离子亲石元素(如,Rb、Ba、U、K和Pb),以及亏损高场强元素(如,Nb、Ta和Ti)。另外,基性岩墙具有相对一致的(⁸⁷Sr/⁸⁶Sr)_i比值(~0.7098),负的ε_Nd(t)值(-14.7~-14.5)、ε_Hf(t)值(-31.4~-26.7)和高的Hf模式年龄(t_DM1=1817~2024Ma)。研究显示基性岩墙来自富集岩石圈地幔的部分熔融作用,并在上升侵位过程中经历了一定程度的地壳混染作用影响。总体研究表明,基性岩墙的成因机制与扬子克拉通与华北克拉通的碰撞有关,岩浆源区为晚中生代前受俯冲扬子地壳沉积物交代后的富集岩石圈地幔。     

浅层气对下伏地层深度预测影响定量研究及在渤海B油田中的应用

浅层气的存在造成下伏地层地震反射出现假象,使得深度预测不准确,增大了油田开发钻井风险。为提高浅层气下伏地层深度预测精度,利用理论模型分析量化描述浅层气对下伏地层的影响范围和影响程度,同时通过正演模拟手段构建时差定量校正量版,指导储层高精度深度预测。根据研究成果和认识,成功解释了渤海B油田两口已钻井深度误差出现的原因,并进一步利用时差校正量版提高了该油田区目标储层深度预测的精度,成功指导了后续多口开发井的准确钻探。     

断层EDF技术在复杂断块构造研究中的应用

复杂断块构造具有断层复杂,小断层广泛发育,断层识别难度大,储层分布及连通性复杂,地震成像不清、资料品质较差等特征。对于此类问题,常规地震资料无法满足断层解释精度要求。提出了一种新的断层EDF解释性处理技术,将地震资料处理与解释融为一体,以提高资料的信噪比和断层的识别能力。断层EDF解释性处理技术是利用扩散滤波和中值倾角滤波相结合的断层增强滤波方法来提高资料的信噪比,突出断层和地层的接触关系,再在滤波后的地震资料数据体上进行分频处理,选择最佳成像频带,突出识别不同规模的断层。通过在涠洲A油田的应用,取得了良好的效果。     

A hydrochemical study of the Hammam Righa geothermal waters in north-central Algeria

This study focuses on the hydrochemical characteristics of 47 water samples collected from thermal and cold springs that emerge from the Hammam Righa geothermal field, located in north-central Algeria. The aquifer that feeds these springs is mainly situated in the deeply fractured Jurassic limestone and dolomite of the Zaccar Mount. Measured discharge temperatures of the cold waters range from 16.0 to 26.5 °C and the hot waters from 32.1 to 68.2 °C. All waters exhibited a near-neutral pH of 6.0–7.6. The thermal waters had a high total dissolved solids (TDS) content of up to 2527 mg/l, while the TDS for cold waters was 659.0–852.0 mg/l. Chemical analyses suggest that two main types of water exist: hot waters in the upflow area of the Ca–Na–SO₄ type (Hammam Righa) and cold waters in the recharge zone of the Ca–Na–HCO₃ type (Zaccar Mount). Reservoir temperatures were estimated using silica geothermometers and fluid/mineral equilibria at 78, 92, and 95 °C for HR4, HR2, and HR1, respectively. Stable isotopic analyses of the δ¹⁸O and δD composition of the waters suggest that the thermal waters of Hammam Righa are of meteoric origin. We conclude that meteoric recharge infiltrates through the fractured dolomitic limestones of the Zaccar Mount and is conductively heated at a depth of 2.1–2.2 km. The hot waters then interact at depth with Triassic evaporites located in the hydrothermal conduit (fault), giving rise to the Ca–Na–SO₄ water type. As they ascend to the surface, the thermal waters mix with shallower Mg-rich groundwater, resulting in waters that plot in the immature water field in the Na–K–Mg diagram. The mixing trend between cold groundwaters from the recharge zone area (Zaccar Mount) and hot waters in the upflow area (Hammam Righa) is apparent via a chloride-enthalpy diagram that shows a mixing ratio of 22.6 < R < 29.2 %. We summarize these results with a geothermal conceptual model of the Hammam Righa geothermal field.