Contraction and extension in northern Borneo driven by subduction rollback

During the Paleogene the Proto-South China Sea was subducted beneath northern Borneo. Subduction ended with Early Miocene collision of the Dangerous Grounds/Reed Bank/North Palawan block and the Sabah–Cagayan Arc. Much of northern Borneo then became emergent forming the Top Crocker Unconformity. Later in the Early Miocene subsidence resumed. It is proposed that northward subduction of the Celebes Sea initiated formation of the Sulu Sea backarc basin, followed by subduction rollback to the SE. This formed a volcanic arc, which emerged briefly above sea level and collapsed in the Middle Miocene. As rollback continued the Sulu Arc was active during Middle and Late Miocene between Sabah and the Philippines. Rollback drove extension in northern Borneo and Palawan, accompanied by elevation of mountains, crustal melting, and deformation offshore. There were two important extensional episodes. The first at about 16 Ma is marked by the Deep Regional Unconformity, and the second at about 10 Ma produced the Shallow Regional Unconformity. Both episodes caused exhumation of deep crust, probably on low angle detachments, and were followed by granite magmatism. The NW Borneo–Palawan Trough and offshore Sabah fold and thrust belt are often interpreted as features resulting from collision, regional compression or subduction. However, there is no seismicity, dipping slab or volcanicity indicating subduction, nor obvious causes of compression. The trough developed after the Middle Miocene and is not the position of the Paleogene trench nor the site of Neogene subduction. Inboard of the trough is a thick sediment wedge composed of an external fold and thrust belt and internal extensional zone with structures broadly parallel to the trough. The trough is interpreted as a flexural response to gravity-driven deformation of the sediment wedge, caused by uplift on land that resulted from extension, with a contribution of deep crustal flow.     

云母复合材料板的合成研制

选择了云母作为纤维矿物材料替换石棉，填料选用叶蜡石、方解石和方镁石等矿物，进行云母复合材料板合成，并详细解析分别由云母、云母 方解石、云母 叶蜡石 方解石、云母 方解石 叶蜡石 方镁石等一元、二元、三元和四元等材料合成的复合材料板的物理性质和机械性能，得出了以多元矿物材料合成的制品的质量优于单元矿物材料合成的制品，以四元矿物材料合成的云母复合材料板可任意切割，复合材料的厚度可达到5mm左右。     

宁波某厂房室内地坪沉降原因分析及处理措施

针对宁波市宁海县宁东区块某厂房室内地坪沉降现象,在分析沉降原因和沉降趋势的基础上,结合本工程的具体条件对几种加固方法进行了对比,确定采用锚杆桩 梁板结构加固方式对地坪进行处理。研制了多功能小型静力压桩机、采用了小创面多级挤扩贯穿排障法等解决了施工中的难题,实现了复杂环境条件的特种专业工程的顺利施工。治理效果良好。     

什么控制了华北克拉通东部在新近纪的构造活动?

在新近纪初期(约23 Ma)的时候,在当时中国大陆周边板块构造环境没有发生重大变化的情况下,华北克拉通东部构造活动性质仍发生了明显的变化.比如,华北克拉通东部的岩石圈增厚了,唐山-邢台断裂开始活动的同时太行山山前断裂却变得不活跃了,华北局部构造变形性质发生了变化等.虽然在古近纪和8 Ma以后,有证据显示印度-欧亚大陆的...     

埃达克岩的原义、特征与成因

论述了埃达克岩的原义与综合特征 ,并针对其与太古宙TTG之间的区别和联系及今后研究埃达克岩的建议提出了自己的见解。埃达克岩 (adakite)的原义是指一类具有镁铁质斑晶的隐晶质火山岩 ,属于岛弧型岩浆钙碱性岩系 ,一般形成于年轻的 (<2 5Ma)、地热高的岛弧环境 ,是俯冲板块和上覆地幔相互作用产生的杂化熔液通过结晶分异形成的。综合总结埃达克岩 (原义 )的地球化学特征如下 :(1)原生标志 ,高Mg# 、低FeO /MgO、高Cr及Ni;(2 )微量元素标志 ,高LILE、高LREE、低HREE、低HFSE以及高分异的REE型式等。对实验岩石学研究资料的总结可知杂化 (hybridized)熔液是由小数量的板块熔液与地幔楔反应经交代作用、同化作用形成的 ,可分异直至出现酸性岩浆 ,这一过程称为“地幔同化及分离结晶作用 (mantle AFC)”。在橄榄岩的同化作用中 ,原有熔液Mg# 迅速上升 ,并在熔液成分加多后 ,向高Mg# 区迅速发展。在近代一些埃达克岩及相关岩石研究中 ,部分学者认为太古宙TTG与新生代板块 (榴辉岩 )重熔的TTD岩系类似。同时 ,亦有学者认为太古宙“绿岩带”中与TTG有关的深成岩系是一类Mg质花岗闪长岩Mg质二长闪长岩 ,成因与Sanukite相似 (太古宙sanuk itoid岩系 ) ,相当于富集橄榄岩重熔形成的岩系。这些研究重新引发了太古宙     

Geochemistry of the Jurassic Mirdita Ophiolite (Albania) and the MORB to SSZ evolution of a marginal basin oceanic crust

The Middle Jurassic Mirdita Ophiolite in northern Albania is part of an ophiolite belt occurring between the Apulian and Pelagonian subcontinents in the Balkan Peninsula. The upper mantle and crustal units of the Mirdita Ophiolite show major changes in thickness, rock types, and chemical compositions from west to east as a result of its complex evolution in a suprasubduction zone (SSZ) environment. The  3–4-km-thick Western Mirdita Ophiolite (WMO) includes lherzolite–harzburgite, plagioclase–lherzolite, plagioclase–dunite in its upper mantle units and a plutonic complex composed of olivine gabbro, troctolite, ferrogabbro, and gabbro. These peridotites and gabbroic rocks are overlain directly by a  600-m-thick extrusive sequence containing basaltic pillow lavas and hyaloclastites. Sheeted dikes are rare in the WMO. The  12-km-thick Eastern Mirdita Ophiolite (EMO) includes tectonized harzburgite and dunite with extensive chromite deposits, as well as ultramafic cumulates including olivine clinopyroxenite, wehrlite, olivine websterite, and dunite forming a transitional Moho with the overlying lower crustal section. The plutonic rocks are made of pyroxenite, gabbronorite, gabbro, amphibole gabbro, diorite, quartz diorite, and plagiogranite. A well-developed sheeted dike complex has mutually intrusive relations with the underlying isotropic gabbros and plagiogranites and feeds into the overlying pillow lavas. Dike compositions change from older basalt to basaltic andesite, andesite, dacite, quartz diorite, to late-stage andesitic and boninitic dikes as constrained by crosscutting relations. The  1.1-km-thick extrusive sequence comprises basaltic and basaltic andesitic pillow lavas in the lower 700 m, and andesitic, dacitic and rhyodacitic massive sheet flows in the upper 400 m. Rare boninitic dikes and lavas occur as the youngest igneous products within the EMO. The basaltic and basaltic andesitic rocks of the WMO extrusive sequence display MORB affinities with Ti and Zr contents decreasing upsection (TiO₂ = 3.5–0.5%, Zr = 300–50 ppm), while _Nd(T) (+ 8 to + 6.5) varies little. These magmas were derived from partial melting of fertile MORB-type mantle. Fractional crystallization was important in the evolution of WMO magmas. The low Ti and HREE abundances and Cs and Ba enrichments in the uppermost basaltic andesites may indicate an increased subduction influence in the evolution of the late-stage WMO magmas. Basaltic andesites in the lower 700 m of the EMO volcanic sequence have lower TiO₂ ( 0.5%) and Zr ( 50 ppm) contents but _Nd(T) values (+ 7 to + 6.5) are similar to those of the WMO lavas. These rocks show variable enrichment in subduction-enriched incompatible elements (Cs, Ba, Th, U, LREE). The basaltic andesites through dacites and boninites within the upper 400 meters of EMO lavas show low TiO₂ ( 0.8–0.3%) and _Nd(T) (+ 6.5 to + 3.0). The mantle source of these rocks was variably enriched in Th by melts derived from subducted sediments as indicated by the large variations in Ba, K, and Pb contents. EMO boninitic dikes and lavas and some gabbroic intrusions with negative _{Nd (T)} values (− 1.4 and − 4.0, respectively) suggest that these magmas were produced from partial melting of previously depleted, ultra-refractory mantle. The MORB to SSZ transition (from west to east and stratigraphically upwards in the Mirdita Ophiolite and the progression of the _Nd(T) values from + 8.0 to − 4.0 towards the east resulted from an eastward shift in protoarc–forearc magmatism, keeping pace with slab rollback in this direction. The mantle flow above the retreating slab and in the arc-wedge corner played a major role in the evolution of the melting column, in which melt generation, aggregation/mixing and differentiation occurred at all levels of the sub-arc/forearc mantle. The SSZ Mirdita Ophiolite evolved during the intra-oceanic collapse and closure of the Pindos marginal basin, which had a protracted tectonic history involving seafloor spreading, protoarc rifting, and trench-continent collision.     

新疆北部的富镁火成岩

本文重点讨论的富镁安山岩(MAs)是指 SiO_2>53%,Mg~#≥55的安山岩,也包括富镁英安岩和富镁闪长岩。阿尔泰南的富锾安山岩形成于中泥盆世,东、西天山和阿拉套山的富镁安山岩形成于石炭纪。本区富镁安山岩 SiO_2 53%～65%,TiO_2含量低于1%(0.21%～1.08%),平均0.72%;MgO 平均5.90%,与国外玻安岩平均值相比,Mg 含量较低,Ti、K、Na 含量较高。稀土元素总合量低(<100×10~(-6),范围15～95×10~(-6)),相对富重稀土(La/Yb)_N0.98～6.4,多数在4±;Eu 弱亏损到无亏损(Eu/Eu~*0.65～1.15)。相容微量元素 Cr、Ni 含量高,分别为72×10~(-6)～790×10~(-6)和29×10~(-6)～276×10~(-6);高场强元素 Nb、Ta、Ti 明显亏损;相对富集流体中富集的大离子亲石元素 Rb、K、Pb;Y 含量较高(>15×10~(-6));Sr/Y 比值较低(4.4～6.2)。(~(143)Nd/~(144)Nd)_i 值变化范围较大0.51221～0.51255,ε_(Nd)(t) 0.28- 7.2,Nd 模式年龄 t_(DM)485～1220Ma;(~(87)Sr/~(86)Sr)_i 值变化范围较大0.7029～0.7065,在ε_(Nd)(t)-(~(87)Sr/~(86)Sr)_i 图解中位于第一象限。上述特点表明,本区富镁安山岩源区为复合源,包括有蚀变洋壳、弧前增生棱柱的不成熟、新生地壳物质及地幔楔橄榄岩。成岩作用具复合性,既有俯冲洋壳板片的部分熔融,又有俯冲板片熔体对地幔楔橄榄岩的熔体交代作用。形成于特殊构造环境:高地热梯度和富挥发分;导致弧前增生棱柱俯冲的俯冲剥蚀作用;由俯冲板片撕裂、断离所形成的软流圈窗或洋脊俯冲。     

无梁板结构的边界元法分析

利用边界元法对无梁板结构进行较为全面的分析,纠正了以往计算中的某些错误结果。     

高桩码头锈蚀破损面板残余承载力评估方法

高桩码头长期工作在具有腐蚀介质的潮湿环境中，因钢筋的锈蚀会使构件表面砼胀裂而破损，目前我国大部分的高桩码头进入了锈蚀破损的高峰期。通过研究指出：以往国内外用构件蚀破损表面积大小或顺筋裂缝大小的标准来确定维修方案的方法是不正确的。根据一般构件为等截面，而沿跨度分布的弯矩不均匀的事实，指出构件在控制断面以外的部位强度有富裕，允许钢筋适当的锈蚀仍能满足设计强度的新见解。提出了锈蚀破损面板的强度安全性评估准则、强度因子新概念及其具体计算式，可以量化评估犭蚀破损面板的残余承载力，为科学制定锈蚀破损面板的维修方案提供参考，在保证码头结构安全的同时，大大节省维修费用。     

Degradation and Mechanism of the Mechanics and Durability of Reinforced Concrete Slab in A Marine Environment

An experimental research was conducted to determine the corrosion and bearing capacity of a reinforced concrete (RC) slab at different ages in a marine environment. Results show that the development of corrosion-induced cracks on a slab in a marine environment can be divided into three stages according to crack morphology at the bottom of the slab. In the first stage, cracks appear. In the second stage, cracks develop from the edges to the middle of the slab. In the third stage, longitudinal and transverse corrosion-induced cracks coexist. The corrosion ratio of reinforcements nonlinearly increases with the age, and the relationship between the corrosion ratio of the reinforcements and the corrosion-induced crack width of the concrete is established. The flexural capacity of the corroded RC slab nonlinearly decreases with the age, and the model for the bearing capacity factor of the corroded RC slab is established. The mid-span deflection of the corroded RC slab that corresponds to the yield of the reinforcements linearly increases with the increase in corrosion ratio. Finally, the mechanisms of corrosion morphology and the degradation of the mechanical properties of an RC slab in a marine environment are discussed on the basis of the basic theories of steel corrosion in concrete and concrete structure design.