Basement framework and geodynamic evolution of the Palaeoproterozoic superbasins of north‐central Australia: An integrated review of geochemical,geochronological and geophysical data

A largely convergent setting is proposed for crustal, tectonic and basin evolution of the intracratonic regions of north‐central Australia between 1800 and 1575 Ma. The new geodynamic model contrasts with previous proposals of widespread extension during the Leichhardt, Calvert and Isa intervals. Local transtensional to extensional structures exist, but these are best explained by a combination of flexural, thermal and dynamic processes related to an active southern margin. The development of thick accumulations of sediments (superbasins) is linked geodynamically to interpreted active margin processes (subduction and magmatic arcs) in central Australia. A synthesis of geochemical data from the 1870–1575 Ma igneous units from the Arnhem, McArthur and Mt Isa regions of north‐central Australia confirms the intracratonic setting of these units and suggests that a long‐lived thermal anomaly was responsible for the generation of both mafic and felsic magmas. The geochemical characteristics suggest the igneous units are derived from the lithospheric mantle and are not typical rift‐ or plume‐related melts. A review of the U–Pb SHRIMP ages for the entire region demonstrates the minimum distribution of correlative igneous rocks was widespread. Exotic populations in the ²⁰⁷Pb/²⁰⁶Pb isotopic data provide insights into the nature and evolution of the crust throughout north‐central Australia. Archaean inheritance is found to be nearly ubiquitous. The data support the temporal subdivision of north‐central Australia into the Leichhardt (1800–1750 Ma), Calvert (1750–1690 Ma) and Isa (1690–1575 Ma) intervals which are marked by superbasins and concomitant episodes of igneous activity. A highly heterogeneous pre‐superbasin crust is interpreted from regional, newly processed geophysical data. The cratonic portion of north‐central Australia is interpreted to consist of three broad northwest‐trending belts or elements that are further distinguished into western, central and eastern geophysically distinct provinces. A map of the superbasin distribution is derived and integrated with structural and stratigraphic data to assess the evolution of the basins and the crust through time. The superbasin successions of north‐central Australia are synchronous and widespread, although not necessarily interconnected. The tectonic model incorporates dynamic tilting of the craton during episodes of subduction and transmission of compressive intraplate stresses through the craton during intervening episodes of orogeny. These processes resulted in flexure, strike‐slip deformation and a complex thermal structure. These mechanisms account for the subsidence and basin evolution that results in widespread ramp and strike‐slip basins. The model also accounts for the thermal history recorded by magmatic events. The proposed geodynamical model provides a unifying crustal evolution scenario for central and northern Australia for approximately 225 million years of the Proterozoic.     

Geochemical fingerprint of hyaloclasts in glassy fragmental rocks of Macquarie Island (Southern Ocean): implications for volcanogenic sedimentary processes at a waning mid-ocean ridge

Two main types of glassy fragmental rocks formed along the Proto-Macquarie Spreading Ridge: (i) hyaloclastite breccia; and (ii) pillow-fragment breccia. Examples now exposed on Macquarie Island, Southern Ocean, were largely sourced from proximal pillow lavas. In each of seven samples examined, hyaloclasts (basaltic glass grains) have a narrow major- and trace-element geochemical range, consistent with derivation of each sample from a single volcanic eruption event. Moreover, every sample analysed within the one stratigraphic section (at three sites) displays distinctive major- and trace-element geochemistry compared with the other two sections. This suggests that hyaloclasts at each site represent discrete magma batches. A single source for these glassy fragmental rocks contrasts with the dominant fault-scarp-derived polymict sedimentary rocks on Macquarie Island. We suggest that the hyaloclasts analysed in this study were deposited in small basins between the slopes of growing pillow cones along the mid-ocean ridge. The geochemical analyses presented here encompass (weakly) fractionated (e.g. Bauer Bay) to near-primitive (e.g. Pyramid Peak) compositions. All samples presented here lie within the range of the enriched- to normal-MORB suites previously reported for the island that include the least fractionated MORB melts known globally. The interpretation of geochemically distinct magma batches over the small area of the island suggests very limited magma mixing consistent with an immature or waning magmatic system. We relate these geochemical characteristics to: (i) volcanism near a very long offset transform; and (ii) genesis of magmas during the waning stages of slow seafloor spreading within a very narrow (<50 km-wide) spreading corridor.     

中国东部中生代岩浆活动与太平洋板块向西俯冲有关吗?

通常认为,中国东部中生代岩浆活动与太平洋板块的向西俯冲有关,而本文的研究表明,中生代时中国东部不属于环太平洋构造带,不处于安第斯活动陆缘环境,没有岛弧玄武岩和岛弧花岗岩.许多资料表明,在中生代早期,太平洋板块基本上是向北俯冲的,至早白垩世中期(125 Ma左右)才转向西俯冲,而中国东部大规模岩浆活动主要发生于侏罗纪—早白垩世(约180～130 Ma),因此,中国东部中生代大规模岩浆活动与太平洋板块的向西俯冲无关.太平洋板块真正向西俯冲的时间非常短暂,只有125～110 Ma和43～0 Ma两个时段.在前一时段,中国东部岩浆活动仅限于中国东部沿海;在后一个时段,中国东部岩浆活动几乎绝迹.因此,中国东部中生代大规模岩浆活动与太平洋板块向西俯冲有关的命题是错误的.     

太平洋板块俯冲对中国东北深浅震影响机理的数值模拟

本文采用与深度有关的不同分层结构模型, 并考虑太平洋板块俯冲角度差异等特征, 建立太平洋板块向中国东北地区俯冲的2D纵向静力学模型。 以太平洋板片俯冲速度为约束条件, 通过变化俯冲板块的俯冲角度, 数值模拟太平洋板块向中国东北的俯冲过程, 探讨太平洋板块俯冲作用对于我国东北深浅震的影响, 得到不同俯冲角度模型的深浅部应力场分布, 揭示区域构造应力场的总体特征和断裂带局部特性, 并讨论了活动断裂带以及邻近区域对东北地区深浅部构造应力场的响应。 结果表明, 太平洋板块俯冲角度的变化对于中国东北地区深浅震的地震活动格局具有重要影响, 断裂带构造环境是浅源地震孕育的基本条件。     

中国东北晚中生代-新生代盆山体系构造演化及成因探讨

中国东北盆山体系主要形成和发展于晚侏罗世晚期-新近纪,经历了晚侏罗世晚期-早白垩世小盆山（盆岭）和晚白垩世-新近纪大盆山（盆山）两个阶段的构造发展过程.盆岭阶段起始于东北高原向盆岭体系转换的张家口期,全盛于义县-九佛堂期,萎缩于盆岭向盆山体系构造转换的沙海-阜新期,结束于张老公屯期（东山期）.盆山阶段经历了晚白垩世早期大规模拗陷、晚白垩世晚期拗陷萎缩、古近纪大规模裂谷和新近纪后裂谷拗陷.认为太平洋板块对盆山体系形成和发展有巨大的影响,但无论是板块、地幔柱和超级地幔柱均不太可能形成如此规模,又具北北东向的中-新生代岩浆岩带和盆山体系,更可能是超级地幔热带、地幔柱和东亚多向板块汇聚背景下,西太平洋板块俯冲共同作用的结果.     

冻融循环作用下节理岩体锚固性能退化机理和模式

岩土锚固的长期性能和耐久性是当前岩土工程界普遍关注的热点问题,也是影响锚固工程长期安全性的关键问题之一。节理岩体存在不同尺度、程度的损伤和缺陷,为地下水的存储和运移提供场所和通道。当达到孔隙水和裂隙水的冻结温度时,岩体中产生冻胀,并伴随着水分迁移,影响锚固系统的锚固性能,在冻融循环作用下,引起锚固系统长期性能和耐久性的退化。依据孔隙介质的冻结理论,建立了砂浆、岩石、砂浆-钢筋和砂浆岩石接触面静水压力学模型,分析其冻结机理。在总结岩石冻融损伤劣化研究成果基础上,深入系统地分析了节理岩体锚固系统的冻融损伤劣化机理及其影响因素,并建立冻融循环作用下节理岩体锚固性能退化的6种模式及其数学模型。     

悬浮颗粒的浓度对其在饱和多孔介质中迁移和沉积特性的影响

多孔介质中悬浮颗粒迁移和沉积特性的研究对地下污染物净化、石油开采、核废料处置、水土保持等有很重要的意义。对4种不同浓度的悬浮颗粒在3种不同的渗流速度下进行室内试验,研究悬浮颗粒的浓度对其迁移和沉积特性的影响。结果表明,在一定的悬浮颗粒浓度下,随着渗流速度的增加,穿透曲线中的悬浮颗粒的相对浓度也增大。同时,渗流速度一定时,悬浮颗粒的浓度存在一个临界值,小于该临界值,穿透曲线中的相对浓度随悬浮颗粒的浓度增大而增大;大于该临界值时,相对浓度随悬浮颗粒的浓度增大而减小。另外,悬浮颗粒的临界浓度是与渗流速度相关的,随着渗流速度增加,悬浮颗粒的临界浓度也逐渐增大     

基于块体集上限分析的锚板试验模型探讨

通过块体集上限分析方法,研究锚板的抗拔承载力和破坏面特性,并将分析结果与Das[1]以及Rowe[2]的锚板模型试验结果进行详细对比,验证块体集上限法的有效性。分析斜坡地形条件下锚板抗拔承载特性,并与Khing等[3]的条形锚板抗拔承载力试验以及Rao和Prasad[4]的圆形锚板抗拔承载力试验进行详细对比,分析斜坡地形条件下锚板模型试验中采用拉杆加载的方式对于试验结果的影响。分析结果表明,斜坡地形条件下拉杆的存在对于锚板抗拔承载力影响较大,模型试验应优先采用Trapdoor模型。     

频域内饱和多孔介质的参数反演分析

基于Biot理论,假定固体颗粒和孔隙内流体均不可压缩,建立了以固体骨架位移表示的的控制方程.考虑单层饱和多孔介质在竖向简谐荷载作用下一维动力响应,通过理论推导获得了骨架位移、应力以及孔隙流体压力等物理量的解析表达式.基于饱和土的简谐动力模型试验数据,与所得到的理论解答相结合,将饱和多孔介质材料参数反演问题归结为非线性多峰函数的最优化问题.全局最优解的求解采用了遗传算法和模拟退火算法,并通过试验和数值算例验证了所得材料参数的正确性.