A Tertiary asthenospheric flow beneath the southern French Massif Central indicated by upper mantle seismic anisotropy and related to the west Mediterranean extension   总被引：1，自引：0，他引：1  

Guilhem Barruol  Michel Granet 《Earth and Planetary Science Letters》2002,202(1):31-47

Upper mantle flow beneath the French Massif Central is investigated using teleseismic shear wave splitting induced by seismic anisotropy. About 25 three-component stations (short period, intermediate and broadband) were installed during the period 1998-1999 in the southern Massif Central, from the Clermont Ferrand volcanic area to the Mediterranean Sea. Teleseismic shear waves (SKS, SKKS and PKS) were used to determine the splitting parameters: the fast polarization direction and the delay time. Delay times ranging between 0.7 and 1.5 s have been observed at most of the sites. The azimuths of the fast split shear waves trend homogeneously NW-SE in the southern Massif Central suggesting a homogeneous mantle flow beneath this area. The observed NW-SE direction differs from the N100°E Pyrenean anisotropy further south. It does not appear to be correlated to Hercynian structures nor to the present-day motion of the plate but is well correlated to the Tertiary extension direction. We propose that the opening of the western Mediterranean induced by the rotation of the Corsica-Sardinia lithospheric block and the roll-back to the SE of the Tethys slab may have generated a large asthenospheric mantle flow beneath the southern Massif Central and a deflection of the up going plume centered beneath the northern Massif Central toward the SE.  相似文献   

拆沉作用(delamination)及其壳—幔演化动力学意义   总被引：45，自引：0，他引：45  

高山  金振民 《地质科技情报》1997,(1)

拆沉作用导致下地壳和岩石圈地幔下沉，相应软流圈上涌至壳—幔边界，使下地壳、岩石圈地幔和软流圈三者发生物质交换，引起岩浆作用、山脉隆升、伸展、垮塌，形成坳陷盆地，并最终使大陆地壳向长英质方向演化，产生与其它行星不同的、独一无二的中性安山质或英云闪长质成分。拆沉作用是对经典板块构造理论的重要补充与完善  相似文献   

动态部分熔融作用及其地球物理意义   总被引：7，自引：1，他引：7  

金振民  白武明 《地质科技情报》1993,12(1):93-100

本文着重阐述了上地幔动态部分熔融动力学的几个基本问题:(1)初始熔融物的产生;(2)渗透和萃取;(3)运移和聚集;(4)研究方法、内容及其地球物理意义。笔者强调指出,在初始熔融阶段,两面角是控制上地幔熔融物的几何分布、渗透性和连通性能的关键参数,少量熔融物(2%~5%)不仅会使软流圈中地震波速下降、导电率增加,而且还引起上地幔非弹性衰减现象。  相似文献   

The crustal and upper-mantle geophysical signature of narrow continental rifts in the Pannonian basin   总被引：1，自引：0，他引：1  

A. Ádám  & M. Bielik 《Geophysical Journal International》1998,134(1):157-171

  相似文献   

中国东部中、新生代软流圈上涌与构造-岩浆-矿集区   总被引：1，自引：0，他引：1       下载免费PDF全文

邢集善  杨巍然  邢作云  刘建华 《地球科学》2019,44(5):1570-1583

以深部地球物理资料为基础,结合大地构造环境、岩浆岩同位素示踪及矿产资源分布规律,加以综合分析.通过热力学计算可知,中国东部近2亿年来的上地幔岩石圈/软流圈构造可以存留至今,且能区分出中、新生代.软流圈上涌与矿集区:(1)中生代金属矿:(a)克拉通区,软流圈沿柱身上涌,其柱头上方形成幔壳混熔花岗质岩及相应Au、Cu、Mo、Pb-Zn等矿集区,并于柱身与岩石圈块体陡接触带,形成中基性杂岩及相应富Fe矿集区;(b)褶皱带区,在软流圈上涌柱上方形成近幔源型花岗质岩,相应为Cu、Au、Pb-Zn、Mo、Ag矿集区;(c)南岭带,软流圈层在适当深度、热量充足、较大范围内"平卧",因热传导而致使地壳内物质部分重熔,形成壳源型花岗质岩及相应的W、Sn、稀有元素矿集区;(2)新生代油气田:(a)与太平洋板块俯冲有关的软流圈上涌,其上方出露玄武岩,形成较大型油田;(b)与裂陷盆地有关的软流圈上涌,其上方形成大型油田,也有中小型油田.软流圈上涌与大地构造:中生代J-K时期,通过构造力特征等的综合分析,阐明燕山运动的根源及其影响;新生代侧重剖析大陆裂谷相关特征.总之,软流圈上涌是岩石圈减薄,以及中、新生代构造-岩浆-矿集区形成的根源.  相似文献   

Isotopic measurements in the Cape York Peninsula area,North Qeensland     

J. A. Cooper  A. W. Webb  W. G. Whitaker 《Australian Journal of Earth Sciences》2013,60(3):285-310

K‐Ar and Rb‐Sr isotopic measurements have been made on the north‐south belt of igneous and metamorphic rocks from the Peninsula Ridge and Yambo Inlier of Cape York Peninsula. Four periods of Palaeozoic igneous activity appear to have been denned. These are (⁸⁷’Rb^λ = 1.39 X 10^–11y–1) about 415 m.y., about 400 m.y., 385–390 m.y., and 255–280 m.y., with the youngest dates to the north and northeast. The largest volume of magma, the Kintore Adamellite was emplaced during the 285–390 m.y. period. Initial ⁸⁷Sr/⁸⁶Sr ratios range from 0.715 (a granodiorite) through 0.72–0.74 (muscovite adamellite) to 0.76 (leuco‐adamellite), which suggests a high component of old crustal material in the latter types.

The host metamorphics grade from greenschist facies in the west to almandine‐amphibolite facies in the centre and south. Limited direct data suggest that the greenschists are older than 1400 m.y. This is supported by intrusive dolerite dating greater than 1800 m.y. Rocks possibly 2000 m.y. old are thus adjacent to the Australian northeast coast and place drastic limitations on the possibility of continual continental growth to the east.

Rb/Sr measurements on minerals of the almandine amphibolite rocks record the major Kintore event. Total rock measurements have high uncertainties but give only slightly older figures. Initial ⁸⁷Sr/⁸⁶Sr ratios of these apparent total rock isochrons are high, 0.735–0.745. Gross isotopic redistribution must have occurred during the Palaeozoic metamorphism.

The Rb/Sr isotopic and geochemical relationships suggest that some of the granitic rocks have been derived from the equivalent of the present greenschist facies suite, and that the almandine amphibolite facies was, in part, remetamorphosed during the Palaeozoic and is possibly partly residual after metamorphic segregation.

The region has been examined from the plate tectonic point of view and shows that many of the requirements of a cordilleran‐type mountain belt of Dewey & Bird (1970) existed during the mid‐upper Palaeozoic. The Palmerville Fault and the Hodgkinson Basin are key units in this interpretation.

Dolerite, possibly 2000 m.y. old, could be contemporaneous with voluminous dolerites of similar age from the Kimberley region (Australia) and of Venezuela and Guyana. They may be a useful continental breakup indicator, as are the Gondwana dolerites.  相似文献   

基于P波三重震相的华南地区上地幔速度结构研究   总被引：2，自引：1，他引：1       下载免费PDF全文

吕苗苗  丁志峰  朱露培 《地球物理学报》2017,60(10):3765-3779

华南块体是研究太平洋板块俯冲和岩石圈减薄机制等问题的最佳场所之一.本文基于中国地震观测台网和大型流动台阵记录到的震中距10°~30°之间的两个中深源地震P波记录,利用三重震相波形拟合技术,获得了中扬子克拉通和华夏地块上地幔高精度P波速度结构.研究结果表明:(1)中扬子克拉通过渡带底部存在高速异常,系太平洋俯冲板块的滞留体.俯冲的板块并没有进入下地幔,660-km间断面下沉约11 km,与后尖晶石相变的克拉伯龙斜率为负有关.而华夏地块过渡带底部并无明显高速异常,接近全球平均模型;(2)整个华南块体,410-km间断面上方普遍存在低速层,主要与上地幔部分熔融有关,与IASP91相比P波速度减小了1.38%~2.29%;(3)在研究区域内,中扬子克拉通和华夏地块都存在岩石圈减薄(80 km),推测可能与太平洋板块俯冲和快速回撤导致的岩石圈拆沉有关.且华夏地块减薄程度较明显,下伏软流圈速度较低,说明其上地幔强度较弱、温度较高.另外,中扬子克拉通过渡带中存在一个较宽的速度梯度带,可能与520-km间断面有关,其具体成因有待进一步研究.  相似文献   

Petrogenesis and mantle source characteristics of Cenozoic alkaline diabase,Jiangxi Province,southeastern China     

《International Geology Review》2012,54(16):1919-1931

Major element, trace element, and Sr–Nd–Pb isotopic compositions of Cenozoic diabase in southeastern China provide insights into the nature of their mantle sources and processes. The diabases are alkaline in lithochemistry (Na₂O + K₂O = 4.37–5.19 wt.%) and have overall oceanic island basalt-like trace element patterns, without negative Nb–Ta anomalies. In addition, they are characterized by lower La/Nb (<1.5) and La/Ta (<22), and higher Ce/Pb (>15) and Nb/U (>30) ratios, indicating an origin in the asthenospheric mantle. The relatively lower ¹⁴³Nd/¹⁴⁴Nd (0.512632–0.512648) and ²⁰⁶Pb/²⁰⁴Pb (18.20–18.22), but intermediate ⁸⁷Sr/⁸⁶Sr (0.7061–0.7063) ratios of the diabases are similar to enriched mantle type 1, suggesting crustal contamination or mixing with metasomatized lithsopheric mantle. However, the low Th and U contents and lack of correlations of Nd isotope compositions and MgO preclude significant crustal contamination. Alternatively, the moderate TiO₂ contents (2.01–2.09 wt.%) and high Cr concentrations (>240 ppm) suggest interaction between asthenosphere-derived melts and metasomatized lithospheric mantle. Petrological modelling suggests that the diabases were generated from a low degree (~3–5%) of partial melting of lherzolite with ~2–3% garnet. Jiangxi diabase was generated in a within-plate extensional regime, probably related to the far effect of the Himalaya–Tibetan orogen.  相似文献   

Behavior of Siderophile and Chalcophile Elements in the Subcontinental Lithospheric Mantle beneath the Changbaishan Volcano,NE China   总被引：1，自引：0，他引：1  

WANG Jian  LIU Jinlin  HATTORI Keiko  XU Wenliang  XIE Zhipeng  SONG Yue 《《地质学报》英文版》2012,86(2):409-421

The mantle xenoliths in the Quaternary ChangbaishanVolcano in southern Jilin Province contain spinel-facies lherzolites. The equilibration temperatures for these samples range from 902oC to 1064oC based on the two-pyroxene thermometer of Brey and K?hler (1990), and using the oxybarometry of Nell and Wood (1991), the oxidation state was estimated from FMQ-1.32 to -0.38 with an average value of FMQ-0.81 (n?=?8), which is comparable to that of abyssal peridotites and the asthenospheric mantle. The fO2 values of peridotites, together with their bulk rock compositions (e.g., Mg#, Al2O3, CaO, Ni, Co, Cr) and mineral compositions (e.g., Mg# of olivine and pyroxene, Cr# [=Cr/[Cr+Al]] and Mg# [=Mg/[Mg+Fe2+] of spinel), suggest that the present-day subcontinental lithospheric mantle (SCLM) beneath the Changbaishan Volcano most likely formed from an upwelling asthenosphere at some time after the late Mesozoic and has undergone a low degree of partial melting. The studied lherzolite xenoliths show low concentrations of S, Cu, and platinum group elements (PGE), which plot a flat pattern on primitive-mantle normalized diagram. Very low concentrations in our samples suggest that PGEs occur as alloys or hosted by silicate and oxide minerals. The compositions of the studied samples are similar to those of peridotite xenoliths in the Longgang volcanic field (LVF) in their mineralogy and bulk rock compositions including the abundance of chalcophile and siderophile elements. However, they are distinctly different from those of peridotite xenoliths in other areas of the North China Craton (NCC) in terms of Cu, S and PGE. Our data suggest that the SCLM underlying the northeastern part of the NCC may represent a distinct unit of the newly formed lithospheric mantle.  相似文献   

中国东部中生代岩石圈演化与太平洋板块俯冲消减关系的讨论   总被引：17，自引：5，他引：12  

肖庆辉  刘勇 冯艳芳邱瑞照张 昱 《中国地质》2010,37(4):1092-1101

国内外不少学者认为中国东部中生代岩石圈演化与太平洋板块向欧亚大陆俯冲、消减有关,近年来作者从岩石圈-软流层深部地质过程审视中国东部岩石圈演化问题发现,中国东部中生代早期(三叠纪至侏罗纪)岩石圈演化与太平洋板块向欧亚大陆俯冲消减没有直接的关系,它们可能是一种源自中国东部周边东亚洋盆系的一些洋盆向中国东部大陆俯冲消减碰撞造山以及由它们引发的中国东部大陆内的软流层上涌的深部地质作用联合作用的结果。软流层上涌作用自始至终控制着中国东部大陆岩石圈与软流层之间以及壳幔之间的层圈拆离,底侵作用以及岩石圈变形缩短、伸展和岩浆活动。  相似文献