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1.
造山带中残存有许多前寒武纪地质体,其中一些被当作前寒武纪基底用于探讨所在微陆块的大地构造属性。由于微陆块属性对于造山带结构和演化具有重要意义,以及所讨论的前寒武纪地质体蕴含地球早期历史演化信息,对微陆块属性的厘定成为造山带研究的重点和难点问题之一。笔者等以中亚造山带南缘中段的微陆块为例,总结梳理了微陆块厘定的相关依据:岩石组合和变质变形特征,碎屑锆石谱峰显示的源区时代特征,地质事件序列,前寒武纪地壳演化信息,继承锆石、捕获锆石和古生代侵入体同位素显示的深源地壳信息,以及地球物理等方面的特征。由于不同学者采用的厘定依据不同,对微陆块属性认识争论不断,即使相同依据也有一定的差异,从而影响对造山带结构和演化的认识。基于以上原因,笔者等认为前寒武纪基底的亲缘性探讨不仅要注重岩石组合和形成时代,还要在精细野外解剖和高精度年代学工作基础上,注意其变质—变形特征、接触关系、源区时代特征、岩石成因和构造环境、地壳增生信息和深源地壳信息等的综合对比分析,以得到较全面依据,探讨其构造属性。当获得一组前寒武纪地质体信息时,可先进行同构造单元内对比,再与其他构造单元对比。当特征相异时则需进行构造单元拆分或考虑构造就位的可能(包括但不限于推覆体、走滑外来体、俯冲刮削的构造岩片);当特征相似时,可能指示了相同微陆块的裂解或破坏或者不同的微陆块共同经历了相似的前寒武纪演化历程。 相似文献
2.
谢国文 《中国地理科学(英文版)》1997,7(3):236-242
EastChinaisoneoftherichestregionsinplantlifeinEastAsiaanditsfloraisthemainpartofSino-Japanesefloristicregion,whichhasattractedtheattentionofmanybotanistsbothathomeandabroad,suchasHuXiansu(1936),LiHuilin(1950,1953),StewardA.N.(1958),WangJingkiang(1988),WangWencai(1992),Wusugong(1987),WuZhengyi(1979)andXieGuowen(1991a,1993),etal.AnumberofpapersdealingwithEastAsian-EasternNorthAmericanphytogeographicalrelationshipshavebeenpublished(Bouffordf1983).However,thefloristicrelationsbetweenEas… 相似文献
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4.
阿拉善地块的大地构造属性是近年来地质界激烈争论的科学问题:是华北克拉通的一部分,还是在前寒武纪尚未与华北克拉通拼合?研究阿拉善地块的基底并与华北克拉通主体进行对比,对探讨这一问题具有重要启示。阿拉善地块的基底仅在其东部和西南缘零星出露,且前人的研究主要集中在地块东部。在阿拉善地块西部的合黎山地区,有正长岩侵入龙首山群,并被震旦系不整合覆盖。该正长岩强烈富钾(K_2O=13.77%),轻、重稀土明显分异((La/Yb)_N=46.62),显示Nb-Ta负异常和Pb-Zr-Hf正异常,并具有高Sr低Nd的同位素特征(ε_(Nd)(t)=-5.05),表明该岩体源于玄武质下地壳的部分熔融。LA-ICP-MS锆石U-Pb定年表明,该正长岩形成于(1872±12) Ma,即古元古代,并记录了~2.7 Ga的地壳生长以及~2.5 Ga和~1.95 Ga的岩浆活动。合黎山古元古代正长岩的发现补充了阿拉善地块前寒武纪基底的组成,进一步完善了阿拉善地块新太古代—古元古代基底和构造热事件的时代格架,且与华北克拉通主体十分相似,指示二者具有明显的亲缘性。 相似文献
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6.
Interplay between equilibrium and kinetics in prograde metamorphism of pelites: an example from the Nelson aureole, British Columbia 总被引:2,自引:0,他引:2
The distribution of metapelitic mineral assemblages in the Nelson aureole, British Columbia, generally conforms to what is predicted from phase equilibria. However, in detail, the sequence and spacing of isograds, mineral textures and mineral compositions and mineral chemical zoning do not. Two of the main disequilibrium features in the aureole are: (i) delay in the onset and progress of several reactions, i.e. overstepping in temperature; and (ii) unreactivity of staurolite and especially garnet porphyroblasts when they are reactants in prograde reactions. The thermal overstepping is ascribed to difficulty of nucleation of the product porphyroblasts and sluggishness of dissolution of porphyroblasts when they are reactants. The extent to which these kinetic barriers delay the onset of reaction is related to the reaction affinity of each reaction, defined herein as the Gibbs free‐energy difference between the thermodynamically stable, but not‐yet‐crystallized, products and the metastable reactants. For oversteps in temperature (ΔT), reaction affinity is, in turn, related to the difference in entropy (ΔS) between these two states through the relation A = ΔT * ΔS. Mineral reactions which release large quantities of H2O, such as chlorite‐consuming reactions, have a higher entropy change per unit of temperature overstep, and therefore a higher reaction affinity, than those which release little or no H2O, such as the chlorite‐free staurolite‐consuming reaction. Thermal overstepping is consequently expected to be less for the former than for the latter, as was estimated in the aureole where 0 to 30 °C overstepping was required for garnet, staurolite and andalusite growth from a muscovite + chlorite‐bearing precursor rock and ~70 °C overstepping was required for the growth of Al2SiO5 from a staurolite‐bearing, chlorite‐free precursor. In all cases, reaction progress was strongly influenced by the presence or absence of fluid, with presence of fluid lowering kinetic barriers to nucleation and growth and therefore the degree of thermal overstepping. Textural features of rocks from the nearly coincident garnet, staurolite and andalusite isograds are suggestive of a fluid‐catalysed ‘cascade effect’ in which reaction took place in a narrow temperature interval; several competing muscovite + chlorite‐consuming reactions, some metastable, appear to have occurred in parallel. Metamorphic reaction, fluid release and possibly fluid presence in general in the aureole were episodic rather than continuous, and in several cases well removed from equilibrium conditions. The extent to which these findings apply to regional metamorphism depends on several factors, a major one being enhanced deformation, which is expected to lower kinetic barriers to nucleation and growth. 相似文献
7.
元素地球化学分类探讨 总被引:1,自引:0,他引:1
戚长谋 《吉林大学学报(地球科学版)》1991,(4)
在评述已有经典分类基础上给予了元素地球化学亲合性的明确概念。强调了阳离子与阴离子或与络阴离子(酸根)之间的选择结合的重要地球化学意义,并以其做为元素地球化学分类的依据,提出了分类的新方案。该分类方案将元素划分为:亲石元素、亲氧元素、亲硫元素、阴离子及两性元素和氢及惰性气体元素五个类。阐述了各类元素亲合规律的基本特征和元素亲合性与地质环境的关系。 相似文献
8.
潘集煤矿二叠纪主采煤层中微量元素亲和性研究 总被引:5,自引:0,他引:5
安徽淮南煤田位于华北地台南端 ,发育了华北地区二叠纪含煤岩系中层位最高的可采煤层。采用仪器中子活化分析法 (INAA)测试了淮南煤田潘集煤矿二叠纪主采煤层 13个样品的 36个微量元素的浓度分布 ,并对其共生组合特点、地球化学特征及稀土元素配比模式作了初步分析 ,结果表明 ,煤中不同微量元素显示出不同的亲和性质。元素Br,As ,Sb ,Ni和Co等趋于在煤中富集 ,其中Br的有机亲和性最大。元素Na ,K ,Rb ,Th ,Hf,Zr ,Ta和REE则在煤层与顶底板接触带的碳质泥岩中富集 ,表现出与细粒陆源碎屑物更强的亲和性。其它元素倾向性不甚明显 ,但Fe ,Ca ,Sr ,HREE等元素在海水影响强度增大的煤层中含量增加。元素As,Cs,Ni,Fe和Ca在煤层中含量变化较大 ,其变异系数大于 1,其它元素则相对稳定 ,表明同一矿区煤层中微量元素含量在不受其它地质作用明显叠加影响时具有一定的稳定性。本区煤层稀土元素配比模式与华北其它地区C—P纪煤基本类似 ,普遍存在Eu亏损现象。 ∑REE在煤中分布范围为30× 10 -6~ 95× 10 -6,在顶板泥岩中超过 2 0 0× 10 -6。煤层中部 ∑REE降低 ,HREE相对富集。聚类分析表明 ,元素As ,Se ,Ag和Fe关系密切 ,这与煤中黄铁矿等成岩矿物有直接关系 ,泥炭沼泽演化期间或之后海水的直接或间接影响会促使这 相似文献
9.
《International Geology Review》2012,54(5):539-561
ABSTRACTThere are voluminous ultrahigh pressure-related orthogneisses and minor metamorphic supracrustal rocks in the northeastern Sulu UHP terrane (NSL), East China. The tectonic affinities of the supracrustal rocks are crucial for unravelling the deep continental subduction processes and locating the tectonic suture between the South China (SCB) and North China (NCB) blocks. In this contribution, we report new zircon U–Pb ages and Hf isotope data for the supracrustal rocks and metagabbros in the Zeku region of the NSL. In the Zeku region, the supracrustal rocks are spatially associated with granitic gneisses, metagabbros, and eclogites. Detrital zircon U–Pb analyses yield ages between 3.39 and 0.65 Ga that cluster as three major age populations including (1) 2.15–1.68 Ga with two subpeaks at ~1.83 Ga and~1.97 Ga, (2) 2.45–2.15 Ga with a peak at ~2.37 Ga, and (3) 0.79–0.65 Ga. In addition, there is a small age population between 3.39 and 2.61 Ga. The youngest age population of 0.79–0.65 Ga indicates that the Zeku supracrustal rocks must have been deposited after 650 Ma rather than during the Palaeoproterozoic as previously thought. The 210–190 Ma metamorphic ages suggest that the Zeku rocks were affected by Triassic collision–subduction and exhumation. Most of the Archaean-Palaeoproterozoic zircons have negative εHf(t) values and two-stage Hf model ages concentrating at 2.4–3.4 Ga (peak at ~2.9 Ga), indicating that source rocks of these zircons were mainly derived from recycling of ancient crustal material. These ages, together with the Hf isotopic compositions and rock assemblages, indicate that the Zeku supracrustal rocks were mainly derived from the Precambrian basement rocks of the northern Yangzte Block and have a tectonic affinity to the SCB, rather than the NCB. Our results, together with previously published data, suggest that there are two types of supracrustal rocks with different zircon U–Pb ages and tectonic affinities in the NSL. On the basis of new data, we suggest that the surface boundary between the SCB and NCB in the Jiaodong Peninsula is a complicated tectonic mélange zone rather than a single fault. 相似文献
10.
本文通过对祁连山南部地区三叠纪沉积充填特征的研究,建立了盆地形成过程中沉积充填与区域构造演化的关联。依据沉积充填特征、构造接触关系及区域地质背景,认为祁连山南部地区三叠纪盆地具有弧后前陆盆地的构造属性;综合分析年代学、沉积物性和盆地内部填充单元的差异划分出与柴达木岛弧带和祁连山南部弧后前陆盆地相关的区域大地构造单元。认为早三叠世-中三叠世中期,南部遭受俯冲作用持续向北挤压推覆导致盆地挠曲沉降;中三叠世中期-晚三叠世中期发生弧(东昆仑-柴北缘)-陆(巴颜喀拉地块)碰撞,祁连山南部盆地挠曲沉降增大,其间形成区域性断裂和不整合等盆地记录的地质事件;晚三叠世晚期祁连山南部盆地发生过补偿陆相填充,弧后前陆盆地消亡。
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