On the Time Evolution of the Turbulent Kinetic Energy Spectrum for Decaying Turbulence in the Convective Boundary Layer

Our focus is the time evolution of the turbulent kinetic energy for decaying turbulence in the convective boundary layer. The theoretical model with buoyancy and inertial transfer terms has been extended by a source term due to mechanical energy and validated against large-eddy simulation data. The mechanical effects in a boundary layer of height z _i at a convective surface-layer height z = 0.05z _i are significant in the time evolution of the vertical component of the spectrum, i.e. they enhance the decay time scale by more than an order of magnitude. Our findings suggest that shear effects seem to feedback to eddies with smaller wavenumbers, preserving the original shape of the spectrum, and preventing the spectrum from shifting towards shorter wavelengths. This occurs in the case where thermal effects only are considered.     

胶东苏鲁地体范家埠金矿成矿作用与矿床成因浅析:兼与胶北地体金矿对比

范家埠金矿是胶东半岛苏鲁地体内规模最大的石英脉型金矿。含金石英脉中锆石阴极发光和LA-ICP-MS微量元素及U-Pb同位素分析结果表明,含金石英脉中的锆石均为捕获围岩(新元古代威海片麻状花岗岩)的岩浆锆石,其中15个颗粒在U-Pb图解上位于谐和线上,其206Pb/238U加权平均年龄为(726±14)Ma(MSWD=4.6);另外7颗锆石位于不一致线上,其上交点年龄为(758±25)Ma,下交点年龄为(123±11)Ma(MSWD=0.45)。这些锆石的下交点年龄与金矿脉旁侧斜闪煌斑岩脉的角闪石40Ar/39Ar年龄分别为(118.8±1.6)Ma和(117.5±1.5)Ma,在误差范围内一致,表明范家埠金矿的成矿时代为120Ma左右。由此认为,苏鲁地体和胶北地体的金矿成矿作用均发生于早白垩世晚期120Ma前后,与目前多数人认为的华北克拉通岩石圈减薄的峰期时间一致,表明苏鲁地体的金矿成矿受岩石圈减薄的构造背景控制。范家埠金矿床成矿流体具中高温、中高盐度15.5%～23.2%(NaCleq)、低δ18OH2O(-3.84‰～-4.05‰)和低δDH2O(-82.5‰～-80.8‰)值等特点,载金矿物黄铁矿富32S(δ34S=-5.5‰～-9.1‰),与含油气盆地热卤水的组成相近,暗示范家埠金矿的成矿流体可能来源于中生代胶莱盆地。这种盆地流体沿断裂——五莲—米山深大断裂及其次级构造迁移,同时萃取基底岩石中的金形成含矿热液并在还原的环境中成矿。相反,胶北地体大量金矿床成矿流体具有低盐度、高δ18OH2O和δDH2O,δ34S(‰)为正值等特点。胶北和苏鲁地体早白垩世金成矿强度和成矿作用的差异可能反映了两者在地壳基底、流体来源和成矿环境等方面的不同。     

华南氧化锰矿晚新生代大规模成矿

氧化锰矿是我国仅次于沉积型碳酸锰矿的重要锰矿床类型,主要分布在广西、湖南、广东和福建等南方省区,但由于定年手段的限制,迄今对我国氧化锰矿形成时代的了解还极其有限.作者近几年利用激光阶段加热40Ar/39Ar同位素分析技术对华南地区典型氧化锰矿进行了系统和精确的年龄测定,获得了一大批可靠的成矿年龄,年龄值介于23.64 ± 0.29 Ma和0.48 ± 0.17 Ma (2σ),表明华南氧化锰矿的大规模成矿至少在渐新世末-中新世初就已开始并一直持续到更新世末期.基于多数氧化锰矿的上部矿石已被剥蚀或开采殆尽这一事实,可将华南氧化锰矿的成矿时间上溯到渐新世早期甚至始新世末期.研究发现,氧化锰矿的保存程度和年龄分布明显受新构造运动的影响;如果剔除后期剥蚀程度和采样系统性的影响,可以认为华南氧化锰矿的形成在区域上具有同时性.本次研究还说明,次生氧化锰矿的成矿是一个极其漫长的过程,形成一个具有工业意义的氧化锰矿可能需要上千万年的时间;这明显有别于多数内生热液矿床的成矿.本项研究为我国氧化锰矿以及其他类型的风化矿床(如红土型金矿和红土型镍矿)的年代学研究提供了新的思路和途径.     

Vertical deformation partitioning across a collapsing large and hot orogen

Featuring 3 000-km-long large and hot orogen, the Mantiqueira Province provides a rare opportunity to study the process of gravitational collapse at mid to deep crustal levels. Distinct but contemporary (~500 Ma) post-collisional intrusions show structures and anisotropy of magnetic susceptibility (AMS) fabrics related to their emplacements, recording different flow patterns. In southern deep-seated intrusions, ellipsoidal-shaped roots with gabbroic-to-hybrid cores surrounded by granitic rocks show concentric patterns of AMS fabrics that cut across the NE-trending regional foliation. In contrast, northern intrusions, exposed as the upper sections of batholith-size bodies of coarse-grained granite emplaced at the shallow to mid-crust, show general NS-trending magnetic fabrics roughly parallel to strike of the orogen and the regional foliation of host rocks. These contrasting magnetic patterns from shallow to deeper crust suggest vertical magma migration from the overthickened orogenic core to be emplaced across its thinner stretched flanks during the gravitational collapse of the orogenic edifice.