大凌河河口地区晚更新世晚期以来的沉积环境演化

对大凌河河口地区ZK3钻孔(孔深36.7 m)岩心开展粒度分析、AMS14C年代测定、有孔虫鉴定分析等综合研究,同时结合该地区5口工程钻孔的岩心以及部分测年资料,初步建立了大凌河河口地区晚更新世晚期以来典型的地层序列格架和时空对比框架,揭示该地区晚更新世晚期以来河道-湖沼-滨海/河口湾-浅海-三角洲的沉积演化过程。研究结果表明:大凌河河口地区在8 500 cal a BP前后开始接受海相沉积,并约在4 000 cal a BP之后进入三角洲沉积阶段;晚更新世晚期以来的海平面变化是大凌河河口沉积演化和沉积环境演变的主要控制因素;大凌河对现代辽河三角洲的形成和演化过程可能有较重要的影响。     

Early Mesozoic Southward Subduction of the Eastern Mongol–Okhotsk Oceanic Plate: Evidence from Zircon U–Pb–Hf Isotopes and Whole‐rock Geochemistry of Triassic Granitic Rocks in the Mohe Area,NE China

In this paper, we present new U–Pb zircon ages, Hf isotope data and major and trace elements for Early Mesozoic granitic rocks in Mohe area in the Erguna Massif of northeast China to elucidate the southward subduction of the eastern Mongol–Okhotsk Oceanic plate in Early Mesozoic. Zircons from two representative intrusions, syenogranites and monzogranites, in the Mohe area are euhedral–subhedral in shape, display oscillatory growth zoning in cathodoluminescence (CL) images, and have Th/U ratios of 0.10–0.72, and in combination these features indicating that the zircons are of igneous origin. U–Pb zircon dating results demonstrate that the syenogranites formed at 245.1 ± 1.4 Ma and monzogranites formed at 212.2 ± 1.7 Ma. These granitic rocks are characterized by high SiO₂, Al₂O₃ and (Na₂O + K₂O), low TFeO, MgO, TiO₂ and P₂O₅ concentrations, belonging to the high‐K calc‐alkaline series. They are enriched in LREE and large ion lithophile elements (e.g., Rb, K, and Sr), depleted in HREE and high field strength elements (e.g., Nb, Ta, Th, and Ti), as well as very weak negative Eu anomalies (Eu/Eu* = 0.48 ~ 1.01). Their zircon εHf(t) values range from −7.9 to −2.0 and range from 0.20 to 0.49, in response to their two‐stage Hf model ages (T_DM2) range from 1.40 Ga to 1.77 Ga range from 0.94 Ga to 1.24 Ga, respectively, indicating that primary magmas of syenogranites were derived from partial melting of newly accreted juvenile crustal material that formed from the enriched mantle during the Mesoproterozoic, monzogranites are generated by partial melting of newly accreted juvenile crustal material that formed from the depleted mantle during the Meso‐ to Neoproterozoic. We conclude, therefore, that the early Mesozoic granitic rocks of the Mohe area are associated with the continuous southward subduction of the Mongol–Okhotsk oceanic plate rather than the Paleo‐Asian and circum‐Pacific tectonic regimes.     

Numerical Analysis of Gravity Coring Using Coupled Eulerian-Lagrangian Method and a New Corer

The shortcomings of gravity corers in sampling marine sediments have been observed extensively in various field tests. In order to optimize the coring, this article provides an alternative numerical way to model the gravity coring and analyze the sampling effect. Based on this analysis, a new hydraulic hammer corer is devised. A coupled Eulerian-Lagrangian method with capability of simulating the problem involving extreme deformation, penetration is used to simulate the coring process. The results show that the hydrostatic pressure and deviator stress increase and reach their peak when the pile tip is slightly above or at the level of the observation point and then drop rapidly when the pile tip slides below the observation point. In addition, the stress path indicates that the soil element sustains plastic compression before yielding and then expands until recovering to the original state. The obvious “under-sampling” phenomenon is also well-captured by the finite element model.     

Mixing of Enriched Lithospheric Mantle-Derived and Crustal Magmas: Evidence from the Habo Cenozoic Porphyry in Western Yunnan

New zircon U–Pb ages, whole-rock geochemistry and zircon Hf isotopes from the Habo porphyry Western Yunnan, China, were determined to provide constraints on the timing of uplift of the Eastern Tibetan Plateau. The intrusive rocks consist of shoshonitic porphyry (syenite porphyry and monzonite porphyry). Zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating indicates coeval emplacement ages of ~35 Ma. The porphyries have alkaline affinities, enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) (e.g., Rb, Th, U, Pb), with depletion of high field strength elements (HFSEs) (e.g., Nb, Ti, Ta) and weak Eu anomalies. They display uniform Lu–Hf isotopic compositions with negative zircon εHf(t) values ranging from -3.9 to -0.6. The chemical characteristics of the syenite porphyries indicated that they most likely originated from the lower crust, with mantle-derived material involved in their generation. Geochemically, the monzonite porphyries are similar to the syenite porphyries; however, the lower MgO contents suggest that they were produced by different degrees of partial melting of the same lower crust source. Combined with the geochemical and isotopic data in this paper, imply that the alkali-rich porphyries of the Habo polymetallic deposit were derived from the partial melting of lower crust, enriched by mantle magma, formed in a conversion stage from stress extrusion (a strike-slip shear process) to local stress relaxation (a strike-slip pull-apart process) at the Ailaoshao tectonic zone.     

高压超高压变泥质岩适用的地质温压计评述

高压超高压变泥质岩形成温压条件及p-T演化轨迹是高压超高压变质作用研究的重要内容。本文介绍了高压超高压变泥质岩适用的几种地质温压计,包括石榴子石-多硅白云母Fe~(2+)-Mg交换温度计、石榴子石-绿泥石Fe~(2+)-Mg交换温度计、硬绿泥石-绿泥石Fe~(2+)-Mg交换温度计、多硅白云母Si含量压力计、金红石Zr含量温度计、榍石Zr含量温压计、锆石Ti含量温度计、石英Ti含量温度计以及氧同位素温度计,并对上述温压计的适用条件及使用时的注意事项做了简要评述。