思茅盆地石盐矿物的原位元素含量特征对成矿模式的启示

思茅盆地江城含盐带勐野井地区在“二层楼”钾盐成矿理论的指导下,逐步在侏罗系钾盐资源调查中取得重要成果,但盆地内其他含盐带研究程度薄弱。本文以整董含盐带的磨黑L2井勐野井组(K₁m)盐岩样品为研究对象,通过显微镜观察、扫描电镜能谱分析、石盐矿物元素含量电子探针微区原位测试方法的建立,精细研究了样品岩相学、石盐矿物学及元素含量特征。同时,测试了江城含盐带勐野井地区MK-1井花开左组(J₂h)石盐样品。对比研究两个井样品中石盐矿物微量元素K和Br含量及10³Br/Cl值(质量分数比)特征,结合研究区地质演化,取得以下认识。L2井K₁m(含)泥砾盐岩中石盐矿物发育两类产状:一类是胶结碎屑颗粒的主体石盐,具塑性流变特征;另一类是析出在碎屑中被盐类或黏土矿物碎屑包裹的石盐,两类包裹体特征指示均属次生成因。电子探针测得L2井K₁m的主体石盐、碎屑包裹和勐野井MK-1井J₂h含钾盐层石盐的K含量分别为≤0.09%、≤0.18%和≤0.13%,Br含量分别为≤60×10^-6、70×10^-6~410×10^-6和70×10^-6~500×10^-6,10³Br/Cl值分别为≤0.10、0.12~0.71和0.12~0.85,主体石盐显著低于后二者,处于陆源或海陆混合源石盐阶段或重结晶石盐阶段,而后二者数值接近,大多处在海源石盐阶段,小部分处在海源母液结晶钾石盐阶段和光卤石阶段。推断磨黑L2井碎屑包裹的石盐属深部古盐体刺穿贯入的证据,可能的成矿模式为深部中侏罗统海相古盐体受盐底辟作用迁移到浅层下白垩统勐野井组后,部分被盆地内侧向迁移来的中侏罗世残留海水、盆地周缘汇入的陆源水以及深部热液的共同溶蚀淋滤和混染改造形成新的卤水,部分以固体古石盐砾保留下来,在早白垩世晚期新母液卤水蒸发成盐过程中被形成的盐类和陆源碎屑矿物包裹,后期在母液结晶的主体石盐胶结下沉积成岩和成矿。以上认识完善了“二层楼”成矿理论在整董含盐带的勘探实践。     

亚洲高山区积雪物候时空动态及其对气候变化的响应

以亚洲高山区为研究区,在对2000—2020年逐日MODIS积雪产品进行去云处理的基础上提取了每一水文年的积雪日数（snow-covered days, SCD）、积雪开始日期（snow onset date, SOD）、积雪结束日期（snow end date, SED）和积雪持续日数（snow duration days, SDD）等积雪物候参数,并分析了积雪物候时空动态特征及其与气候变化的响应关系。结果表明：亚洲高山区积雪物候空间差异较大,并呈现出主要受海拔影响的垂直地带性分布规律。研究区SED主要集中在3—6月,在低海拔区SED出现在3月份及以前,而高海拔山区则推迟到6月份及以后;SOD主要集中在9—12月,高海拔山脉及高纬度地区的SOD出现较早,而低海拔区的SOD多出现在11月及以后。近20年,研究区SDD主要呈缩短趋势,在13.5%的区域呈显著缩短,而仅7.4%的区域为显著延长;SED主要呈提前趋势,在15.8%的区域显著提前,而仅8.8%的区域为显著推迟;SOD主要呈推迟趋势,在11.4%的区域表现为显著推迟,在8.2%的区域为显著提前。亚洲高山区积雪物候年际变化对气候变化的响应关系明显,积雪累积期气温是影响SOD年际变化的主导因子,而融雪期气温是影响SED年际变化的主导因子;气温的上升,导致了SOD的推迟、SED的提前和SDD的缩短。     

Magmatic history during late Carboniferous to early Permian in the North of the central Xing’an-Mongolia Orogenic Belt: a case study of the Houtoumiao pluton,Inner Mongolia

We undertake zircon U–Pb dating, Hf isotopes, and geochemical analyses of the Houtoumiao pluton in the Xilinhot microcontinent (XLMC) in the central Inner Mongolia with an aim of determining their ages, petrogenesis, and sources, which are important for understanding the late Palaeozoic tectonic evolution of the Xing’an-Mongolia Orogenic Belt. The Houtoumiao pluton consists of medium-grained granodiorite, coarse- and medium-grained syenogranite. Mafic microgranular enclaves (MMEs) are common in the Houtoumiao pluton. Zircon U–Pb dating has yielded ages of 303 ± 2 and 301 ± 2 Ma for the granodiorite, 295 ± 2 Ma for the syenogranite, and 292 ± 1 Ma for the MMEs. The granodiorite and syenogranite have features of high-K high silica content, rich in Rb, U, and Th, but low content of HFSE, belong to calc-alkaline series. The P₂O₅ concentration decreases with the increasing SiO₂ content, suggesting I-type affinity. The MMEs, which are characterized by low SiO₂, relatively high and variable TiO₂, Al₂O₃, FeO^T, MgO, CaO, Ni, and Cr contents, also have much higher total rare earth element concentrations that the REE patterns are subparallel to those of the host rocks. Zircons from the host rocks have ε_Hf(t) values from +3.91 to +7.73 and T_DM2 values of 820–1067 Ma, suggesting that the granitoids were probably dominated by remelting of juvenile crust materials. The MMEs are of ε_Hf(t) value ranging from +6.23 to +11.04 and T_DM1 values from 490 to 693 Ma, suggesting that the primary magma probably was derived from partial melting of a depleted lithospheric mantle, the mafic mineral fractional crystallization and crustal contamination occurred during the magma evolution. Combined with previous studies on the contemporaneous magma-tectonic activities in the Uliastai Continental Margin and XLMC, we suggest that the Houtoumiao pluton formed in a post-orogenic setting.     

Increasing resolution of reverse‐time migration using time‐shift gathers

Reverse‐time migration has become an industry standard for imaging in complex geological areas. We present an approach for increasing its imaging resolution by employing time‐shift gathers. The method consists of two steps: (i) migrating seismic data with the extended imaging condition to get time‐shift gathers and (ii) accumulating the information from time‐shift gathers after they are transformed to zero‐lag time‐shift by a post‐stack depth migration on a finer grid. The final image is generated on a grid, which is denser than that of the original image, thus improving the resolution of the migrated images. Our method is based on the observation that non‐zero‐lag time‐shift images recorded on the regular computing grid contain the information of zero‐lag time‐shift image on a denser grid, and such information can be continued to zero‐lag time‐shift and refocused at the correct locations on the denser grid. The extra computational cost of the proposed method amounts to the computational cost of zero‐offset migration and is almost negligible compared with the cost of pre‐stack shot‐record reverse‐time migration. Numerical tests on synthetic models demonstrate that the method can effectively improve reverse‐time migration resolution. It can also be regarded as an approach to improve the efficiency of reverse‐time migration by performing wavefield extrapolation on a coarse grid and by generating the final image on the desired fine grid.     

Studies on the solid acidity of heated and cation-exchanged montmorillonite using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy

The effects of heating and cation exchange on the solid acidity of montmorillonite were investigated using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared spectroscopy. The number of total, Brønsted, and Lewis acid sites showed the same modulation tendency with increasing heating temperature, reaching a maximum at 120 °C and subsequently decreasing until it reaches a minimum at 600 °C. The Lewis acid sites result from unsaturated Al³⁺ cations, and their number increased with the heating temperature due to the dehydration and dehydroxylation of montmorillonite. The generation and evolution of Brønsted acidity were mainly related to interlayer-polarized water molecules. Water adsorbed on the unsaturated Al³⁺ ions also acted as a Brønsted acid. The acid strength of the Brønsted acid sites was dependent on the polarization ability of the exchangeable cation, the amount of interlayer water, and the degree of dissociation of the interlayer water coordinated to exchangeable cations. All cation-exchanged montmorillonites exhibited different numbers of acid sites and various distributions of acid strength. Brønsted acidity was predominant in Al³⁺-exchanged montmorillonite, whereas the Na⁺- and K⁺-exchanged montmorillonites showed predominantly Lewis acidity. Moreover, Mg²⁺- and Li⁺-exchanged montmorillonites exhibited approximately equal numbers of Brønsted and Lewis acid sites. The Brønsted acidity of cation-exchanged montmorillonite was positively correlated with the charge-to-radius ratios of the cations, whereas the Lewis acidity was highly dependent on the electronegativity of the cations. The acid strengths of Al³⁺- and Mg²⁺-exchanged montmorillonites were remarkably higher than those of monovalent cation-exchanged montmorillonites, showing the highest acid strength (H ₀ ≤ ?3.0). Li⁺- and Na⁺-exchanged montmorillonites exhibited an acid strength distribution of ?3.0 < H ₀ ≤ 4.8, with the acid strength ranging primarily from 1.5 to 3.3 in Li⁺-exchanged montmorillonite, whereas only weaker-strength acid sites (1.5 < H ₀ ≤ 4.8) were present in K⁺-exchanged montmorillonite. The results of the catalysis experiments indicated that montmorillonite promoted the thermal decomposition of the model organic. The catalytic activity showed a positive correlation with the solid acidity of montmorillonite and was affected by cation exchange, which occurs naturally in geological processes.     

上扬子区古生界页岩的微观孔隙结构特征及其勘探启示

页岩的微观孔隙是评价页岩气资源潜力以及是否具有开采价值的重要指标。对上扬子区遵义、通江、广元等地下寒武统牛蹄塘组、下志留统龙马溪组和上二叠统大隆组的页岩进行采样,运用扫描电镜、氮气吸附和压汞实验对这些页岩的孔隙结构特征及其影响因素进行了研究。结果表明,大隆组页岩具有很低的比表面积和孔隙度,其中孔径小于100 nm的孔对孔隙度的贡献率在10%左右,主要孔隙类型为草莓体黄铁矿晶间孔;龙马溪组和牛蹄塘组页岩则具有较高的比表面积和孔隙度,50%~80%以上的孔隙度来自小于100 nm孔的贡献,主要孔隙类型是干酪根孔隙和溶蚀孔隙。认为页岩微观孔隙的发育与页岩的类型、溶蚀作用以及成熟度等因素有关。     

藏南萨迦县赛区“混杂岩”放射虫的发现及其意义

在藏南萨迦县赛区北部发育一套滑塌混杂沉积。对于这套混杂沉积的时代及地层归属,长期以来一直存有争议,主要原因是未能在其中获得足够的化石证据。本次工作在该套混杂岩中首次发现大量白垩纪放射虫化石,并建立4个放射虫组合:①Holocryptocaniumaff.barbui-Dictyomitraturris组合;②Acanthocircusdicrancanthos-Thanarlapulchra组合;③Thanarlaveneta-Pseudodictyomitrapseudomacrocephala组合;④Dictyomitramegnifica-Dictyomitratur-ritu组合。赛区“混杂岩”无论是古生物还是岩性组合特征,均可以与相邻地区的宗卓组进行对比,从而确认该套“混杂岩”属上白垩统宗卓组而非三叠系“修康群”。     

飓风的启示：渤海湾西岸现状与趋势分析

墨西哥湾飓风促使本文作者再次反思渤海湾西岸的现状:海岸线由曲折转为平直的、以侵蚀为主的自然进程,人为活动为主因造成的潮间带变宽变缓的、以淤积为主的干扰进程,以及二者之间的交互作用。提出在海面上升、地面下沉伴随下,在淤积进程达到其顶点后、重归以侵蚀为主的自然进程的可能前景,届时的“沼泽化”威胁,将加剧目前以“封闭治理”理念为主导的防洪措施对环境的不良影响。     

内蒙古西拉木伦成矿带库里吐钼(铜)矿区二长花岗岩地球化学、构造环境及含矿性分析

西拉木伦成矿带库里吐钼(铜)矿大地构造位于华北板块北缘造山带中段。通过对矿区含矿岩体的主量、微量元素及同位素组成进行测试和研究,表明矿区含矿岩石主要为二长花岗岩,其SiO_2含量为70.60%～72.95%,Na_2O和K_2O的含量分别为3.98%～4.40%和4.57%～5.49%,里特曼指数σ介于2.9～3.1之间,均小于3.3,指示其属钙碱性岩石系列;微量元素测试结果表明,二长花岗岩重稀土元素(HREE)分馏轻微[(Gd/Yb)_N=1.05～1.86],轻稀土元素有一定分馏[(La/Sm)_N =4.27～6.41],轻重稀土元素之间分馏较强[(La/Yb)_N=8.03～19.27],具有较明显的Eu负异常(δEu=0.65～0.77);在原始地幔标准化的微量元素蛛网图解上,都显示出Nb、Ta、Ti、P、Ba等元素亏损,Rb、Th、U、K等元素富集的特征;同位素测试结果表明,岩石初始~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb和~(208)Pb/~(204)Pb组成变化范围分别为18.3281～18.9980、15.5902～15.6644和37.7778～38.4129;(~(87)Sr/~(86)Sr)_i及ε_(Nd)(t)变化范围分别为O.706113～0.706783和-0.90～ 2.04。通过研究该区含矿岩石地球化学特征结合区域构造背景,本文初步认为该区二长花岗质岩浆来源于新生陆壳,形成于中朝板块和西伯利亚板块间的后碰撞阶段;同时本文还对含矿二长花岗岩含矿性进行了初步分析,为矿床研究和进一步找矿预测工作提供依据。     

白垩纪缺氧事件期间分子有机碳同位素偏移的二种不同机制

对我国业已发现的白垩纪大洋缺氧事件进行了对比研究.结果显示,我国河北滦平盆地高等植物叶腊碳同位素正偏,是weissert缺氧事件的陆地响应,weissert缺氧事件可能是全球性缺氧事件,而不是区域性的缺氧事件.叶腊烷烃单分子碳同位素正偏有两种不同的机制:早白垩世分子碳同位素正偏主要反映的是大气CO2水平增加;晚白垩世分子碳同位素正偏主要反映的是陆地植物类型的变化.