巽他地块的构造演化与介质特性的动力学意义

基于近年来国内外关于青藏高原及川、滇、缅、印支地区大地构造演化、现今地壳运动观测、地壳与上地幔结构反演等领域取得的大量观测与研究成果,结合对泰、越等国的野外地质考察与认识,以探索建立对该地区现今地壳运动与变形状态起控制作用的构造框架为目的,提出了相对于"活动地块"的"相对稳定地块"的概念。综合分析认为,巽他地块在构造演化、介质特性及现今运动与变形等方面类似于青藏高原周缘的塔里木、阿拉善、扬子等地块,具有"相对稳定地块"的特征,它们共同构成了调节青藏高原物质东向挤出后围绕东喜马拉雅构造结发生顺时针旋转的刚性约束边界。这同时意味着,青藏高原侧向挤出动力作用的势力范围可能覆盖了川、滇、缅及印度支那北部的广大地区,这有助于加深对该地区强震动力学环境的认识。     

混炼挤压改性对膨润土分散影响的试验研究

通过对天然钙基膨润土钠化改性过程以及有机改性过程中混炼挤压的实验,分析了混炼挤压对膨润土分散的影响。实验结果表明,混炼挤压作用可以有效地提高钙基膨润土的钠化度以及膨润土颗粒的分散度和ξ电位。     

JFSAS04.##2对海南万宁降水预报的统计分析

通过对 jfsas0 4.# # 2的预报质量统计 ,从而了解它在什么时候的预报效果较佳 ,在什么时候不够理想 ,有利于提高预报准确率。     

青藏高原现今构造变形特征与GPS速度场

文章以青藏高原的GPS观测数据为基础 ,结合活动地质构造资料 ,研究了青藏高原的现今构造变形状态和机制 ,并探讨青藏高原现今构造变形所反映的大陆内部动力学过程。GPS观测的速度矢量揭示了青藏高原整体向北和向东运动的趋势 ,平行于印度和欧亚板块碰撞方向上的地壳缩短量约是 38mm/a ,而青藏高原周边主要断裂带的滑动速率均在 10mm/a以下。大约 90 %的印度与欧亚板块相对运动量被青藏高原的地壳缩短所吸收和调节。GPS速度矢量由南向北逐渐向东偏转 ,向东的分量也增加 ,形成了以羌塘地块北部 (或玛尼—玉树—鲜水河断裂 )和祁连山中部为中心的两个地壳物质向东流动带。青藏高原的向东挤出实际上是地壳物质在印度板块推挤下和周边刚性地块阻挡下围绕东构造结发生的顺时针旋转。     

西秦岭断裂走滑与盆地的耦合——西秦岭—松甘块体新生代向东走滑挤出的证据

新生代西秦岭—松甘块体向东挤出是印度—欧亚大陆碰撞后青藏东北部一种主要应变响应形式 ,它构成青藏高原东部走滑调节带的北支 ,并与南部印支挤出构造一起共同调节和吸收大陆碰撞后青藏东部的变形。西秦岭岷县—宕昌断裂的走滑与新生代盆地在时空上的耦合 ,明显展示出西秦岭—松甘块体向东走滑挤出历程并提供了走滑作用的定量标尺。古近纪岷县—宕昌断裂的走滑位移量为 36km ,而新近纪则为 76km ,相应的平均走滑速率分别为 0 .0 86mm/a和 0 .37mm/a ,表明新生代西秦岭—松甘块体向东挤出的幅度至少为 112km。西秦岭新生代幔源岩浆活动是在块体挤出背景下 ,块体旋转停止、断裂面弯曲和走滑加速等诸事件耦合的结果 ,同时也是断裂走滑的物质和时间记录器 ,表明岷县—宕昌断裂新生代的走滑波及到了岩石圈底部 ,记录了青藏东北部变形响应的动力学机制从以块体旋转为主向快速走滑为转变的时间 ,即西秦岭—松甘块体向东快速挤出的可能时间为 2 1.1～ 2 5 .4Ma。     

Exhumation of the Main Central Thrust from Lower Crustal Depths, Eastern Bhutan Himalaya

Geothermometry and mineral assemblages show an increase of temperature structurally upwards across the Main Central Thrust (MCT); however, peak metamorphic pressures are similar across the boundary, and correspond to depths of 35–45 km. Garnet‐bearing samples from the uppermost Lesser Himalayan sequence (LHS) yield metamorphic conditions of 650–675 °C and 9–13 kbar. Staurolite‐kyanite schists, about 30 m above the MCT, yield P‐T conditions near 650 °C, 8–10 kbar. Kyanite‐bearing migmatites from the Greater Himalayan sequence (GHS) yield pressures of 10–14 kbar at 750–800 °C. Top‐to‐the‐south shearing is synchronous with, and postdates peak metamorphic mineral growth. Metamorphic monazite from a deformed and metamorphosed Proterozoic gneiss within the upper LHS yield U/Pb ages of 20–18 Ma. Staurolite‐kyanite schists within the GHS, a few metres above the MCT, yield monazite ages of c. 22 ± 1 Ma. We interpret these ages to reflect that prograde metamorphism and deformation within the Main Central Thrust Zone (MCTZ) was underway by c. 23 Ma. U/Pb crystallization ages of monazite and xenotime in a deformed kyanite‐bearing leucogranite and kyanite‐garnet migmatites about 2 km above the MCT suggest crystallization of partial melts at 18–16 Ma. Higher in the hanging wall, south‐verging shear bands filled with leucogranite and pegmatite yield U/Pb crystallization ages for monazite and xenotime of 14–15 Ma, and a 1–2 km thick leucogranite sill is 13.4 ± 0.2 Ma. Thus, metamorphism, plutonism and deformation within the GHS continued until at least 13 Ma. P‐T conditions at this time are estimated to be 500–600 °C and near 5 kbar. From these data we infer that the exhumation of the MCT zone from 35 to 45 km to around 18 km, occurred from 18 to 16 to c. 13 Ma, yielding an average exhumation rate of 3–9 mm year^?1. This process of exhumation may reflect the ductile extrusion (by channel flow) of the MCTZ from between the overlying Tibetan Plateau and the underthrusting Indian plate, coupled with rapid erosion.     

Southward extrusion of eclogite-bearing mafic–ultramafic bodies in the Sanbagawa belt, central Shikoku, Japan

Several mafic rock masses, which have experienced eclogite facies metamorphism, are distributed in flat-lying non-eclogitic schists in an intermediate structural level (thermal core) of the Sanbagawa belt. The largest, Iratsu mass, and an associated peridotite, the Higashi-Akaishi mass, extend E–W for about 8 km, and N–S for about 3 km, and are surrounded by pelitic, basic and quartz schists. The Iratsu mass consists of metabasites of gabbroic and basaltic origin, with intercalations of ultramafic rocks, felsic gneiss, quartz schist and metacarbonate. The Iratsu mass can be divided into two layers along a WNW-trending metacarbonate layer. The Higashi-Akaishi mass consists of peridotite with intercalations of garnet clinopyroxenite. It is situated beneath the western half of the Iratsu mass, and their mutual boundary dips gently or steeply to the N or NE. These masses underwent eclogite, and subsequent epidote-amphibolite facies metamorphism as has been reported elsewhere. The Iratsu–Higashi-Akaishi masses and the surrounding rocks underwent ductile deformation under epidote-amphibolite facies (or lower P–T) metamorphic conditions. Their foliation generally trends WNW and dips moderately to the NNE, and the mineral lineation mostly plunges to the N and NE. In non-eclogitic schists surrounding the Iratsu–Higashi-Akaishi masses, the foliation generally trends WNW and dips gently or steeply to the N or S and the mineral lineation mostly plunges to the NW, N and NE. Kinematic analysis of deformation structures in outcrops and oriented samples has been performed to determine shear senses. Consistent top-to-the-north, normal fault displacements are observed in peridotite layers of the Higashi-Akaishi mass and eclogite-bearing epidote amphibolite layers of the Iratsu mass. Top-to-the-northeast or top-to-the-northwest displacements also occur in non-eclogitic pelitic–quartz schists on the northern side of the Iratsu mass. In the structural bottom of the Iratsu–Higashi-Akaishi masses and to the south, reverse fault (top-to-the-south) movements are recognized in serpentinized peridotite and non-eclogitic schists. These observations provide the following constraints on the kinematics of the rock masses: (1) northward normal displacement of Iratsu relative to Higashi-Akaishi, (2) northward normal displacement of non-eclogitic schists on the north of the Iratsu mass and (3) southward thrusting of the Iratsu–Higashi-Akaishi masses upon non-eclogitic schists in the south. The exhumation process of the Iratsu–Higashi-Akaishi masses can be explained by their southward extrusion.     

Detrital zircon provenance evidence for large-scale extrusion along the Altyn Tagh fault

The question of whether or not the Altyn Tagh fault is a large-scale extrusion boundary is critical for understanding the role of lateral extrusion in accommodating the Indo-Asian convergence and in building the Tibetan Plateau. Oligocene conglomerate clasts in the eastern Xorkol basin are low-grade slate, phyllite, sandstone, dacite and carbonate, and associated paleocurrent indicators evince sediment derivation from the opposing side of the Altyn Tagh fault. Matching these clasts with similar basement rocks in the North Qilian and Tuolainanshan terranes requires post-Oligocene left-lateral offset of 380 ± 60 km on the eastern segment of the Altyn Tagh fault, suggesting large-scale extrusion along the fault in the Cenozoic (Yue, Y.J., Ritts, B.D., Graham, S.A., 2001b. Initiation and long-term slip history of the Altyn Tagh fault. International Geological Review 43, 1087–1094.). In order to further define this piercing point, the detrital zircon pattern of Oligocene sandstone from the Xorkol basin and the zircon ages of basement on the southern side of the fault were established by ion microprobe dating. Characterized by strong peaks between 850 and 950 Ma and the absence of Paleozoic and Mesozoic ages, the detrital zircon age pattern of the Oligocene sandstone matches the age distribution of zircon-bearing rocks of the Tuolainanshan terrane. This match requires 360 ± 40 km of post-Oligocene left-lateral displacement on the eastern segment of the Altyn Tagh fault, supporting as well as refining the previously reported lithology-based cross-fault match. At least one of the following three extrusion scenarios must have existed to accommodate this large offset: (1) northeastward extrusion along the Altyn Tagh–Alxa–East Mongolia fault, (2) eastward extrusion along the Altyn Tagh–North Qilian–Haiyuan fault, and (3) northeastward extrusion of northern Tibet as a Himalaya-scale thrust sheet along the North Qilian–Haiyuan fault. We prefer the first scenario inasmuch as rapidly growing evidence for Cenozoic strike-slip activity on the Alxa–East Mongolia fault and mid-Miocene exhumation of northern Tibet supports it.     

Tectonic overpressure in competent mafic layers and the development of isolated eclogites

Abstract Variation in the state of stress during heterogeneous deformation should be reflected in variation in the effective pressure of metamorphic reactions, whether this is mean stress or the normal stress acting across the reacting interface. The magnitude of this pressure variation will determine whether it is discernible in the preserved metamorphic mineral assemblages of heterogeneously deformed rocks. The magnitude of the mean stress difference across a non-slipping interface between two materials with viscosity ratio >c. 20:1 is effectively equal to the maximum shear stress for flow in the more viscous material. Progressive shortening of the interface results in a higher mean stress in the more competent material, whereas extension results in a lower mean stress. For high-P/low-T eclogite facies conditions, current experimental data indicate that clinopyroxene- and garnet-rich layers of eclogite should be very strong and that pressure differences of up to 800 MPa (8 kbar) between competent layer and weaker matrix may be possible. Such high values can be obtained in widely separated competent layers for values of bulk stress in the overall multilayer that are much lower (by a factor approaching the viscosity ratio). Extrusion of material between more rigid plates, which has been proposed as a regional mechanism of lateral ‘continental escape’for both the Alps and the Himalayas, should also be accompanied by a lateral gradient in effective pressure; otherwise extrusion could not occur. Maximum mean stresses with magnitudes that are many times the maximum shear stress required for plastic flow should develop for deformation zones that are long relative to their width (e.g. around 20 times for a width-to-thickness ratio of 10). Tectonic overpressure in progressively shortened competent layers, particularly in regions of extrusion between more rigid plates, might help explain the occurrence of isolated layers and pods of low-T eclogite (<550°C) with estimated peak pressures markedly in excess of those in the surrounding matrix. It cannot explain the occurrence of isolated high-T eclogites, because at temperatures >c. 550°C, the dramatic weakening of clinopyroxene in the power-law creep field precludes the development of significant overpressures in eclogite layers.     

中亚低压东移的动力学分析

本文根据热成风适应原理,分析了中亚低压的东移问题。结果表明,温度场扰动的斜压发展与流场扰动的正压发展的两种热成风平流过程,对于东移低压和不东移低压的作用是完全不同的。