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1.
《International Geology Review》2012,54(13):1641-1659
Eocene mafic volcanic rocks occurring in an E–W-trending, curvilinear belt along and north of the Izmir–Ankara–Erzincan suture zone (IAESZ) in northern Anatolia, Turkey, represent a discrete episode of magmatism following a series of early Cenozoic collisions between Eurasia and the Gondwana-derived microcontinents. Based on our new geochronological, geochemical, and isotope data from the Kartepe volcanic units in northwest Anatolia and the extant data in the literature, we evaluate the petrogenetic evolution, mantle melt sources, and possible causes of this Eocene volcanism. The Kartepe volcanic rocks and spatially associated dikes range from basalt and basaltic andesite to trachybasalt and basaltic trachyandesite in composition, and display calc-alkaline and transitional calc-alkaline to tholeiitic geochemical affinities. They are slightly to moderately enriched in large ion lithophile (LILE) and light rare earth elements (LREE) with respect to high-field strength elements (HFSE) and show negative Nb, Ta, and Ti anomalies reminiscent of subduction-influenced magmatic rocks. The analysed rocks have 87Sr/86Sr(i) values between 0.70570 and 0.70399, positive ?Nd values between 2.7 and 6.6, and Pb isotope ratios of 206Pb/204Pb(i) = 18.6–18.7, 207Pb/204Pb(i) = 15.6–15.7, and 208Pb/204Pb(i) = 38.7–39.1. The 40Ar/39Ar cooling ages of 52.7 ± 0.5 and 41.7 ± 0.3 Ma obtained from basaltic andesite and basalt samples indicate middle to late Eocene timing of this volcanic episode in northwest Anatolia. Calculated two-stage Nd depleted mantle model (TDM) ages of the Eocene mafic lavas range from 0.6 to 0.3 Ga, falling between the TDM ages of the K-enriched subcontinental lithospheric mantle of the Sakarya Continent (1.0–0.9 Ga) to the north, and the young depleted mantle beneath central Western Anatolia (0.4–0.25 Ga) to the south. These geochemical and isotopic features collectively point to the interaction of melts derived from a sublithospheric, MORB-like mantle and a subduction-metasomatized, subcontinental lithospheric mantle during the evolution of the Eocene mafic volcanism. We infer triggering of partial melting by asthenospheric upwelling beneath the suture zone in the absence of active subduction in the Northern Neotethys. The geochemical signature of the volcanic rocks changed from subduction- and collision-related to intra-plate affinities through time, indicating an increased asthenospheric melt input in the later stages of Eocene volcanism, accompanied by extensional deformation and rifting.  相似文献   

2.
ABSTRACT

The northern zone of the Chon Aike Igneous Province, located in the North Patagonian Massif, exhibits extensive outcrops of Jurassic volcanic rocks of the Marifil Formation. In the Arroyo Verde area, the initial volcanic stage of the Marifil Formation, that we denominate V0 (192.6 ± 2.5 Ma), includes coulées, megabreccias and lapilli tuffs assigned to plinian-type volcanism. This magmatism was generated by cold-wet-oxidized magmas that resemble those produced in active continental margins and volcanic arcs. The second stage, located unconformably over the first, includes welded lava-like ignimbrites, massive lapilli tuff and rhyolitic lava flow that resemble the Snake River-type volcanism. The magma that produces this volcanic stage exhibit the characteristics of hot-dry-reduced magmas emplaced in intraplate continental environments associated with continental rifting. This stage coincides with the V1 volcanic episode early recorded in the Marifil Formation.  相似文献   

3.
An age of 3112 ± 6 (2σ) Ma, determined by conventional techniques on single zircons from a felsic volcanic rock from the Sholl Belt in the western part of the Archaean Pilbara Craton of Western Australia, is interpreted as the age of felsic volcanism. This is about 100 Ma older than felsic volcanic rocks in the nearby but unconnected Whim Creek Belt and is significantly younger than felsic volcanism in the East Pilbara, which took place during two distinct episodes at 3450 Ma and 3300 Ma. The present results rule out previous correlations between the felsic volcanic rocks of the Sholt Belt and the 3452 ± 16 Ma old Duffer Formation in the East Pilbara.  相似文献   

4.
《International Geology Review》2012,54(11):1409-1428
ABSTRACT

The Mauranipur and Babina greenstone belts of the Bundelkhand Craton are formed of the Central Bundelkhand greenstone complex (CBGC). This complex represents tectonic collage which has not been previously studied in depth. The purpose of this study is to contribute to the understanding of the main features of the Archaean crustal evolution of the Bundelkhand Craton. The CBGC consists of two assemblages: (1) the early assemblage, which is composed of basic-ultramafic, rhyolitic–dacitic, and banded iron formation units, and (2) the late assemblage, which is a felsic volcanic unit. The units and assemblages are tectonically unified with epidote–quartz–plagioclase metasomatic rocks formed locally in these tectonic zones.

The early assemblage of the Mauranipur greenstone belt is estimated at 2810 ± 13 Ma, from the U–Pb dating (SHRIMP, zircon) of the felsic volcanics. Also, there are inherited 3242 ± 65 Ma zircons in this rock. It is deduced that this assemblage is related to early felsic subduction volcanism during the Mesoarchaean that occurred in the Bundelkhand Craton.

Zircons extracted from metasomatic rocks in the early assemblage’s high-Mg basalts show a concordant age of 2687 ± 11 Ma. This age is interpreted as a time of metamorphism that occurred simultaneously with an early accretion stage in the evolution of the Mauranipur greenstone belt.

The felsic volcanism, appearing as subvolcanic bodies in the late assemblage of the Mauranipur greenstone belt, is estimated to be 2557 ± 33 Ma from the U–Pb dating (SHRIMP, zircon) of the felsic volcanic rocks. This rock also contains inherited 2864 ± 46 Ma zircons. The late assemblage of the Mauranipur greenstone belt corresponds with a geodynamic setting of active subduction along the continental margin during Neoarchaean.

The late assemblage Neoarchaean felsic volcanic rocks from the Mauranipur and Babina greenstone belts are comparable in age and geochemical characteristics. The Neoarchaean rocks are more enriched in Sr and Ba and are more depleted in Cr and Ni than the Mesoarchaean felsic volcanic rocks of the early assemblage.

Through isotopic dating and the geochemical analysis of the volcanic and metasomatic rocks of the CBGC, this study has revealed two subduction–accretion events, the Meso–Neoarchaean (2.81–2.7 Ga) and Neoarchaean (2.56–2.53 Ga), during the crustal evolution of the Bundelkhand Craton (Indian Shield).  相似文献   

5.
《International Geology Review》2012,54(10):1189-1206
ABSTRACT

Volcaniclastic units are exposed at the base of the Puerto Blanco Formation in the Caborca region, northwestern Mexico. The lower unit reveals the presence of Early Cambrian mafic volcanism in this region. It consists of a volcano-sedimentary sequence represented by tuffaceous conglomerates, agglomerates, lapillistones, tuffs, and altered mafic volcanic flows. Petrographic analysis classified the volcanic clasts as albite-sphene-calcite-actinolite granofels, with a moderate to intense hydrothermal alteration, precisely characterized by EPMA analysis. Albite-actinolite geothermometry indicates temperatures from 400 to 500°C, suggesting metamorphic conditions in the upper temperature greenschist facies. Geochemistry analysis shows a high TiO2 basic–ultrabasic volcanism that originated the volcanic clasts. Rock protoliths were studied using immobile trace elements, which classified them as OIB-type alkaline basalts with the characteristic spider hump-shaped pattern, situated in an anorogenic intracontinental tectonic setting with enriched mantle signatures. 40Ar/39Ar geochronology shows metamorphic ages of 52.58 ± 2.0 and 91.67 ± 0.55 Ma, consistent with the emplacement of Laramidic granitoids identified in the region. Possible correlations of this alkaline volcanism include the Southern Oklahoma Aulacogen and the late stages of the rifting of north western Laurentia represented in western United States.  相似文献   

6.
为揭示额仁陶勒盖银矿床火山岩与成矿作用的关系,对矿区内赋矿围岩火山岩展开了系统的年代学和元素地球化学研究。成果揭示:(1)赋矿围岩粗面安山岩的单颗粒锆石U-Pb年龄为(173.4±4.6)Ma;(2)粗面安山岩具有富集大离子亲石元素、亏损高场强元素以及弱的负铕异常的特征;对比洋壳成分,成矿元素呈现强烈亏损V、Cr、Ni、Co、Mo、Cu,富集W、Bi、Pb和相对富集Au、As、Sb、Te以及相似的Zn、Ag、B含量为特征。结合前人的研究成果,认为矿区内火山岩是成矿早期的产物,岩浆起源于流体交代过的大洋性质的岩石圈地幔,岩浆演化过程中有少量斜长石等矿物分离结晶作用和微弱的地壳物质混染,形成的构造环境可能为华北板块、蒙古块体与西伯利亚板块对接碰撞后的初期地壳伸展环境,且该阶段火山作用不具有直接提供成矿流体的属性,提供成矿流体的岩浆作用可能是早白垩世早期石英二长斑岩岩浆(138 Ma)。  相似文献   

7.
The Oligocene Ethiopian continental flood basalt province (ca. 29–31 Ma) contains significant silicic pyroclastic rocks (>60,000 km3 constituting up to 20% of the volcanic stratigraphy). Rhyolitic tephras, synchronous with the Ethiopian silicic pyroclastic rocks, are found in Indian Ocean ODP holes 711A. They are geochemically akin to the Ethiopian silicic pyroclastic rocks. This suggests that the Indian Ocean tephras originated from Ethiopian silicic eruptions and represents more distal fallout of this volcanism. The temporal coincidence of the Ethiopian flood volcanism with the Oligocene global cooling event (Oi2?～?30.3 Ma) and the emplacement of the Ethiopian silicic pyroclastic eruptions on a near-global scale strongly suggest that the Ethiopian continental flood basalt province may have contributed or at least accelerated the climate change that was already underway.  相似文献   

8.
The Yamansu belt,an important tectonic component of Eastern Tianshan Mountains,of the Central Asian Orogenic Belt,NW China hosts many Fe-(Cu)deposit.In this study,we present new zircon U-Pb geochronology and geochemical data of the volcanic rocks of Shaquanzi Formation and diorite intrusions in the Yamansu belt.The Shaquanzi Formation comprises mainly basalt,andesite/andesitic tuff,rhyolite and sub-volcanic diabase with local diorite intrusions.The volcanic rocks and diorites contain ca.315-305 Ma and ca.298 Ma zircons respectively.These rocks show calc-alkaline affinity with enrichment in large-ion lithophile elements(LILEs),light rare-earth elements(LREEs),and depletion in high field strength elements(HFSEs)in primitive mantle normalized multi-element diagrams,which resemble typical back-arc basin rocks.They show depleted mantle signature with ε_(Nd)(t)ranging from+3.1 to +5.6 for basalt;+2.1 to+4.7 for andesite;-0.2 to+1.5 for rhyolite and the ε_(Hf)(t)ranges from-0.1 to +13.0 for andesites;+5.8 to +10.7 for andesitic tuffs.We suggest that the Shaquanzi Formation basalt might have originated from a depleted,metasomatized lithospheric mantle source mixed with minor(3-5%)subduction-derived materials,whereas the andesite and rhyolite could be fractional crystallization products of the basaltic magma.The Shaquanzi Formation volcanic rocks could have formed in an intracontinental back-arc basin setting,probably via the southward subduction of the Kangguer Ocean beneath the Middle Tianshan Massif.The Yamansu mineralization belt might have undergone a continental arc to back-arc basin transition during the Late Carboniferous and the intra-continental back-arc basin might have closed in the Early Permian,marked by the emplacement of dioritic magma in the Shaquanzi belt.  相似文献   

9.
Mafic to felsic gneisses along the northern margin of the North China Craton (NMNCC), in western Liaoning province, China, were previously assumed to be part of Archean metamorphic basement but are here identified as younger (Permian–Early Triassic) intrusions. LA–ICP–MS zircon U–Pb isotopic dating reveals that the magmatic precursors of the mafic gneisses were emplaced from 295 ± 3 to 259 ± 2 Ma and that the magmatic precursors of the dioritic and monzogranitic gneisses were emplaced at 267 ± 1 and 251 ± 2 Ma, respectively, thus recording a continuum of Permian to Early Triassic magmatism. The mafic and dioritic rocks exhibit zircon εHf(t) values from ?20.7 to ?3.3, suggesting they were mainly derived from a metasomatized lithospheric mantle source, possibly involving some crustal contamination. The monzogranitic rocks display their zircon εHf(t) values of +0.9 to +4.7, indicating the acidic magma was derived from partial melting of juvenile crustal materials from the depleted mantle source. Crustal model ages (T DM C ) obtained from zircon Hf isotopes of these monzogranitic rocks range from 976 to 1,215 Ma, with an average of 1,074 ± 32 Ma, possibly implying an episode of Grenvillian crustal growth in western Liaoning province. These new lines of evidence show that the NMNCC witnessed abundant magmatic activity and interaction of the crust and mantle during the Permian and Early Triassic and that the mafic magmatism was earlier than the monzogranitic activity. These findings indicate that the monzogranitic activity was the result of underplating of mafic magma with an enriched mantle source. In the context of regional Late Paleozoic to Early Mesozoic magmatic activity, the Permian magmatism occurred in an Andean-style continental margin setting when the Paleo-Asian oceanic plate was subducted beneath the NMNCC, and in this context, the Late Permian to Early Triassic magmatism may have been linked to post-collisional extension and asthenospheric upwelling, suggesting that the western Liaoning province in the NMNCC may be an eastward extension of the Late Paleozoic to Early Mesozoic active continental margin.  相似文献   

10.
The Boliden deposit (8.3 Mt at 15.9 g/t Au) is interpreted to have been formed between ca. 1894 and 1891 Ma, based on two new U–Pb ID-TIMS ages: a maximum age of 1893.9?+?2.0/?1.9 Ma obtained from an altered quartz and feldspar porphyritic rhyolite in the deposit footwall in the volcanic Skellefte group and a minimum age of 1890.8?±?1 Ma obtained from a felsic mass-flow deposit in the lowermost part of the volcano-sedimentary Vargfors group, which forms the stratigraphic hanging wall to the deposit. These ages are in agreement with the alteration and mineralization being formed at or near the sea floor in the volcanogenic massive sulfide environment. These two ages and the geologic relationships imply that: (1) volcanism and hydrothermal activity in the Skellefte group were initiated earlier than 1.89 Ga which was previously considered to be the onset of volcanism in the Skellefte group; (2) the volcano-sedimentary succession of the Vargfors group is perhaps as old as 1892 Ma in the eastern part of the Skellefte district; and (3) an early (synvolcanic) deformation event in the Skellefte group is evidenced by the unconformity between the ≤1893.9?+?2.0/?1.9 Ma Skellefte group upper volcanic rocks and the ≤1890.8?±?1 Ma Vargfors sedimentary and volcanic rocks in the Boliden domain. Differential block tilting, uplift, and subsidence controlled by synvolcanic faults in an extensional environment is likely, perhaps explaining some hybrid VMS-epithermal characteristics shown by the VMS deposits of the district.  相似文献   

11.
Mesozoic volcanic rocks in southeastern Jilin Province are an important component of the huge Mesozoic volcanic belt in the northeastern area. Study of the age of their formation is of great significance to recognize Mesozoic volcanic rule in northeastern China. Along with the research of rare Mesozoic biota and extensive Mesozoic mineralization in western Liaoning, a number of researchers have focused on Mesozoic volcanic events. The authors studied the ages of the Cretaceous volcanic rocks in southeastern Jilin Province using single Zircon U-Pb. The result shows that the Sankeyushu Formation volcanic rocks in the Tonghua area are 119.2 Ma in age, the Yingcheng Formation in the Jiutai area 113.4±3.1 Ma, the Jinjiatun Formation in Pinggang Town of Liaoyuan City and the Wufeng volcanic rocks in the Yanji area 103.2±4.7 Ma and 103.6±1 Ma, respectively. Combined with the data of recent publication on volcanic rocks ages; the Cretaceous volcanic events in southeastern Jilin Province can be tentatively subdivided into three eruption periods： 119 Ma, 113 Ma and 103 Ma. The result not only provides important chronology data for subdividing Mesozoic strata in southeastern Jilin Province, establishing Mesozoic volcanic event sequence, discussing geological tectonic background, and surveying the relation between noble metals to the Cretaceous volcanic rocks, but also offers important information of Mesozoic volcanism in northeastern China.  相似文献   

12.
Ultrapotassic rocks are a common, but volumetrically minor, hallmark of post‐collisional magmatism along the Alpine–Himalayan orogenic belt. Here, we document the occurrence of ultrapotassic volcanic rocks from the Eslamy peninsula, NW Iran in the Arabia–Eurasia collision zone. Our results indicate that magma genesis involved melting of phlogopite‐ and apatite‐bearing peridotites in the sub‐continental lithospheric mantle at ~11 Ma. These peridotites likely formed by metasomatism involving components derived from subducted sediments during Neotethyan subduction. The ~11 Ma ultrapotassic volcanism was preceded by a magmatic gap of ~11 Ma after the cessation of arc magmatism in NW Iran and Armenia, thus likely representing the initiation of post‐collisional magmatism. The age coincides with the onset of collision‐related magmatic activity and topographic uplift in the Caucasus–Iran–Anatolia region, and also with other regional geological events including the closure of the eastern Tethys gateway, the end of Arabian underthrusting and the start of escape tectonics in Anatolia.  相似文献   

13.
赣南版石和蔡坊盆地流纹质火山岩LA-ICP-MS锆石U-Pb定年结果分别为129.2±2.3 Ma和138.0±2.4 Ma。综合报道的同时期火山岩年龄,可以确定武夷山西缘发育的早白垩世火山岩形成时限大约在145~130 Ma。版石和蔡坊火山岩SiO_270%,属于高硅流纹质岩石,具有较低的Fe_2O_3~t/MgO比值(平均值10),富集大离子亲石元素和轻稀土元素,亏损中-重稀土元素,具显著的Eu负异常(δEu=0.06~0.20),类似于湿冷氧化性流纹岩,可能由来自交代岩石圈地幔的富钾岩浆结晶分异形成。湿冷氧化性的版石和蔡坊流纹质火山岩在武夷山西缘出现,并没有扩展到华南内陆,很可能表明古太平洋俯冲对华南地幔的影响范围主要位于武夷山西缘及其以东地区。  相似文献   

14.
The southeastern Georgetown Inlier (Greenvale Province) consists of Early Palaeozoic metamorphic rocks in fault contact along the Lynd Mylonite Zone with the Palaeoproterozoic to Mesoproterozoic craton of northeastern Australia. It has a central assemblage of metamorphosed silicic volcanic and sedimentary rocks considered equivalent to the Late Cambrian to Early Ordovician Seventy Mile Range Group that developed in an extensional backarc in the Charters Towers Province to the southeast. In the western part of the Greenvale Province, the Oasis Metamorphics have a U – Pb zircon SHRIMP metamorphic age of 476 ± 5 Ma and are intruded by the granodioritic Lynwater Complex with U – Pb zircon ages of 486 ± 5 Ma and 477 ± 6 Ma. These ages are consistent with these rocks forming basement and intrusive equivalents to the extensional volcanic basin. Existing geochronological constraints on the Halls Reward domain, located at the eastern margin of the province, are consistent with it being basement to the extensional basin. Several domains are recognised in the Greenvale Province with either dominantly steep or low to moderate dips of the main foliation, and each experienced multiple deformation with locally up to four overprinting structural phases. Steepening of foliation in several of the domains is attributed to contractional deformation in the Early Silurian that is inferred to have overprinted low-angle foliation developed during extensional tectonics in the backarc setting. Contractional deformation related to the Early Silurian Benambran Orogeny is considered responsible for multiple deformation in the Greenvale Province and reactivation of domain-bounding faults.  相似文献   

15.
The study of lavas and pyroclastics from Anyui Volcano made it possible to reconstruct succession of its eruption events. The age of the eruption is estimated by isotopic methods to be 0.248 ± 0.030 Ma. It is established that the last episode of volcanic activity in northeastern Russia occurred 0.2?0.5 Ma ago (in its continental part, 0.2?0.3 Ma ago). This episode is chronologically close to the last peak in activation of volcanism in the Arctic and Subarctic regions. The absence of features indicating glacial influence on lavas from Anyui Volcano provides grounds for an assumption that no significant glaciations took place in the continental areas of western Chukotka during the last 250 ka.  相似文献   

16.
The vast expanse of Mesozoic igneous rocks in Hong Kong contain important geological records of late Mesozoic magmatic events and tectonic processes from the coastal region of Southeast China. Of these,the Ping Chau Formation in the northwestern New Territories is the youngest known stratum. We perform a detailed study of the volcanic rocks of the Ping Chau Formation utilizing zircon U-Pb dating,with major and trace elements geochemistry. LA-ICP-MS zircon U-Pb data reveal Early Cretaceous age from two volcanic rock samples, with zircon crystallization from magmas at 140.3 ± 0.8 Ma and 139.3 ± 0.9 Ma,respectively. These rocks have high contents of total alkalis(Na_2O + K_2O = 5.58-9.45 wt.%), high-field-strength elements and light rare earth elements, conspicuous negative Eu anomalies, and depletions in Nb, Ta, Ti, Sr, Ba and P. Using this data, in combination with previous studies on the late Mesozoic volcanic belt in Southeast China, we propose that the volcanic rocks of the Ping Chau Formation probably originated from deep melting of the crust in a back-arc extensional setting induced by the subduction of the paleo-Pacific Plate. This formation represents the final stages of Early Cretaceous volcanic activity in Hong Kong, as associated with large-scale lithospheric extension, thinning and magmatism. Our results provide new information that can be used in evaluating the significance of Early Cretaceous volcanism and tectonics in Southeast China.  相似文献   

17.
We report petrologic, geochemical, and zircon U?Pb and Hf isotope data from an early Palaeozoic mafic-intermediate suite of rocks in Baluntai, heartland of the Central Tianshan. Analysed major elements of the intermediate rocks show a close affinity to metaluminous I-type granitoids, resembling arc plutons. The mafic rocks display depletions of Nb, Ta, and Ti typical of volcanic arc basalts (VAB). All of the samples fall within the subduction-related field in tectonic discrimination diagrams. Zircons from a granodiorite and a hornblende diorite yield indistinguishable crystallization ages of 475.1 ± 1.7 million years and 473.7 ± 1.6 Ma, indicating an early Palaeozoic magmatic event. Zircons in the mafic rocks yield younger crystallization ages of 427 ± 1 Ma and 426.5 ± 1.4 Ma. Combined with previous published results, our data suggest that the southward subduction of the Palaeo-Tianshan oceanic crust beneath the northern margin of the Tarim block probably began no later than Early Ordovician time and did not end prior to the middle Silurian. Zircons from the granodiorite and hornblende diorite show ?Hf(t) values of??11.19 to??5.98 and??12.85 to??6.01, respectively, suggesting the reworking of ancient crust. Correspondingly, these zircons yield two T DM2 age ranges: 2140–1812 Ma and 2241–1812 Ma, probably representing a significant episode of juvenile addition during the assembly of Columbia. In contrast, zircons from the mafic rocks yield ?Hf(t) values of 3.12–8.91 and 3.19–8.76, corresponding to the T DM1 ages ranging from 911 to 685 Ma and from 905 to 688 Ma, respectively, suggesting crustal growth in the Central Tianshan microcontinent associated with the initial break-up of Rodinia.  相似文献   

18.
In the Cerro Carro Quebrado and Cerro Catri Cura area, located at the border between the Neuquén Basin and the North Patagonian Massif, the Garamilla Formation is composed of four volcanic stages: 1) andesitic lava-flows related to the beginning of the volcanic system; 2) basal massive lithic breccias that represent the caldera collapse; 3) voluminous, coarse-crystal rich massive lava-like ignimbrites related to multiple, steady eruptions that represent the principal infill of the system; and, finally 4) domes, dykes, lava flows, and lava domes of rhyolitic composition indicative of a post-collapse stage.The analysis of the regional and local structures, as well as, the architectures of the volcanic facies, indicates the existence of a highly oblique rift, with its principal extensional strain in an NNE–SSW direction (∼N10°).The analyzed rocks are mainly high-potassium dacites and rhyolites with trace and RE elements contents of an intraplate signature. The age of these rocks (189 ± 0.76 Ma) agree well with other volcanic sequences of the western North Patagonian Massif, as well as, the Neuquén Basin, indicating that Pliensbachian magmatism was widespread in both regions. The age is also coincident with phase 1 of volcanism of the eastern North Patagonia Massif (188–178 Ma) represented by ignimbrites, domes, and pyroclastic rocks of the Marifil Complex, related to intraplate magmatism.  相似文献   

19.
Extensive Late Mesozoic igneous rocks in SE China have been widely considered to be generated under the paleo-Pacific tectonic regime. Previous studies suggested a fundamental oceanward younging trend for the igneous rocks, further implying a NW-ward paleo-Pacific subduction model with gradual slab rollback. New LA–ICP–MS zircon U–Pb dating results show that early stage of the Late Mesozoic volcanic sequences (also known as the lower volcanic series) in Fujian Province was formed in three episodes: 160–148 Ma for the Changlin Formation, 145–130 Ma for the Nanyuan Formation, and 130–127 Ma for the Xiaoxi Formation, among which the second episode made the volcanism climax. Thus the entire lower volcanic series in Fujian were formed earlier than those in Zhejiang (140–118 Ma), displaying a NE-ward younging trend parallel to the potential subduction belt. Besides, in situ Hf isotope analyses on dated zircons yield an εHf(t) range of − 19.2 to + 1.7 for the lower volcanic series in Fujian. The majority of the studied volcanic rocks have more radiogenic Hf than that of the metamorphic basement, requiring the involvement of juvenile components in their origin. Moreover, the zircon εHf(t) value increases with time in each single area, as well as the igneous rocks elsewhere in SE China, except for the Changlin Formation which shows very opposite isotopic varying trend. Increasing zircon εHf(t) values imply an increasing material contribution of contemporaneous underplated mantle-derived magmas, which was plausibly induced by gradual crustal decompression. As well as the NE-ward younging trend of the lower volcanic series, it is also identified that the juvenile material contribution in the igneous petrogenesis gradually took place in the same direction along the coastal area. Thus here we propose an asynchronizing paleo-Pacific slab rollback model during 150–120 Ma to account for the episodic magmatism and crustal extension in SE China. On the contrary, decreasing zircon εHf(t) values of the Changlin Formation volcanics indicate that they were formed under enhanced crustal compression probably induced by slab advance. On the other hand, the upper volcanic series in Fujian were formed during 110–88 Ma coevally to those in Zhejiang, with more depleted zircon Hf isotopic compositions than the lower volcanic series as well, indicating that the entire coastal SE China was under the back-arc tectonic setting during that time.  相似文献   

20.
The Afyon stratovolcano exhibits lamprophyric rocks, emplaced as hydrovolcanic products, aphanitic lava flows and dyke intrusions, during the final stages of volcanic activity. Most of the Afyon volcanics belong to the silica-saturated alkaline suite, as potassic trachyandesites and trachytes, while the products of the latest activity are lamproitic lamprophyres (jumillite, orendite, verite, fitztroyite) and alkaline lamprophyres (campto-sannaite, sannaite, hyalo-monchiquite, analcime–monchiquite). Afyon lamprophyres exhibit LILE and Zr enrichments, related to mantle metasomatism.  相似文献   

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