Geochronology of Pliocene volcanism in the Dzhavakheti Highland (the Lesser Caucasus). Part 2: Eastern part of the Dzhavakheti Highland. Regional geological correlation     

V. A. Lebedev  S. N. Bubnov  O. Z. Dudauri  G. T. Vashakidze 《Stratigraphy and Geological Correlation》2008,16(5):553-574

The results of isotopic-geochronological study of the Pliocene volcanic rocks in reference sections and volcanic edifices of eastern part of the Dzhavakheti Highland (the northwestern Lesser Caucasus) are considered. The isotopic-geochronological data obtained here are correlated with data on western part of the Dzhavakheti Highland, which have been considered in previous part of this work. Based on correlation, time spans of principal volcanic events of the Pliocene in the study region as a whole are determined, and general trends of the young magmatism evolution within the region are established. In sum, the isotopic-geochronological dates evidence that the Pliocene magmatism of the Dzhavakheti Highland developed practically without essential breaks during the period of about 2 Ma long, from 3.75 to 1.75–1.55 Ma ago. The areal basic volcanism that was most widespread at that time is divisible into five discrete phases according to the isotopic dates obtained. Comparatively short pauses, which separated these phases of magmatic activity, were a few hundreds thousand years long, not more. Chemical composition of moderately acidic to silicic volcanics, which are of a limited distribution in the Dzhavakheti Highland, and their age relations with basic lavas of the region suggest that they are most likely the differentiation products of parental basic mantle-derived magmas. The analyzed distribution of volcanic centers, which erupted basic lavas of the Dzhavakheti Highland, evidence that first two phases of basic magmatism were connected here with volcanic activity in southwestern part of the region (northern termination of the Egnakhag Ridge), whereas activity of volcanoes situated on the east, predominantly in water-shed part and on slopes of the submeridional Dzhavakheti Ridge, controlled development of the third and fourth phases. Consequently, magmatic activity of the Pliocene stage in history of the Neogene-Quaternary magmatism of the Dzhavakheti Highland laterally migrated from the west to the east, being controlled by development of regional submeridional extension zones. Volcanic ridges marking the latter are formed by volcanic edifices, which are amalgamated at their bases and have erupted lavas of close age and composition. The migration of volcanic activity can be described in terms of the “domino effect,” when cessation of volcanism in one zone led to formation of the other submeridional zone of extension and magmatic activity displaced from the west eastward in sublatitudinal direction. In general, evolution of the Pliocene magmatism of the Dzhavakheti Highland, was similar, despite the essential regional peculiarities, to the generalized trend of magmatism evolution in the continental rifts and intraplate zones of the “hot-spot” type.  相似文献   

望天鹅火山岩石地球化学特征及其成因   总被引：1，自引：1，他引：0  

陈晓雨  刘嘉麒  郭正府  路放  江东辉 《岩石学报》2008,24(11):2576-2584

东北吉林望天鹅新生代火山岩（7．04—1．86Ma）主要由玄武粗安岩和碱性流纹岩组成。玄武粗安岩的SiO2介于49．38％-53．31％之间;K2O＋Na2O为4．27％-7．72％;∑REE为163．69×10^-6-258．55×10^-6,Eu异常不明显,δEu为0．72～1．17;碱性流纹岩具高SiO2（70．39％～71．49％）含量,高碱（K2O＋Na2O为9．28％～9．49％）,高稀土总量（∑REE介于309．30×10^-6～465．03×10^-6之间）,明显的Eu负异常,3Eu为0．52～0．71。碱性流纹岩的微量元素含量较玄武粗安岩高,且具有明显的Sr、P、Ti负异常。望天鹅火山岩的^87Sr／^86Sr比值在0．705156-0．709029之间,而^144Nd／^143Nd比值变化较小,介于0．512295～0．512602之间;放射性成因Pb同位素变化范围也较小,^206Ph／^204Pb为17．254～18．090,^207Ph／^204Pb为15．460～15．507,^208Pb／^204Ph为37．278—38．048。综合分析火山岩的主量元素、微量元素和Sr-Nd—Pb同位素特点,初步认为望天鹅火山的玄武粗安岩和碱性流纹岩具有相同的地幔源区。玄武粗安岩起源于微弱富集上地幔,在上升过程中结晶分异形成了碱性流纹岩。  相似文献   

Timing of low-temperature metamorphism and cooling of the Paleozoic and Mesozoic formations of the Bükkium,innermost Western Carpathians,Hungary     

P. Árkai  K. Balogh  I. Dunkl 《International Journal of Earth Sciences》1995,84(2):334-344

K-Ar ages of illite-muscovite and fission track ages of zircon and apatite were determined from various lithotypes of the Bükkium, which forms the innermost segment of the Western Carpathians. The stratigraphic ages of these Dinaric type formations cover a wide range from the Late Ordovician up to the Late Jurassic. The grade of the orogenic dynamo-thermal metamorphism varies from the late diagenetic zone through the anchizone up to the epizone (chlorite, maximally biotite isograd of the greenschist facies). The K-Ar system of the illite-muscovite in the < 2 m grain-size fraction approached equilibrium only in epizonal and high-temperature anchizonal conditions. The orogenic metamorphism culminated between the eo-Hellenic (160-120 Ma) phase connected to the beginning of the subduction in the Dinarides, and the Austrian (100-95 Ma) phase characterized by compressional crustal thickening. No isotope geochronological evidence was found for proving any Hercynian recrystallization. The stability field of fission tracks in zircon was approached using the thermal histories of the different tectonic units. A temperature less than 250°C and effective heating time of 20–30 Ma had only negligible effects on the tracks, whereas total annealing was reached between 250 and 300°C. Apatite fission track ages from the Paleozoic and Mesozoic formations show that the uplift of the Bükk Mountains occurred only in the Tertiary (not earlier than ca. 40 Ma ago). Thermal modeling based on apatite fission track length spectra and preserved Paleogene sediment thickness data proved that the Late Neogene burial of the recently exhumed plateau of the Bükk Mountains exceeded 1 km.  相似文献   

海绿石 K-Ar、40Ar/39Ar 年代学研究   总被引：1，自引：0，他引：1  

李明荣  王松山  裘冀 《地球学报》1994,15(Z1):218-225

海绿石是与沉积岩同时形成的高钾层状硅酸盐自生矿物，其 K-Ar、40Ar/39Ar 年龄存在失真现象。笔者认为，引起年龄失真的主要原因是由于该矿物结构中含有可膨胀层。通过测量可膨胀层含量及中子活化过程中39Ar的丢失率，使可对海绿石常规 K-Ar、40Ar/39Ar 年龄进行校正，得到其年龄校正公式。  相似文献   

西昆仑新藏公路118～323km段基性、酸性岩脉K—Ar年龄   总被引：3，自引：1，他引：3  

计文化周辉  李亚民 《地质通报》2005,24(3):243-245

在西昆仑西段新藏公路沿线广泛发育数量众多的岩脉，野外出露有煌斑岩脉、辉绿岩脉、闪长岩脉、花岗岩脉。对以上岩脉进行了全岩K-Ar同位素测年，其侵位年龄与该区的地质构造事件有很好的对应关系：辉绿岩脉273～280Ma的侵位年龄对应着弧后扩张的时间，闪长岩脉和花岗岩脉230～244Ma的侵位年龄对应着碰撞造山的时间。  相似文献   

Correlation of the Late Cenozoic endogenic events and climatic variations in Central Asia     

V. V. Yarmolyuk  M. I. Kuzmin 《Stratigraphy and Geological Correlation》2006,14(2):105-125

Trend of climatic changes in geological history of the Earth was determined by gradual decrease in the global surface temperature. Substantial deviations from this trend depended on the prevalent type of volcanism: predominantly explosive volcanism at convergent boundaries between lithospheric plates led to cooling and onset of glacial epochs, while intense intraplate volcanism strengthened greenhouse effect and resulted in global warming. During cold epochs, orogenic processes played an important role in climatic variations. The most frequent and regular climatic variations are controlled by the Earth position in solar orbit (Milankovitch cycles). The Late Cenozoic variations of cold climate were interrelated with orogenic processes caused by collision between the Indian and North Asian lithospheric plates. The first event of considerable cooling in the Northern Hemisphere (2.8–2.5 Ma ago) coincided with a rapid growth of mountains throughout the collision belt. The Tibetan Plateau formed in South Asia. In Central Asia, the large (> 1.5 × 10⁶ km²) Khangai-Altai-Sayan mountain system appeared 3 Ma ago. Total area subjected to orogenic processes in Central and South Asia exceeded 9 × 10⁶ km². The intense intraplate volcanism suggests that sublithospheric mantle was involved into orogenic processes. Alternation of glacial and interglacial climatic epochs during the last 1.8 m.y. is recorded in Central Asia. These climatic variations are compatible with the Milankovitch cycles. As is established, climatic events recognizable in the Baikal sedimentary record are correlative with interglacial and glacial epochs detectable in volcanic lavas of the East Sayan Mountains. There are indications of lava eruptions into ice during the cold periods. It is assumed therefore that all the cooling epochs detectable in the Baikal sedimentary record after 1.8 Ma were associated with development of mountain glaciation that formed glacial sheet up to 3 km thick and 100 000 km² in size. During the Brunhes Chron, there were eight glaciations at least. The endogenic (volcanism and orogeny) and exogenic (glaciation) processes during the last 3 m.y. are shown to be correlative. The intermittent development and degradation of thick ice sheets was responsible for oscillation of lithospheric load on the asthenosphere, and this caused periodical magma generation in marginal parts of volcanic provinces.  相似文献   

Polymetallic and Au-Ag Mineralizations at the Mutnovskoe Deposit in South Kamchatka, Russia     

Ryohei Takahashi    Hiroharu Matsueda  Victor M. Okrugin  Shuji Ono 《Resource Geology》2006,56(2):141-156

Abstract. The Mutnovskoe deposit located in the Porozhisto‐Asachinskaya metallogenic province of South Kamchatka, Russia, is a polymetallic vein and Au‐Ag quartz vein associated type of hydrothermal deposit. The Mutnovskoe deposit is located inside a paleo‐caldera structure at the center of the Mutnovsko‐Asachinskaya geothermal field of Pliocene ‐ Quaternary age, where active gold deposition is identified in hot spring precipitate. The Mutnovskoe deposit is subdivided into the north flank, the central flank and the south flank based on the vein distributions and mineral parageneses. The mineralized vein system is oriented N‐S hosted in diorite ‐ gabbroic diorite stock, volcanic rocks and sedimentary rocks of Miocene ‐ Pleistocene age. The mineralization stage I (polymetallic vein) mainly in the central and the south flanks is Zn‐Pb‐Cu‐Au‐Ag contained in sphalerite, galena and tetrahedrite‐tennantite group mineral. The stage II (Au‐Ag quartz vein) occurs in the north and the central flanks. The stage III (Mn‐sulfide and Mn‐Ca‐carbonate vein) occurs in the whole deposit area. Stage II is the typical Au‐Ag quartz‐adularia vein of low‐sulfidation type. Stage III is alabandite‐rhodochrosite‐quartz‐calcite vein. The K‐Ar ages are 1.3±0.1 Ma for stage I sericite in alteration zone, and 0.7±0.1 Ma for the stage II adularia in mineralized vein. Based on the fluid inclusion study, range of ore forming temperature of the Mutnovskoe deposit is 200 to 260d?C (av. 230d?C). Salinities of fluid inclusions indicate 2.2 to 5.7 wt% NaCl in sphalerite and 0.8 to 3.3 wt% NaCl in quartz for the stage I. Mineral paragenesis of the polymetallic vein (stage I) is characterized by a district zoning of tennantite and Cd‐rich sphalerite in the south flank and tetrahedrite and Mn‐rich sphalerite in the central flank, which is due to the fractional crystallizations of ore‐forming fluid. Depositional condition of the low sulfidation state is inferred for the Mutnovskoe deposit, where the polymetallic vein of the south flank is in relatively higher sulfidation state than the central flank.  相似文献   

甘肃北山地区煌斑岩的年代学和地球化学及其壳幔作用过程讨论   总被引：10，自引：10，他引：10  

刘畅赵泽辉  郭召杰 《岩石学报》2006,22(5):1294-1306

柳园地区下二叠统中发育多条煌斑岩脉，并且在空间上和二叠纪玄武岩、辉长岩和超镁铁岩关系密切。煌斑岩K-Ar、Ar-Ar定年测定表明岩脉侵入时间在220～240Ma之间。地球化学表现为富集大离子亲石元素和轻稀土，亏损高场强元素（Ta-Nb-Ti、Zr、Hf）的特征。Sr-Nd同位素以高的（^87Sr／^86Sr）i 0．708616～0．708744，较低的εNd（t）-3．89～-2．14为特征。Nb／Ta（16．16～19．14，相对于原始地幔的17．5）、Zr／Hf（42．14～43．95，相对于原始地幔的36．7）以及Ta．Nd．Ti的亏损，显示源区可能和早期俯冲洋壳或造山带根部拆沉组份脱水、富集流体交代岩石圈地幔有关。本区煌斑岩为二叠纪裂谷发展到后期，富集流体上涌，交代岩石圈地幔部分熔融，并沿断裂侵入的产物；是二叠纪开始的裂谷作用和火山活动晚期阶段产物。  相似文献   

Isotopic Evaluation on the Genesis of the Kanamaru Pegmatite Deposit, Niigata Prefecture, Japan     

Shunso Ishihara    Koji Hamano  Asami Ikegami 《Resource Geology》1998,48(1):1-6

Abstract: The Kanamaru pegmatite is one of the two largest pegmatite deposits in Japan and is rich in K–feldspar, which is maximum microcline. The mica minerals and microcline from this ore deposit were studied for K-Ar ages and δ¹⁸O ratios. Biotite gives K-Ar age of 78. 5 Ma, but microcline is much younger in age of 66. 0 and 58. 3 Ma. Oxygen isotopic equilibrium temperature of the biotite-quartz pair is 625°C. Using closure temperature of the K-Ar system for biotite and microcline, cooling rate of the pegmatite is calculated to be 88°C/m. y. at the beginning but 12°C/m. y. in the later period of the cooling history. The microcline is slightly depleted in ¹⁸O, yielding apparent equilibrium temperatures of 230°C and 155°C on quartz-microcline pairs. It is suggested that the fluid phase, magmatic and partly meteoric in origin, contained in the solidifying pegmatite, was interacted with the original orthoclase and converted it to microcline during the subsolidus stage.  相似文献   

恩施球粒陨石热历史及原始氩特征     

王松山  桑海清  裘冀 《地质论评》1997,43(3):303-309

H_s型恩施球粒陨石K-Ar年龄为4503±91Ma,~(40)Ar-~(39)Ar坪年龄为4518±8Ma,总气体年龄为4515±23Ma,等时线年龄为4505±16Ma,年龄的一致性表明该陨石未经受过明显的热扰动,它是我国首次发现的Ar保存年龄高达45亿年以上的陨石。陨石形成早期有过短期的快速冷却。陨石母体在4.66±0.04Ma时破裂。恩施球粒陨石原始捕获(~(40)Ar/~(36)Ar)_t为0.89±0.44,推测4.5Ga前太阳风中~(40)Ar/~(36)Ar近于l。  相似文献