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1.
云南曲靖盆地内的蔡家冲火山岩作为扬子克拉通内部深断裂受青藏高原向东南逃逸而影响强度的标志之一,具有重要意义。在该区新发现的新生代火山岩的斑晶成分主要为正长石和少量黑云母,为钾质火山岩(粗面质火山岩);结合火山岩的全岩成分、微量元素分析,确定蔡家冲火山岩为粗面质火山岩(超钾质火山岩),经湖相水解后K、Na等碱质组分部分流失,导致该区火山岩在火山岩分类图解中落入碱质稍低的花岗闪长岩区域,其本质是水解的粗面质火山岩;全岩K/Ar同位素测年显示:火山岩活动时间范围在44.9±0.8~48.4±0.9Ma之间;火山岩下部至上部年龄差大致为3.5Ma,属于古近纪始新世路特阶的产物。该区的新生代火山岩反映出,曲靖深断裂的走滑拉分不仅形成了曲靖、陆良、弥勒、开远等一系列盆地,其活动强度还导致新生代始新世路特阶的蔡家冲组火山岩的喷发,曲靖深断裂同小江深断裂一样,新生代活动显示为超壳深断裂。火山岩显著富集Cd、Pb、Zn等元素,综合考虑东川播卡等地深部发现同时期的富碱侵入岩及金矿床,该区火山岩显示的金矿、铅锌矿的找矿潜力值得关注。曲靖深断裂还与地震活动、热水资源、农业生态环境、油气资源、固体矿产等密切相关,值得深入研究。 相似文献
2.
E. P. Terekhov A. V. Mozherovsky M. T. Gorovaya I. B. Tsoy N. G. Vashchenkova 《Russian Journal of Pacific Geology》2010,4(3):260-273
This paper reports and discusses the composition of the rocks of the Kotikovo Group (the Uchir, Zaslonovskaya, Turovskay,
and Ol’don formations) of the Terpeniya Peninsula (East Sakhalin). It is suggested that the Cenozoic deposits unconformably
overlay the Maastrichtian-Danian rocks with basal conglomerates at the base. Two main stages were distinguished in the Late
Cretaceous-Paleogene evolution of this area on the basis of our study. The first stage was responsible for the formation of
the Maastrichtian-Danian volcaniclastic and volcanogenic-sedimentary rocks of the Uchir Group, while the second stage produced
the Paleocene-Eocene sedimentary rocks of the Zaslonovskaya, Turovskaya, and Ol’don formations. The end of the first stage
(at the boundary of the Uchir and Zaslonovskaya formations) was marked by a change in the tectonic regime. This was expressed
in the weakening of the volcanic activity, the uplift of the territory, and the exposure of new provenances to erosion. During
the second, Early Paleogene stage, the area of the East Sakhalin Mountains, the Terpeniya Peninsula, and the submarine Terpeniya
Ridge represented a shallow-water marine sedimentary basin representing the western flank of the Cenozoic Pogranichnyi Basin.
The formation of the anticlinal East Sakhalin Mountains-Terpeniya Peninsula-submarine Terpeniya Ridge structure occurred during
the Late Cenozoic period of the East Sakhalin evolution. 相似文献
3.
Zahra Alaminia Mohammad Hassan Karimpour Seyed Massoud Homam Fritz Finger 《International Journal of Earth Sciences》2013,102(6):1603-1625
The area of Arghash in northeast Iran, prominent for its gold mineralization, was newly mapped on a scale of 1:20,000 with particular attention to the occurring generations of igneous rocks. In addition, geochronological and geochemical investigations were carried out. The oldest geological unit is a late Precambrian, hornblende-bearing diorite pluton with low-K composition and primitive isotope signatures. This diorite (U–Pb zircon age 554 ± 6 Ma) is most likely a remnant from a Peri-Gondwana island-arc or back-arc basin. About one-third of the map area is interpreted as an Upper Cretaceous magmatic arc consisting of a volcanic and a plutonic part. The plutonic part is represented by a suite of hornblende-bearing medium-K, I-type granitoids (minor diorite, mainly quartz–monzodiorite and granodiorite) dated at 92.8 ± 1.3 Ma (U–Pb zircon age). The volcanic part comprises medium-K andesite, dacite and tuffitic rocks and must be at least slightly older, because it is locally affected by contact metamorphism through the hornblende–granitoids. The Upper Cretaceous arc magmatism in the Arghash Massif is probably related to the northward subduction of the Sabzevar oceanic basin, which holds a back-arc position behind the main Neotethys subduction front. Small occurrences of pillow basalts and sediments (sandstone, conglomerate, limestone) tectonically intercalated in the older volcanic series may be relics of earlier Cretaceous or even pre-Cretaceous rocks. In the early Cenozoic, the Cretaceous magmatic arc was intruded by bodies of felsic, weakly peraluminous granite (U–Pb zircon age 55.4 ± 2.3 Ma). Another strong pulse of magmatism followed slightly later in the Eocene, producing large masses of andesitic to dacitic volcanic rocks. The geochemistry of this prominent Eocene volcanism is very distinct, with a high-K signature and trace element contents similar to shoshonitic series (high P, Zr, Cr, Sr and Ba). High Sr/Y ratios feature affinities to adakite magmas. The Eocene magmatism in the Arghash Massif is interpreted as related to thermal anomalies in crust and mantle that developed when the Sabzevar subduction system collapsed. The youngest magmatic activities in the Arghash Massif are lamprophyres and small intrusions of quartz–monzodiorite porphyries, which cut through all other rocks including an Oligocene–Miocene conglomerate cover series. 相似文献
4.
The Eocene and Miocene volcanic rocks between the cities of Trabzon and Giresun in the Eastern Pontides (NE Turkey) erupted as mildly and moderately alkaline magmas ranging from silica-saturated to silica-undersaturated types. 40Ar-39Ar dating and petrochemical data reveal that the studied volcanic rocks are discriminated in two: Lutetian (Middle Eocene) mildly alkaline, (basaltic rocks: 45.31 ± 0.18 to 43.86 ± 0.19 Ma; trachytic rocks: 44.87 ± 0.22 to 41.32 ± 0.12 Ma), and Messinian (Late Miocene) moderately alkaline volcanic rocks (tephrytic rocks: 6.05 ± 0.06 and 5.65 ± 0.06 Ma). The trace and the rare earth element systematic, characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios in the Eocene basaltic and trachytic rocks, high LREE/HREE ratios in the Miocene tephrytic rocks, and different degrees of depletion in Nb, Ta, Ti coupled with high Th/Yb ratios, show that the parental magmas of the volcanic rocks were derived from mantle sources previously enriched by slab-derived fluids and subducted sediments. The Sr, Nd and Pb isotopic composition of the Eocene and Miocene volcanic rocks support the presence of subduction-modified subcontinental lithospheric mantle. During the magma ascent in the crust, parental magmas of both the Eocene and Miocene volcanic rocks were mostly affected by fractional crystallisation rather than assimilation coupled with fractional crystallisation and mixing. The silica-undersaturated character of the Miocene tephrytic rocks could be attributed to assimilation of carbonate rocks within shallow-level magma chambers. The parental magmas of the Eocene volcanic rocks resulted from a relatively high melting degree of a net veined mantle and surrounding peridotites in the spinel stability field due to an increase in temperature, resulting from asthenospheric upwelling related to the extension of lithosphere subsequent to delamination. The parental magmas for the Miocene volcanic rocks resulted from a relatively low melting degree of a net veined mantle domain previously modified by metasomatic melts derived from a garnet peridotite source after decompression due to extensional tectonics, combined with strike-slip movement at a regional scale related to ongoing delamination. 相似文献
5.
Cenozoic volcanic rocks widespread in eastern China constitute an important part of the circum-Pacific volcanic belt.This paper presents more than 150K-Ar dates and a great deal of petrochemical analysis data from the Cenozoic volcanic rocks distributed in Tengchong,China‘s southeast coast,Shandong,Hebei,Nei Monggol and Northeast China.An integrated study shows that ubiquitous but uneven volcanic activities prevailed from the Eogene to the Holocene,characterized as being multi-eqisodic and multicycled.For example,in the Paleocene(67-58Ma),Eocene(57-37.5Ma),Miocene(22-18,16-19Ma),Pliocene(8-3Ma),and Early Pleistocene-Middle Pleistocene(1.2-0.5Ma) there were upsurges of volcanism,while in the Oligocene there was a repose period.In space,the older Eogene volcanic rocks are distributed within the region or in the central part of the NE-NNE-striking fault depression,while the younger Neogene and Quaternary volcanic rocks are distributed in the eastern and western parts.Petrologically,they belong essentially to tholeiite-series and alkali-series basalts,with alkalinity in the rocks increasing from old to youg.The above regularities are controlled by both global plate movement and regional inherent tectonic pattern. 相似文献
6.
The western flank of the Paleoproterozoic Imandra-Varzuga rift zone consists of three volcanogenic-sedimentary series and layered mafic-ultramafic intrusions of different age (2.50–2.45 Ga). The earliest Monchegorsk and Monche Tundra layered massifs were formed about 2.50 Ga during the prerift stage of the evolution of the Imandra-Varzuga zone. The early rift stage (～2.45 Ga) produced layered intrusions of the Imandra complex and volcanic rocks of the Strelna Group, consisting of the Kuksha and Seidorechka formations. In terms of chemical composition, the volcanic rocks of the Seidorechka Formation belong to a single basalt-rhyolite series, mostly of normal alkalinity and both tholeiitic and calc-alkaline affinity. The rocks of the Imandra Complex are characterized by moderate LREE enrichment, relatively flat HREE patterns, and a positive Eu anomaly. Similar REE distribution patterns were observed in the volcanic rocks of the Seidorechka Formation, which show a gradual increase in REE content with increasing SiO2. The upper part of the Seidorechka Formation in the southern Khibiny region is composed of metarhyodacites. They terminate the sequence of the Strelna Group and have a U-Pb zircon age of 2448 ± 8 Ma. This age presumably reflects the upper age boundary of the rocks of the Seidorechka Formation and the end of the early stage of the evolution of the Imandra-Varzuga zone. Xenogenic zircon from the same sample yielded a U-Pb zircon age of 2715 ± 42 Ma. A U-Pb age of 2202 ± 17 Ma was obtained for titanite and rutile and interpreted as the metamorphic age of the Seidorechka Formation. The metavolcanic rocks of the Seidorechka Formation have negative ?Nd (T) varying from ?2.84 to ?2.32, and ISr values of 0.7041–0.7038, which are higher than those of the depleted mantle and suggest their derivation from an enriched mantle reservoir (EM1). The spatial association of the volcanic rocks of the Seidorechka Formation and the rocks of the Imandra Complex, similarity in the behavior of most major elements, similar REE distribution patterns, and close formation ages and isotope signatures give grounds to combine them in a single volcanoplutonic association. 相似文献
7.
Mehmet Arslan İrfan Temizel Emel Abdioğlu Hasan Kolaylı Cem Yücel Durmuş Boztuğ Cüneyt Şen 《Contributions to Mineralogy and Petrology》2013,166(1):113-142
The Eocene volcano-sedimentary units in the southern part of the Eastern Pontides (NE Turkey) are confined within a narrow zone of east–west trending, semi-isolated basins in Bayburt, Gümü?hane, ?iran and Alucra areas. The volcanic rocks in these areas are mainly basalt and andesite through dacite, with a dominant calc-alkaline to rare tholeiitic tendency. 40Ar–39Ar dating of these volcanic rocks places them between 37.7 ± 0.2 and 44.5 ± 0.2 Ma (Middle Eocene). Differences in the major and trace element variations can be explained by the fractionation of clinopyroxene ± magnetite in basaltic rocks and that of hornblende + plagioclase ± magnetite ± apatite in andesitic rocks. Primitive mantle-normalized multi-element variations exhibit enrichment of large-ion lithophile elements and to a lesser extent, of light rare earth elements, as well as depletion of high field strength elements, thus revealing that volcanic rocks evolved from a parental magma derived from an enriched mantle source. Chondrite-normalized rare earth element patterns of the aforementioned volcanic rocks resemble each other and are spoon-shaped with low-to-medium enrichment (LaN/LuN = 2–14), indicating similar spinel lherzolitic mantle source(s). Sr, Nd and Pb isotopic systematics imply that the volcanic rocks are derived from a subduction-modified subcontinental lithospheric mantle. Furthermore, post-collisional thickened continental crust, lithospheric delamination and a subduction-imposed thermal structure are very important in generating Tertiary magma(s). The predominantly calc-alkaline nature of Eocene volcanic rocks is associated with increasing geodynamic regime-extension, whereas tholeiitic volcanism results from local variations in the stress regime of the ongoing extension and the thermal structure, as well as the thickness of the crust and the mantle-crust source regions. Based on volcanic variety and distribution, as well as on petrological data, Tertiary magmatic activity in Eastern Pontides is closely related to post-collisional thinning of the young lithosphere, which, in turn, is caused by extension and lithospheric delamination after collisional events between the Tauride–Anatolide Platform and the Eurasian Plate. 相似文献
8.
新生代青藏高原钾质火山岩发育,主要集中于藏北地区和拉萨地块内,仲巴地块中鲜见报道。对仲巴地块中发现的加达钾质火山岩进行研究,其岩石类型以粗面质为主,岩浆以溢流相-喷发相不间断喷发。样品普遍显示高钾高铝,低碱,偏酸性,富集轻稀土元素和大离子亲石元素,亏损高场强元素,具弱负Eu异常,贫Y和Yb,Sr含量较高,类似于典型的埃达克质岩的地球化学特征。粗面玄武安山岩样品LA-ICP-MS锆石U-Pb年龄为17.03±0.32Ma,形成时代为中新世。加达钾质火山岩浆来源于挤压增厚的下地壳部分熔融,其产出的构造背景是后碰撞伸展环境。 相似文献
9.
The results of the K-Ar, Rb-Sr, and U-Pb (SHRIMP zircon method) dating of the Middle Paleozoic volcanogenic rocks of the Omolon
Massif are summarized. It was concluded that they are principally consistent with each other, as well as with the geological
data. The formation of the Kedon Group, which makes up the main volume of the Middle Paleozoic volcanics, began at the Early-Middle
Devonian boundary about 400 Ma ago (U-Pb dates of 400.5 ± 4.4 and 387 ± 6.4; Rb-Sr isochron age of 402 ± 6 Ma). The isotopic
age of the upper boundary of the Kedon Group remains unclear due to disagreements concerning its stratigraphic assignment.
The histogram based on the 111 K-Ar dates of the volcanic rocks from the Kedon Group gives a polymodal distribution, which
indicates that the K-Ar isotopic system was disturbed by thermal events, which occurred 310–290 (terminal Carboniferous—beginning
of the Permian) and 240–220 (Middle-beginning of the Late Triassic) Ma ago. Both thermal events were associated with mantle
(ultrabasic-basic) magmatism, which spanned a significantly wider territory than the distribution area of the Kedon Group 相似文献
10.
《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
11.
Three—Phase Uplift of the Qinghai—Tibet Plateau Druing the Cenozoic Period：Igneous Petrology Constraints 总被引：1，自引：1，他引：0
Shaocong Lai 《中国地球化学学报》2000,19(2):152-160
In northern Qinghai-Tibet plateau there are developed Cenozoic volcanic rocks. They constitute a trachybasalt-shoshonite-latite-trachydacite
assemblage. According to the forming ages, three Cenozoic volcanic rock lithozones can be distinguished in the northern part
of the plateau. Cenozoic volcanic rocks and muscovite/two-mica granites forming the three belts in pairs represent the northern
and southern margins of the plateau in different periods. In fact, the tectonic setting of the northern part of the Qinghai-Tibet
plateau is significantly different from that of the southern part—Himalayas. The southern part has experienced subduction
and continent-continent collision. There are developed the Cenozoic S-type granites (muscovite/ two-mica granites) there.
But the northern part is characterized by Cenozoic basaltic magmatism which obviously comes from the upper mantle. Slight
doming of the upper mantle is recognized underneath the northern part of the plateau, which is the result of resistance of
the Tarim plate to the north direction-sense movement of the Tibetan plate. And at the same time, the uplift machanism shows
that the formation of the Qinghai-Tibet plateau involved three orogenic stages (35−23 Ma, 23−10 Ma and <2 Ma) of uplift in
the vertical direction and extension in the horizontal direction with the Gangdise-Qiangtang orogenic belt as its core. 相似文献
12.
13.
THE EARLY UPLIFT IN NORTHERN TIBETAN PLATEAU: EVIDENCE FROM THE STUDY ON CENOZOIC VOLCANIC ROCKS IN QIANGTANG REGION 相似文献
14.
通过1:50000区域地质调查，运用"火山构造-岩性岩相-火山地层"三重填图方法，将内蒙古东乌旗高尧乌拉白音高老组划分为3个岩性段，一段为火山碎屑沉积岩，二段为中性火山岩，三段为酸性火山岩，构成一个完整的沉积-喷发旋回。早期至晚期岩浆具有由中性向酸性演化的特征。划分出爆发相、侵出相、溢流相、火山通道相、喷发-沉积相及潜火山相等火山岩相；圈出12个Ⅴ级火山机构。获得高尧乌拉白音高老组二段粗安岩和三段流纹岩的LA-ICP-MS锆石U-Pb年龄分别为128.2±0.9 Ma和125.5±0.5 Ma，表明其形成时代为早白垩世。 相似文献
15.
Zafer Aslan Mehmet Arslan İrfan Temizel Abdullah Kaygusuz 《Mineralogy and Petrology》2014,108(2):245-267
Volcanic rocks from the Gümü?hane area in the southern part of the Eastern Pontides (NE Turkey) consist mainly of andesitic lava flows associated with tuffs, and rare basaltic dykes. The K-Ar whole-rock dating of these rocks range from 37.62?±?3.33 Ma (Middle Eocene) to 30.02?±?2.84 Ma (Early Oligocene) for the andesitic lava flows, but are 15.80?±?1.71 Ma (Middle Miocene) for the basaltic dykes. Petrochemically, the volcanic rocks are dominantly medium-K calc-alkaline in composition and show enrichment of large ion lithophile elements, as well as depletion of high field strength elements, thus revealing that volcanic rocks evolved from a parental magmas derived from an enriched mantle source. Chondrite-normalized rare-earth element patterns of the volcanic rocks are concave upwards with low- to-medium enrichment (LaCN/LuCN?=?3.39 to 12.56), thereby revealing clinopyroxene- and hornblende-dominated fractionations for andesitic-basaltic rocks and tuffs, respectively. The volcanic rocks have low initial 87Sr/86Sr ratios (0.70464 to 0.70494) and εNd(i) values (+1.11 to +3.08), with Nd-model ages (TDM) of 0.68 to 1.02 Ga, suggesting an enriched lithospheric mantle source of Proterozoic age. Trace element and isotopic data, as well as the modelling results, show that fractional crystallization and minor assimilation played an important role in the evolution of the volcanic rocks studied. The Eocene to Miocene volcanism in the region has resulted from lithospheric delamination and the associated convective thinning of the mantle, which led to the partial melting of the subduction-metasomatized lithospheric mantle. 相似文献
16.
The Wild Bight Group (WBG) and South Lake Igneous Complex (SLIC) together comprise one of the Ordovician accreted oceanic
terranes of the central mobile belt of the Newfoundland Appalachians. Combined detailed mapping, geochemistry, Sm-Nd isotopic
studies and U-Pb geochronology have shown that sheeted dykes and hornblende diorite and tonalite plutons of the SLIC are genetically
related to a discrete package of volcanic rocks in the WBG. These igneous rocks are geochemically, isotopically and temporally
distinct from volcanic rocks in the rest of the WBG. Plutonic rocks of the SLIC range in age from 486 ± 3 Ma to 489 ± 3 Ma,
and a cross-cutting gabbro dyke gives a minimum age of 486 ± 4 Ma for the related volcanic sequence. Volcanic rocks in the
rest of the WBG sequence are predominantly younger than 472 ± 3 Ma. The older volcanic sequence of the WBG and the SLIC occur
as fault-bounded packages interleaved within the younger WBG sequence. A conformable stratigraphic relationship between the
older and younger sequences of the WBG has not been demonstrated. The mafic rocks of the older package include boninites and
low-Ti, high-Mg tholeiitic island arc basalts which are interpreted to be genetically related, and normal island arc tholeiites
(IAT). The high-Mg mafic rocks are interpreted to have formed in an extensional setting during subduction zone initiation,
and the normal IAT are thought to represent stabilisation of the volcanic front. The associated high-Si, low-K rhyolite and
tonalite are interpreted to be the products of secondary melting at the base of thickened early arc crust. Sm-Nd isotopic
compositions indicate that the characteristic trace element signature of the boninites developed at or near their time of
generation and was not a long lived characteristic of the source region. The boninites and low-Ti tholeiites are interpreted
to have originated from a similar source, which was metasomatized by different subduction-related components. Apparent decoupling
of Sm-Nd geochemical and isotopic compositions suggests that these very depleted rocks may be recording the effect of subduction
zone processes not yet fully understood.
Received: 31 October 1997 / Accepted: 6 May 1998 相似文献
17.
A.Encinas A.Folguera R.Riffo P.Molina L.Fernández Paz V.D.Litvak D.A.Colwyn V.A.Valencia M.Carrasco 《地学前缘(英文版)》2019,10(3):1139-1165
The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geologic evolution of the Central Patagonian Andes, we carried out geochronologic(U-Pb and40Ar/39Ar), provenance, stratigraphic, sedimentologic, and geochemical studies on the sedimentary and volcanic Cenozoic deposits that crop out in the Meseta Guadal and Chile Chico areas(～47°S). Our data indicate the presence of a nearly complete Cenozoic record, which refutes previous interpretations of a hiatus during the middle Eocene-late Oligocene in the Central Patagonian Andes. Our study suggests that the fluvial strata of the Ligorio Marquez Formation and the flood basalts of the Basaltos Inferiores de la Meseta Chile Chico Formation were deposited in an extensional setting related to the subduction of the Aluk-Farallon spreading ridge during the late Paleocene-Eocene. Geochemical data on volcanic rocks interbedded with fluvial strata of the San Jose Formation suggest that this unit was deposited in an extensional setting during the middle Eocene to late Oligocene. Progressive crustal thinning allowed the transgression of marine waters of Atlantic origin and deposition of the upper Oligocene-lower Miocene Guadal Formation. The fluvial synorogenic strata of the Santa Cruz Formation were deposited as a consequence of an important phase of compressive deformation and Andean uplift during the early-middle Miocene. Finally, alkali flood basalts of the late middle to late Miocene Basaltos Superiores de la Meseta Chile Chico Formation were extruded in the area in response to the suduction of the Chile Ridge under an extensional regime. Our studies indicate that the tectonic evolution of the Central Patagonian Andes is similar to that of the North Patagonian Andes and appears to differ from that of the Southern Patagonian Andes, which is thought to have been the subject of continuous compressive deformation since the late Early Cretaceous. 相似文献
18.
Gökhan Büyükkahraman 《Arabian Journal of Geosciences》2016,9(16):675
In this study, petrological characteristics of the Early-Middle Eocene Bozaniç volcanic rocks resulting from the closure of the Neotethys Ocean in the Central Sakarya region and geodynamic evolution of the Eocene magmatism in the region were investigated. Although previous researchers attained insightful findings about the geodynamic evolution of the region, the age of the post-collisional volcanism, petrological characteristics, and source of the magma remain uncertain. Therefore, volcanic rocks outcropping nearby Sar?cakaya-Mihalgazi (Eski?ehir) are investigated in this study. For that purpose, geological map of the study area was drawn and mineralogical, petrographic, geochemical, and isotopic analyses were performed on rock samples collected from different locations. Bozaniç volcanic rocks outcropping as lavas and pyroclastics (agglomerate, lapillistone, and tuff) seem to be derived from four separate volcanic chimneys located in the study area and their composition are typically andesite. According to petrographic data, hypocrystalline porphyritic and microlitic porphyritic are the dominant textures of the rocks. Plagioclase, amphibole, clinopyroxene, and biotite are the main minerals, while sanidine, opaque minerals, chalcedony, calcite, and chlorite can also be observed in small amounts. Geochemically, they show calc-alkaline characteristics and contain medium-high K. Fractional crystallization is the most important process in the development of the rocks. Bozaniç volcanic rocks were derived from a lithospheric mantle source that developed in the active continental margin. According to 40Ar/39Ar age spectra of the samples, the ranges of 48.13 ± 0.15–48.78 ± 0.23 Ma plateau ages were obtained. (87Sr/86Sr) i ratios of the rocks range between 0.705404 and 0.705502, while (143Nd/144Nd) i ratios range between 0.512570 and 0.512581. Consequently, the age data obtained in this study show that the formation time of the first products of the post-collisional volcanism be as early as the Early Eocene and the presence of those is important in terms of the elucidation of geodynamic evolution of the region. 相似文献
19.
Shaocong Lai 《中国地球化学学报》1999,18(4):361-371
Based on electron probe analyses of the minerals and bulk composition of the Cenozoic volcanic rocks from Yumen and Hoh Xil
lithodistricts, Qinghai-Xizang plateau, the forming conditions including the temperature and pressure of those rocks are studied
in this paper. According to the thermodynamic calculation results of mineral-melt equilibrium, the depth of the asthenosphere
superface (about 75 – 130 km) for the northern part of the Qinghai-Xizang plateau during the Cenozoic is suggested. Finally,
this paper indicates that the Cenozoic volcanic rocks in the northern part of the Qinghai-Xizang plateau mainly consist of
shoshonite series. Their forming temperature is 630 – 1039°C and forming pressure is between 2.3 – 4.0 GPa. The rocks were
formed in the intracontinental orogenic belt, of which the primary magma was originated from a particular enrichment upper
mantle and accreted crust-mantle belt or directly from asthenospheric superface as a result of partial melting of pyrolite.
The project was supported by the National Natural Science Foundation of China (No. 49234080), the Geological Sectional Foundation
of MGMR (No. 8506201, 8506207) and the Science Foundation of Northwest University (97NW23). 相似文献
20.
三水盆地是南海北部邻区陆域唯一具有新生代火山活动记录的盆地,最晚一期火山喷发时间是38Ma,也是南海北部陆域已知的在南海扩张之前最晚的火山喷发年代。应用K-Ar同位素年代测定方法,首次发现三水盆地存在29.27±1.52Ma的玄武岩和28.25±1.14Ma的流纹岩,构造判别图解指示其产出环境是板内拉张,与盆地之前火山类型一致,为双峰式火山岩,玄武岩具有与洋岛玄武岩相似的地球化学特征,流纹岩具有与A型花岗岩相似的地球化学特征,且玄武岩与流纹岩均与其他地区地幔柱成因火山岩具有相似的地球化学特征。这一代表板内破裂的双峰式火山记录将南海北部陆缘的火山喷发活动从早先已知的古新世—中始新世延续至渐新世中期,众所周知,南海的开裂起始时间约在32Ma,对于南海扩张期间周边陆域是否存在相关联的火山活动及建立南海早期开裂模式具有重要意义。 相似文献