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1.
We investigate the Mesozoic–Cenozoic thermal history of the Daxi region (central SE South China Block) to evaluate the influence of the subduction of the Paleo-Pacific oceanic plate beneath the SE South China Block along the block's southeast margin on the tectonothermal evolution of the upper plate. We apply a multi-chronological approach that includes U-Pb geochronology on zircon, 40Ar/39Ar dating on muscovite and biotite from granitic rocks as well as fission-track and (U-Th-Sm)/He analyses on zircon and apatite from granitic and sedimentary rocks. The Heping granite, located in the Daxi region, has a magmatic age of ca. 441 Ma. The biotite 40Ar/39Ar ages of ca. 193 Ma for the Early Jurassic Shibei granite and ca. 160 Ma for the Late Jurassic Fogang granite, respectively, reflect magmatic cooling. The Triassic Longyuanba granite yielded a muscovite 40Ar/39Ar age of ca. 167 Ma, recording heating to ≥ 350 °C induced by nearby intrusion of Middle Jurassic granites. Zircon fission-track and (U-Th-Sm)/He ages from Lower Carboniferous–Lower Jurassic sandstones (140–70 Ma) record continuous cooling during the Cretaceous that followed extensive Middle–Late Jurassic magmatism in the Daxi region. Cretaceous cooling is related to exhumation in an extensional tectonic setting, consistent with lithospheric rebound due to foundering and rollback of the subducted Paleo-Pacific oceanic plate. Apatite fission-track (53–42 Ma) and (U-Th-Sm)/He ages (43–36 Ma), and thermal modelling document rapid cooling in the Paleocene–Eocene, which temporally coincides with continental rifting in the SE South China Block in the leadup to the opening of the South China Sea. 相似文献
2.
R. DAVID DALLMEYER MICHAEL BROWN RICHARD S. D'LEMOS ROBIN A. STRACHAN 《Journal of Metamorphic Geology》1993,11(1):137-154
Abstract The St Malo region in north-west France contains migmatites and anatectic granites derived by partial melting of metasedimentary protoliths during Cadomian orogenesis at c. 540 Ma. Previously reported Rb–Sr model ages for muscovite and biotite range from c. 550 to c. 300 Ma, and suggest variable resetting of mineral isotopic systems. These rocks display microscopic evidence for variably intense Cadomian intracrystalline plastic strain but record no obvious evidence of penetrative Palaeozoic regional deformation. 40Ar/39Ar mineral ages have been determined to evaluate better the extent, timing and significance of Palaeozoic overprinting. Eleven muscovite concentrates and one whole-rock phyllite have been prepared from various units exposed in the St Malo and adjacent Mancellian regions. In the Mancellian region, muscovite from two facies of the Bonnemain Granite Complex record 40Ar/39Ar plateau ages of c. 527 and 521 Ma. An internally discordant 40Ar/39Ar release spectrum characterizes muscovite from protomylonitic granite within the Cadomian Alexain-Deux Evailles-Izé Granite Complex, and probably records the effects of Variscan displacement along the North Armorican Shear Zone. Muscovite concentrates from anatectic granite and from Cadomian mylonites along ductile shear zones within the north-western sector of the St Malo region exhibit internally discordant 40Ar/39Ar release spectra which suggest variable and partial late Palaeozoic rejuvenation. By contrast, muscovite concentrates from samples of variably mylonitic Brioverian metasedimentary rocks exposed within the south-eastern sector of the St Malo region display internally concordant apparent age spectra which define plateaux of 326–320 Ma. A whole-rock phyllite sample from Brioverian metasedimentary rocks exposed along the eastern boundary of the St Malo region displays an internally discordant argon release pattern which is interpreted to reflect the effects of a partial late Palaeozoic thermal overprint. Muscovite from the Plélan granite, part of the Variscan Plélan-Bobital Granite Complex, yields a 40Ar/39Ar plateau age of c. 307 Ma. The 40Ar/39Ar results indicate that Cadomian rocks of the St Malo region have undergone a widespread and variable Palaeozoic (Carboniferous) rejuvenation of intracrystalline argon systems which apparently did not affect the Mancellian region. This rejuvenation was not accompanied by penetrative regional deformation, and was probably of a static thermal–hydrothermal origin. The heat source for rejuvenation was probably either the result of heating during Variscan extension or advection from Variscan granites which are argued to underlie the St Malo region. 相似文献
3.
He–Ar Isotopic Tracing of Pyrite from Ore-forming Fluids of the Sanshandao Au Deposit, Jiaodong Area
HAN Zhenyu YU Xiaowei LI Shoujun Tian Jingxiang WANG Zhongliang YU Xiaojing WANG Ligong 《《地质学报》英文版》2019,93(6):1797-1807
The Sanshandao Au deposit is located in the famous Sanshandao metallogenic belt, Jiaodong area. To date, accumulative Au resources of 1000 t have been identified from the belt. Sanshandao is a world-class gold deposit with Au mineralization hosted in Early Cretaceous Guojialing-type granites. Thus, studies on the genesis and ore-forming element sources of the Sanshandao Au deposit are crucial. He and Ar isotopic analyses of fluid inclusions from pyrite(the carrier of Au) indicate that the fluid inclusions have 3 He/4 He=0.043–0.21 Ra with an average of 0.096 Ra and 40 Ar/36 Ar=488–664 with an average of 570.8. These values represent the initial He and Ar isotopic compositions of ore-forming fluids for trapped fluid inclusions. The comparison of H–O isotopic characteristics combined with deposit geology and wall rock alteration reveals that the ore-forming fluids of the Sanshandao Au deposit show mixed crust–mantle origin characteristics, and they mainly comprise crust-derived fluid mixed with minor mantle-derived fluid and meteoric water during the uprising process. The ore-forming elements were generally sourced from pre-Cambrian meta-basement rocks formed by Mesozoic reactivation and mixed with minor shallow crustal and mantle components. 相似文献
4.
《Chemical Geology》2003,193(3-4):195-214
In most orogenic belts, the age of HP metamorphism and subsequent exhumation events still remain open to debate since geochronology can yield results which appear to conflict with the closure temperature concept [Dodson, M.H., 1973. Contrib. Mineral. Petrol. 40, 259–274], and because the behaviour of daughter radiogenic isotopes under HP to UHP conditions is poorly constrained. To obtain new data on isotope migration under high-pressure conditions, two undeformed HP metagranites with partially preserved magmatic assemblages from the French Variscan belt were investigated using the 40Ar/39Ar laser probe and U–Pb ion probe methods. In both cases, 40Ar/39Ar biotite and U–Pb zircon ages are consistent and could be related to the emplacement of pre-orogenic granites, despite petrological evidence of a strong metamorphic overprint during the Variscan orogeny. Temperatures experienced by the granites during subduction and exhumation events were more than 400 °C above that normally estimated for argon retention in biotite, but failed to cause significant resetting of the mica 40Ar/39Ar chronometer. Only a weak intragrain redistribution of argon is evidenced with the laser probe up to the contact with metamorphic garnet fringing biotite. By contrast, a complete resetting of biotite ages occurs in gneisses enclosing the metagranites. These results suggest that, in these dry undeformed HP metagranites, the thermally activated diffusion was relatively ineffective and that recrystallisation is the main process which controlled isotopic exchanges of Ar and Pb. It is likely that the absence of pervasive deformation and fluid circulation has also exercised some control on the preservation of pre-metamorphic isotopic signature in the studied rocks. The possible influence of several other parameters is also discussed. This example reveals that recovering thermochronological information in high-pressure metamorphic rocks is not straightforward and that great caution must be paid in the use of ages for the reconstruction of P–T–t paths. 相似文献
5.
Valeria Murgulov William L. Griffin Suzanne Y. O’Reilly 《International Journal of Earth Sciences》2013,102(3):647-669
In situ U–Pb dating and Lu–Hf systematics of zircon in granites of the Hodgkinson Province in the northern Tasman orogenic belt, Queensland, Australia, reveal input of isotopically more evolved crustal magmas and larger ranges in 176Hf/177Hf in the Carboniferous I-type granites (0.28219–0.28269; weighted average ~0.28245) than in the Permian S-type granites (0.28249–0.28280; weighted average ~0.28262) and Permian I-type granites (0.28253–0.28274; weighted average ~0.28260). The wide range in the Hf-isotope compositions of zircons in the Carboniferous and Permian granites can be explained by remelting of a heterogeneous Mesoproterozoic crustal source, whereas a narrow range reflects the subsequent dissolution of inherited grains/cores and magma homogenisation before zircon crystallisation. Alternatively, mixing between the most radiogenic and unradiogenic magmas can produce the isotopic variation seen in other Carboniferous granites. Remelting of Neoproterozoic average crust or mafic younger crust can produce the more radiogenic Hf-isotope compositions of zircons in the Permian S-type granites. An overlap between the Hf-isotope signatures of the Carboniferous I-type granites in the southwestern Hodgkinson Province and the northeastern Australian craton (0.28211–0.28254) and evidence for major magmatic events at 1,585–1,545 and 345–300 Ma imply that the southwestern province is underlain by cratonic crust, which wedges out towards the northeast. The more radiogenic Hf-isotope signature of the Permian granites and a lack of evidence for these major magmatic events in the southeastern and central Hodgkinson Province imply that these parts are characterised by different crustal sources and crustal evolution histories. 相似文献
6.
The Attic‐Cycladic crystalline belt in the central Aegean region records a complex structural and metamorphic evolution that documents Cenozoic subduction zone processes and exhumation. A prerequisite to develop an improved tectono‐metamorphic understanding of this area is dating of distinct P–T–D stages. To evaluate the geological significance of phengite ages of variably overprinted rocks, 40Ar/39Ar and Rb–Sr analyses were undertaken on transitional blueschist–greenschist and greenschist facies samples from the islands of Syros and Sifnos. White mica geochronology indicates a large age variability (40Ar/39Ar: 41–27 Ma; Rb–Sr: 34–20 Ma). Petrologically similar samples have either experienced greenschist facies overprinting at different times or variations in ages record variable degrees of greenschist facies retrogression and incomplete resetting of isotopic systematics. The 40Ar/39Ar and Rb–Sr data for metamorphic rocks from both islands record only minor, localized evidence for Miocene ages (c. 21 Ma) that are well documented elsewhere in the Cyclades and interpreted to result from retrogression of high‐pressure mineral assemblages during lower pressure metamorphism. Field and textural evidence suggests that heterogeneous overprinting may be due to a lack of permeability and/or limited availability of fluids in some bulk compositions and that retrogression was more or less parallel to lithological layering and/or foliation as a result of, possibly deformation‐enhanced, channelized fluid ingress. Published and new 40Ar/39Ar and Rb–Sr data for both islands indicate apparent age variations that can be broadly linked to mineral assemblages documenting transitional blueschist‐to‐greenschist‐ and/or greenschist facies metamorphism. The data do not record the timing of peak HP metamorphism, but may accurately record continuous (partial) resetting of isotopic systematics and/or (re)crystallization of white mica during exhumation and greenschist facies retrogression. The form of 40Ar/39Ar phengite age spectra are complex with the lowest temperature steps yielding Middle to Late Miocene ages. The youngest Rb–Sr ages suggest maximum ages of 20.6 ± 0.8 Ma (Syros) and 22.5 ± 0.6 Ma (Sifnos) for the timing of greenschist facies overprinting. The results of this study further accentuate the challenges of interpreting isotopic data for white mica from polymetamorphic terranes, particularly when mixing of populations and/or incomplete resetting of isotopic systematics occurs during exhumation. These data capture the full range of isotopic age variations in retrogressed HP rocks documented in previous isotopic studies, and can be interpreted in terms of the geodynamic evolution of the Aegean. 相似文献
7.
Zijinshan is a large porphyry–epithermal Cu–Au–Mo–Ag ore system located in the Zijinshan mineral field (ZMF) of southwestern Fujian Province, China. Although it is commonly accepted that the early Cretaceous magmatism and the metallogenesis of the mineral field are closely related, the tectonic setting for the ore-forming event(s) has been controversial and regarded as either extensional or subduction-related. New U–Pb zircon geochronology, Sr–Nd–Pb isotopic systematics, and geochemical data presented here from granites and volcanic rocks in the mineral field help to clarify this uncertainty.LA–MC–ICP-MS U–Pb zircon analyses yield weighted mean ages of between ca. 165 and 157 for the monzogranite, ca. 112 Ma for granodiorite, and between ca. 111 and 102 Ma for nine samples of volcanic units in the study area. These dates, integrated with previous geochronological data, indicate that there were two magmatic events in the area during the Middle to Late Jurassic and the Early Cretaceous. Major and trace element geochemistry indicates that these rocks are high-K, calc-alkaline granites, are enriched in LREE and Th, U, Ta, Nd, Sm and Yb, and depleted in Ba, K, Sr, P, Ti and Y. These features are characteristic of volcanic-arc granites or active-continental margin granites. The Middle to Late Jurassic monzogranitic plutons in the region have initial 87Sr/86Sr ratios of 0.7096 to 0.7173, εNdT values of − 10.1 to − 7.6, 206Pb/204Pb isotope ratios of 18.51–18.86, 207Pb/204Pb isotope ratios of 15.64–15.73, and 208Pb/204Pb isotope ratios of 38.76–39.18. The Early Cretaceous granodiorite and volcanic rocks are distinctly different with initial 87Sr/86Sr ratios of 0.7055–0.7116, εNdT values of − 8 to 0.5, 206Pb/204Pb ratios ranging between 18.49 and 19.77, 207Pb/204Pb ratios of 15.63–15.71, and 208Pb/204Pb ratios of 38.71–40.62. These characteristics suggest that the source for the Middle to Late Jurassic monzogranitic plutons is a partially melted Mesoproterozoic substrate, with a minor component from Paleozoic material, whereas the Early Cretaceous granodiorite and volcanic rocks may represent mixing of crustal and mantle-derived melts. It is therefore suggested that the Middle to Late Jurassic monzogranitic plutons, and the Early Cretaceous granodiorite and volcanic rocks in the ZMF are the result of an active continental-margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent. Given that the mineralization and the early Cretaceous granodiorite and volcanic rocks in the area are genetically related, the Zijinshan porphyry–epithermal ore system formed in the subduction-related tectonic setting. 相似文献
8.
O. R. Minina N. A. Doronina G. E. Nekrasov L. I. Vetluzhskikh V. S. Lantseva V. A. Aristov S. V. Naugol’nykh A. V. Kurilenko E. V. Khodyreva 《Geotectonics》2016,50(3):276-294
New data on the composition, age, structure, and geodynamic settings of the Upper Silurian–lower Middle Carboniferous rocks in the Baikal–Vitim Fold System (BVFS) are reported. These rocks make up the Early Hercynian structural stage of the BVFS, within which the Uda–Vitim, Vitimkan–Tsipa, and Turka–Kurba lithotectonic zones are recognized. The Early Hercynian stage combines rocks of two stratigraphic levels: Upper Silurian–Upper Devonian (S2–D3) and Upper–Devonian–Middle Carboniferous (D3–C21). On the basis of lithostratigraphic and spatiotemporal relationships between sedimentary and volcanic–sedimentary complexes of the Early Hercynian stage three formations are identified, which characterize the main tectonic regimes of the early half of the Late Paleozoic. It has been established that a common paleobasin that evolved through consecutively changing geodynamic settings at the passive and active continental margins existed in the Silurian (?)–early Middle Carboniferous in the northeastern part (in present-day coordinates) of the western Transbaikal region. 相似文献
9.
《International Geology Review》2012,54(14):1801-1816
We present new geochronological and geochemical data for granites and volcanic rocks of the Erguna massif, NE China. These data are integrated with previous findings to better constrain the nature of the massif basement and to provide new insights into the subduction history of Mongol–Okhotsk oceanic crust and its closure. U–Pb dating of zircons from 12 granites previously mapped as Palaeoproterozoic and from three granites reported as Neoproterozoic yield exclusively Phanerozoic ages. These new ages, together with recently reported isotopic dates for the metamorphic and igneous basement rocks, as well as Nd–Hf crustal-residence ages, suggest that it is unlikely that pre-Mesoproterozoic basement exists in the Erguna massif. The geochronological and geochemical results are consistent with a three-stage subduction history of Mongol–Okhotsk oceanic crust beneath the Erguna massif, as follows. (1) The Erguna massif records a transition from Late Devonian A-type magmatism to Carboniferous adakitic magmatism. This indicates that southward subduction of the Mongol–Okhotsk oceanic crust along the northern margin of the Erguna massif began in the Carboniferous. (2) Late Permian–Middle Triassic granitoids in the Erguna massif are distributed along the Mongol–Okhotsk suture zone and coeval magmatic rocks in the Xing’an terrane are scarce, suggesting that they are unlikely to have formed in association with the collision between the North China Craton and the Jiamusi–Mongolia block along the Solonker–Xra Moron–Changchun–Yanji suture zone. Instead, the apparent subduction-related signature of the granites and their proximity to the Mongol–Okhotsk suture zone suggest that they are related to southward subduction of Mongol–Okhotsk oceanic crust. (3) A conspicuous lack of magmatic activity during the Middle Jurassic marks an abrupt shift in magmatic style from Late Triassic–Early Jurassic normal and adakite-like calc-alkaline magmatism (pre-quiescent episode) to Late Jurassic–Early Cretaceous A-type felsic magmatism (post-quiescent episode). Evidently a significant change in geodynamic processes took place during the Middle Jurassic. Late Triassic–Early Jurassic subduction-related signatures and adakitic affinities confirm the existence of subduction during this time. Late Jurassic–Early Cretaceous post-collision magmatism constrains the timing of the final closure of the Mongol–Okhotsk Ocean involving collision between the Jiamusi–Mongolia block and the Siberian Craton to the Middle Jurassic. 相似文献
10.
A.S. Mekhonoshin A.G. Vladimirov V.G. Vladimirov N.I. Volkova T.B. Kolotilina E.I. Mikheev A.V. Travin D.S. Yudin V.V. Khlestov S.V. Khromykh 《Russian Geology and Geophysics》2013,54(10):1219-1235
Early Caledonides in the Olkhon region of western Cisbaikalia, being part of the folded framing of the Siberian craton, are a unique geologic object for studying processes of mantle–crust interaction at deep levels of the Earth’s crust. This paper describes restitic ultramafic bodies and boudins spatially confined to faults (blastomylonite sutures), as well as synkinematic granites related to amphibolite facies of metamorphism. Estimates are given for the PT-conditions of metamorphic rocks from the folded framing of the ultramafic bodies, the chemical and mineral compositions of ultramafic rocks, blastomylonites and synkinematic granites, and the results of U–Pb and Ar–Ar isotopic dating. Particular attention is paid to the thermal history of tectonic exposure of the ultramafic bodies as relics of the paleo-oceanic crust in the Early Caledonian collisional system of western Cisbaikalia. 相似文献
11.
Early–Middle Jurassic igneous rocks (190–170 Ma) are distributed in an E–W-trending band within the Nanling Tectonic Belt, and have a wide range of compositions but are only present in limited volumes. This scenario contrasts with the uniform but voluminous Middle–Late Jurassic igneous rocks (165–150 Ma) in this area. The Early–Middle Jurassic rocks include oceanic-island basalt (OIB)-type alkali basalts, tholeiitic basalts and gabbros, bimodal volcanic rocks, syenites, A-type granites, and high-K calc–alkaline granodiorites. Geochemical and isotopic data indicate that alkaline and tholeiitic basalts and syenites were derived from melting of the asthenospheric mantle, with asthenosphere-derived magmas mixing with variable amounts of magmas derived from melting of metasomatized lithospheric mantle. In comparison, A-type granites in the study area were probably generated by shallow dehydration-related melting of hornblende-bearing continental crustal rocks that were heated by contemporaneous intrusion of mantle-derived basaltic magmas, and high-K calc-alkaline granodiorites resulted from the interaction between melts from upwelling asthenospheric mantle and the lower crust. The Early–Middle Jurassic magmatic event is spatially variable in terms of lithology, geochemistry, and isotopic systematics. This indicates that the deep mantle sources of the magmas that formed these igneous rocks were significantly heterogeneous, and magmatism had a gradual decrease in the involvement of the asthenospheric mantle from west to east. These variations in composition and sourcing of magmas, in addition to the spatial distribution and the thermal structure of the crust–mantle boundary during this magmatic event, indicates that these igneous rocks formed during a period of rifting after the Indosinian Orogeny rather than during subduction of the paleo-Pacific oceanic crust. 相似文献
12.
18O/16O ratios have been obtained for 99 minerals from rocks of the Hiroshima granite complex and adjacent Ryoke granites. Zonal distribution of oxygen isotopes is observed on a regional scale almost parallel to the extension of the Ryoke plutono-metamorphic belt, granites in or around the metamorphic belt being 2–3%0 richer in 18O than those farther away from the belt. Isotopic fractionations among coexisting minerals indicate that isotopic zonation existed at a magmatic stage. The zonal enrichment of 18O in the granite magma in the Ryoke belt and its periphery is a result of isotopic interaction between country rocks and the magma through fluid media. Genetic relationship between granites of the Ryoke and Chugoku belts are discussed with regard to the geological situation of the former belt. 相似文献
13.
In eastern China, the Dabie Shan–Su–Lu orogenic belt has been separated by the Tan–Lu sinistral strike–slip fault. Mylonites are exposed along the strike–slip fault system in the southern segment, and along the eastern margin of the Dabie Shan orogenic belt. The country rocks of the mylonites are retrograde UHP eclogites, gneissic granites, muscovite granites and gneisses. The ductile strike–slip shear zone trends 30–40°N (NE30–40°‐trending) and exhibits stretching lineations and nearly vertical, SE‐dipping foliations. Most of the zircon grains separated from mylonites have a weighted average radiometric age of 233 ± 6–225 ± 6 Myr. These data constrain the onset of the Tan–Lu sinistral strike–slip movement and imply that the Tan–Lu sinistral strike–slip motion developed after retrograde UHP metamorphism. The related phengite within the eclogite rocks on the western side of the Tan–Lu fault, with 40Ar/39Ar plateau ages of c. 182–190 Myr, is also deformed and aligned parallel to the almost NE trending stretching lineations. Non‐metamorphosed granites exhibit sinistral strike–slip shearing and indicate that the Tan–Lu fault initially developed after 182–190 Myr. Muscovite collected from the mylonite yields 40Ar/39Ar plateau ages of 162 ± 1–156 ± 2 Myr. The zircon SHRIMP age data, the muscovite 40Ar/39Ar plateau ages, together with structural and petrological field information support the interpretation that the Tan–Lu strike–slip fault was not related to the Yangtze–north China plates collision, but corresponded to the formation of a NE‐trending tectonic framework in eastern China starting c. 165–160 Ma. 相似文献
14.
Whole-rock Rb-Sr isochron dating of Sn-bearing granites and alkaline rocks from Gejiu, Yunnan Province has been conducted
for their emplacement ages and initial87Sr/86Sr ratios. The Sr isotopic compositions of apatites from some basic rocks in Jiasha, and granite bodies also have been studied
in detail. The genesis and evolution of Gejiu Sn-bearing granites as well as ore-search indicators are discussed on the basis
of the available data in conjunction with the geochemical data on trace elements (such as Rb and Sr), Sr isotopic characteristics
of the volcanic rocks, meta-diabase and host rocks and the isotopic features of ore leads. 相似文献
15.
《International Geology Review》2012,54(4):393-407
U–Pb zircon geochronological, geochemical, and whole-rock Sr–Nd isotopic analyses are reported for a suite of Karamay A-type granites from the Central Asian Orogenic Belt (CAOB) in the western Junggar region of northern Xinjiang, Northwest China, with the aim of investigating the sources and petrogenesis of A-type granites. The Karamay pluton includes monzogranite and syenogranite. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating yielded a concordant weighted mean 206Pb/238U age of 304 ± 5 Ma (n = 11), defining a late Carboniferous magmatic event. Geochemically, the rock suite is characterized by high SiO2, FeOt/MgO, total alkalies (K2O + Na2O), Zr, Nb, Y, Ta, Ga/Al, and rare earth elements (REEs) (except for Eu), and low contents of MgO, CaO, and P2O5, with negative Ba, Sr, P, Eu, and Ti anomalies. These features indicate an A-type affinity for the Karamay granitic intrusions. Isotopically, they display consistently depleted Sr–Nd isotopic compositions (initial 87Sr/86Sr = 0.7014–0.7022, ?Nd(t) = +5.6–+7.0). Geochronological, geochemical, and isotopic data suggest that the Karamay A-type granites were derived from remelting juvenile lower crust, followed by fractional crystallization. The Karamay A-type granites as well as widespread late Carboniferous magmatism in the western Junggar region of the southwestern CAOB may have been related to ridge subduction and a resultant slab window. This further demonstrates the importance of the late Palaeozoic granitic magmatism in terms of vertical crustal growth in northern Xinjiang. 相似文献
16.
U-Pb and 39Ar/40Ar dating and Sm-Nd and Pb-Pb isotopic study of the Kalguty molybdenum-tungsten ore-magmatic system, Southern Altai 总被引：1，自引：0，他引：1
I. Yu. Annikova A. G. Vladimirov S. A. Vystavnoi D. Z. Zhuravlev N. N. Kruk E. N. Lepekhina D. I. Matukov E. N. Moroz S. V. Palesskii V. A. Ponomarchuk S. N. Rudnev S. A. Sergeev 《Petrology》2006,14(1):81-97
The Kalguty ore-magmatic system comprises two intrusive complexes: the Kalguty granite-leucogranite complex and Eastern Kalguty complex of dikes and small intrusions. U-Pb dating of individual zircon grains from granites of the main intrusive phase demonstrated that the crystallization age of small grains of magmatic habits and outer rims of large grains is almost concordant and is 216 ± 3 Ma. Ar-Ar isotope study shows that the K-Ar system of biotites from granites of the main phase within the Kalguty ore field was disturbed (radiogenic Ar was partially lost) and gave an age of 202 ± 1 Ma. The Ar-Ar dating of muscovites from intraore and postore dikes of the Eastern Kalguty complex devoid of signatures of postmagmatic recrystallization and superimposed greisenization gave similar ages of 205–201 Ma. This date is considered as the emplacement age of the Eastern Kalguty dikes and associated complex W-Mo-Bi-Be ore mineralization. Sm-Nd and Pb-Pb isotopic study of granites, ongonites, and elvans of the Kalguty ore-magmatic system and host rocks shows that these systems were closed. For example, recalculation of Nd isotopic ratios for corresponding ages of crystallization of magmatic systems (216 and 205 Ma) shows that ?Nd(T) values decrease from ?1.9 to ?3.5 ... ?5.08 with transition from granite-leucogranite to subvolcanic granite porphyry, ongonite, and elvan dikes with corresponding increase of model ages of protoliths from 1.0 to 1.25 Ga. Lead isotopic ratios for leaching residues of whole-rock samples of all rock varieties (206Pb/204Pb = 18.305–18.831; 207Pb/204Pb = 15.527–15.571) are plotted well below the line of average crustal lead evolution according to the Stacey-Kramers model. 相似文献
17.
K. R. Kovalev O. N. Kuzmina B. A. Dyachkov A. G. Vladimirov Yu. A. Kalinin E. A. Naumov M. V. Kirillov I. Yu. Annikova 《Geology of Ore Deposits》2016,58(2):116-133
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
18.
《Australian Journal of Earth Sciences》2013,60(5):645-664
Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analysis of zircons confirm a Late Devonian to Early Carboniferous age (ca 360–350 Ma) for silicic volcanic rocks of the Campwyn Volcanics and Yarrol terrane of the northern New England Fold Belt (Queensland). These rocks are coeval with silicic volcanism recorded elsewhere in the fold belt at this time (Connors Arch, Drummond Basin). The new U–Pb zircon ages, in combination with those from previous studies, show that silicic magmatism was both widespread across the northern New England Fold Belt (>250 000 km2 and ≥500 km inboard of plate margin) and protracted, occurring over a period of ～15 million years. Zircon inheritance is commonplace in the Late Devonian — Early Carboniferous volcanics, reflecting anatectic melting and considerable reworking of continental crust. Inherited zircon components range from ca 370 to ca 2050 Ma, with Middle Devonian (385–370 Ma) zircons being common to almost all dated units. Precambrian zircon components record either Precambrian crystalline crust or sedimentary accumulations that were present above or within the zone of magma formation. This contrasts with a lack of significant zircon inheritance in younger Permo‐Carboniferous igneous rocks intruded through, and emplaced on top of, the Devonian‐Carboniferous successions. The inheritance data and location of these volcanic rocks at the eastern margins of the northern New England Fold Belt, coupled with Sr–Nd, Pb isotopic data and depleted mantle model ages for Late Palaeozoic and Mesozoic magmatism, imply that Precambrian mafic and felsic crustal materials (potentially as old as 2050 Ma), or at the very least Lower Palaeozoic rocks derived from the reworking of Precambrian rocks, comprise basement to the eastern parts of the fold belt. This crustal basement architecture may be a relict from the Late Proterozoic breakup of the Rodinian supercontinent. 相似文献
19.
Magnesium isotopic compositions, along with new Sr–Nd–Pb isotopic data and elemental analyses, are reported for 12 Miocene tourmaline-bearing leucogranites, 15 Eocene two-mica granites and 40 metamorphic rocks to investigate magnesium isotopic behaviors during metamorphic processes and associated magmatism and constrain the tectonic-magmatic-metamorphic evolution of the Himalayan orogeny. The gneisses, granulites and amphibolites represent samples of the Indian lower crust and display large range in δ26Mg from −0.44‰ to −0.09‰ in mafic granulites, −0.44‰ to −0.10‰ in amphibolites, and −0.70‰ to −0.03‰ in granitic gneisses. The average Mg isotopic compositions of the granitic gneisses (−0.19 ± 0.34‰), mafic granulites (−0.22 ± 0.17‰) and amphibolites (−0.25 ± 0.24‰) are similar, indicating the limited Mg isotope fractionation during prograde metamorphism from granitic gneisses to mafic granulites and retrograde metamorphism from mafic granulites to amphibolites. The Eocene two-mica granites and Miocene leucogranites are characterized by large variations in elemental and Sr–Nd–Pb isotopic compositions. The leucogranites and two-mica granites have their corresponding (87Sr/86Sr)i varying from 0.7282 to 0.7860 and 0.7163 to 0.7191, (143Nd/144Nd)i from 0.511888 to 0.512040 and 0.511953 to 0.512076, 207Pb/204Pb from 15.7215 to 15.7891 and 15.7031 to 15.7317, 208Pb/204Pb from 38.8521 to 39.5286 and 39.2710 to 39.4035, and 206Pb/204Pb from 18.4748 to 19.0139 and 18.7834 to 18.9339. However, they have similar Mg isotopic compositions (−0.21‰ to +0.06‰ versus −0.24‰ to +0.09‰), which did not originate from fractional crystallization nor source heterogeneity. Based on hornblende/biotite/muscovite dehydration melting reaction and Mg isotopic variations in two-mica granites and leucogranites with the proceeding metamorphism, along with elemental discrimination diagrams, Eocene two-mica granites and Miocene leucogranites could be related to hornblende dehydration melting and muscovite dehydration melting, respectively. Mg isotopic compositions of Eocene two-mica granites become heavier compared to the source because of residues of isotopically light garnet in the source; while those of Miocene leucogranites become lighter because of entrainment of isotopically light garnet from the source region. Thus, a new model for crustal anatexis and Himalayan orogenesis was proposed based on the Mg isotope fractionation in the leucogranites and metamorphic rocks. This model emphasizes a successive process from Indian continental subduction to rapid exhumation of the Higher Himalayan Crystalline Series (HHCS). The former underwent high-temperature (HT) and high-pressure (HP) granulite-facies prograde metamorphism, which resulted in the hornblende dehydration melting and the formation of Eocene two-mica granites; while the latter experienced amphibolite-facies retrogression and decompression, which resulted in the muscovite dehydration melting and the formation of Miocene leucogranites. 相似文献
20.
Geochemical and Nd, Sr Isotopic Study of the Post-Orogenic Granites in the Yidun Arc Belt of Northern Sanjiang Region, Southwestern China 总被引：7，自引：0，他引：7
Abstract: In the arc (basin)–back area of the Yidun arc belt in the north segment of the Sanjiang tectonic zone, southwestern China, there occurs a post‐orogenic granite belt extending for more than 300 km in NNW direction. It strides across two different tectonic units of the arc (basin)–back area and the subduction area, and is accompanied by extensive Ag‐Sn polymetal–lic mineralizations. More than ten granite bodies have very similar geochemical characteristics: high SiO2 (73.8–76.3 wt%) and K2O+Na2O (7.16‐8.41 %), and low Al2O3 (11.9–13.6 %), CaO (0.46‐1.54 %) and MgO (0.16‐0.61 %), as well as high enrichment of Nb, Ta, Ga and Y, and strong depletion of Sr and Eu. Most of these features are peculiar to A‐type granite. Rb‐Sr and 40Ar/39Ar isotopic dating results indicate that the formation ages of the granites decrease from 103.7 Ma of the north end to 75.2 Ma near the south end, and that the magmatism became younger from north to south. The tectonic environment analysis clearly reveals that they were formed in post‐orogenic within–plate extension settings. The magma genesis was controlled by a united crustal extension regime after the arc‐continent collision. The granites have low Nd values ranging from –4.96 to –8.40, whereas the Sr values vary greatly ranging from –31.7 to 296, reflecting that the source composition transited from mantle – differentiated igneous rocks in the north to basement – dominated metamorphosed sedimentary rocks in the south. Under high temperature and water‐absent conditions, the anatexes of the crustal rocks made a great amount of plagioclase separated from melts and left in magma sources. Through this mechanism, the post‐orogenic granites took geo‐chemical characteristics such as low Al2O3 and CaO, and strong depletion of Sr and Eu. 相似文献