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1.
华北克拉通中部造山带被认为是由东西部陆块碰撞而产生的陆陆碰撞带,而恒山-五台-阜平地区位于中部造山带的中部,是该地区最大也是最具代表性的基底岩石剖面。总体上,五台杂岩可以分为变质表壳岩和花岗质岩体两大类,前者又被划分为五台群和滹沱群,而后者可划分为2560~2520Ma侵位的强烈变形的闪长岩-英云闪长岩-奥长花岗岩-花岗闪长岩系列、2176~2084Ma侵位的弱变形的斑状正长-钾质花岗岩以及约1810Ma侵位的未变形的A型花岗岩。在晚太古代花岗岩中普遍发育有斜长角闪岩包体,它们在露头上不连续分布,呈绿色到黑色,强烈拉伸成扁条状或透镜状,直径一般在几米到十几米之间。根据地球化学特征恢复它们的原岩为拉斑玄武岩。锆石U-Pb定年结果表明它们的结晶时代为2.7Ga,变质时代为1.85Ga。全岩εNd(t)值为-3.1~+3.5,亏损地幔模式年龄为2.83~3.65Ga。原始地幔均一化蛛网图解上,斜长角闪岩具有明显的Nb、Ta和Ti的负异常,而在球粒陨石均一化稀土元素配分图解中它们具有轻稀土弱富集[(La/Yb)N=1.36~3.52]以及重稀土平坦[(Gd/Yb)N=0.94~1.38]的特征。地球化学以及同位素特征表明它们很可能来自于受到俯冲板片流体改造的轻度富集地幔中尖晶石二辉橄榄岩的部分熔融。更重要地,这些斜长角闪岩包体的锆石U-Pb年龄与全岩Nd亏损地幔模式年龄相似,都为27~28亿年左右,这说明在华北克拉通中部造山带很可能存在过大量的27亿年左右的新生地壳岩石,它们代表了一期重要的地壳生长事件。 相似文献
2.
缅甸含硬玉的蛇纹石化橄榄岩及其围岩的岩石学研究 总被引：13，自引：6，他引：13
以缅甸帕敢地区含硬玉岩的蛇纹石化橄榄岩及其围岩－未细分的变质岩为研究对象，较详细地研究了各类岩石的岩相学，岩石化学及主要矿物的组成，认为该区超基性岩为含铬铁矿的蛇纹石化纯橄岩，它的围岩由含多硅白母蓝闪石片岩，石榴斜长角闪岩，大理岩及透辉石大理岩，石英岩等构成。通过其中典型的变质反应分析与计算，认为围岩的变质程度分别为蓝闪石片岩相和的高角闪岩相，其中蓝闪石片岩相的压力大于0．8－1．0GPa，斜长角闪岩相的温度为582度，通过对比分析世界上不同产地硬玉岩的特征，认为硬玉岩，尤其是优质者，产出环境如下：（1）容矿岩体属超基性岩，以含铬铁矿的纯橄岩为最佳；（2）围岩中存在低温高压变质岩，即蓝闪石片岩－榴辉岩类；（3）位于与俯冲带有关大地构造单元内。 相似文献
3.
The 117.38 m of gabbroic core drilled during the Ocean Drilling Program (ODP) Leg 153 at Sites 921 to 924 in the Mid-Atlantic Ridge (MAR) between 23 °N and the Kane Fracture Zone, exhibits a remarkable primary compositional heterogeneity, such as magmatic layering, intrusive contacts and late magmatic veining, which express a succession of magmatic events. Textural indicators suggest that the cooling of the crystal mush occurred in a dynamic environment, with infiltration of progressively evolved liquids. Magmatic features include random shape fabric and magmatic lamination; the subsequent deformational overprint occurred in subsolidus conditions. The ductile deformation, generally concentrated in discrete domains of the gabbro, is associated with continuous re-equilibration of the metamorphic assemblages of (1) olivine + clinopyroxene + orthopyroxene + plagioclase + ilmenite + Ti-magnetite, (2) olivine + clinopyroxene + plagioclase + ilmenite + Ti-magnetite + red hornblende. At lower temperatures brittle deformation prevails and subsequent fractures control the development of metamorphic assemblages: (3) clinopyroxene + plagioclase + red brown hornblende + Ti-magnetite + magnetite (?) + ilmenite, (4) plagioclase + brown hornblende + Ti-magnetite + magnetite + hematite + titanite ± Ti-oxide, (5) plagioclase + green hornblende + magnetite + titanite, (6) plagioclase + actinolite + chlorite + titanite + magnetite, (7) albite + actinolite + chlorite + prehnite ± epidote ± titanite and (8) albite + prehnite + chlorite ± smectite. Assemblages 1 to 8 express increasing water/rock ratios and decreasing degrees of recrystallization.
During the ductile phase, red hornblende is stable and its abundance increases with deformation intensity, possibly as an effect of the introduction of hydrous fluids. During the brittle phase, water diffusion controls the development of the fracture-filling mineral assemblages and re-equilibration of the adjacent rock; temperatures decrease further, as demonstrated by mineral zoning and incompletely re-equilibrated assemblages. The lowest temperatures correspond to the development of hydrothermal assemblages.
Compared with oceanic gabbros from fast-spreading transform environments, high-temperature ductile phases (granulite and amphibolite) are well developed, whereas brittle phases are widespread, as microcracks, prevalent on fracturing associated with discrete veins. 相似文献
4.
阿尔泰塔尔浪地区斜长角闪岩和辉长岩的形成时代、地球化学特征和构造意义 总被引：3，自引：0，他引：3
阿尔泰塔尔浪地区出露一些斜长角闪岩和辉长岩。其中,斜长角闪岩为基性岩浆岩变质的产物,SiO_2含量为45.42%～52.96%,具有较高的Al_2O_3(13.14%～17.92%)、Fe_2O_3~T(9.08%～16.88%)和TiO_2(0.82%～3.23%)含量。斜长角闪岩样品稀土元素曲线比较平坦,轻重稀土元素分馏不明显(La/Yb_N=1.53～1.79),无明显的Nb和Ta亏损。通过野外产状及地球化学特征分析,认为该斜长角闪岩形成于海山的构造环境。辉长岩SiO_2(46.96%～49.86%)含量稍低,TiO_2(0.38%～1.89%)变化较大,并富Al_2O_3(15.0%～20.81%)、CaO(10.13%～11.60%),具有中等至较高MgO含量(7.3%～8.3%)和相对较低的钾含量(K_2O=0.34%～1.03%),属亚碱性岩石系列(Na_2O>K_2O)。辉长岩呈现两种稀土元素组成特征。一种轻重稀土分馏不明显,配分曲线比较平坦(La/Yb_N=1.10～1.67),具有轻微的Eu正异常(δEu=1.03～1.10);另一种轻重稀土元素分馏较明显(La/Yb_N=5.97～6.39)并具有正的Eu异常(δEu=1.31～1.44),反映其形成过程中可能受到斜长石堆晶的影响。在微量元素蛛网图上,辉长岩具有明显的Ti、Nb和Ta负异常和Pb、Sr正异常,反映出明显的消减带岩浆特征。角闪石的~(40)Ar-~(39)Ar测年结果显示,辉长岩样品的坪年龄为266.9±6.1Ma,且年龄坪谱显示在其形成之后没有受到后期热事件的明显干扰,基本上反映了辉长岩的形成年龄。斜长角闪岩的~(40)Ar-~(39)Ar结果呈现出似马鞍型坪谱,其中最小的年龄坪(297.3±6.1Ma)可能反映了最近一期的变质事件,而且明显早于辉长岩的侵入。斜长角闪岩和辉长岩不同的形成时代和地球化学组成表明二者可能代表了两期不同的基性岩浆活动。斜长角闪岩所具有的板内和消减带的复合特征表明其原岩可能是洋壳在俯冲消减过程中增生的海山残片,而辉长岩所具有消减带特征显示在二叠纪时期阿尔秦地区仍存在受俯冲作用影响的地幔源区。阿尔泰二叠纪岩浆活动无论在岩浆属性还是规模上都与泥盆和石炭纪的岩浆活动存在巨大差异,表明这两个时期的构造背景存在较大不同,可能反映阿尔泰正处于某种构造转换机制的控制之下。 相似文献
5.
Ductile extensional movements along the steeply inclined Hoher-Bogen shear zone caused the juxtaposition of Teplá-Barrandian
amphibolites, granulites, and metaperidotites against Moldanubian mica schists and paragneisses. Garnet pyriclasites are well
preserved within low-strain domains of this shear zone. Their degree of metamorphism is significantly higher than that of
the surrounding rocks. Microstructural and mineral chemical data suggest in situ formation of the garnet pyriclasite by dehydration
of pyroxene amphibolite at T>750–840°C and P<10–13 kbar including recrystallization-accommodated grain-size reduction of plagioclase
and clinopyroxene, nucleation of garnet, and breakdown of amphibole into garnet+clinopyroxene+rutile. Subsequent decompression
and retrograde extensional shearing led to the formation of mylonitic epidote amphibolite. The presence of lower crustal and
mantle-derived slices within the Hoher-Bogen shear zone supports the view that (a) in Upper Devonian times the Teplá-Barrandian
unit was thrust over Moldanubian rocks as a complete crustal unit, and (b) that during the subsequent Lower Carboniferous
orogenic collapse, the garnet pyriclasite and metaperidotite were scraped off from the basal parts of the Teplá-Barrandian
unit being dragged into the Hoher-Bogen shear zone due to dramatic and large-scale elevator-style movements.
Received: 23 March 1999 / Accepted: 25 August 1999 相似文献
6.
苏鲁超高压变质带北缘古-新元古代浅变质基性岩的构造属性及其意义 总被引：1，自引：1，他引：0
苏鲁超高压变质带北缘发育的少量以浅变质基性杂岩为代表的非超高压变质岩片,为深入探讨造山带的大陆深俯冲作用及板块缝合线位置提供了重要的制约。1∶5万区域填图表明,浅变质基性杂岩分布于从家屯、胡家和海眼口等地,它们以石门-薛家庄韧性剪切带与超高压变质带分界。同位素测年结果指示,胡家斜长角闪岩时代为古元古代末(1790±27Ma、1853±15Ma),而从家屯斜长角闪岩时代为新元古代(797±11Ma、782±16Ma)。地球化学分析表明,从家屯和胡家斜长角闪岩的SiO_2、TiO_2、Fe_2OT_3和MgO含量分别为47. 20%～52. 60%、0. 98%～3. 30%、9. 31%～16. 78%和3. 76%～7. 13%,为拉斑玄武岩成分。岩石的稀土总量介于45. 8×10~(-6)～289. 0×10~(-6)之间,LREE/HREE=1. 29～11. 6,(La/Yb)_N=0. 45～17. 3,稀土配分曲线较平坦,无铕异常(δEu=0. 75～1. 37)。微量元素相对富集Ba、Rb和Sr,亏损Zr、Hf、Th和Nb。从家屯斜长角闪岩的地球化学特征与E型洋中脊玄武岩相似,而胡家斜长角闪岩则具有洋岛玄武岩特点。综合分析认为,从家屯和胡家斜长角闪岩分别与扬子板块和华北板块具有构造亲缘性,在三叠纪扬子板块向华北板块俯冲碰撞过程中,这些不同大地构造位置和性质的基性岩被刮削叠置于板块缝合线附近,构成了大陆板块俯冲的加积杂岩。同时认为,分布在超高压变质带与非超高压变质岩片之间的石门-薛家庄韧性剪切带为一条重要的板块缝合线。 相似文献
7.
《Chemie der Erde / Geochemistry》2015,75(1):51-54
Our reply deals with the investigations of Kropáč et al. (2012) concerning the evolution of Mn-rich garnetites (=coticules) in the Silesian Desná Unit which are closely associated with Fe-rich rocks. Pouba (1970) who described these mineralizations in greater detail, postulated an origin identical with banded iron-formations of the Algoma type. However, Mücke and Losos (2007) excluded a banded iron-formation origin for the magnetite mineralizations and came to the conclusion that these are connected with the Devonian amphibolite of the Sobotín Massif. The older garnetites were inferred to be identical with coticules and, therefore, are comparable with Mn-rich iron-formations of the Algoma type. Concerning the coticules, Kropáč et al. (2012) confirmed the same origin as proposed by us. For the magnetite-rich rocks, on the other hand, Kropáč et al. (2012) strictly followed Pouba (1970), but did neither present new results or data, nor considered the arguments of Mücke and Losos (2007). In this reply, the most important results of Mücke and Losos (2007) are discussed in comparison with banded iron-formations. 相似文献
8.
G. Wrner J. Lezaun A. Beck V. Heber F. Lucassen E. Zinngrebe R. Rssling H. G. Wilke 《Journal of South American Earth Sciences》2000,13(8):717
Exposures of metamorphic basement in the Central Andes are scarce and reconstructions of the history of the Pacific margin of Gondwanaland must rely on a few isolated outcrops. We studied two areas of exposed basement in northernmost Chile (Belen) and westernmost Bolivia (Cerro Uyarani). The Belen metamorphic complex has been known for some time and consists of fault-bounded amphibolites, gneisses, schists, and minor quartzites overlain by folded Mesozoic to Cenozoic strata. The Cerro Uyarani is the only basement outcrop on the Bolivian Altiplano and has only recently been found and studied by geological reconnaissance. It consists of foliated mafic and felsic granulites, charnockites, and amphibolites. How do these basement occurrences compare and how do they relate to the other Precambrian crustal domains in the Central Andes? To answer these questions, we used geothermobarometers to reconstruct the P–T conditions of metamorphism, as well as geochemical analyses and petrological methods to study these rocks. The two basement blocks were found to have distinct geological histories and are probably separated by a major crustal domain boundary. Isotopic fingerprinting by Pb-isotopes clearly exclude Laurentian crustal components either in the protoliths or as reworked material. This signature is quite distinct from basement rocks farther south in Chile and northwestern Argentina. 相似文献
9.
辽宁本溪歪头山条带状铁矿的成因类型、形成时代及构造背景 总被引：12，自引：9，他引：3
辽宁鞍本地区位于华北克拉通东北缘,分布有诸多大型-特大型条带状铁矿床。本文对该区歪头山铁矿进行了岩石学、矿物学及年代学研究。歪头山铁建造以条带状铁矿石为主,兼含有少量的块状矿石,其顶底板围岩及矿体夹层主要为太古界鞍山群斜长角闪岩。元素地球化学分析表明,铁矿石富集重稀土[(La/Yb)PAAS=0.24~0.33],具La正异常(La/La*=1.43~1.61)、Eu正异常(Eu/Eu*=2.40~4.54)及Y正异常(Y/Y*=1.10~1.30),Y/Ho值平均30.59,Sr/Ba值平均17.62,Ti/V值平均19.45,反映成矿物质可能来源于由海底火山活动带来的高温热液与海水的混合溶液。铁矿石无明显Ce负异常(Ce/Ce*=0.92~1.06),暗示BIF沉积时海水处于缺氧环境。除Fe2O3T与SiO2外,铁矿石中其它氧化物含量均非常低,且贫Th、U、Zr等具有陆源性质的元素,表明大陆碎屑物质对BIF贡献极少。斜长角闪岩稀土元素配分型式近于平坦[(La/Yb)N=0.80~1.10],无明显Ce异常(Ce/Ce*=0.95~0.99)与Eu异常(Eu/Eu*=0.88~1.16);其大离子亲石元素富集,高场强元素无明显亏损。地球化学分析表明,斜长角闪岩原岩可能为产于弧后盆地的玄武质火山岩。锆石形态与微量元素分析显示,斜长角闪岩中的锆石均属岩浆成因。SIMS锆石U-Pb定年显示斜长角闪岩原岩形成于2533±11Ma,代表了歪头山BIF的成矿年龄;在玄武质岩浆喷发过程中,还捕获了一组年龄为2610±5Ma的锆石。电子探针分析显示磁铁矿成分纯净(FeOT=92.04%~93.05%),其标型组分特征暗示歪头山BIF属沉积变质型铁矿。综合分析认为,歪头山铁矿属Algoma型BIF,成矿与弧后盆地岩浆活动密切相关,指示了新太古代末华北克拉通普遍发育的一期BIF成矿事件。 相似文献
10.
Lycian ophiolites located in the Western Taurides, are cut at all structural levels by dolerite and gabbro dikes. The dolerite
dikes from this area are both pristine and metamorphosed. The non-metamorphosed dikes are observed both in the peridotites
and in the metamorphic sole rocks. Accordingly, the non-metamorphosed dikes cutting the metamorphic sole were generated after
cooling of the metamorphic sole rocks. The metamorphosed dolerite dikes are only observed in the peridotites. The physical
conditions and timing of the metamorphism for the metamorphosed dolerite dikes are similar to those of the metamorphic sole
rocks of the Lycian ophiolites suggesting that the metamorphosed dolerite dikes were metamorphosed together with the metamorphic
sole rocks. Therefore, the dike injections in the western part of the Tauride Belt Ophiolites occurred before and after the
generation of the metamorphic sole rocks. All metamorphosed and non-metamorphosed dikes are considered to have the same origin
and all of them are subduction-related as inferred from whole-rock geochemistry and lead isotopes. Lead isotope compositions
of whole rocks of both dike groups cluster in a narrow field in conventional Pb isotope diagrams (206Pb/204Pb = 18.40–18.64; 207Pb/204Pb = 15.56–15.58; 208Pb/204Pb = 38.23–38.56) indicating a derivation from an isotopically homogeneous source. On the 207Pb/204Pb versus 206Pb/204Pb diagram, isotope compositions of the dikes plot slightly below the orogen curve suggesting contributions from mantle reservoir
enriched by subducted oceanic lithosphere. Such a signature is typical of island arc magmatic rocks and supports the formation
of the investigated rocks in a subduction-related environment. 相似文献