南秦岭铁瓦殿岩体的成岩时代及地质意义   总被引：4，自引：0，他引：4  

杨朋涛  刘树文  李秋根  王宗起  王伟  白翔 《地质学报》2012,86(9):1525-1540

铁瓦殿岩体位于陕西省南部汉阴县、石泉县和紫阳县交界部位,大地构造位置属于南秦岭构造带南部,主要由闪长岩、石英闪长岩、石英二长闪长岩、石英二长岩和二长花岗岩组成。LA-ICP-MS锆石U-Pb同位素定年结果表明铁瓦殿岩体存在3阶段的岩浆侵位:早期阶段的石英二长岩形成于742±5Ma,中期阶段的石英闪长岩、石英二长闪长岩及二长花岗岩形成于～722Ma;晚期阶段的石英闪长岩形成于704±4Ma。通过与扬子北缘汉南杂岩中的中酸性火山岩及侵入岩的岩石组合和形成时代对比,发现铁瓦殿深成侵入岩与扬子克拉通北缘汉南杂岩中中酸性侵入岩具有相似的岩石组合和形成时代,表明它们经历了相似的构造-岩浆演化。铁瓦殿岩体是南秦岭地区新元古代俯冲作用相关的重要地质记录。  相似文献   

Genesis and evolution of subduction-zone andesites: evidence from melt inclusions     

《International Geology Review》2012,54(10):1179-1190

Andesite magmatism plays a major role in continental crustal growth, but its subduction-zone origin and evolution is still a hotly debated topic. Compared with whole-rock analyses, melt inclusions (MIs) can provide important direct information on the processes of magma evolution. In this article, we synthesize data for melt inclusions hosted by phenocrysts in andesites, extracted from the GEOROC global compilation. These data show that melt inclusions entrapped by different phenocrysts have distinct compositions: olivine-hosted melt inclusions have basalt and basaltic andesite compositions, whereas melt inclusions in clinopyroxene and othopyroxene are mainly dacitic to rhyolitic. Hornblende-hosted melt inclusions have rhyolite composition. The compositions of melt inclusions entrapped by plagioclase are scattered, spanning from andesite to rhyolite. On the basis of the compositional data, we propose a mixing model for the genesis of the andesite, and a two-chamber mechanism to account for the evolution of the andesite. First, andesite melt is generated in the lower chamber by mixing of a basaltic melt derived from the mantle and emplaced in the lower crust with a felsic melt resulting from partial melting of crustal rocks. Olivine and minor plagioclase likely crystallize in the lower magma chamber. Secondly, the andesite melt ascends into the upper chamber where other phenocrysts crystallize. According to SiO₂-MgO diagrams of the MIs, evolution of the andesite in the upper chamber can be subdivided into two distinct stages. The early stage (I) is characterized by a phenocrystal assemblage of clinopyroxene + othopyroxene + plagioclase, whereas the late stage (II) is dominated by crystallization of plagioclase + hornblende.  相似文献   

贵州独山-广西天峨地区中二叠世岩相古地理特征、相类型及几何形态     

谯文浪  安亚运  王波  马义波  唐佐其 《贵州地质》2012,29(4):301-306

通过对贵州独山-广西天峨地区二叠系岩石地层、生物组合及沉积相的详细调查,重点收集中二叠时期岩性组合特征、生物组合特征和相等方面资料。从研究区该时期沉积旋回性、沉积相类型、岩相组合等进行研究,得出研究区为台地边缘沉积环境,并弄清了该台地边缘类型、几何形态及岩相古地理等。为区域上建立完善该时期的岩相古地理提供了宝贵的资料。  相似文献   

Age and paleoclimatic implication of middle to upper Miocene plant-bearing strata in the southern Kanazawa area,Ishikawa Prefecture,Central Japan,based on refined Neogene palynostratigraphy in the Hokuriku district     

Shota Teduka  Toshihiro Yamada 《Island Arc》2021,30(1):e12428

13–8 Ma (middle to late Miocene) is a key period for understanding how the unique vegetation was established in Japan. Palynostratigraphy is useful for estimating the ages of plant-bearing strata deposited in shallow-marine and non-marine environments, but has low temporal resolution for this key period in Japan. We compiled Neogene and early Quaternary palynological records for the Hokuriku district of Central Japan to clarify palynostratigraphic events that may improve the temporal resolution. Our results showed that palynoassemblages changed considerably during 10–6.4 Ma in the Hokuriku district, following a relatively stable period during 13–10 Ma. We found that evergreen Quercus abundance increased at 11.5–10 Ma. We used these palynostratigraphic signatures, along with other biostratigraphic markers, to infer the ages of the Miocene plant-bearing Saikawa and Koderayama Formations in the southern Kanazawa area of Ishikawa Prefecture in the Hokuriku district. The ages of the Saikawa and Koderayama Formations were inferred as ~13 and 10–6.4 Ma, respectively. The palynoflora of the Koderayama Formation shows floristic similarity to that of present south China, implying that the unique flora of Japan established after the age of the Koderayama Formation.  相似文献   

Eemian landscape response to climatic shifts and evidence for northerly Neanderthal occupation at a palaeolake margin in northern Germany     

Michael Hein  Brigitte Urban  David Colin Tanner  Anton Hermann Buness  Mario Tucci  Philipp Hoelzmann  Sabine Dietel  Marie Kaniecki  Jonathan Schultz  Thomas Kasper  Hans von Suchodoletz  Antje Schwalb  Marcel Weiss  Tobias Lauer 《地球表面变化过程与地形》2021,46(14):2884-2901

The prevailing view suggests that the Eemian interglacial on the European Plain was characterized by largely negligible geomorphic activity beyond the coastal areas. However, systematic geomorphological studies are sparse. Here we present a detailed reconstruction of Eemian to Early Weichselian landscape evolution in the vicinity of a small fingerlake on the northern margin of the Salzwedel Palaeolake in Lower Saxony (Germany). We apply a combination of seismics, sediment coring, pollen analysis and luminescence dating on a complex sequence of colluvial, paludal and lacustrine sediments. Results suggest two pronounced phases of geomorphic activity, directly before the onset and at the end of the Eemian period, with an intermediate period of pronounced landscape stability. The dynamic phases were largely driven by incomplete vegetation cover, but likely accentuated by fluvial incision in the neighbouring Elbe Valley. Furthermore, we discovered Neanderthal occupation at the lakeshore during Eemian pollen zone (PZ) E IV, which is chronologically in line with other known Eemian sites of central Europe. Our highly-resolved spatio-temporal data substantially contribute to the understanding of climate-induced geomorphic processes throughout and directly after the last interglacial period. It helps unraveling the landscape dynamics between the coastal areas to the north and the loess belt to the south.  相似文献   

翡翠的化学成分和矿物组成特征   总被引：2，自引：0，他引：2  

唐俊  奥岩 《安徽地质》2000,(1)

对不同颜色的翡翠进行了较系统的化学成分和矿物成分研究，发现翡翠的化学成分和矿物 成分与翡翠的颜色之间有一定的内在规律。随着翡翠的绿色由浅变深，Ｃｒ、Ｍｇ、Ｃａ等元素的含量逐渐增 高，硬玉和绿辉石矿物成分逐渐向透辉石－钙铁辉石系列演化。  相似文献   

Danish pollen records radiocarbon-dated to between 50000 and 57000 yr BP     

Else Kolstrup 《第四纪科学杂志》1992,7(2):163-172

Radiocarbon-dated pollen diagrams from four Danish sequences are presented in their sedimentological context. The pollen diagrams indicate the former presence of stands of Betula and Pinus and of Ericales, Poaceae, Cyperaceae and other herbs. From a straightforward comparison with other diagrams, one of the present series is tentatively correlated with part of the Early Weichselian Brørup Interstadial and two with parts of the Odderade Interstadial, which has not been demonstrated previously in Denmark. One diagram and part of another do not seem to match previously published records in northwest Europe. Yet, the possibility that the sediments date to hitherto unrecorded periods with environmental conditions similar to those reflected in known Weichselian deposits is not excluded. In two of the sequences high percentages of charcoal particles suggest the former occurrence of fires, which influenced the palaeovegetation and soil surface stability. It is suggested that counting of charcoal particles is included in future investigations in order to establish whether periods with fires can be identified in the sedimentary sequences.  相似文献   

山西中条山地区表土花粉分析   总被引：22，自引：2，他引：20  

姚祖驹 《地理学报》1989,44(4):469-477

本文通过对中条山地区表土花粉的百比图谱分析和几何平均法线性回归分析认为：表土花粉谱基本上反映了当地植被的基本特征，但不能准确反映植物在植被中的数量关系。几何平均法回归分析是研究植物和花粉数量关系的一个切实可行的方法。并对影响回归分析结果的几种主要因素进行了讨论。  相似文献   

Glacier response to climatic change during the Loch Lomond Stadial and early Flandrian: Geomorphological and palynological evidence from the Isle of Skye,Scotland     

Douglas I. Benn  J. John Lowe  Michael J. C. Walker 《第四纪科学杂志》1992,7(2):125-144

The deglaciation of Skye at the close of the Loch Lomond Stadial is assessed on the basis of detailed geomorphological mapping and pollen-stratigraphic correlations. It is concluded that deglaciation proceeded in two distinct stages. The first was marked by numerous glacier stillstands and readvances, while uninterrupted retreat and local glacier stagnation occurred during the second and final stage. The pollen evidence indicates that the first stage was well advanced before the marked thermal improvement at the start of the Flandrian, and it is inferred that initial glacier retreat occurred in response to a decline in precipitation in the later part of the Loch Lomond Stadial. The first stage of glacier retreat continued into the early Flandrian, during which climatic amelioration was interrupted briefly. Final deglaciation appears to have occurred rapidly in response to sustained temperature increases. The collective evidence also indicates spatial variations in the timing of deglaciation, which appear to reflect differences in glacier morphology.  相似文献   

Resolving the chronology of recent lake sediments: an example from Devils Lake,North Dakota     

Heather A. Jacobson  Daniel R. Engstrom 《Journal of Paleolimnology》1989,2(2):81-97

Devils Lake is a closed, saline lake in North Dakota; it is typical of lake basins in the Great Plains Region, where windy conditions and fluctuating water-levels disturb sediment and confound chronostratigraphy. Pollen analysis and ²¹⁰Pb dating of two cores collected from bathymetrically contrasting embayments demonstrate (1) how certain agriculture-related pollen types differ in their value as chronostratigraphic markers, (2) how pollen and ²¹⁰Pb stratigraphies can be reconciled to determine the approximate depth of sediment mixing, and (3) the importance of coring-site selection, especially in lakes with unstable sedimentary conditions.  相似文献