Sediment contribution in post-collisional high Ba-Sr magmatism: Evidence from the Xijing pluton in the Alxa block,NW China     

《Gondwana Research》2019

High Ba-Sr granitoids occur in a number of tectonic settings, and variable petrogenetic models have been proposed. Those from post-collisional settings are rarely studied and are the focus of this study. Zircon U-Pb geochronology and whole-rock elemental and Sr-Nd-Hf isotopic data are presented for a suite of high Ba-Sr granitoids from the southern margin of the Alxa block, NW China. U-Pb zircon dating shows that the Xijing high Ba-Sr granitoids were emplaced in two periods at ~440 Ma and ~410 Ma, and they are characterized by elevated Ba and Sr contents. The older ~440 Ma high Ba-Sr granitoids range from monzodiorite to quartz monzonite, and the younger ~410 Ma high Ba-Sr granites tend to be more evolved. Both suites have similar enriched Sr-Nd-Hf isotopic ratios, low Ba/Th and Sr/Th ratios, and high Th contents and Th/Ce ratios indicative of a sediment contribution. This is potentially linked to previous subduction of the North Qilian ocean slab. Major and trace element calculations suggest that the older ~440 Ma granitoids experienced up to ~60% fractionation at 4–6 kbar with a crystallizing assemblage dominated by amphibole and plagioclase. The younger ~410 Ma granites could in turn have been formed by a further 80% fractional crystallization at lower pressures (1–2 kbar). Trace element and Sr-Nd isotopic modeling suggest incorporation of ~5% slab-derived sediment into mantle magma source of these high Ba-Sr granitoids. We note that post-collisional granitoids with high Ba and Sr characteristics may also reflect a sediment contribution in their source region, and this may be a key aspect of why such granites plot in the field of post-collisional granites in the Rb vs Y + Nb diagram. Some sanukitoids with high Ba and Sr contents in the late Archean also appear to reflect sediment subduction and they hence may represent early stages of crustal recycling.  相似文献   

Harzburgite found in the Hegenshan ophiolite,southeastern Central Asian Orogenic Belt: Petrogenesis and geological implications     

《Gondwana Research》2019

This paper reports detailed studies on harzburgite and serpentinite in the Hegenshan ophiolitic mélange. Harzburgite consists mainly of olivine and orthopyroxene with trace amounts of clinopyroxene and chromian spinel. Clinopyroxene occurs as isolated crystals or in the intergrowth of chromian spinel–clinopyroxene–orthopyroxene. Harzburgite is moderately to highly depleted, displaying high Fo contents in olivine (90.8–92.2), moderate Al₂O₃ contents in orthopyroxene (1.59–2.79 wt%), low heavy REE abundances in clinopyroxene, and moderate Cr# values of spinel (0.50–0.62). The modal proportions of olivine and orthopyroxene pseudomorph grains imply that the parent of the Hegenshan serpentinite should be harzburgite. Whole-rock compositions of the harzburgite and serpentinite samples are characterized by depletions in Al₂O₃ and CaO and enrichments in light REE, Sr, and U. Geochemical modeling suggests that the Hegenshan harzburgite represents residues after 17–18% partial melting of the primitive mantle. The melt in equilibrium with clinopyroxene is more depleted than typical forearc basalt and boninite. Various pyroxene thermobarometers yield equilibrated temperatures of 945–1067 °C and pressures of 4.8–8.0 kbar for the Hegenshan harzburgite. The oxygen barometer yields results of +0.4 to +1.7 log units above the fayalite–magnetite–quartz buffer for the Hegenshan harzburgite. These petrological and geochemical characteristics, as well as the estimated P–T–fO₂ conditions support a back-arc setting for the Hegenshan ophiolitic mélange.  相似文献   

Provenance and tectonic settings of the Late Paleozoic sandstones in central Inner Mongolia,NE China: Constraints on the evolution of the southeastern Central Asian Orogenic Belt     

《Gondwana Research》2020

Late Paleozoic sedimentary strata outcrop extensively in central Inner Mongolia, and are a key to understanding the tectonic evolution of the southeastern Central Orogenic Belt. A combined analysis of petrography, whole-rock major and trace element, and Nd isotope is carried out on representative sandstones from the Late Paleozoic sedimentary strata (420–270 Ma). The sandstones are mainly wackes and litharenites in lithology, with low SiO₂/Al₂O₃ of 2.85–9.47 (averagely 5.22) and poor textural and compositional maturities, implying short sediment transportation between the depositional basins and provenances. The trace element compositions are generally comparable to that of the average upper continent crust (UCC), with negatively-sloping chondrite-normalized rare earth element distribution patterns ((La/Yb)_N = 3.43–11; averagely 6.94) and flat UCC-normalized trace element distribution patterns. The Nd isotopic compositions show great variation (Ԑ_Nd(t) = −5.01 to 5.35) with depositional time of the sandstones, and coincide well with the arc magmatic phases in central Inner Mongolia. The geochemical signatures of the sandstones indicate that the dominant provenances are intermediate to felsic arc magmatic rocks that have ages approximating the deposition, although old, recycled sediments may have made a minor contribution. An active continental arc setting during the Late Paleozoic in central Inner Mongolia, controlled by the northward subduction of the Paleo-Asian oceanic slab, was the most likely depositional tectonic setting of the sandstones. This active continental arc setting continued to at least 270 Ma, implying that the final closure of the Paleo-Asian Ocean along the Solonker suture zone most likely occurred sometime during the Late Permian to Early Triassic. The northward subduction of the Paleo-Asian Ocean is likely of West Pacific-style, in which the present-day Baolidao arc has a close genetic link with the South Mongolian microcontinent and, likely, the former originally formed as the arc margin of the latter.  相似文献   

The Dir-Utror metavolcanic sequence,Kohistan arc terrane,northern Pakistan     

《Journal of Asian Earth Sciences》1999,17(4):459-475

The Dir-Utror volcanic series forms a NE–SW trending belt within the northwestern portion of the Kohistan island arc terrane in the western Himalayas of northern Pakistan. The Kohistan arc terrane comprises a diverse suite of volcanic, plutonic, and subordinate sedimentary rocks of late Mesozoic to Tertiary age, developed prior to and after suturing of the Indo-Pakistan and Asiatic continental blocks. The Dir-Utror volcanic series near Dir is dominated by basaltic-andesite and andesite, with subordinate basalt, high-MgO basalt, dacite, and rhyolite. Porphyritic textures are dominant, with less common aphyric and seriate textures. Plagioclase is the dominant phenocryst in mafic to intermediate rocks, K-feldspar and quartz phenocrysts predominate in the dacites and rhyolites. Chlorite, epidote, albite, and actinolite are the most common metamorphic phases; blue-green amphibole, andesine, muscovite, biotite, kaolinite, sericite, carbonate, and opaques are widespread but less abundant. Phase assemblages and chemistry suggest predominant greenschist facies metamorphism with epidote-amphibolite facies conditions attained locally.Whole rock major element compositions define a calc-alkaline trend: CaO, FeO, MgO, TiO₂, Al₂O₃, V, Cr, Ni, and Sc all decrease with increasing silica, whereas alkalis, Rb, Ba, and Y increase. MORB-normalized trace element concentrations show enrichment of the low-field strength incompatible elements (Ce, La, Ba, Rb, K) and deep negative Nb, P, and Ti anomalies—patterns typical of subduction related magmas. Mafic volcanic rocks plot in fields for calc-alkaline volcanics on trace element discrimination diagrams, showing that pre-existing oceanic crust is not preserved here. All rocks are LREE-enriched, with La=16–112×chondrite, La/Lu=2.6–9.8×chondrite, and Eu/Eu*=0.5–0.9. Dacites and rhyolites have the lowest La/Lu and Eu/Eu* ratios, reflecting the dominant role of plagioclase fractionation in their formation. Some andesites have La/Lu ratios which are too high to result from fractionation of the more mafic lavas; chondrite-normalized REE patterns for these andesites cross those of the basaltic andesites, indicating that these lavas cannot be related to a common parent.The high proportion of mafic lavas rules out older continental crust as the main source of the volcanic rocks. The scarcity of more evolved felsic volcanics (dacite, rhyolite) can be explained by the nature of the underlying crust, which consists of accreted intra-oceanic arc volcanic and plutonic rocks, and is mafic relative to normal continental margins. Andesites with high La, La/Lu, K₂O, and Rb may be crustal melts; we suggest that garnet-rich high-pressure granulites similar to those exposed in the Jijal complex may be restites formed during partial melting of the crust.  相似文献   

新疆哈密卡拉塔格铜(锌)矿红石幅1∶50 000矿产地质图数据库          下载免费PDF全文

王丰丰  邓小华  李德东  卫晓锋  吕晓强  王燕超  李永胜 《中国地质》2020,47(S2):185-195

新疆哈密卡拉塔格铜(锌)矿红石幅(K46E009008)1∶50 000矿产地质图数据库是根据《固体矿产地质调查技术要求(1∶50 000)》(DD2019-02)和行业其他标准及要求,在充分利用1∶200 000、1∶50 000等区域地质调查工作成果资料的基础上,采用数字填图系统进行野外地质专项填图,并应用室内与室外填编图相结合的方法完成。本数据库将中-上奥陶统荒草坡群大柳沟组、下志留统红柳峡组和卡拉塔格组的建造类型进行了重新划分,把图幅内侵入岩时代划分为志留纪、泥盆纪、二叠纪等3期,建立了岩浆岩演化序列。图幅区内有大中小型矿床和矿点共8个,成矿时代集中分布在志留纪、石炭纪,赋矿围岩为火山碎屑岩和次火山岩,该区优势矿产以铜锌金为主,矿床类型以VMS型和次火山热液脉型矿床为主,分布在图幅东南一带。除金属矿产外,尚有膨润土矿床产出,具有较好的找矿潜力。本数据库包含5个地层单位和3期岩浆岩资料,数据量约为 15.1 MB。这些数据充分反映了该图幅 1∶50 000 矿产地质调查示范性成果,对该区矿产资源研究和勘查等具有参考意义。  相似文献   

Geochemical study of the Neoproterozoic clastic sedimentary rocks of the Khambal Formation (Sindreth Basin), Aravalli Craton,NW Indian Shield: Implications for paleoweathering,provenance, and geodynamic evolution     

《Chemie der Erde / Geochemistry》2020,80(1):125596

Petrographic and geochemical studies characterize lithologies of the Khambal Formation deposited in the Sindreth Basin as arkosic, subarkosic, and quartzarenite. Weathering indices, such as CIA and CIW in conjunction with the ACNK diagram, prescribe mostly moderate chemical weathering with intermittent pulses of extreme weathering in the source area. The discrimination diagrams suggest that these Neoproterozoic clastics were deposited in an active rift basin. Provenance indicators of the detritus components point to a terrane possessing subordinate mafic material in conjunction with large felsic components. A comparison of immobile element ratios with probable source rocks suggest that the Mesoproterozoic Delhi arc situated to the east of the Sindreth Basin could be the possible source. Our mixing calculation defines the proportion of end member components in the Delhi arc. Geodynamic considerations relate the origin of the Sindreth Basin to the processes of disintegration and reassembly of supercontinents.  相似文献   

西天山小于赞金矿成矿流体、成矿年代学特征及其地质意义     

于杰  李诺  张博  疏孙平  陈衍景 《地学前缘》2018,25(5):83-95

小于赞金矿床是产于新疆西天山也列莫顿盆地的浅成低温热液型金矿床,赋存于晚古生代大哈拉军山组火山岩中。矿石类型主要为蚀变岩型和石英脉型,主要发育硅化、黄铁绢英岩化、伊利石化、青磐岩化蚀变。流体成矿过程可分为3个阶段,分别为石英黄铁矿、石英玉髓黄铁矿和石英方解石黄铁矿阶段。小于赞金矿床流体包裹体类型单一,主要为水溶液包裹体,可分为纯液相水溶液包裹体(PL类)、富液相水溶液包裹体(L类)和富气相水溶液包裹体(V类)。石英黄铁矿阶段包裹体均一温度集中于130~190 ℃,盐度w(NaCleqv.)为0.2%~8.0%;石英玉髓黄铁矿阶段均一温度介于115~161 ℃,盐度w(NaCleqv.)为0.7%~3.4%;石英方解石黄铁矿阶段均一温度介于110~138 ℃,盐度w(NaCleqv.)为0.2%~3.4%。鉴于赋矿角砾凝灰岩的锆石U-Pb年龄为(353.8±1.8) Ma,且被下石炭统阿恰勒河组不整合覆盖,故可将小于赞金矿床的成矿时代限定在(353.8±1.8) Ma至早石炭世维宪期。锆石εHf(t)变化范围为+4.1~+8.4,平均值+6.1,两阶段Hf模式年龄tDM2变化范围为822~1 095 Ma,指示该区岩浆演化过程中有少量地幔物质的加入。综合考量矿床地质特征、流体包裹体特征和成矿时代,认为小于赞矿床为早石炭世低硫型浅成低温热液型金矿。  相似文献   

Geochronology,petrogenesis and tectonic implication of Late Paleozoic volcanic rocks from the Dashizhai Formation in Inner Mongolia,NE China     

《Gondwana Research》2017

In this paper we present geochemical, zircon U–Pb and Hf isotopic data on the late Paleozoic volcanic rocks of the Dashizhai Formation, which are exposed along the northwestern margin of the Songnen terrane in eastern Inner Mongolia. Our aim is to constrain the petrogenesis and tectonic setting of the volcanic rocks and to unravel the late Paleozoic tectonic evolution of the northwestern part of the Songnen terrane, along the eastern segment of the Central Asian Orogenic Belt. Lithologically, the Dashizhai Formation is composed mainly of rhyolitic tuff, rhyolite, dacite, andesite, basaltic andesite and basalt, with minor basaltic trachyandesite. The zircons separated from these rocks are euhedral–subhedral, have high Th/U ratios (0.2–1.6), and display broad oscillatory growth zoning, indicating a magmatic origin. The results of zircon U–Pb dating indicate the volcanic rocks formed during the early Permian (295–283 Ma). Geochemically, these volcanic rocks belong to the mid-K to high-K calc-alkaline series and are characterized by an enrichment in large ion lithophile elements (LILEs) and a depletion in high field strength elements (HFSEs, such as Nb, Ta, and Ti), similar to igneous rocks that form in active continental margin settings. Most magmatic zircons of the rhyolites show positive ε_Hf(t) values (+ 3.65 to + 13.0) and two-stage model ages (T_DM2) of 1396–551 Ma. These geochemical characteristics indicate that the acidic volcanic rocks of the Dashizhai Formation were most likely derived from the partial melting of dominantly juvenile crustal components with a possible addition of “old” materials. In contrast, the basic to intermediate volcanic rocks were derived from the partial melting of a depleted lithospheric mantle that had been metasomatized by fluids derived from a subducted slab. These data, together with regional geological investigations, suggest that the generation of the early Permian volcanic rocks of the Dashizhai Formation was related to the southward subduction of the Paleo–Asian oceanic plate beneath the Songnen terrane. This also implies that the terminal collision between the Songnen and Xing'an terranes did not occur before the early Permian.  相似文献   

Juvenile versus recycled crust in the Central Asian Orogenic Belt: Implications from ocean plate stratigraphy,blueschist belts and intra-oceanic arcs     

《Gondwana Research》2017

New or “juvenile” crust forms and grows mainly through mafic to andesitic magmatism at Pacific-type or accretionary type convergent margins as well as via tectonic accretion of oceanic and island-arc terranes and translation of continental terranes. During the last decades the juvenile or recycled nature of crust has been commonly evaluated using whole-rock isotope and Hf-in-zircon isotope methods. However, evidence for the accretionary or Pacific-type nature of an orogenic belt comes from geological data, for example, from the presence of accretionary complexes (AC), intra-oceanic arcs (IOA), oceanic plate stratigraphy units (OPS), and MORB-OIB derived blueschist belts (BSB). The Central Asian Orogenic Belt (CAOB) represents the world's largest province of Phanerozoic juvenile crustal growth during ca. 800 m.y. between the East European, Siberian, North China and Tarim cratons. From geological point of view, the CAOB is a typical Pacific-type belt as it hosts numerous occurrences of accretionary complexes, intra-oceanic arcs, OPS units, and MORB-OIB derived blueschist belts. In spite of its accretionary nature, supported by positive whole rock Nd isotope characteristics in CAOB granitoids, the Hf-in-zircon isotope data reveal a big portion of recycled crust. Such a controversy can be explained by presence of accreted microcontinents, isotopically mixed igneous reservoirs and by the tectonic erosion of juvenile crust. The most probable localities of tectonic erosion in the CAOB are the middle and southern Tienshan and southern Transbaikalia because these regions comprise a predominantly recycled crust (based on isotope data), but the geological data show the presence of intra-oceanic arcs, blueschist belts and accreted OPS with oceanic island basalts (OIB) and tectonically juxtaposed coeval arc granitoids and accretionary units. This warrants combination of detailed geological studies with isotopic results, as on their own they may not reflect such processes as tectonic erosion of juvenile crust and/or arc subduction.  相似文献   

Geochemical signature and rock associations of ocean ridge-subduction: Evidence from the Karamaili Paleo-Asian ophiolite in east Junggar,NW China     

《Gondwana Research》2017

Subduction of active spreading ridges most likely occurs throughout Earth's history. Interaction or collision between spreading center and trench, with the active spreading ridge downgoing and shallowly being buried in subduction zone, results in low-pressure but high-temperature near-trench magmatism in the forearc and accretionary prism setting. The Central Asian region, a complex orogenic belt created during the evolution and closure of the Paleo-Asian Ocean (PAO) at ~ 1000–300 Ma, provides an ideal place to study the subduction of PAO spreading ridges beneath ancient continental margins. It had been suggested that the low-pressure and high-temperature mafic and intermediate to felsic magmas from the Karamaili ophiolite (KO) in the NE corner of the Junggar basin (NW China) in Central Asia were likely produced by ridge subduction (Liu et al., 2007). In this paper, we combine our new geochemical data with previous results to show that the geochemical characteristics of the bulk of KO mafic rocks range from arc basalt-like to mid-ocean ridge basalt-like and ocean island basalt-like. Their trace element patterns range from depleted to enriched in highly incompatible elements, but depleted in Nb and Ta, indicating a subduction-influenced origin. The KO intermediate to felsic rocks are calc-alkaline and boninitic in composition and have trace element signatures similar to the associated mafic rocks. The low Nb/Ta ratios of some of the mafic rocks and boninitic character of some of the intermediate to felsic rocks reflect a highly depleted source, perhaps due to prior backarc magmatism. Major and trace element models indicate complex fractional crystallization histories of parental KO magmas to generate both the mafic and intermediate to felsic rocks, but in general, crystal fractionation occurred at 1000 to 1200 °C and moderate to low (0.5 kbar to 10 kbar) pressure or < 23 km depth. We conclude that the KO was formed in a forearc region of a subduction system that experienced ridge subduction.  相似文献