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1.
The Zhaima gold–sulfide deposit is located in the northwestern part of the West Kalba gold belt in eastern Kazakhstan. The mineralization is hosted in Lower Carboniferous volcanic and carbonate rocks formed under conditions of marginal-sea and island-arc volcanic activity. The paper considers the mineralogy and geochemistry of primary gold–sulfide ore and Au-bearing weathering crusts. Au-bearing arsenopyrite–pyrite mineralization formed during only one productive stage. Disseminated, stringer–disseminated, and massive rocks are enriched in Ti, Cr, V, Cu, and Ni, which correspond to the mafic profile of basement. The main ores minerals are represented by finely acicular arsenopyrite containing Au (up to few tens of ppm) and cubic and pentagonal dodecahedral pyrite with sporadic submicroscopic inclusions of native gold. The sulfur isotopic composition of sulfides is close to that of the meteoritic standard (δ34S =–0.2 to +0.2). The 40Ar/39Ar age of three sericite samples from ore veinlets corresponds to the Early Permian: 279 ± 3.3, 275.6 ± 2.9, and 272.2 ± 2.9 Ma. The mantle source of sulfur, ore geochemistry, and spatial compatibility of mineralization with basic dikes allow us to speak about the existence of deep fluid–magmatic systems apparently conjugate with the Tarim plume.  相似文献   

2.
Our results present a taxonomic and palaeoecological study on non-marine gastropods from the latest Cretaceous to Paleocene deposits of the Pingyi Basin, Shandong Province, eastern China. These gastropods are systematically described: three species belonging to three genera including Physa dongtaiensis Gu, 1989, Hydrobia datangensis Yü, 1977, and the newly established species Cyathopoma pingyiensis sp. nov.; two indeterminata genera and species including Truncatelloidea gen. et sp. indet., and Pomatiopsidae gen. et sp. indet. Among them, Truncatelloidea gen. et sp. indet. and Cyathopoma pingyiensis sp. nov. are the dominant species with the longest record. Cyathopoma pingyiensis, sp. nov. is the earliest representative of this widely distributed Asian extant genus. Sedimentological facies analysis of the gastropod-bearing beds suggested that Truncatelloidea gen. et sp. indet. lived in a small pond with a river inlet and a shallow lake, while Ph. dongtaiensis, ?Pomatiopsidae gen. et sp. indet, and ?H. datangensis only thrived in the shallow lake. Cyathopoma pingyiensis sp. nov. inhabited the land area around the shallow lake. Our results showed that no significant species change of the gastropod fauna across the K/Pg (Cretaceous/Paleogene) boundary was observed in the Pingyi Basin.  相似文献   

3.
Late Pleistocene tephras derived by large explosive volcanic eruptions are widespread in the Mediterranean and surrounding areas. They are important isochronous markers in stratigraphic sections and therefore it is important to constrain their sources. We report here tephrochronology results using multiple criteria to characterize the volcanic products of the Late Pleistocene Ciomadul volcano in eastern–central Europe. This dacitic volcano had an explosive eruption stage between 57 and 30 ka. The specific petrological character (ash texture, occurrence of plagioclase and amphibole phenocrysts and their compositions), the high-K calc-alkaline major element composition and particularly the distinct trace element characteristics provide a strong fingerprint of the Ciomadul volcano. This can be used for correlating tephra and cryptotephra occurrences within this timeframe. Remarkably, during this period several volcanic eruptions produced tephras with similar glass major element composition. However, they differ from Ciomadul tephras by glass trace element abundances, ratios of strongly incompatible trace elements and their mineral cargo that serve as discrimination tools. We used (U-Th)/He zircon dates combined with U-Th in situ rim dates along with luminescence and radiocarbon dating to constrain the age of the explosive eruptions of Ciomadul that yielded distal tephra layers but lack of identified proximal deposits.  相似文献   

4.
Noble gas recharge temperatures (NGTs) and radiocarbon ages were determined for 43 groundwater samples collected in the eastern Espa?ola Basin, New Mexico (USA), to identify mountain-block recharge in waters <10 thousand years (ka) old and to evaluate possible changes in mountain-block recharge over the past ??35?ka. For Holocene samples from the southeastern area, NGTs are dominantly 2?C4° cooler than the measured water-table temperature near the mountain front. Computed minimum mountain-block recharge fractions are dominantly 0.2?C0.5, consistent with previous large mountain-block recharge estimates. NGTs do not display the distinct low during the last glacial maximum observed in other paleorecharge studies; samples recharged 15?C25?ka ago are on average only 1.3° cooler than Holocene samples. Instead, samples with the coldest NGTs were recharged 25?C35?ka ago. A proposed explanation is that higher precipitation rates during the last glacial maximum resulted in a lower mean recharge elevation for the basin, essentially buffering the effect of the lower mean annual air temperature and producing NGTs similar to the Holocene. In the period preceding the last glacial maximum, precipitation rates more like today??s resulted in Holocene-like mountain-block recharge fractions, producing a mean NGT ??5° cooler than the Holocene, as expected.  相似文献   

5.
The Bagassi gold deposits are situated on the West African craton and hosted in Palaeoproterozoic rocks of the Houndé greenstone belt, southwest Burkina Faso. High-grade gold mineralisation is hosted in quartz–gold ± pyrite veins-lodes (V1A), in dilational zones and narrow shears in the Bagassi granitoid, and forms the majority of the resource–reserve portfolio in the Bagassi exploration permits, with gold grades of 18–21 g/t. Shear hosted gold-pyrite mineralisation in quartz veins in dilational jogs (V1B) occurs along narrow discontinuous shear zones that trend north-northwest in Birimian-aged metabasaltic units, and forms a secondary gold resource. Gold mineralisation is restricted to formation in the late Eburnean Orogeny and formed during a change from east-west to transcurrent compression and shearing. The Bagassi deposits demonstrate that granitoids emplaced prior to onset of the Eburnean Orogeny represent viable gold mineralisation in host rocks that are increasingly seen to be associated with significant gold resources.  相似文献   

6.
《China Geology》2018,1(4):477-484
Lichi mélange, located in the southern coastal range, eastern Taiwan, China, is a typical tectonic mélange of the plate’s boundary zone between the Eurasian Plate and the Philippine Sea Plate. It formed during the collision of the Luzon arc with the Eurasian Continent (arc-continent collision). It is composed of sandstone and/or mudstone matrix and many kinds and sizes of rock fragments, including some sedimentary rocks, volcanic rocks and a few metamorphic rocks. The serpentinite is one of the common fragments in the Lichi mélange. By the petrographic characteristics and the zircon U-Pb chronology analyses, protolith of the serpentinite is peridotite, the age is 17.7 ± 0.5 Ma. Taking the tectonic background into account, it is inferred that the serpentinite (serpentinised peridotite) come from the forearc basin (the North Luzon Trough) and was taken into the mélange by a second thrust westwards. The origin of the serpentinite in Lichi mélange is helpful to understand the formation of the Lichi mélange and can provide reliable detailed information for the study of the arc-continent collision orogenic activity in and offshore Taiwan.  相似文献   

7.
The Ching-dar syncline is located to the west of the city of Birjand, in the east of han. The ca. 500 m thick studied section at the eastern flank of the syncline contains a sequence of almost continuous shallow- marine limestones that exhibit no major sedimentary breaks or evidence for volcanic activity. Skeletal grains consist of large benthic foraminifera and green algae whereas non-skeletal grains are mostly peloids and intraclasts. They were deposited on a shallow-marine carbonate ramp. The limestones have undergone extensive diagenetic processes with varying intensities, the most important of which are micritization, cementation, compaction （chemical and mechanical）, internal filling and stylolitization. Chemical analysis of the limestone samples revealed high calcium and low magnesium content. Major and minor element values were used to determine the original carbonate mineralogy of these lime- stones. Petrographic evidence and elemental values indicate that calcite was the original carbonate mineral in the limestones of the Ching-dar syncline. The elemental composition of the Ching-dar car- bonates also demonstrates that they have stabilized in a meteoric phreatic environment. Variation of Sr/ Ca vs. Mn values suggests that diagenetic alteration occurred in an open geochemical system.  相似文献   

8.
This article discusses the Meso–Cenozoic thermal history, thermal lithospheric thinning, and thermal structure of the lithosphere of the Bohai Bay Basin, North China. The present-day thermal regime of the basin features an average heat flow of 64.5 ± 8.1 mW m–2, a lithospheric thickness of 76–102 km, and a ‘hot mantle but cold crust’-type lithospheric thermal structure. The Meso–Cenozoic thermal history experienced two heat flow peaks in the late Early Cretaceous and in the middle to late Palaeogene, with heat flow values of 82–86 mW m?2 and 81–88 mW m?2, respectively. Corresponding to these peaks, the thermal lithosphere experienced two thinning stages during the Cretaceous and Palaeogene, reaching a minimum thickness of 43–61 km. The lithospheric thermal structure transformed from the ‘hot crust but cold mantle’ type in the Triassic–Jurassic to the ‘cold crust but hot mantle’ type in the Cretaceous–Cenozoic, according to the ratio of mantle to surface heat flow (qm/qs). The research on the thermal history and lithospheric thermal structure of sedimentary basins can effectively reveal the thermal regime at depth in the sedimentary basins and provide significance for the study of the basin dynamics during the Meso–Cenozoic.  相似文献   

9.
Interpretations of palaeodepositional environments are important for reconstructing Earth history. Only a few maps showing the Jurassic depositional environments in eastern Australia currently exist. Consequently, a detailed understanding of the setting of Australia in Gondwana is lacking. Core, wireline logs, two-dimensional and three-dimensional seismic from the Precipice Sandstone and Evergreen Formation in the Surat Basin have been used to construct maps showing the evolution of depositional environments through the Early Jurassic. The results indicate the succession consists of three third-order sequences (Sequence 1 to Sequence 3) that were controlled by eustatic sea level. The lowstand systems tract in Sequence 1 comprises braidplain deposits, confined to a fairway that parallels the basin centre. The strata were initially deposited in two sub-basins, with rivers flowing in different orientations in each sub-basin. The transgressive systems tract of Sequence 1 to lowstand systems tract of Sequence 3 is dominated by fluvio–deltaic systems infilling a single merged basin centre. Finally, the transgressive and highstand systems tracts of Sequence 3 show nearshore environments depositing sediment into a shallow marine basin. In the youngest part of this interval, ironstone shoals are the most conspicuous facies, the thickness and number of which increase towards the north and east. This study interprets a corridor to the open ocean through the Clarence–Moreton Basin, or the Carpentaria and Papuan basins, evidence of which has been eroded. These results challenge a commonly held view that eastern Australia was not influenced by eustasy, and propose a more dynamic palaeogeographic setting comprising a mixture of fluvial, deltaic and shallow marine sedimentary environments. This work can be used to unravel the stratigraphic relationships between Mesozoic eastern Australian basins, or in other basins globally as an analogue for understanding the complex interplay of paralic depositional systems in data poor areas.  相似文献   

10.
Sa'ar–Nayfa reservoir is mainly made up of carbonate sediments with bands of shale that contain a substantial amount of proven oil in the Hiswah Oilfield, Sayun–Masila Basin, eastern Yemen. Several vertical wells have been drilled and penetrated these sequences. This study is concerned on the petrophysical evaluation and well log analysis of the Lower Cretaceous of 11 wells at the Hiswah Oilfield, Hadramawt Governorate, eastern Yemen. Computer-assisted log analyses were used to evaluate the petrophysical parameters such as shale volume, total porosity, effective porosity, water saturation, hydrocarbon saturation, flushed zone saturation and reservoir and pay flags. Cross-plots of the petrophysical parameters versus depth were illustrated. The Lower Cretaceous Sa'ar–Nayfa reservoir reflects that the matrix components are mainly carbonates and shales. Moreover, the lithological-geologic model reflected that these shales are strongly affecting the porosity and, consequently, the fluid saturation in the Sa'ar–Nayfa reservoir. In this study, the thickness of the Sa'ar–Nayfa reservoir increases from central toward north-eastern and north-western parts within the Hiswah Oilfield. The porosities analyses of the investigation of the Sa'ar–Nayfa reservoir for the 11 studied wells concluded that the average total porosity ranges from 5.4 % to 16.8 % while the effective porosity ranges from 5.2 % to 14.8 %. Water saturation of the Sa'ar–Nayfa reservoir ranges from 6.9 % to 75.8 %. On the other hand, hydrocarbon saturation matches with water saturation in a reverse relationship. Sa'ar–Nayfa reservoir is interpreted as good quality reservoir rocks with high average effective porosity reaching to 20 % and high hydrocarbon saturation exceeding 93 %. The Sa'ar–Nayfa reservoir reveals promising reservoir characteristics especially the upper reservoir unit, which should be taken into consideration during future development of the oilfields area. The hydrocarbon saturation map of the Sa'ar–Nayfa reservoir shows a regular pattern of distribution with a general increasing to the northeast, northwest and east directions while decreasing southwest wards, recording the maximum value of 93.1 % at the Hiswah-21 well.  相似文献   

11.
《Comptes Rendus Geoscience》2008,340(2-3):112-126
Permo-Triassic intermediate–felsic magmatism is developed along the Truong Son fold belt, located in the eastern margin of the Indochina Block. It comprises a succession of the active continental margin associations: calc-alkaline volcano-plutonic associations (272–248 Ma), peraluminous granites (259–245 Ma), and subalkaline felsic volcano-plutonic associations (younger than 245 Ma). Detailed study of geochemical characteristics such as trace elements (LILE, REE, HFSE) and isotopes (Sr, Nd, Pb) indicates that they are homogeneous and that they are products of the Palaeotethys subduction process in relation to Indochina (IC)/North Vietnam–South China (NV–SC) amalgamation (S.L. Chung et al., Abstr., GEOSEA 98, Malaysia, 1998, pp. 17–19). The Indosinian characteristics are represented by mantle–crust interaction in magma generation, controlled by their emplacement localities in relation to the Kontum Uplift. The spatial and temporal evolution of Permo-Triassic magmatism allows reconstructing the geodynamic history of the Indosinian orogeny. It confirms that this event ended in Early to Middle Triassic (246–240 Ma, after C. Lepvrier et al., Tectonophysics 393 (2004) 87–118).  相似文献   

12.
In the Shoalhaven River Gorge, in the eastern Lachlan Fold Belt, the Ordovician quartz‐turbidite succession (Adaminaby Group) is affected by one major phase of deformation with northerly trending, gently plunging, upright, close to tight folds (F1) characterised by a range in half wavelengths up to 3 km. Several anticlinoria and synclinoria are developed and folds occur in at least four orders; these characteristics are consistent with buckling occurring at several scales and are controlled by the thickness of competent units in the multilayered succession. F1 folding is thick‐skinned in style with the whole crust probably having been affected by deformation. D1 occurred during the Silurian to Middle Devonian interval and was associated with crustal thickening and the shallowing of depositional environments over time. Locally, F1 is overprinted by south‐southeast‐trending, steeply to moderately inclined F2 that reorients F1 to recumbent attitudes. D2 is of Early to Middle Carboniferous age. Both deformations are related to convergence in an intra‐arc to backarc region and occurred inboard of a subduction zone, remnants of which occur in the New England Fold Belt.  相似文献   

13.
Reconstructions of the Cambrian–Silurian tectonic evolution of eastern Gondwanaland, when the Australian Tasmanides and Antarctic Ross Orogen developed, rely on correlation between structural elements in SE Australia and Northern Victoria Land (NVL), Antarctica. A variety of published models exist but none completely solve the tectonic puzzle that is the Delamerian–Lachlan transition in the Tasmanides. This paper summarizes the understanding of Cambrian (Delamerian) to Silurian (Lachlan) geological evolution of the eastern Tasmanides, taking into account new deep seismic data that clarifies the geological connection between Victoria and Tasmania — the ‘Selwyn Block’ model. It evaluates previous attempts at correlation between NVL, Tasmania and Victoria, and presents a new scenario that encompasses the most robust correlations. Tasmania together with the Selwyn Block is reinterpreted as an exotic Proterozoic microcontinental block – ‘VanDieland’ – that collided into the east Gondwanaland margin south of western Victoria, and north of NVL in the Late Cambrian, perhaps terminating the Delamerian Orogeny in SE Australia. Subsequent north-east ‘tectonic escape’ of VanDieland in the Early Ordovician explains the present-day outboard position of Tasmania with respect to the rest of the Delamerian orogen, the origin of the hiatus that separates the Delamerian and Lachlan orogenic cycles in Australia, and how western Lachlan oceanic crust developed as a ‘trapped plate-segment’. The model establishes a new structural template for subsequent Lachlan Orogen development and Mesozoic Australia–Antarctica separation.  相似文献   

14.
One of the most expanded upper Campanian–Maastrichtian successions worldwide has been cored in a series of boreholes in eastern Denmark. A high-resolution holostratigraphic analysis of this part of the Chalk Group has been undertaken on these cores, notably Stevns-1, in order to provide a record of changes in chalk facies, water depths and sea-water temperatures. Combined lithological data, a suite of petrophysical logs including gamma ray (GR) logs, nannofossil and dinoflagellate palaeontology, stable carbon isotopes, seismic reflection and refraction sections form the basis for the definition of two new formations and six members, three of which are new, and for recognition of Boreal nannofossil subzones UC15eBP to UC20dBP. The upper Campanian–lowermost Maastrichtian Mandehoved Formation is subdivided into the Flagbanke and Boesdal Members and the Maastrichtian Møns Klint Formation is subdivided into the Hvidskud, Rørdal, Sigerslev, Kjølby Gaard Marl and Højerup Members. The Boesdal and Rørdal Members show high GR values and a pronounced chalk-marl cyclicity. The Rørdal and the thin Kjølby Gaard Marl Members have a regional distribution and can be traced over most of the Danish Basin, whereas the Højerup Member is restricted to the easternmost part of Sjælland. The other members consist of rather featureless white chalk.  相似文献   

15.
Many rocks mapped as felsic metavolcanics in the eastern part of the Lukavice Group are shown to be altered mafic metavolcanics, similar to those in the Noranda and Flin Flon-Snow Lake mining districts, Canada. The relatively fresh rocks of the Lukavice Group are rhyolite, dacite-andesite, and andesite-basalt of calcalka-line character. Assuming no substantial volume change during alteration, Ti, P, La, Ce, Yb, Lu, Th (partly), Sc and V contents remained unchanged. Altered rocks are enriched in (Fe + Mg), K and Si and depleted in Na, Ca and Zr. Some elements show both increased and decreased contents in altered rocks (Mg, Ba, Sm, eu, Tb and Hf). Although hydrothermal alteration in the Lukavice Group is of large extent, it is of the proximal Kuroko style and not of regional Amulet Rhyolite style. Implications for a large hydrothermal system within a volcanic pile are discussed in relation to the Ordovician Lukavice Group and its mineral deposits and to some other parts of the Bohemian Massif with volcanosedimentary sequences of the same age.  相似文献   

16.
The numerical results of thermal modeling studies indicate that the lithosphere is cold and strong beneath the Black Sea basin.The thermal lithospheric thickness increases southward from the eastern Pontides orogenic belt（49.4 km） to Black Sea basin（152.2 km）.The Moho temperature increases from 367℃in the trench to 978℃in the arc region.The heat flow values for the Moho surface change between 16.4 mW m-2 in the Black Sea basin and 56.9 mW m-2 in the eastern Pontides orogenic belt. Along the southern Black Sea coast,the trench region has a relatively low geothermal potential with respect to the arc and back-arc region.The numerical studies support the existence of southward subduction beneath the Pontides during the late Mesozoic-Cenozoic.  相似文献   

17.
This paper presents new petrologic data for high-pressure, low-temperature (HP–LT) metamorphic rocks at Juisui. We reinterpret the so-called “Tamayen block” (Yang and Wang, 1985) or “Juisui block” (Liou, 1981, Beyssac et al., 2008) as a tectonic mélange. It is not a coherent sheet but rather a mixture dominated by greenschist and pelitic schist with pods of serpentinite, epidote amphibolite, and rare blueschist. Four types of glaucophane-bearing rocks are newly recognized in this mélange. Type I is in contact with greenschist lacking glaucophane and garnet. Glaucophane is present only as rare inclusions within pargasite. This type records metamorphic evolution from epidote blueschists-, epidote amphibolite-, to greenschist-facies. Type II contains characteristic zoned amphiboles from barroisite core to Mg-katophorite mantle and glaucophane rim, implying an epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Type III includes winchite and indicates P–T conditions of about 6–8 kbar, approaching 400 °C. Type IV contains paragonite but lacks garnet; amphibole shows a Na–Ca core surrounded by a glaucophane rim. This type shows a high-pressure (?) epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Amphibole zoning trends and mineral assemblages imply contradictory P–T paths for the four types of glaucophane-bearing rocks—consistent with the nature of a tectonic mélange. The new P–T constraints and petrologic findings differ from previous studies (Liou et al., 1975, Beyssac et al., 2008).  相似文献   

18.
Late Mesozoic dioritic and quartz dioritic plutons are widespread in the Daye region, eastern Yangtze craton, eastern China. Detailed geochronological, geochemical, and Sr–Nd isotopic studies have been undertaken for most of these plutons, in an attempt to provide a comprehensive understanding in the age, genesis and geodynamical control of the extensive magmatism. SHRIMP and LA-ICP-MS zircon U–Pb dating indicate that the plutons were emplaced in the range of latest Jurassic (ca. 152 Ma) to early Cretaceous (ca. 132 Ma), which was followed by dyke emplacement between 127 and 121 Ma and volcanism during the 130–113 Ma interval. Both diorites and quartz diorites are sodic, metaluminous, high-K calc-alkaline, and characterized by strongly fractionated, sub-parallel REE patterns without obvious Eu anomalies. The rocks are enriched in highly incompatible elements and large ion lithophile elements, but depleted in high field strength elements. Samples of diorite and quartz diorite have similar Sr–Nd isotopic compositions that are consistent with the early Cretaceous basalts and mafic intrusions throughout the eastern Yangtze craton. The geochemical and isotopic data, together with results of geochemical modeling, indicate an enriched mantle source for the plutonic rocks. The quartz diorites have geochemical signatures resembling adakites, such as high Al2O3 (15–19 wt.%), Sr (630–2,080 ppm), Na2O (>3.5 wt.%), negative Nb–Ta anomalies, low Y (7–19 ppm), Yb (0.5–1.8 ppm), Sc (5–15 ppm), and resultant high Sr/Y (45–200) and La/Yb (31–63) ratios. Genesis of the adakitic quartz diorites is best explained in terms of low-pressure intracrustal fractional crystallization of cumulates consisting of hornblende, plagioclase, K-feldspar, magnetite, and apatite from mantle-derived dioritic magmas. Mantle-derived magmatism broadly coeval with that of the Daye region also is widespread in other regions of the eastern Yangtze craton, reflecting large-scale melting of the lithospheric mantle during the Late Mesozoic. The large-scale magmatism was most likely driven by lithospheric extension associated with thinning of lithospheric mantle beneath the eastern China continent.  相似文献   

19.
The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigations of its Mesozoic and Cenozoic lithospheric thermal structure are limited. Therefore, in this study,the distributions of mantle heat flow, crustal heat flow, and Moho temperatures during the Meso-Cenozoic are calculated based on analyses of the thermal history of the Bohai Bay Basin. The results indicate that the ratio of mantle heat flow to surface heat flow peaked during the late stages of the early Cretaceous and during the middle to late Paleogene. The corresponding mantle heat flow was more than 65% of the surface heat flow. Moho temperatures reached three peaks: 900-1100℃ in the late stages of the early Cretaceous;820-900℃ in the middle to late Paleogene; and(in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770-810℃ during the early Neogene. These results reveal that the Bohai Bay Basin experienced significant geological change during the Cretaceous, including the transformation of lithospheric thermal structure from "cold mantle and hot crust" before the Cretaceous to "hot mantle and cold crust" after the Cretaceous. The results also indicate that the basin experienced two large-scale rifting events.Therefore, this work may provide the thermal parameters for further investigations of the geodynamic evolution of eastern China.  相似文献   

20.
在华北克拉通北缘阴山地块东部固阳地区发现了假白榴石粗面玄武岩和钾质粗面岩两种高钾准铝质碱性火山岩。地质年代学数据显示,假白榴石粗面玄武岩的磷灰石U-Pb年龄为322±14Ma,钾质粗面岩的锆石U-Pb年龄为315.6±7.5Ma,说明其形成时代均为晚石炭世。岩石地球化学特征显示,二者均富Al、Fe,贫Mg;富集大离子亲石元素(如Rb、Ba和K),相对亏损高场强元素(如Ta、Nb和Ti),轻重稀土分异明显,富集轻稀土,相对亏损重稀土,Eu异常不明显;高(87Sr/86Sr)i比值(0.710028~0.714745),低εNd(t)值(-9.0~-17.2),表现出相似的交代岩石圈地幔源区和地壳混染特征。将该碱性火山岩与兴蒙造山带晚石炭世-早二叠世中基性火山岩和阴山地块白垩纪中基性火山岩进行岩石类型对比,发现华北克拉通北缘产出的火山岩多为高钾碱性系列,而兴蒙造山带中产出的火山岩则多为钙碱性系列;与兴蒙造山带晚石炭世-早二叠世中基性火山岩进行岩石成因对比,发现它们的岩浆源区和混染程度并不相同,即固阳地区碱性火山岩为受到早古生代俯冲沉积物交代的岩石圈地幔部分熔融所形成的岩浆在上升过程中混染华北克拉通TTG片麻岩后喷发的产物,而兴蒙造山带中火山岩的产出则多为亏损地幔部分熔融所形成的岩浆在上升过程中轻度混染地壳物质后喷发的结果。在固阳地区发现晚石炭世碱性火山岩,代表着古亚洲洋在该时期的后造山伸展作用范围已延伸至华北克拉通北缘。  相似文献   

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