压重顶进框构下穿高铁引起桥墩变形及控制技术

以某高速公路下穿京沪高铁工程为例,提出一种基于"卸载-加载平衡"理念的压重顶进框构方案,并对高铁桥墩变形及控制技术进行研究。结果表明,高速公路在高铁桥下开挖10 m深,开挖体量近10万方。采用压重顶进框构方案,施工中边顶进、边监测、边通过框顶堆土、桥下堆土、框内留土等措施加载压重,可有效控制高铁的隆起变形。在通车运营3个月后,高铁相邻桥墩累计最大差异沉降为2.7mm,距离规范限值留有46%的余量,满足规范要求。轨检表明,无砟轨道平顺性满足运营要求。对比分析表明,数值模型中粉质黏土压缩模量可采用P0~P0+100 kPa(P0为土体自重应力)应力区间对应的模量值,卸载模量可取为压缩模量的3~5倍。     

辽东桓仁西部古元古代侵入岩年代学及岩石地球化学

华北克拉通东部辽东地区出露古元古代侵入岩,为准确认识辽东地区古元古代构造演化过程,选取北沟岩体、正岔岩体和树柳林子岩体的岩相学、岩石地球化学及年代学特征,探讨了岩体的形成时代、岩石成因及其构造环境。锆石SHRIMP U-Pb年代学研究表明,柳林子岩体年龄为(2 490±8) Ma,北沟岩体年龄为(2 457±11) Ma。北沟岩体高硅富钾,富集Rb、U、Th、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,为过铝质高钾钙碱性I型花岗岩,Nb/Ta平均值5. 75,Rb/Nb平均值4. 21,源于太古宙古老地壳的部分熔融;正岔岩体高硅富钾,富集Rb、Ba、U、Th、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,为弱过铝质高钾钙碱性A型花岗岩,Nb/Ta平均值16. 06,Rb/Nb平均值4. 81,源区可能由幔源岩浆底侵带来的热量加热地壳,导致其重熔并与之混合后形成的。柳林子岩体为变质角闪辉长岩,呈亚碱性,富集Rb、Ba、K等大离子亲石元素,亏损Nb、Ti、P等高场强元素,显示其岩浆可能形成于受陆壳微弱混染的软流圈地幔或岩石圈地幔。认为研究区古元古代侵入岩形成于东、西陆块碰撞拼合后的后造山挤压向板内伸展转换的构造环境,为构造体质转换的产物。     

Rock Mass Characteristics in Beishan, A Preselected Area for China’s High-Level Radioactive Waste Disposal

Geological and hydrological characteristics, joint geometric features, rock physical and mechanical properties and rock mass quality are studied in the Beishan area, preselected for China’s high-level radioactive waste (HLW) disposal engineering. A comprehensive survey method is developed to study joint geometric features in the outcrop and samples from borehole BS06 into the Xinchang rock mass were tested. The optimal joint sets are determined by rose diagrams and equal-area lower hemisphere plots of joint poles. Results show that: 1) the distribution of joint occurrence obeys a normal distribution, while the distribution of joint spacing obeys a negative exponential distribution; 2) concentric circular and tangent circular sampling windows are applied to study the trace length and the trace midpoint density. Results indicate that tangent circular sampling window is more stable and reasonable; 3) Beishan granite shows high density, low porosity and high strength based on many laboratory tests and the physical properties and mechanical properties are closely related; and 4) a synthesis index, Joint Structure Rating (JSR), is applied to evaluate the quality of rock mass. Through the research results of rock mass characteristics, the Xinchang rock mass in the Beishan preselected area has the favorable conditions for China’s HLW disposal repository site.     

A New Oogenus of Dendroolithidae from the Late Cretaceous in the Quyuangang Area,Henan Province,China

正Objective The oofamily Dendroolithidae is elliptical or oblate eggs with loosely arranged dendritic eggshell units and large cavities between eggshell units (Zhang et al., 2018).Dendroolithidae is represented by two oogenera,Dendroolithus (Zhao Zikui and Li Zuocong, 1988), and Placoolithus (Zhao Hong and Zhao Zikui, 1998)according to the latest classification (Zhang et al., 2018).     

Ordovician Granitoids and Silurian Mafic Dikes in the Western Kunlun Orogen, Northwest China: Implications for Evolution of the Proto-Tethys

The western Kunlun orogen in the northwest Tibet Plateau is related to subduction and collision of Proto-and Paleo-Tethys from early Paleozoic to early Mesozoic. This paper presents new LA-ICPMS zircon U-Pb ages and Lu-Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotopes of two Ordovician granitoid plutons(466–455 Ma) and their Silurian mafic dikes(～436 Ma) in the western Kunlun orogen. These granitoids show peraluminous high-K calcalkaline characteristics, with(⁸⁷Sr/⁸⁶Sr)_i value of 0.7129–0.7224, ε_Nd(t) values of -9.3 to -7.0 and zircon ε_Hf(t) values of -17.3 to -0.2, indicating that they were formed by partial melting of ancient lower-crust(metaigneous rocks mixed with metasedimentary rocks) with some mantle materials in response to subduction of the Proto-Tethyan Ocean and following collision. The Silurian mafic dikes were considered to have been derived from a low degree of partial melting of primary mafic magma. These mafic dikes show initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7101–0.7152 and ε_Nd(t) values of -3.8 to -3.4 and zircon ε_Hf(t) values of -8.8 to -4.9, indicating that they were derived from enriched mantle in response to post-collisional slab break-off. Combined with regional geology, our new data provide valuable insight into late evolution of the Proto-Tethys.     

High‐ and low‐Cr chromitite in a Tibetan Ophiolite: Evolution from Mature Subduction System to Incipient Forearc in the Neo‐Tethyan Ocean

The microstructures, major‐ and trace‐element compositions of minerals and electron backscattered diffraction (EBSD) maps of high‐ and low‐Cr# [spinel Cr# = Cr³⁺/(Cr³⁺+Al³⁺)] chromitites and dunites from the Zedang ophiolite in the Yarlung Zangbo Suture (South Tibet) have been used to reveal their genesis and the related geodynamic processes in the Neo‐Tethyan Ocean. The high‐Cr# (0.77‐0.80) chromitites (with or without diopside exsolution) have chromite compositions consistent with initial crystallization by interaction between boninitic magmas, harzburgite and reaction‐produced magmas in a shallow, mature mantle wedge. Some high‐Cr# chromitites show crystal‐plastic deformation and grain growth on previous chromite relics that have exsolved needles of diopside. These features are similar to those of the Luobusa high‐Cr# chromitites, possibly recycled from the deep upper mantle in a mature subduction system. In contrast, mineralogical, chemical and EBSD features of the Zedang low‐Cr# (0.49‐0.67) chromitites and dunites and the silicate inclusions in chromite indicate that they formed by rapid interaction between forearc basaltic magmas (MORB‐like but with rare subduction input) and the Zedang harzburgites in a dynamically extended, incipient forearc lithosphere. The evidence implies that the high‐Cr# chromitites were produced or emplaced in an earlier mature arc (possibly Jurassic), while the low‐Cr# associations formed in an incipient forearc during the initiation of a new episode of Neo‐Tethyan subduction at ～130‐120 Ma. This two‐episode subduction model can provide a new explanation for the coexistence of high‐ and low‐Cr# chromitites in the same volume of ophiolitic mantle.     

Zircon growth during subduction and exhumation metamorphism of mafic rocks,Aktyuz terrain,North Tiahshan,Kyrgyzstan

The interpretation of whether a dated metamorphic zircon generation grew during the prograde, peak or retrograde stage of a metamorphic cycle is critical to geological interpretation. This study documents a case at Aktyuz metamorphic terrain, in the southern of Kokchetav‐North Tianshan belt, involving progressive metamorphic recrystallization of mafic rock to eclogite and associated behavior of zircon. Zircons in eclogites are mainly fine grains (5 to 20 μm), and preferentially concentrated with rutile/ilmenite. They also occur as individual grains or clusters in amphibole coronas of garnet. A few larger grains commonly preserve inherited cores and evidence of dissolution and metamorphic outgrowths. Zircon grains separated from amphibolites show inherited zircons with typically magmatic feature, although this become progressively blurred in response to resorption and recrystallization. Mineral inclusions represent epidote‐amphibolite facies in the prograde metamorphism, and the embayed boundary between recrystallized domains and inherited zircons suggest fluid/melt participation. The metamorphic domains are mainly simple overgrowth around the inherited cores or recrystallization domains. The absence of peak metamorphic mineral inclusions and steep pattern of MREE‐HREE indicate no sufficient garnet formed before the metamorphic zircon overgrowth. A tiny rim with homogeneously bright CL image can be distinguished in most zircons. Amphibole inclusions have similar compositions to those in the coronas of garnets, suggesting a retrograde metamorphic origin. The inherited zircon crystallized at 880‐730 Ma, revealing similar age range to the gneiss in Aktyuz area, whereas metamorphic zircon dates prograde metamorphism at 497.9 ±1.4 Ma. In this case, the bulk Zr budget in rocks will become locked into Zr‐bearing minerals during the mafic magma intrusion, when the inherited zircon melting and resorption. The texture shows that metamorphic zircon grew both in the prograde and retrograde stage, and Zr‐bearing magmatic minerals and rutile/ilmenite are by far the main source of Zr for the two stages, respectively.     

四川盐源西范坪渐新世含矿二长斑岩成因浅析

四川盐源西范坪斑岩型铜矿位于扬子板块西南缘,通过对含矿二长斑岩进行锆石U-Pb定年,获得年龄为31.68±0.28 Ma(MSWD=1.2;2σ),表明其形成时代为古近纪渐新世早期,与区内碱性斑岩岩浆活动的高峰期一致。岩石碱度率指数(A.R.)为3.59～3.69,K/N为0.89～1.11,A/NK为1.16～1.24,A/CNK为0.97～1.13,属准铝—过铝质碱性石英二长斑岩;岩石高度富集轻稀土元素,相对亏损重稀土元素,δEu(0.80～0.85)异常不明显,并且富Sr贫Yb(Y),具高Sr/Yb和Sr/Y比值,系典型的埃达克岩。西范坪埃达克质含矿斑岩为印度板块与欧亚大陆板块碰撞造山晚期远程压力释放环境下,拆沉下地壳部分熔融的产物。