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1.
《International Geology Review》2012,54(4):428-445
The Triassic (Indosinian) granites in the South China Block (SCB) have important tectonic significance for understanding the evolution of Eastern Asia. The Dengfuxian biotite granite in eastern Hunan Province, China, reported in this article, was recognized as Late Triassic (late Indosinian) weakly peraluminous A-type granite with a zircon laser ablation inductively coupled plasma mass spectrometry U–Pb age of 225.7 ± 1.6 Ma. It is enriched in F, Cs, Rb, Th, high field strength elements, and rare earth elements (REEs) and depleted in Ba, Sr, P, Ti, Nb, and Ta, with high Ga/Al ratios and zircon saturation temperatures. The Dengfuxian biotite granite shows high initial Sr isotope values (0.715932 to 0.716499) and negative ?Nd(t) (?10.46 to ?9.67) and ?Hf(t) (?9.92 to ?6.29) values, corresponding to the Nd model ages of 1.79 to 1.85 Ga and the Hf model ages of 1.65 to 1.88 Ga. It is proposed that the Dengfuxian biotite granite was derived from high-temperature partial melting of the Palaeoproterozoic lower crust undergoing granulitization. Some Late Triassic A-type granites were recently identified in the SCB with the ages between 202 and 232 Ma. These A-type granites have the same geochemical characteristics and petrogenesis as Dengfuxian A-type granite, and show A2-subtype granite affinity. The Late Triassic A-type granite formed a NE-trending granite belt, which is consistent with the main NE-trending faults in the SCB. The formation of these A-type granites was in response to the subduction of the palaeo-Pacific plate underneath the SCB, and indicates an extensional tectonic environment in the SCB. Combined with previous studies on tectonic evolution, we suggest that there may be a tectonic transition inside the SCB from compression to extension at least from 225 to 230 Ma. 相似文献
2.
Whole rock major and trace element and Sr-, Nd- and Hf-isotope data, together with zircon U-Pb, Hf- and O-isotope data, are reported for the Nb-Ta ore bearing granites from the Lingshan pluton in the Southeastern China, in order to trace their petrogenesis and related Nb-Ta mineralization. The Lingshan pluton contains hornblende-bearing biotite granite in the core and biotite granite, albite granite and pegmatite at the rim. In addition, numerous mafic microgranular enclaves occur in the Lingshan granites. Zircon SIMS U-Pb dating gives consistent crystallization ages of ca. 132 Ma for the Lingshan granitoids and enclaves, consistent with the Nb-Ta mineralization age of ∼132 Ma, indicating that mafic and felsic magmatism and Nb-Ta mineralization are coeval. The biotite granites contain hornblende, and are metaluminous to weakly peraluminous, with high initial 87Sr/86Sr ratios of 0.7071–0.7219, negative εNd(t) value of −5.9 to −0.3, εHf(t) values of −3.63 to −0.32 for whole rocks, high δ18O values and negative εHf(t) values for zircons, and ancient Hf and Nd model ages of 1.41–0.95 Ga and 1.23–1.04 Ga, indicating that they are I-type granites and were derived from partial melting of ancient lower crustal materials. They have variable mineral components and geochemical features, corresponding extensive fractionation of hornblende, biotite and feldspar, with minor fractionation of apatite. Existence of mafic microgranular enclaves in the biotite granites suggests a magma mixing/mingling process for the origin of the Lingshan granitoids, and mantle-derived mafic magmas provided the heat for felsic magma generation. In contrast, the Nb-Ta mineralized albite granites and pegmatites have distinct mineral components and geochemical features, which show that they are highly-fractionated granites with extensive melt and F-rich fluid interaction in the generation of these rocks. The fluoride-rich fluids induce the enrichment in Nb and Ta in the highly evolved melts. Therefore, we conclude that the Nb-Ta mineralization is the result of hydrothermal process rather than crystal fractionation in the Lingshan pluton, which provides a case to identify magmatic and hydrothermal processes and evaluate their relative importance as ore-forming processes. 相似文献
3.
The Miao'ershan uranium ore district is one of the most important granite-hosted uranium producers in South China. There are several Triassic granite plutons in the Miao'ershan batholith, but uranium ore deposits mainly occur within the Douzhashan granitic body. Precise zircon U–Pb dating indicated that these Triassic granite plutons were emplaced during 204 to 215 Ma. The Douzhashan U-bearing granite lies in the central part of the Miao'ershan batholith, and has higher U contents (8.0 to 26.1 ppm, average 17.0 ppm) than the nearby Xiangcaoping granite (5.0 to 9.3 ppm, average 7.0 ppm) and the Yangqiaoling granite (6.4 to 18.3 ppm, average 11.5 ppm) in the south part of the batholith. The Douzhashan granite is composed of medium-grained two-mica granite, whereas the Xiangcaoping and Yangqiaoling granites are composed of porphyritic biotite granite. Both the Xiangcaoping and Douzhashan granites have high A/CNK ratios (> 1.10), high (87Sr/86Sr)i ratios (> 0.720) and low εNd(t) values (− 11.3 to − 10.4), suggesting that they belong to strongly peraluminous S-type granites. The Douzhashan granite has low CaO/Na2O ratios, high Rb/Sr and Rb/Ba ratios, indicating a partial melting origin of clay-rich pelitic rocks. In contrast, the Xiangcaoping granite formed from clay-poor psammite-derived melt. The Yangqiaoling granite shows different geochemical characteristics with the Douzhashan and Xiangcaoping granites, indicating a different magma source. The Yangqiaoling granite has higher εNd(t) of − 9.4 to − 8.3 and variable A/CNK values from 0.98 to 1.19, suggesting a mixture source of meta-sedimentary rocks and meta-igneous rocks. Crystallization fractionation is not the main mechanism for U enrichment in the Douzhashan granite. We suggest that U-rich pelitic rock sources may be the key factor to generate peraluminous U-bearing granites in South China. Searching for those granites which are reduced, strongly peraluminous and were derived from U-rich pelitic rocks, is the most effective way for exploring granite-hosted U deposits. 相似文献
4.
Xiaolonghe is a poorly studied greisen-type tin deposit that is hosted by biotite granite in the western Yunnan tin belt. The mineralisation-related metaluminous and weak peraluminous granite is characterised by high Si, Al and K and low Mg, Fe and Ca, with an average A/CNK of 1.02. The granite is enriched in LILEs (K and Rb), LREEs and HFSEs (Zr, Hf, Th, U and Ce) and depleted in Ba, Nb, Sr, P, and Ti, with zircon εHf(t) = − 10.8 to − 7.5 (TDM2 = 1.61–1.82 Ga). These characteristics indicate that the magma was generated by the partial melting of a thickened ancient crust. LA-ICP-MS U–Pb dating of igneous zircon and hydrothermal cassiterite yield ages of 71.4 ± 0.4 Ma and 71.6 ± 4.8 Ma, respectively. The igneous biotite and hydrothermal muscovite samples show Ar–Ar plateau ages of 72.3 ± 0.4 Ma and 70.6 ± 0.2 Ma, respectively. The close temporal relationship between the igneous emplacement and hydrothermal activity suggests that the tin mineralisation was closely linked to the igneous emplacement. The δ18O and δD values for the deposit range from + 3.11‰ to − 4.5‰ and from − 127.3‰ to − 94.7‰, respectively. The hydrothermal calcite C and O isotopic data show a wide range of δ13CPDB values from − 5.7‰ to − 4.4‰, and the δ18OSMOW values range from + 1.4‰ to + 11.2‰. The δ34SV-CDT data range from + 4.8‰ to + 8.9‰ for pyrite, and the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios range from 18.708 to 18.760, from 15.728 to 15.754 and from 39.237 to 39.341, respectively. The stable isotopic (C–H–O–S–Pb) compositions are all similar to those of magmatic and mantle-derived fluids, which indicate that the ore-forming fluids and materials were mainly derived from magmatic sources that were accompanied by meteoric water. The tin mineralisation in the Xiaolonghe district was closely associated with the Late Cretaceous crustal-melting S-type granites that formed during the subduction of the Neo-Tethys oceanic lithosphere. Combined with the tin deposits in the Southeast Asian tin belt, Tengchong block and Central Lhasa, we interpreted that a giant intermittent tin mineralisation belt should be present along the Asian Neo-Tethys margin. 相似文献
5.
In north-central Brazil, a number of granite plutons, which intrude Paleoproterozoic gneiss-granulite terrains of the Goiás Massif, crop out along a thermal axis parallel to the Transbrasiliano Lineament. Single zircon lead evaporation ages from three granitic bodies span between 552 and 545 Ma. Sm–Nd model ages (TDM) vary between 2.1 and 1.7 Ga and negative εNd(0.55 Ga) values between −10 and −13 show that Paleoproterozoic crust was involved in the genesis of these granites. These plutons, which form the Lajeado Intrusive Suite are part of an important Ediacaran magmatic event in central-northern of the Tocantins Tectonic Province, composed of metaluminous to slightly peraluminous granites with geochemical characteristics similar to A-type granites, whose crystallization occurred under low water activity during magmatic emplacement. The granitic intrusive bodies are related to a crustal extensional/transtensional tectonic event at the end of the Neoproterozoic. They may have connection with the granitic plutons of similar age (0.56–0.52 Ga) in northwestern Ceará state, on the other side of the Paleozoic Parnaíba Basin in northwest of Borborema Province, along the Transbrasiliano Lineament. 相似文献
6.
We report in the paper integrated analyses of in situ zircon U–Pb ages, Hf–O isotopes, whole-rock geochemistry and Sr–Nd isotopes for the Longlou granite in northern Hainan Island, southeast China. SIMS zircon U–Pb dating results yield a crystallization age of ∼73 Ma for the Longlou granite, which is the youngest granite recognized in southeast China. The granite rocks are characterized by high SiO2 and K2O, weakly peraluminous (A/CNK = 1.04–1.10), depletion in Sr, Ba and high field strength elements (HFSE) and enrichment in LREE and large ion lithophile elements (LILE). Chemical variations of the granite are dominated by fractional crystallization of feldspar, biotite, Ti–Fe oxides and apatite. Their whole-rock initial 87Sr/86Sr ratios (0.7073–0.7107) and εNd(t) (−4.6 to −6.6) and zircon εHf(t) (−5.0 to 0.8) values are broadly consistent with those of the Late Mesozoic granites in southeast China coast. Zircon δ18O values of 6.9–8.3‰ suggest insignificant involvement of supracrustal materials in the granites. These granites are likely generated by partial melting of medium- to high-K basaltic rocks in an active continental margin related to subduction of the Pacific plate. The ca. 73 Ma Longlou granite is broadly coeval with the Campanian (ca. 80–70 Ma) granitoid rocks in southwest Japan and South Korea, indicating that they might be formed along a common Andean-type active continental margin of east–southeast Asia. Tectonic transition from the Andean-type to the West Pacific-type continental margin of southeast China likely took place at ca.70 Ma, rather than ca. 90–85 Ma as previously thought. 相似文献
7.
This work presents an integrated study of zircon U–Pb ages and Hf isotope along with whole-rock geochemistry on Silurian Fengdingshan I-type granites and Taoyuan mafic–felsic intrusive Complex located at the southeastern margin of the Yangtze Block, filling in a gap in understanding of Paleozoic I-type granites and mafic-intermediate igneous rocks in the eastern South China Craton (SCC). The Fengdingshan granite and Taoyuan hornblende gabbro are dated at 436 ± 5 Ma and 409 ± 2 Ma, respectively. The Fengdingshan granites display characteristics of calc-alkaline I-type granite with high initial 87Sr/86Sr ratios of 0.7093–0.7127, low εNd(t) values ranging from −5.6 to −5.4 and corresponding Nd model ages (T2DM) of 1.6 Ga. Their zircon grains have εHf(t) values ranging from −2.7 to 2.6 and model ages of 951–1164 Ma. The Taoyuan mafic rocks exhibit typical arc-like geochemistry, with enrichment in Rb, Th, U and Pb and depletion in Nb, Ta. They have initial 87Sr/86Sr ratios of 0.7053–0.7058, εNd(t) values of 0.2–1.6 and corresponding T2DM of 1.0–1.1 Ga. Their zircon grains have εHf(t) values ranging from 3.2 to 6.1 and model ages of 774–911 Ma. Diorite and granodiorite from the Taoyuan Complex have initial 87Sr/86Sr ratios of 0.7065–0.7117, εNd(t) values from −5.7 to −1.9 and Nd model ages of 1.3–1.6 Ga. The petrographic and geochemical characteristics indicate that the Fengdingshan granites probably formed by reworking of Neoproterozoic basalts with very little of juvenile mantle-derived magma. The Taoyuan Complex formed by magma mixing and mingling, in which the mafic member originated from a metasomatized lithospheric mantle. Both the Fengdingshan and Taoyuan Plutons formed in a post-orogenic collapse stage in an intracontinental tectonic regime. Besides the Paleozoic Fengdingshan granites and Taoyuan hornblende gabbro, other Neoproterozoic and Indosinian igneous rocks located along the southeastern and western margin of the Yangtze Block also exhibit decoupled Nd–Hf isotopic systemics, which may be a fingerprint of a previous late Mesoproterozoic to early Neoproterozoic oceanic subduction. 相似文献
8.
The Taoxihu deposit (eastern Guangdong, SE China) is a newly discovered Sn polymetallic deposit. Zircon U-Pb dating yielded 141.8 ± 1.0 Ma for the Sn-bearing granite porphyry and 145.5 ± 1.6 Ma for the biotite granite batholith it intruded. The age of the granite porphyry is consistent (within error) with the molybdenite Re–Os isochron age (139.0 ± 1.1 Ma) of the Sn mineralization, indicating a temporal link between the two. Geochemical data show that the granite porphyry is weakly peraluminous, contain high Si, Na and K, low Fe, Mg, Ca and P, and relatively high Rb/Sr and low K/Rb values. The rocks are enriched in Rb, Th, U, K, and Pb and depleted in Ba, Sr, Ti and Eu, resembling highly fractionated I-type granites. They contain bulk rock initial 87Sr/87Sr of 0.707371–0.707730 and εNd(t) of −5.17 to −4.67, and zircon εHf(t) values from −6.67 to −2.32, with late Mesoproterozoic TDM2 ages for both Nd and Hf isotopes. This suggests that the granite porphyry was likely formed by the partial melting of the crustal basement of Mesoproterozoic overall residence age with minor mantle input.δ34SCDT values of the Taoxihu chalcopyrite and pyrite range from 0.1 to 2.1‰ (average: 0.9‰), implying a dominantly magmatic sulfur source. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the Taoxihu sulfide ores are 18.497–18.669, 15.642–15.673 and 38.764–38.934, respectively, indicating a mainly upper continental crustal lead source with minor mantle contribution. The highly fractionated and reduced (low calculated zircon Ce4+/Ce3+ and EuN/EuN1 values) nature of the ore-forming granitic magma may have facilitated the Sn enrichment and played a key role in the Sn mineralization. We propose that the ore-forming fluids at Taoxihu were of magmatic-hydrothermal origin derived from the granite porphyry, and that both the granite porphyry and the Sn mineralization were likely formed in an extensional setting, possibly related to the subduction slab rollback of the Paleo-Pacific Plate. 相似文献
9.
《International Geology Review》2012,54(7):795-820
ABSTRACTThe magmatic generation for the Late Triassic–Early Jurassic (~215–200 Ma) and Early Cretaceous–Late Cretaceous (~108–79 Ma) post-collisional granites in the Sanjiang Tethys orogeny remain enigmatic. The Xiuwacu complex, located in the southern Yidun Terrane, consists of biotite granite with a weight mean 206Pb/238U age of 199.8 ± 2.5 Ma, aplite granite of 108.2 ± 2.3 Ma, monzogranite porphyry of 80.8 ± 1.0 Ma, and diorite enclaves of 79.2 ± 0.9 Ma and 77.9 ± 0.8 Ma. The Late Triassic biotite granites show I-type granite affinities, with high SiO2 contents, high Mg# values, high zircon δ18O values, and negative whole-rock ?Nd(t) values, indicating a predominant ancient crustal source with the input of juvenile materials. Their fractionated REE patterns and concave-upward middle-to-heavy REE patterns require garnet-bearing amphibolite as the melt source. The Cretaceous highly fractionated aplite granites and monzogranite porphyries have relatively high SiO2 contents, high (Na2O + K2O)/CaO ratios, high zircon δ18O values, and enriched whole-rock Sr–Nd isotopic signatures, suggesting that their parent magmas were likely originated from the ancient middle- to lower crust. Their significant negative Eu anomalies and obvious depletions in Nb, Sr, and Ti demonstrate that the Cretaceous granitic magmas had experienced more fractionation than the Late Triassic felsic magmas. The Late Cretaceous diorite enclaves show low SiO2 contents, high Mg# values, and high zircon δ18O values, suggesting that they were probably derived from the partial melting of subcontinental lithospheric mantle enriched by the Late Triassic subduction. The Late Triassic–Early Jurassic and Early Cretaceous–Late Cretaceous magmatism witnessed the post-collisional setting and intraplate extensional setting in response to the slab break-off and lithospheric-scale transtensional faulting, respectively. The partial melting of subduction-modified lithospheric mantle or/and residual sulphide cumulates within the lower crust during the origination of Late Cretaceous magmas could have provided metals for the formation of Xiuwacu deposit. 相似文献
10.
《Lithos》2007,93(1-2):17-38
A suite of schists, gneisses, migmatites, and biotite granitoids from the Puerto Edén Igneous and Metamorphic Complex (PEIMC) and biotite–hornblende granitoids of the South Patagonian batholith (southern Chile) has been studied. For that purpose, the chemistry of minerals and the bulk rock composition of major and trace elements including Rb–Sr and Sm–Nd isotopes were determined. Mineralogical observations and geothermobarometric calculations indicate high-temperature and low-pressure conditions (ca. 600–700 °C and 3 to 4.5 kbar) for an event of metamorphism and partial melting of metapelites in Late Jurassic times (previously determined by SHRIMP U–Pb zircon ages). Structures in schists, gneisses, migmatites and mylonites indicate non-coaxial deformation flow during and after peak metamorphic and anatectic conditions. Andalusite schists and sillimanite gneisses yield initial 87Sr/86Sr ratios of up to 0.7134 and εNd150 values as low as − 7.6. Contemporaneous biotite granitoids and a coarse-grained orthogneiss have initial 87Sr/86Sr ratios between 0.7073 and 0.7089, and εNd150 values in the range − 7.6 to − 4.4. This indicates that metamorphic rocks do not represent the natural isotopic variation in the migmatite source. Thus, a heterogeneous source with a least radiogenic component was involved in the production of the biotite granitoids. The PEIMC is considered as a segment of an evolving kilometre-sized and deep crustal shear zone in which partial melts were generated and segregated into a large reservoir of magmas forming composite plutons in Late Jurassic times. A biotite–hornblende granodiorite and a muscovite–garnet leucogranite show initial 87Sr/86Sr ratios of 0.7048 and 0.7061, and εNd100 values of − 2.6 and − 1.8, respectively, and are thus probably related to Early Cretaceous magmas not involved in the anatexis of the metasedimentary rocks. 相似文献
11.
Two of the major granite belts of Southeast Asia are the Main Range and Eastern Province. Together, these are interpreted to represent the magmatic expression of the closure of Palaeo-Tethys during Late Palaeozoic to Early Mesozoic times. Recent geochronological and geochemical work has better delineated these belts within Peninsular Malaysia, thereby providing important constraints on the timing of Palaeo-Tethys suturing. However, the northern extension of this Palaeo-Tethyan suture is less well understood. Here we present new ion microprobe U–Pb zircon age data from northern Thailand and eastern Myanmar. Measured ages of 219 and 220 Ma from the Kyaing Tong granite imply northern extension of the Main Range Province into eastern Myanmar. The Tachileik granite in far eastern Myanmar yields an age of 266 Ma, consistent with published Eastern Province ages, and this therefore constrains the northern extension of the Palaeo-Tethys suture in eastern Myanmar. We further discuss how this suture may extend northwards into Yunnan. A Late Cretaceous age (70 Ma) measured in Thailand represents later magmatic activity, and is similar to published magmatic ages from central Myanmar. This younger magmatism is interpreted to be related to the subduction of Neo-Tethys prior to India–Asia collision. Further, we present new laser ablation zircon Hf isotope data from eastern Myanmar which suggest that Palaeoproterozoic crust underlies both the Main Range and Eastern Province granites. Our εHf model age of ca. 1750 Ma from Sibumasu, the basement underlying eastern Myanmar, lies within the range of other model ages reported thus far for the Baoshan Block north in Yunnan, interpreted by some to be the northern extension of Sibumasu. 相似文献
12.
相比较丰富的前寒武纪和早古生代地质记录, 云开地区燕山晚期花岗岩类分布很少, 且未见详细的研究报道.对云开地区广西陆川米场、三叉冲钨矿床以及松旺钨锡钼矿床等3个典型地区的燕山晚期花岗岩进行了系统的LA-MC-ICP-MS锆石U-Pb和Lu-Hf同位素研究.定年结果表明, 米场黑云母花岗岩、三叉冲黑云母花岗岩和松旺花岗岩的侵位年龄分别为113±1 Ma, 103±1 Ma和88±1 Ma, 为燕山晚期岩浆作用的产物.三叉冲黑云母花岗岩和松旺花岗岩具有较一致锆石εHf(t)值(分别为-5.2~-2.7和-5.2~-3.6)和二阶段模式年龄TDM2(分别为1.3~1.5 Ga和1.4~1.5 Ga), 指示为中元古代地壳物质再造的产物.米场黑云母花岗岩具有相对较高的εHf(t)值(-2.3~1.4)和TDM2(1.1~1.3 Ga), 并且其含有大量的镁铁质微粒包体(MME), 表明米场黑云母花岗岩很可能是壳源-幔源岩浆混合的产物.结合中国东南部构造-岩浆演化来看, 云开地区燕山晚期花岗岩的形成可能与白垩纪时太平洋板块向华南板块俯冲后板片的折返-断离有关. 相似文献
13.
The recently-discovered Wenquan porphyry Mo deposit hosted in the Wenquan granite of the West Qinling Orogen has been recognized as a product of the Indosinian metallogenesis. Three generations of mineral assemblage for the deposit are identified as follows: (1) quartz–biotite–K-feldspar; (2) quartz–sulfide and (3) sulfide–calcite. Geochemical study shows that the mafic microgranular enclaves (MMEs) in the ore-bearing Wenquan granite have lower SiO2, and higher Mg# and Nb/Ta ratios than the host granite itself. Different from the granite which have zircon εHf(t) values of − 3.6–3.0 and TDM2 of 1234–890 Ma, the MMEs are characterized by the εHf(t) values of − 10.1–10.8 and TDM1 of 865–441 Ma. This can be interpreted to indicate a mixture origin of the Meso- and Neoproterozoic crust-derived component and Neoproterozoic SCLM-derived materials for the formation of the Wenquan granite, which played an essential role in the Mo mineralization. Comparative Pb isotopic data between ores and K-feldspar suggest that the Wenquan granitic magma originated from the middle-lower crust of the South China Block and the ore-forming materials were incorporated by hydrothermal fluid differentiated from the Triassic magmatic system, with minor contribution of sedimentary rocks. The δ34S values of 5.0–11.7‰ with a pronounced mode at 5.0 to 6.1‰ for the ores probably represent the sulfur incorporation of a typical magmatic hydrothermal fluid contaminated by heavy sulfur of Devonian sediments. The granite yielded the zircon U–Pb ages of 218 ± 2.4 Ma and 221 ± 1.3 Ma, as the same as the ages of 217 ± 2.0 Ma and 218 ± 2.5 Ma obtained for the MMEs. These ages are indistinguishable with the molybdenite Re–Os isochron age of 219 ± 5.2 Ma which is the timing for the Mo mineralization. Tectonically, the magmatic mixture processes of the Wenquan granite and the Mo mineralization to form the Wenquan Mo deposit contemporaneously occurred during the transition of tectonic regime from syn- to post-collision orogeny in the Qinling Orogen in the Late Triassic. 相似文献
14.
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
15.
以往将位于湘南、桂东北的都庞岭花岗岩基分为西体、中体和东体三部分。野外观察和岩相学研究表明,都庞岭中体和东体主要由黑云母正长花岗岩、黑云母二长花岗岩和二云母二长花岗岩组成,岩石具斑状结构,部分钾长石斑晶呈椭球状至球状,具斜长石环边,构成环斑结构。采用锆石SHRIMP U-Pb法获得都庞岭中体和东体中环斑花岗岩的侵位年龄分别为226.6±6.9 Ma和209.7±3.1 Ma,均属于晚三叠世,相当于印支晚期。都庞岭环斑花岗岩富硅、碱,贫钛、磷、镁和钙,其Rb、Cs、Th、U、REE、Pb、Y含量和Rb/Sr、Rb/Ba比值较高,而Sr、Ba含量和Zr/Hf比值(8.16~25.01)较低,具强烈的Eu负异常(δEu=0.02~0.13),10000×Ga/Al比值(2.64~4.38,平均3.15)高,显示A型花岗岩的地球化学特征。与华南印支早期S型花岗岩相比,都庞岭环斑花岗岩的εNd(t)值(-8.0~-8.3)明显偏高(前者低于-10),而tDM2值(1624~1645 Ma)则明显偏低(前者1800 Ma),表明它们可能直接源于地壳物质的部分熔融,但成岩过程中有地幔物质的参与。都庞岭环斑花岗岩的发现及其时代的确定,揭示了晚三叠世华南东部处于大陆裂解或造山后伸展的构造环境。结合华南东部沉积/岩石大地构造分析,认为华南早中生代构造体制的转换发生在中、晚三叠世,而非前人所认为的发生在中、晚侏罗世;同时,环斑花岗岩的出现,指示了华南中生代大规模成矿作用的来临,晚三叠世是华南中生代大规模成矿的第一个高峰期。 相似文献
16.
Late Variscan wolframite (± molybdenite) and cassiterite–wolframite greisen, skarn and vein deposits occur in a close spatial association with the granites of the Krušné hory/Erzgebirge batholith (KHEB) in Central Europe. We examined the distribution of the deposits in relation to the gravity field affected by Late Variscan granites using the data from previous gravity and metallogenic studies. Late Variscan granites are differentiated into earlier biotite monzogranites (low-F granites) and later biotite or lithium mica syenogranites (high-F granites) in accordance with the previous classifications. All the outcrops of granites in the KHEB region and their hidden continuation are confined to the Bouguer anomaly contour of − 20 mGal. The Sn–W–Mo (rare metal) deposits and occurrences are within the gravity contour of − 30 mGal with the exception of the Grossschirma stratiform tin deposit in the Freiberg polymetallic ore district. We constructed a geological model based on the gravity data along two profiles across the KHEB showing the position of some rare metal deposits and of outcropping and hidden granite bodies. The models show that the overlapping of earlier and later granites is in the areas of the most intense regional gravity minima. These coincide with the Eastern Volcano-Plutonic Complex (Altenberg minimum), which encloses large volumes of felsic extrusives, microgranite dikes and granites, and the Western Plutonic Complex (Eibenstock minimum), with small volumes of felsic dikes and predominance of earlier and later granites, with no extrusives preserved. There is no distinct relationship between the masses of Late Variscan granites and the distribution and the sizes of associated W ± Mo and Sn–W deposits. We prefer the idea that rare metal mineralization was formed by hydrothermal fluids derived from outside of presently outcropping granites. It originated in two cycles: one connected with the formation of earlier granites producing W ± Mo associations and the other one associated with later granites connected with Sn–W mineralization. Mineralizing fluids were probably generated by mantle–crustal interaction in the crust near the mantle–crust boundary as also indicated by lamprophyric intrusions coeval with the Late Variscan granitic magmatism. 相似文献
17.
The Late Triassic igneous rocks in the Yidun terrane can provide vital insights into the evolution of Plaeo-Tethys in western China. We present new zircon U-Pb, whole-rock geochemistry, and Sr-Nd-Pb-Hf isotopic data for the Litang biotite monzogranites, Yidun terrane. The biotite monzogranites have a zircon U-Pb age of 206.1±1.0 Ma(MSWD=1.9,n=30), which indicates Late Triassic magmatism. The biotite monzogranites display I-type affinity, high Na_2O(3.38-3.60 wt%) contente,medii SiO_2(67.12-69.13 wt%), and low P_2 O_5 contents(0.10～0.12 wt%). They enriched in Rb,and Ba and depleted in Nb and Ta, with negative Eu anomalies(Eu/Eu*=0.74—0.81). They have evolved Sr-Nd-Pb-Hf isotopic composition, i.e.,(~(87) Sr/~(86 )Sr)i=0.714225 to 0.714763, negative ?_(Nd(t)) values of -2.0 to-2.6 with two-stage Nd model ages ranging from 1.01 to 1.05 Ga, negative ?_(Ht)(t)) values o f-3.4 to-4.1 with two-stage Hf model ages of 1.85 to1.88 Ga, suggesting a matured crustal sources. Their low Al_2O_3/TiO_2 ratios and medium Cao/Na_2O ratios, medium Mg~# and SiO_2 contents, low [molar Al_2O_3/(MgO+FeO~T)] values, and high [molar Cao/(MgO+FeO~T)] values indicate that the Litang biotite monzogranite was formed by partial melting of metabasaltic rocks. Based on the previous studies, we propose that the Litang biotite monzogranite derived from the westward subduction and closure of the Ganzi-Litang ocean during the Late Triassic-The mantle wedge-derived mafic melts provided sufficient heat for partial melting of ancient metabasalt protolith within the middle-lower crust. 相似文献
18.
This paper reports the results of geological, geochronological, and isotope geochemical investigations of two premetamorphic granite massifs of the Goloustnaya block of the Baikal salient of the basement of the Siberian craton and granite gneisses from the migmatite–gneiss sequence of this block. The U–Pb zircon age of the granites of the Khomut massif is 2153 ± 11 Ma. The age of the Elovka massif was previously determined by us as 2018 ± 28 Ma. The Khomut and Elovka granites underwent structural and metamorphic transformations accompanied by migmatization. An age of 1.98–1.97 Ga was obtained for the structural and metamorphic processes in the Goloustnaya block from the analysis of margins of zircon grains from the Khomut granites and zircon from the granite gneisses. The biotite granites of the Khomut massif show transitional I–S-type geochemical characteristics, which allowed us to suggest that they were derived by melting of a crustal source of intermediate–acid composition. The Khomut granites show positive εNd(T) values from +2.0 to +2.2 and a Nd model age of 2.4 Ga, which may indicate their formation owing to the reworking of the Paleoproterozoic juvenile continental crust. The combined isotope geochemical data are consistent with collision of island arcs as a possible environment for the formation of the Khomut granites. The formation of these granites was not related to the development of the structure of the Siberian craton, similar to a few other anorogenic magmatic complexes of the margin of the Chara–Olekma terrane of the Aldan shield with ages of ~2.2–2.1 Ga, including the granites of the Katugin complex. The biotite–amphibole granites of the Elovka massif with an age of ~2.02 Ga are geochemically similar to I-type granites. The geochemical characteristics of these granites, including elevated Sr and Ba and low Nb and Ta contents, were inherited from a subduction-related source. Negative εNd(T) values from–0.9 to–1.8 and rather high contents of K2O and Th allow us to suppose a metamagmatic crustal source for the granites of the Elovka massif. The combined isotope geochemical characteristics of the Elovka granites suggest that a mature island arc or an active continental margin is the most probable environment of their formation. The estimates of the age of structural and metamorphic processes affecting the Goloustnaya block (1.98–1.97 Ga) coinciding with the time of similar transformations in the central part of the Aldan shield and eastern Anabar shield (1.99–1.96 Ga) indicate wide occurrence of collisional events of similar age in the Siberian craton and allow us to consider this age interval as an early large-scale stage of the formaiton of the structure of the Siberian craton. 相似文献
19.
The tectonic transition from the palaeo-Tethyan to palaeo-Pacific dynamic domains in the South China Block (SCB) is still a matter of debate. The A-type granites collected from the southeastern SCB offered an opportunity to illustrate this tectonic transition. This article records a set of petrographic, geochronological, and geochemical data for the Wengong granitic pluton from the eastern Nanling Range. LA-ICP-MS zircon U–Pb dating shows a crystallization age of 196.9 ± 4.4 Ma with εHf(t) values ranging from +2.1 to +7.7. The samples have high SiO2, Zr+Nb+Ce+Y, FeOt/MgO, Ga/Al, and Y/Nb and are depleted in Nb–Ta, Zr–Hf, Ba, Sr, Ti, and Eu, similar to those of the A2-type granite. Their initial 87Sr/86Sr ratios range from 0.70885 to 0.70983 and the εNd(t) values range from ?2.9 to ?1.1, close to those of the Early Palaeozoic mafic rocks in the southeastern SCB. The Wengong A2-type granite was derived from partial melting of the mafic rocks underplated into the lower crust during the Early Palaeozoic.The Mesozoic A-type granites in the southeastern SCB can be subdivided into 229–215 Ma (Late Triassic), 197–152 Ma (Jurassic), and 135–92 Ma (Cretaceous). They differ in geochemical and spatial distribution characteristics. The Late Triassic A-type granites were formed in the post-collision extensional setting associated with the palaeo-Tethyan dynamic domain, whereas the Cretaceous A-type granites were under the control of the palaeo-Pacific dynamic domain. The A-type granites were hardly exposed during the Late Triassic–Early Jurassic and Late Jurassic–Early Cretaceous. The Jurassic A-type granites were formed in the intra-plate extensional setting, a response to the tectonic transition from the palaeo-Tethyan to palaeo-Pacific dynamic domains. Thus, the occurrence of the Wengong A2-type granite indicates that this tectonic transition possibly initiated at the earliest Early Jurassic. 相似文献
20.
The Mangabeira deposit is the only known Brazilian tin mineralization with indium. It is hosted in the Paleo- to Mesoproterozoic Mangabeira within-plate granitic massif, which has geochemical characteristics of NYF fertile granites. The granitic massif is hosted in Archean to Paleoproterozoic metasedimentary rocks (Ticunzal formation), Paleoproterozoic peraluminous granites (Aurumina suite) and a granite–gneiss complex. The mineralized area comprises evolved Li-siderophyllite granite, topaz–albite granite, Li–F-rich mica greisens and a quartz–topaz rock, similar to topazite. Two types of greisens are recognized in the mineralized area: zinnwaldite greisen and Li-rich muscovite greisen, formed by metasomatism of topaz–albite granite and Li-siderophyllite granite, respectively. Cassiterite occurs in the quartz–topaz rock and in the greisens. Indium minerals, such as roquesite (CuInS2), yanomamite (InAsO4·2H2O) and dzhalindite (In(OH3)), and In-rich cassiterite, sphalerite, stannite group minerals and scorodite are more abundant in the quartz–topaz rock, and are also recognized in albitized biotite granite and in Li-rich muscovite greisen. The host rocks and mineralized zones were subsequently overprinted by the Brasiliano orogenic event.Primary widespread two-phase aqueous and rare coeval aqueous-carbonic fluid inclusions are preserved in quartz from the topaz–albite granite, in quartz and topaz from the quartz–topaz rock and in cassiterite from the Li-rich muscovite greisen. Eutectic temperatures are − 25 °C to − 23 °C, allowing modeling of the aqueous fluids in the system H2O–NaCl(–KCl). Rare three-phase H2O–NaCl fluid inclusions (45–50 wt.% NaCl equiv.) are restricted to the topaz–albite granite. Salinities and homogenization temperatures of the aqueous and aqueous-carbonic fluid inclusions decrease from the topaz–albite granite (15–20 wt.% NaCl equiv.; 400 °C–450 °C), to the quartz–topaz rock (10–15 wt.% NaCl equiv.; 250 °C–350 °C) and to the greisen (0–5 wt.% NaCl equiv.; 200 °C–250 °C). Secondary fluid inclusions have the same range of salinities as the primary fluid inclusions, and homogenize between 150 and 210 °C.The estimated equilibrium temperatures based on δ18O of quartz–mica pairs are 610–680 °C for the topaz–albite granite and 285–370 °C for the Li-rich muscovite greisens. These data are coherent with measured fluid inclusion homogenization temperatures. Temperatures estimated using arsenopyrite geothermometry yield crystallization temperatures of 490–530 °C for the quartz–topaz rock and 415–505 °C for the zinnwaldite greisens. The fluids in equilibrium with the topaz–albite granite have calculated δ18O and δD values of 5.6–7.5‰ and − 67 to − 58‰, respectively. Estimated δ18O and δD values are mainly 4.8–7.9‰ and − 60 to − 30‰, respectively, for the fluids in equilibrium with the quartz–topaz rock and zinnwaldite greisen; and 3.4–3.9‰ and − 25 to − 17‰, respectively, for the Li-rich muscovite greisen fluid. δ34S data on arsenopyrite from the quartz–topaz rock vary from − 1.74 to − 0.74‰, consistent with a magmatic origin for the sulfur. The integration of fluid inclusion with oxygen isotopic data allows for estimation of the minimum crystallization pressure at ca. 770 bar for the host topaz–albite granite, which is consistent with its evolved signature.Based on petrological, fluid inclusion and isotope data it is proposed that the greisens and related Mangabeira Sn–In mineralization had a similar hydrothermal genesis, which involved exsolution of F-rich, Sn–In-bearing magmatic fluids from the topaz–albite granite, early formation of the quartz–topaz rock and zinnwaldite greisen, progressive cooling and Li-rich muscovite greisen formation due to interaction with meteoric water. The quartz–topaz rock is considered to have formed in the magmatic-hydrothermal transition. The mineralizing saline and CO2-bearing fluids are interpreted to be of magmatic origin, based on the isotopic data and paragenesis, which has been documented as characteristic of the tin mineralization genetically related to Proterozoic within-plate granitic magmatism in the Goias Tin Province, Central Brazil. 相似文献