北京潭柘寺地区第四纪冰川遗迹的宏观和微观特征

以北京西山潭柘寺地区第四纪冰川遗迹的宏观特征研究为基础,对管坨岭冰期和赵家台冰期的古冰川沉积进行了石英颗粒表面结构形貌组合特征的分析。结果表明,管坨岭冰期的管坨岭冰碛层和大富庄冰碛层,以及赵家台冰期的太平庄冰碛层中的石英颗粒表面结构,以冰川成因的形貌组合占优势,而赵家台冰期鲁家滩冰水沉积中的石英颗粒表面结构,则以冰川和流水共有成因的形貌占优势。所以,据冰川遗迹的宏观和微观特征,可以肯定该区分别在早更新世和中更新世曾发育过两次古冰川作用。      

辽西兰家沟钼矿床成矿流体特征及成因探讨

兰家沟钼矿床是中国北方重要的独立钼矿床,矿体主要赋存于细粒花岗岩体内部及与粗粒花岗岩的接触部位,矿石类型以辉钼矿-石英大脉为主。流体包裹体研究表明,兰家沟钼矿床含钼石英脉中流体包裹体较少,类型主要为气液两相,个别含子矿物多相包裹体;激光拉曼光谱测试表明,成矿流体成分主要为H2O,微量的CO2、CO23-。成矿期流体包裹体的均一温度为160~405℃,集中于180~320℃;盐度w(NaCleq)为2.4%~16.5%,多数在8%~14%。成矿流体在演化过程中发生了中等盐度和低盐度流体的混合作用,2种不同成分流体的混合作用使得辉钼矿大量沉淀而成矿。氢氧同位素研究表明,成矿流体的δD为-81‰~-101‰,δ18O水为-0.1‰~4.5‰,小于兰家沟花岗岩全岩δ18O水值,反映成矿流体来自混合的岩浆水与大气降水。通过与典型斑岩型钼矿床地质特征、矿化、围岩蚀变、流体包裹体特征及同位素组成的对比,认为兰家沟钼矿床属于热液脉型向斑岩型过渡类钼矿床。     

石英标准生长曲线在青藏高原东缘黄土光释光测年中的应用

石英标准生长曲线（SGC）法在黄土高分辨率光释光定年中有大幅节省测试时间的潜力,然而目前对该方法在不同时空尺度上的适用性尚存在争议。本文选取青藏高原东缘的典型黄土样品,通过系统地分析石英光释光生长曲线特征,检验SGC法和最小二乘法标准化生长曲线（LS-SGC）法在高原东缘黄土光释光定年中的适用性,结果显示：1）高原东缘黄土石英光释光信号以快组分为主,且同一地点不同样品、不同测片的生长曲线形态相似;2）当等效剂量（D_e）小于100 Gy时,不同地点样品石英生长曲线形态一致;大于100 Gy时生长曲线则具有不同的剂量响应特征;3）通过SGC法获得的D_e仅在0~100 Gy与实测值一致;LS-SGC法拟合的生长曲线结果更佳,并且LS-SGC法计算的D_e在100~200 Gy与实测D_e仍具有较好的一致性。研究结果有助于深入研究高原黄土光释光测年和风成沉积过程,同时也可为其他区域建立石英光释光标准生长曲线提供借鉴。

     

Relationship Between Electrical Properties and Sedimentary Environment of the Longmaxi Formation Shale, Southern Sichuan

The Lower Silurian Longmaxi Formation in the south of Sichuan is a key player in the exploration and development of shale gas in China. Due to a highly complex topographic area, electromagnetic methods(EM) become important exploration means in this area. Many studies have been conducted on the shale mineral composition and electrical properties of shale, however, the correlation between sedimentary environments and the electrical properties of shale remain poorly understood. The electrical prope...     

内蒙古维拉斯托锡多金属矿石英脉形态分带定量分析

为探讨维拉斯托锡多金属矿床含锡石英脉形态分带的成矿动力学机制,通过利用分形和混合分布工具对断层脉带和上、下节理脉带进行定量分析。上、下节理脉带在脉厚、钨锡品位分形维数和混合筛分分布方面均具有相似性,暗示了两者可能具有相似的成矿机制。与上、下节理脉带相比,断层脉带的脉厚和钨锡品位分形维数均较小,断层脉带内的聚焦化流动、较低的脉体成核率、脉体叠加生长和矿化叠加富集可能是导致断层脉带的厚脉和富矿比例均高于上、下节理脉带的重要原因。     

基于BSA及固定碘速率探讨不同浓度对比剂对肝静脉CT成像效果的影响

目的：探讨基于体表面积（BSA）和固定碘速率给药,不同浓度对比剂对CT肝静脉成像质量的影响。方法：选取2020年1月至11月符合纳入标准,行上腹部增强CT扫描的患者130例,根据所用对比剂浓度不同,分为高浓度组（62例）和低浓度组（68例）,高浓度组对比剂为碘帕醇（含碘370mg/mL）,低浓度组对比剂为碘佛醇（含碘320mg/mL）;根据BSA计算患者所用对比剂的总量,固定碘速率注射,进行分期动态扫描。选取肝静脉期数据行肝静脉血管重建,对图像质量进行评价,测量两组图像肝静脉和肝实质的CT值及其标准差值,计算信噪比和对比噪声比,并对图像质量进行主观评分;采用独立样本t检验比较两组间客观评价指标的差异,采用Mann-Whitney U检验比较主观评分的差异。结果：高、低浓度组图像评分分别为（3.74±0.47）分和（3.77±0.53）分,差异无统计学意义;两组间肝静脉左、中、右三支主干和同层面肝实质的CT值、SD值、SNR及肝静脉相对于肝实质的CNR,差异无统计学意义。结论：基于BSA及固定碘速率注射对比剂,两种不同浓度对比剂在肝静脉CT成像中的效果同样清晰利于诊断。     

南京周家山下蜀黄土石英颗粒特征及其物源意义

下蜀黄土的成因和物源一直是学术界研究的热点。对南京周家山下蜀黄土的石英粒度和石英表面微结构进行分析,结果显示:粉砂粒级石英颗粒（5~50 μm）占绝对优势;<20 μm组分平均含量为42.76%,<30 μm组分平均含量为62.98%;粒度分布曲线和累积曲线总体具有颗粒偏细,呈正偏态,分选较差,峰形尖锐,双峰曲线不对称的特征;粒级-标准偏差曲线呈“双峰”分布,两个明显的标准偏差峰值分别出现在7.962 1 μm和39.905 2 μm。石英颗粒表面形态主要以次棱角状为主;表面机械结构具有丰富的蝶形坑、曲脊、贝壳状断口,部分表面出现平行节理面、V形坑;不同粒级组分表面形态和机械结构特征存在差异。分析表明,南京周家山下蜀黄土属典型风成成因堆积物,是多源区物质高度混合搬运堆积的结果。     

大兴安岭扎兰屯地区晚奥陶世石英闪长岩体岩石地球化学特征及其地质意义

扎兰屯音河岩体被音河水系分为南、北两部分,研究发现南、北岩体形成年代不同,选取南部岩体(称为二村岩体)进行研究。二村岩体主要由石英闪长岩-英云闪长岩组成,石英闪长岩的LA-ICP-MS锆石U-Pb年龄为444.0±4.6Ma,时代为晚奥陶世。岩石化学组成相对富钠、贫钾,Na2O/K2O值大于1(1.73~3.17),属中钾钙碱性系列。岩石富含轻稀土元素、亏损重稀土元素,富集大离子亲石元素Rb、Ba、K,显著亏损Nb、Ta、P、Ti等高场强元素。矿物组成及岩石地球化学特征指示其为I型花岗岩。岩体的形成时代、构造背景与多宝山岛弧火成岩相似,为区域多宝山岛弧西南向延伸提供了新的制约。     

Sugarloaf Mountain,central Arizona,USA: A small-scale example of Miocene basalt-rhyolite magma mixing to yield andesitic magmas

Sugarloaf Mountain is a 200-m high volcanic landform in central Arizona, USA, within the transition from the southern Basin and Range to the Colorado Plateau. It is composed of Miocene alkalic basalt (47.2–49.1?wt.% SiO₂; 6.7–7.7?wt.% MgO) and overlying andesite and dacite lavas (61.4–63.9?wt.% SiO₂; 3.5–4.7?wt.% MgO). Sugarloaf Mountain therefore offers an opportunity to evaluate the origin of andesite magmas with respect to coexisting basalt. Important for evaluating Sugarloaf basalt and andesite (plus dacite) is that the andesites contain basaltic minerals olivine (cores Fo_76-86) and clinopyroxene (～Fs_9-18Wo_35-44) coexisting with Na-plagioclase (An_48-28Or_1.4–7), quartz, amphibole, and minor orthopyroxene, biotite, and sanidine. Noteworthy is that andesite mineral textures include reaction and spongy zones and embayments in and on Na-plagioclase and quartz phenocrysts, where some reacted Na-plagioclases have higher-An mantles, plus some similarly reacted and embayed olivine, clinopyroxene, and amphibole phenocrysts.Fractional crystallization of Sugarloaf basaltic magmas cannot alone yield the andesites because their ～61 to 64?wt.% SiO₂ is attended by incompatible REE and HFSE abundances lower than in the basalts (e.g., Ce 77–105 in andesites vs 114–166?ppm in basalts; Zr 149–173 vs 183–237; Nb 21–25 vs 34–42). On the other hand, andesite mineral assemblages, textures, and compositions are consistent with basaltic magmas having mixed with rhyolitic magmas, provided the rhyolite(s) had relatively low REE and HFSE abundances. Linear binary mixing calculations yield good first approximation results for producing andesitic compositions from Sugarloaf basalt compositions and a central Arizona low-REE, low-HFSE rhyolite. For example, mixing proportions 52:48 of Sugarloaf basalt and low incompatible-element rhyolite yields a hybrid composition that matches Sugarloaf andesite well ? although we do not claim to have exact endmembers, but rather, viable proxies. Additionally, the observed mineral textures are all consistent with hot basalt magma mixing into rhyolite magma. Compositional differences among the phenocrysts of Na-plagioclase, clinopyroxene, and amphibole in the andesites suggest several mixing events, and amphibole thermobarometry calculates depths corresponding to 8–16?km and 850° to 980?°C. The amphibole P-T observed for a rather tight compositional range of andesite compositions is consistent with the gathering of several different basalt-rhyolite hybrids into a homogenizing ‘collection' zone prior to eruptions. We interpret Sugarloaf Mountain to represent basalt-rhyolite mixings on a relatively small scale as part of the large scale Miocene (～20 to 15 Ma) magmatism of central Arizona. A particular qualification for this example of hybridization, however, is that the rhyolite endmember have relatively low REE and HFSE abundances.