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1.
《Gondwana Research》2014,25(3-4):1108-1126
Detailed petrology and zircon U–Pb dating data indicate that the Wulong pluton is a zoned granitic intrusive, formed from successive increments of magmas. An age range of at least 30 Ma is recorded from the 225–235 Ma quartz diorite on the pluton margin, the ca. 218 Ma granodiorite in the intermediate zone, and the ca. 207 Ma monzogranite at the pluton center. All the granitoids display evolved Sr–Nd–Pb isotopic compositions, with 87Sr/86Sr(i) of 0.7044–0.7062, unradiogenic Nd (εNd(t) values of − 6.1 to − 3.0, Nd model ages of 1.1–1.3 Ga, and moderately radiogenic Pb compositions (206Pb/204Pb(i) = 17.500–17.872, 207Pb/204Pb(i) = 15.513–15.549, 208Pb/204Pb(i) = 37.743–38.001), in combination with variations in zircon Hf isotopic compositions (with εHf(t) values in each stage span 12 units) and the Hf isotopic model ages of 800–1600 Ma. These features suggest that the granitoids might have been derived from the reworking of an old lower crust, mixed with Paleozoic and Proterozoic materials. The rocks also display an adakitic affinity with Sr (479–973 ppm), high Sr/Y ratios (mostly > 60) and negligible Eu anomalies (Eu/Eu* = 0.78–0.97) but low Rb/Sr ratios, low Y (4.6–17 ppm), HREE (Yb = 0.95–1.7 ppm), Yb/Lu (6–7) and Dy/Yb (1.9–2.4) ratios, suggesting the absence of plagioclase and presence of garnet + amphibole in their residue. Considering a large gap among their crystallization ages, we propose that the geochemical evolution from pluton margin to center was controlled mainly by melting conditions and source compositions rather than fractional crystallization. Mafic enclaves that were hosted in the quartz diorite and granodiorite are mainly syenogabbroic to syenodioritic in composition, and are metaluminous and enriched in LREE and LILEs, but are depleted in HFSE, and display an evolved Sr–Nd–Pb isotopic composition, suggesting that they may have been derived from the partial melting of an enriched mantle lithosphere, which was metasomatized by adakitic melts and fluids from a subducted continental crust.In combination with the results of the Triassic ultra-high pressure metamorphic rocks in the Dabie orogenic belt, we apply a model involving the exhumation of subducted continental crust to explain the formation of the Wulong pluton. At the first stage, a dense and refractory mafic lower crust that was trapped at mantle depth by continental subduction witnessed melting under high temperature conditions to produce the quartz diorite magma, characterized by low SiO2 (60.65–63.98 wt.%) and high TiO2 (0.39–0.86 wt.%). The magma subsequently interacted with mantle peridotite, leading to high Mg# (57–67) and the metasomatism of the overriding mantle wedge. At the second stage, an asthenosphere upwelling that was probably caused by slab break-off at ca. 220 Ma melted the enriched sub-continental lithospheric mantle (SCLM) to produce mafic magmas, represented by the mafic enclaves that are hosted in the quartz and granodiorite, resulting in the partial melting of the shallower subducted crust, and generating the granodiorite that is distinguished by high SiO2 (69.16–70.82 wt.%), high Al2O3 (15.33–16.22 wt.%) and A/CNK values (mostly > 1.05). At the third stage, the final collapse of the Triassic Qinling–Dabie Orogenic Belt at ca. 215–205 Ma caused extensive partial melting of the thickened orogenic lower crust to produce the monzogranite, which is characterized by high SiO2 (67.68–70.29 wt.%), low TiO2 (mostly < 0.35 wt.%) and high Sr/Y ratios of 86–151. 相似文献
2.
We performed zircon U–Pb dating and analyses of major and trace elements, and Sr–Nd–Pb isotopes for granitoids in the Bengbu area, central China, with the aim of constraining the magma sources and tectonic evolution of the eastern North China Craton (NCC). The analyzed zircons show typical fine-scale oscillatory zoning, indicating a magmatic origin. Zircon U–Pb dating reveals granitoids of two ages: Late Jurassic and Early Cretaceous (206Pb/238U ages of 160 Ma and 130–110 Ma, respectively). The Late Jurassic rocks (Jingshan intrusion) consist of biotite-syenogranite, whereas the Early Cretaceous rocks (Huaiguang, Xilushan, Nushan, and Caoshan intrusions) are granodiorite, syenogranite, and monzogranite. The Late Jurassic biotite-syenogranites and Early Cretaceous granitoids have the following common geochemical characteristics: SiO2 = 70.35–74.56 wt.%, K2O/Na2O = 0.66–1.27 (mainly < 1.0), and A/CNK = 0.96–1.06, similar to I-type granite. The examined rocks are characterized by enrichment in light rare earth elements, large ion lithophile elements, and U; depletion in heavy rare earth elements, Nb, and Ta; and high initial 87Sr/86Sr ratios (0.7081–0.7110) and low εNd (t) values (? 14.40 to ? 22.77), indicating a crustal origin.The occurrence of Neoproterozoic magmatic zircons (850 Ma) and inherited early Mesozoic (208–228 Ma) metamorphic zircons within the Late Jurassic biotite-syenogranites, together with the occurrence of Neoproterozoic magmatic zircons (657 and 759 Ma) and inherited early Mesozoic (206–231 Ma) metamorphic zircons within the Early Cretaceous Nushan and Xilushan granitoids, suggests that the primary magmas were derived from partial melting of the Yangtze Craton (YC) basement. In contrast, the occurrence of Paleoproterozoic and Paleoarchean inherited zircons within the Huaiguang granitoids indicates that their primary magmas mainly originated from partial melting of the NCC basement. The occurrence of YC basement within the lower continental crust of the eastern NCC indicates that the YC was subducted to the northwest beneath the NCC, along the Tan-Lu fault zone, during the early Mesozoic. 相似文献
3.
The petrology, geochemistry, geochronology, and Sr–Nd–Hf isotopes of the backarc granitoids from the central part of the Qilian block are studied in the present work. Both S- and I-type granitoids are present. In petrographic classification, they are granite, alkali feldspar granite, felsic granite, diorite, quartz diorite, granodiorite, and albite syenite. The SHRIMP ages are 402–447 Ma for the S-type and 419–451 Ma for the I-type granitoids. They are mostly high-K calc-alkaline granitoids. The S-type granitoids are weakly to strongly peraluminous and are characterized by negative Eu anomalies (Eu/Eu* = 0.18–0.79). The I-type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive Eu anomalies (Eu/Eu* = 0.71–1.16). The initial (87Sr/86Sr) values are 0.708848–0.713651 for the S-type and 0.704230–0.718108 for the I-type granitoids. The εNd(450 Ma) values are − 8.9–−4.1 and − 9.7–+ 1.9 for the S-type and I-type granitoids, respectively. The TDM values are 1.5–2.4 Ga for the S-type and 1.0–2.3 Ga for the I-type granitoids. For the Qilian block, the backarc granitoid magmatism took place approximately 60 million years after the onset of the southward subduction of the north Qilian oceanic lithosphere and lasted approximately 50 million years. Partial melting of the source rocks consisting of the Neoproterozoic metasedimentary rocks of the Huangyuan Group and the intruding lower Paleozoic basaltic rocks could produce the S-type granitoid magmas. Partial melting of basaltic rocks mixed with lower continental crustal materials could produce the I-type granitoid magmas. Major crustal growth occurred in the late Archean and Meso-Paleoproterozoic time for the Qilian block. The magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1.0 Ga for the Qilian block. 相似文献
4.
It is generally accepted that the low-Mg adakitic rocks were derived from the partial melting of metabasalts/eclogites. In this study, we demonstrate that the early Cretaceous low-Mg adakitic granites in the North Dabie Complex (NDC) were generated by the partial melting of the NDC orthogneisses. Here we present in-situ U–Pb and Lu–Hf isotopes in zircon with whole-rock geochemical and Sr–Nd isotopic compositions were carried out for the Tiantangzhai porphyritic monzogranites from the Dabie orogen, eastern China. The monzogranites are characterized by high Sr (576–988 ppm), low Y (7.3–19.0 ppm), and depletion in HREE (Yb: 0.50–1.78 ppm) (thus resulting in high Sr/Y (34.3–135.2) and (La/Yb)N (17.0–105.2) ratios) without a negative Eu anomaly. They also exhibit high SiO2 (66.5–73.5 wt.%) and K2O (2.7–4.7 wt.%), and low MgO (0.4–1.6 wt.%) or Mg# (28.2–45.3, mostly < 40) values. Whole-rock geochemical compositions suggest that the monzogranites represent low-Mg adakitic rock with high-Si and rich-K features equilibrated with residues rich in garnet. Sr–Nd isotopic compositions (εNd (t) = ? 16.2 to ? 20.3, (87Sr/86Sr)i = 0.707798–0.708804, tDM2(Nd) = 2.3–2.6 Ga) of the monzogranites are distinct from that of the eclogites and amphibolites in the Dabie orogen, but similar to that of the Neoproterozoic (700–800 Ma) gneisses in the NDC. U–Pb dating of zircons gives a consistent age of 130.0 ± 3.4 Ma with discordia upper intercept age of 716 ± 34 Ma for inherited cores identified by CL imaging. Correspondingly, in-situ Lu–Hf analyses of early Cretaceous young age-spots from zircons yield initial 176Hf/177Hf ratios from 0.281898 to 0.282361, εHf(t) values from ? 28.1 to ? 17.6 and two-stage “crust” Hf model ages (tDM2) from 2293 ± 89 to 2949 ± 108 Ma, which are generally in agreement with values of 0.281891 to 0.282218, ? 28.2 to ? 11.7 and 1927 ± 87 to 2963 ± 92 Ma for the pre-Mesozoic inherited cores, respectively. As for individual core-rim pairs in zircon, Th/U ratios increase from the inherited cores to the young growth rims possibly due to variable degrees of partial melting, whereas 176Lu/177Hf ratios greatly decrease because of the garnet effect in residues. Thus, we suggest that the early Cretaceous low-Mg adakitic granites were derived from the partial melting of the NDC Neoproterozoic (700–800 Ma) gneisses, and the foundering of the garnet-bearing residues could have caused the destruction of the over-thickened lower continental crust. 相似文献
5.
The Balkhash Metallogenic Belt (BMB) in Kazakhstan, Central Asia, with the occurrence of the super-large Kounrad and Aktogai, the large Borly porphyry Cu–Mo deposits, and the large Sayak skarn polymetallic ore-field, is one of the central regions of the Paleozoic Central Asian metallogenic domain and orogenic belt. In this study, newly obtained SHRIMP zircon U–Pb ages of nine samples and 40Ar/39Ar ages of six mineral samples (inclding hornblende, biotite and K-feldspar) give more detailed constraints on the timing of the granitic intrusions and their metallogeny. Porphyritic monzonite granite and tonalite porphyry from the Kounrad deposit yield U–Pb zircon SHRIMP ages of 327.3 ± 2.1 Ma and 308.7 ± 2.2 Ma, respectively. Quartz diorite and porphyritic granodiorite from the Aktogai deposit yield U–Pb SHRIMP ages of 335.7 ± 1.3 Ma and 327.5 ± 1.9 Ma, respectively. Porphyritic granodiorite and granodiorite from the Borly deposit yield U–Pb SHRIMP ages of 316.3 ± 0.8 Ma and 305 ± 3 Ma, respectively. Diorite, granodiorite, and monzonite from the Sayak ore-field yield U–Pb SHRIMP ages of 335 ± 2 Ma, 308 ± 10 Ma, and 297 ± 3 Ma, respectively. Hornblende, biotite, and K-feldspar from the Aktogai deposit yield 40Ar/39Ar cooling ages of 310.6 Ma, 271.5 Ma, and 274.9 Ma, respectively. Hornblende, biotite, and K-feldspar from the Sayak ore-field yield 40Ar/39Ar cooling ages of 287.3 ± 2.8 Ma, 307.9 ± 1.8 Ma, and 249.8 ± 1.6 Ma, respectively. The new ages constrain the timing of Late Paleozoic felsic magmatism to ∼336 to ∼297 Ma. Skarn mineralization in the Sayak ore-field formed at ∼335 and ∼308 Ma. Porphyry Cu–Mo mineralization in the Kounrad deposit and the Aktogai deposit formed at ∼327 Ma, and in the Borly deposit at ∼316 Ma. The Late Paleozoic regional cooling in the temperature range of ∼600 °C to ∼150 °C occurred from ∼307 to ∼257 Ma. 相似文献
6.
Wen-Liang Xu Wei-Qiang Ji Fu-Ping Pei En Meng Yang Yu De-Bin Yang Xingzhou Zhang 《Journal of Asian Earth Sciences》2009,34(3):392-402
With the aim of constraining the Early Mesozoic tectonic evolution of the eastern section of the Central Asian Orogenic Belt (CAOB), we undertook zircon U–Pb dating and geochemical analyses (major and trace elements, Sr–Nd isotopes) of volcanic rocks of the Luoquanzhan Formation and Daxinggou Group in eastern Heilongjiang and Jilin provinces, China. The analyzed rocks consist mainly of dacite and rhyolite, with SiO2 contents of 68.52–76.65 wt%. Three samples from the Luoquanzhan Formation and one from the Daxinggou Group were analyzed using laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb zircon techniques. Three zircons with well-defined oscillatory zoning yielded weighted mean 206Pb/238U ages of 217 ± 1, 214 ± 2, and 208 ± 1 Ma, and one zircon with oscillatory zoning yielded a weighted mean 206Pb/238U age of 201 ± 1 Ma. These ages are interpreted to represent the timing of eruption of the volcanic rocks. The Triassic volcanic rocks are characterized by high SiO2 and low MgO concentrations, enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs) and heavy rare earth elements (HREEs), (87Sr/86Sr)i = 0.7040–0.7050 (Luoquanzhan Formation) and 0.7163–0.7381 (Daxinggou Group), and εNd (t) = 1.89–3.94 (Luoquanzhan Formation) and 3.42–3.68 (Daxinggou Group). These geochemical features indicate an origin involving the partial melting of juvenile lower crust (Nd model ages (TDM2) of 651–821 Ma) and that compositional variation among the volcanic rocks arose from mineral fractionation and minor assimilation. These volcanic rocks formed within an extensional environment following collision of the NCC and Jiamusi-Khanka Massif during the Late Paleozoic–Early Triassic. 相似文献
7.
《Journal of Asian Earth Sciences》2011,40(6):668-683
This paper presents geochemical, Sr–Nd isotopic, and U–Pb zircon geochronological data on the Alvand plutonic complex in Sanandaj–Sirjan zone (SSZ), Western Iran. The gabbroic rocks show a trend of a calc-alkaline magma suite and are characterized by low initial 87Sr/86Sr ratios (0.7023–0.7037) and positive εNd(t) values (2.9–3.3), which suggest derivation from a moderately depleted mantle source. Geochemical features of the granites illustrate a high-K calc-alkaline magma series, whereas the leucocratic granitoids form part of a low-K series. Granites have intermediate 87Sr/86Sr ratios (0.707–0.719) and negative εNd(t) values (−1.0 to −3.4), while leucocratic granitoids have higher initial 87Sr/86Sr ratio (0.713–0.714) and more negative εNd(t) values (−3.5 to −4.5). Potential basement source lithologies for the granites are Proterozoic granites and orthogneisses, and those for the leucocratic granites are plagioclase-rich sources such as meta-arkoses or tonalites. The U–Pb dating results demonstrate that all granitoids were exclusively emplaced during the Jurassic instead of being Cretaceous or younger in age as suggested previously. The pluton was assembled incrementally over c. 10 Ma. Gabbros formed at 166.5 ± 1.8 Ma, granites between 163.9 ± 0.9 Ma and 161.7 ± 0.6 Ma, and leucocratic granitoids between 154.4 ± 1.3 and 153.3 ± 2.7 Ma. Granites and leucocratic granitoids show some A-type affinity. It is concluded that the Alvand plutonic complex was generated in a continental-arc-related extensional regime during subduction of Neo-Tethyan oceanic crust beneath the SSZ. The U/Pb zircon age data, recently corroborated by similar results in the central and southern SSZ, indicate that Jurassic granitoids are more areally extensive in this belt than previously thought. 相似文献
8.
The Kuh-e Dom Pluton is located along the central northeastern margin of the Urumieh–Dokhtar Magmatic Arc, spanning a wide range of compositions from felsic rocks, including granite, granodiorite, and quartz monzonite, through to intermediate-mafic rocks comprising monzonite, monzodiorite, diorite, monzogabbro, and gabbro. The Urumieh–Dokhtar Magmatic Arc forms a distinct linear magmatic complex that is aligned parallel with the orogenic suture of the Zagros fold-thrust belt. Most samples display characteristics of metaluminous, high-K calc-alkaline, I-type granitoids. The initial isotopic signatures range from εNd (47 Ma) = −4.77 to −5.89 and 87Sr/86Sr(i) = 0.7069 to 0.7074 for felsic rocks and εNd (47 Ma) = −3.04 to −4.06 and 87Sr/86Sr(i) = 0.7063 to 0.7067 for intermediate to mafic rocks. This geochemical and isotopic evidence support a mixed origin for the Kuh-e Dom hybrid granitoid with a range of contributions of both the crust and mantle, most probably by the interaction between lower crust- and mantle-derived magmas. It is seem, the felsic rocks incorporate about 56–74% lower crust-derived magma and about 26–44% of the enriched mantle-derived mafic magma. In contrast, 66–84% of the enriched mantle-derived mafic magma incorporates 16–34% of lower crust-derived magma to generate the intermediate-mafic rocks. According to the differences in chemical composition, the felsic rocks contain a higher proportion of crustal material than the intermediate to mafic ones. Enrichment in LILEs and depletion in HFSEs with marked negative Nb, Ba, and Ti anomalies are consistent with subduction-related magmatism in an active continental margin arc environment. This suggestion is consistent with the interpretation of the Urumieh–Dokhtar Magmatic Arc as an active continental margin during subduction of the Neotethys oceanic crust beneath the Central Iranian microcontinent. 相似文献
9.
《Chemical Geology》2007,236(1-2):112-133
The Cida A-type granitic stock (∼ 4 km2) and Ailanghe I-type granite batholith (∼ 100 km2) in the Pan-Xi (Panzhihua-Xichang) area, SW China, are two important examples of granites formed during an episode of magmatism associated with the Permian Emeishan mantle plume activity. This is a classic setting of plume-related, anorogenic magmatism exhibiting the typical association of mantle-derived mafic and alkaline rocks along with silicic units. SHRIMP zircon U–Pb data reveal that the Cida granitic pluton (261 ± 4 Ma) was emplaced shortly before the Ailanghe granites (251 ± 6 Ma). The Cida granitoids display mineralogical and geochemical characteristics of A-type granites including high FeO⁎/MgO ratios, elevated high-field-strength elements (HFSE) contents and high Ga/Al ratios, which are much higher than those of the Ailanghe granites. All the granitic rocks show significant negative Eu anomalies and demonstrate the characteristic negative anomalies in Ba, Sr, and Ti in the spidergrams. It can be concluded that the Cida granitic rocks are highly fractionated A-type granitoids whereas the Ailanghe granitic rocks belong to highly evolved I-type granites.The Cida granitoids and enclaves have Nd and Sr isotopic initial ratios (εNd(t) = − 0.25 to + 1.35 and (87Sr/86Sr)i = 0.7023 to 0.7053) close to those of the associated mafic intrusions and Emeishan basalts, indicating the involvement of a major mantle plume component. The Ailanghe granites exhibit prominent negative Nb and Ta anomalies and weakly positive Pb anomalies in the spidergram and have nonradiogenic εNd(t) ratios (− 6.34 to − 6.26) and high (87Sr/86Sr)i values (0.7102 to 0.7111), which indicate a significant contribution from crustal material. These observations combined with geochemical modeling suggest that the Cida A-type granitoids were produced by extensive fractional crystallization from basaltic parental magmas. In contrast, the Ailanghe I-type granites most probably originated by partial melting of the mid-upper crustal, metasedimentary–metavolcanic rocks from the Paleo-Mesoproterozoic Huili group and newly underplated basaltic rocks.In the present study, it is proposed that petrogenetic distinctions between A-type and I-type granites may not be as clear-cut as previously supposed, and that many compositional and genetically different granites of the A- and I-types can be produced in the plume-related setting. Their ultimate nature depends more importantly on the type and proportion of mantle and crustal material involved and melting conditions. Significant melt production and possible underplating and/or intrusion into the lower crust, may play an important role in generating the juvenile mafic lower crust (average 20 km) in the central part of the Emeishan mantle plume. 相似文献
10.
Late Silurian–early Devonian magmatism of the NW Junggar region in the Central Asian Orogenic Belt provides a critical geological record that is important for unraveling regional tectonic history and constraining geodynamic processes. In this study, we report results of Zircon U–Pb ages and systematic geochemical data for late Silurian–early Devonian largely granitic rocks in NW Junggar, aiming to constrain their emplacement ages, origin and geodynamic significance. The magmatism consists of a variety of mafic to felsic intrusions and volcanic rocks, e.g. adakitic granodiorite, K-feldspar granite, syenitic granite, gabbro and rhyrolite. U–Pb zircon ages suggest that the granitoids and gabbros were emplaced in the late Silurian–early Devonian (420–405 Ma). Adakitic granodiorites are calc-alkaline, characterized by high Sr (407–532 ppm), low Y (12.2–14.7 ppm), Yb (1.53–1.77 ppm), Cr (mostly < 8.00 ppm), Co (mostly < 11.0 ppm) and Ni (mostly < 4.10 ppm) and relatively high Sr/Y (31–42) ratios, analogous to those of modern adakites. K-feldspar granites and rhyolites are characterized by alkali- and Fe-enriched, with high Zr, Nb and Ga/Al ratios, geochemically similar to those of A-type granites. Syenitic granites show high alkaline (Na2O + K2O = 8.39–9.34 wt.%) contents, low Fe# values (0.73–0.80) and are weakly peraluminous (A/CNK = 1.00–1.07). Gabbros are characterized by low MgO (6.86–7.15 wt.%), Mg# (52–53), Cr (124–133 ppm) and Ni (84.7–86.6 ppm) contents. The geochemical characteristics of the gabbroic samples show affinity to both MORB- and arc-like sources. All granitoids have positive εNd(t) (+ 3.9 to + 6.9) and zircon εHf(t) (+ 9.8 to + 15.2) values and low initial 87Sr/86Sr ratios (0.7035–0.7043), with young TDM(Nd) (605–791 Ma) and TDM(Hf) (425–773 Ma) ages, suggesting significant addition of juvenile material. The adakitic granodiorites probably resulted from partial melting of mafic lower crust, leaving an amphibolite and garnet residue. The K-feldspar granites, rhyolites and syenitic granites probably formed from partial melting of the Xiemisitai mid-lower crust, while the gabbroic intrusion was probably generated by interactions between asthenospheric and metasomatized lithospheric mantle. Voluminous plutons of various types (adakites, A-type granites, I-type granites, and gabbros) formed during 420–405 Ma, and their isotopic data suggest significant additions of juvenile material. We propose that a slab roll-back model can account for the 420–405 Ma magmatic “flare up” in NW Junggar as well as an extensional setting. 相似文献
11.
Neoproterozoic igneous rocks are widely distributed in the Kuluketage block along the northern margin of the Tarim Craton. However, the published literature mainly focuses on the ca. 800 Ma adakitic granitoids in the area, with the granites that intrude the 735–760 Ma mafic–ultramafic rocks poorly studied. Here we report the ages, petrography and geochemistry of two granites in the Xingdi mafic–ultramafic rocks, in order to construct a new view of the non-adakitic younger granites. LA-ICP-MS zircon U–Pb dating provided weighted mean 206Pb/238U ages of 743.0 ± 2.5 Ma for the No.I granite (G1) and 739.0 ± 3.5 Ma for the No.II granite (G2). A clear core-rim texture of similar age and a high zircon saturation temperature of ca. 849 ± 14 °C were observed for the No.I granite; in contrast, G2 has no apparent core-rim texture but rather inherited older zircons and a lower zircon saturation temperature of ca. 763 ± 17 °C. Geochemical analysis revealed that G1 is an alkaline A-type granite and G2 is a high-K calc-alkaline I-type granite. Both granites share similar geochemical characteristics of arc-related magmatic rocks and enriched Sr–Nd–Hf isotopes, likely due to their enriched sources or mixing with enriched magma. Whereas G1 and its host mafic rocks form typical bimodal intrusions of the same age and similar Sr–Nd–Hf isotope compositions, G2 is younger than its host mafic rocks and its Sr–Nd–Hf isotope composition indicates a lower crust origin. Although they exhibit arc-related geochemical features, the two granites likely formed in a rift setting, as inferred from thier petrology, Sr–Nd–Hf isotopes and regional tectonic evolution. 相似文献
12.
Huaying Wu Lianchang Zhang Bo Wan Zhiguang Chen Xiaojing Zhang Peng Xiang 《Ore Geology Reviews》2011,43(1):78-91
The Aolunhua porphyry Mo–Cu deposit is located in the northern margin of the North China Craton (NCC), and belongs to the northern part of the Xilamulun metallogenic belt. More than 90% of the mineralization occurs within the Aolunhua monzogranite-porphyry; a small part is hosted within quartz veins that crosscut Late Permian strata. The syenogranite, occurring as dikes and cutting through the Aolunhua monzogranite-porphyry, is radially distributed in the mining district. Zircon U–Pb ages show that the Aolunhua monzogranite-porphyry and the post-ore syenogranite have concordant 206Pb/238U ages of 138.7 ± 1.2 Ma and 131.4 ± 2.8 Ma, respectively. Based on analyses of major, trace elements and Hf-isotopes, the Aolunhua porphyry is characterized by high Sr low Y with high La/Yb and Sr/Y ratios typical of adakitic granites, whereas the post-ore syenogranite has lower Sr and higher Y values, showing apparently negative Eu anomalies (δEu = 0.26 to 0.31). The Hf isotopic composition of the Aolunhua porphyry [εHf(t) = + 3.6 to + 9.2] and the post-ore syenogranite [εHf(t) = + 3.6 to + 8.7] indicates that both juvenile crustal sources and depleted mantle contributed to their origin. The regional geological setting together with the discrepancy of geochemistry between the Aolunhua porphyry and the post-ore syenogranite probably indicates that they formed in different tectonic regimes. The Aolunhua porphyry is derived from partial melting of the thickened crust due to underplating of the basaltic magma under the transformation tectonic regime, while the post-ore syenogranite comes from the crustal root melting during the lithospheric delamination stage under the lithosphere thinning regime of northeast China. 相似文献
13.
The northeastern Gangdese Pb–Zn–Ag–Fe–Mo–W polymetallic belt (NGPB), characterized by skarn and porphyry deposits, is one of the most important metallogenic belts in the Himalaya–Tibetan continental orogenic system. This belt extends for nearly four hundred kilometers along the Luobadui–Milashan Fault in the central Lhasa subterrane, and contains more than 10 large ore deposits with high potential for development. Three major types of mineralization system have been identified: skarn Fe systems, skarn/breccia Pb–Zn–Ag systems, and porphyry/skarn Mo–Cu–W systems. In this study, we conducted a whole-rock geochemical, U–Pb zircon geochronological, and in situ zircon Hf isotopic study of ore-forming rocks in the NGPB, specifically the Jiangga, Jiaduopule, and Rema skarn Fe deposits, and the Yaguila Pb–Zn–Ag deposit. Although some of these deposits (porphyry Mo systems) formed during the post-collisional stage (21–14 Ma), the majority (these three systems) developed during the main (‘soft collision’) stage of the India–Asia continental collision (65–50 Ma). The skarn Fe deposits are commonly associated with granodiorites, monzogranites, and granites, and formed between 65 and 50 Ma. The ore-forming intrusions of the Pb–Zn–Ag deposits are characterized by granite, quartz porphyry, and granite porphyry, which developed in the interval of 65–55 Ma. The ore-forming porphyries in the Sharang Mo deposit, formed at 53 Ma. The rocks from Fe deposits are metaluminous, and have relatively lower SiO2, and higher CaO, MgO, FeO contents than the intrusions associated with Mo and Pb–Zn–Ag mineralization, while the Pb–Zn–Ag deposits are peraluminous, and have high SiO2 and high total alkali concentrations. They all exhibit moderately fractionated REE patterns characterized by lower contents of heavy REE relative to light REE, and they are enriched in large-ion lithophile elements and relatively depleted in high-field-strength elements. Ore-forming granites from Fe deposits display 87Sr/86Sr(i) = 0.7054–0.7074 and εNd(t) = − 4.7 to + 1.3, whereas rocks from the Yaguila Pb–Zn–Ag deposit have 87Sr/86Sr(i) = 0.7266–0.7281 and εNd(t) = − 13.5 to − 13.3. In situ Lu–Hf isotopic analyses of zircons from Fe deposits show that εHf(t) values range from − 7.3 to + 6.6, with TDM(Hf)C model ages of 712 to 1589 Ma, and Yaguila Pb–Zn–Ag deposit has εHf(t) values from − 13.9 to − 1.3 with TDM(Hf)C model ages of 1216 to 2016 Ma. Combined with existing data from the Sharang Mo deposit, we conclude that the ore-forming intrusions associated with the skarn Fe and porphyry Mo deposits were derived from partial melting of metasomatized lithospheric mantle and rejuvenated lower crust beneath the central Lhasa subterrane, respectively. Melting of the ancient continental material was critical for the development of the Pb–Zn–Ag system. Therefore, it is likely that the source rocks play an important role in determining the metal endowment of intrusions formed during the initial stage of the India–Asia continental collision. 相似文献
14.
Jiang-Feng Qin Shao-Cong Lai Rodney Grapes Chun-rong Diwu Yin-Juan Ju Yong-Fei Li 《Lithos》2010,120(3-4):347-367
The origin of high-Mg adakitic granitoids in collisional orogens can provide important information about the nature of the lower crust and upper mantle during the orogenic process. Late-Triassic high-Mg adakitic granite and its mafic enclaves from the Dongjiangkou area, the Qinling orogenic belt, central China, were derived by partial melting of subducted continental crust and underwent interaction with the overlying mantle wedge peridotite. Adakitic affinity of the different facies of the Dongjiangkou granite body are: high Sr, Ba, high La/Yb and Sr/Y, low Y,Yb, Yb/Lu and Dy/Yb, and no significant Eu anomalies, suggesting amphibole + garnet and plagioclase-free restite in their source region. Evolved Sr-Nd-Pb isotopic compositions [(87Sr/86Sr)i = 0.7050 to 0.7055,εNd(t) = –6.6 to –3.3; (206Pb/204Pb)i = 17.599 to 17.799, (207Pb/204Pb)i = 15.507 to 15.526, (208Pb/204Pb)i = 37.775 to 37.795] and high K2O, Rb, together with a large variation in zircon Hf isotopic composition (εHf(t) = ?9.8 to + 5.0), suggest that the granite was derived from reworking of the ancient lower continental crust. CaO, P2O5, K2O/Na2O, Cr, Ni, Nb/Ta, Rb/Sr and Y increase, and SiO2, Sr/Y and Eu/Eu* decrease with increasing MgO, consistent with interaction of primitive adakitic melt and overlying mantle peridotite. Zircons separated from the host granites have U-Pb concordia ages of 214 ± 2 Ma to 222 ± 2 Ma, compatible with exhumation ages of Triassic UHP metamorphic rocks in the Dabie orogenic belt. Mafic microgranular enclaves and mafic dykes associated with the granite have identical zircon U-Pb ages of 220 Ma, and are characterized by lower SiO2, high TiO2, Mg# and similar evolved Sr-Nd-Pb isotopic composition. Zircons from mafic microgranular enclaves (MMEs) and mafic dykes also show a large variation in Hf isotopic composition with εHf(t) between ?11.3 and + 11.3. It is inferred that they were formed by partial melting of enriched mantle lithosphere and contaminated by the host adakitic granite magma.In combination with the regional geology, high-Mg# adakitic granitoid rocks in the Dongjiangkou area are considered to have resulted from interaction between subducted Yangtze continental crust and the overlying mantle wedge. Triassic continental collision caused detachment of the Yangtze continental lithosphere subducted beneath the North China Craton, at ca. 220 Ma causing asthenosphere upwelling and exhumation of the continental crust. Triassic clockwise rotation of the Yangtze Craton caused extension in the Dabie area which led to rapid exhumation of the subducted continental lithosphere, while compression in the Qinling area and high-P partial melting (amphibole ± garnet stability field) of the subducted continental crust produced adakitic granitic magma that reacted with peridotite to form Mg-rich hybrid magma. 相似文献
15.
U–Pb dating and Hf isotopic analyses of zircons from various granitoids, combined with major and trace element analyses, were undertaken to determine the petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli–Erguna area of Inner Mongolia, China. The Neoproterozoic granitoids are mainly biotite monzogranites with zircon U–Pb ages of 894 ± 13 Ma and 880 ± 10 Ma, and they are characterised by enrichment in large ion lithophile elements (LILEs; e.g., Rb, Ba, K) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Ti) and heavy rare earth elements (HREEs). The Late Devonian granitoids are dominantly syenogranites and mylonitised syenogranites with zircon U–Pb ages of 360 ± 4 Ma, and they form a bimodal magmatic association with subordinate gabbroic rocks of the same age. The Late Devonian syenogranites have A-type characteristics including high total alkalis, Zr, Nb, Ce and Y contents, and high FeOt/MgO, Ga/Al and Rb/Sr ratios. The Carboniferous granitoids are mainly tonalites, granodiorites and monzogranites with U–Pb ages varying from 319 to 306 Ma, and they show very strong adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. The Late Permian granitoids are dominated by monzogranites and syenogranites with zircon U–Pb ages ranging between 257 and 251 Ma. Isotopically, the εHf(t) values of the Neoproterozoic granitoids range from +4.3 to +8.3, and the two-stage model ages (TDM2) from 1.2 to 1.5 Ga. The Late Devonian granitoids are less radiogenic [εHf(t) from +12.0 to +12.8 and TDM2 from 545 to 598 Ma] than the Carboniferous [εHf(t) from +6.8 to +9.5 and TDM2 from 722 to 894 Ma] and Late Permian granitoids [εHf(t) from +6.1 to +9.4 and TDM2 in the range of 680–895 Ma]. These data indicate (1) the Neoproterozoic granitoids may have been generated by melting of a juvenile crust extracted from the mantle during the Mesoproterozoic, probably during or following the final stages of assembly of Rodinia as a result of the collision and amalgamation of Australia and the Tarim Craton; (2) the Late Devonian granitoids may have formed by partial melting of a new mantle-derived juvenile crust in a post-orogenic extensional setting; (3) the Carboniferous granitoids appear to have been produced by melting of garnet-bearing amphibolites within a thickened continental crust during and following the collision of the Songnen and Erguna–Xing’an terranes; and (4) the Late Permian granitoids may have been generated by melting of garnet-free amphibolites within the Neoproterozoic juvenile continental crust, probably in the post-collisional tectonic setting that followed the collision of the North China and Siberian cratons. 相似文献
16.
The juvenile component of accretionary orogenic belts has been declining since the Archean. As a result, there is often controversy regarding the contribution of oceanic basalts to Phanerozoic crustal growth, as in the case of the Central Asian Orogenic Belt (CAOB). Here we report on three groups of Late Carboniferous (316–305 Ma) granitoids in the western Junggar region of northern Xinjiang, NW China, which is part of the southwestern CAOB. They consist of adakites and I and A-type granites, and as a whole have the most depleted isotopic compositions (εNd(t) = + 6–+9, (87Sr/86Sr)i = 0.7030–0.7045, and εHf(t) = + 12–+16) among the granitoids of the CAOB. These features are nearly identical to those of pre-Permian ophiolites in northern Xinjiang, and are clearly different from those of Carboniferous basalts in the western Junggar region. These relationships indicate that the granitoids were mainly derived from recycled oceanic crust by melting of subducted oceanic crust (e.g., adakites), and of the middle–lower crust of intra-oceanic arc that mainly consisted of oceanic crust (e.g., I and A-type granites). Based on evidence from the CAOB, we suggest that recycling of oceanic crust has made a significant contribution to continental crustal growth and evolution during the Phanerozoic. 相似文献
17.
The Gaoligong belt is located in the southeastern margin of the Tibetan plateau, and is bound by the Tengchong and Baoshan blocks. This paper presents new data from zircon geochronology, geochemistry, and whole-rock Sr–Nd–Pb–Hf isotopes to evaluate the tectonic evolution of the Gaoligong belt. The major rock types analysed in the present study are granitic gneiss, granodiorite, and granite. They are metaluminous to peraluminous and belong to high-K, calc-alkaline series. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses of zircons from nine granitic rocks yielded crystallization ages of 495–487 Ma, 121 Ma, 89 Ma, and 70–63 Ma. The granitoids can be subdivided into the following four groups. (1) Early Paleozoic granitic gneisses with high εNd(t) and εHf(t) values of − 1.06 to − 3.45 and − 1.16 to 2.09, and model ages of 1.16 Ga to 1.33 Ga and 1.47 Ga to 1.63 Ga, respectively. Their variable 87Sr/86Sr and Pb values resemble the characteristics of the Early Paleozoic Pinghe granite in the Baoshan block. Our data suggest that the rocks were derived from the break-off of the Proto-Tethyan oceanic slab between the outboard continent and the Baoshan block, which induced the partial melting of Mesoproterozoic pelitic sources mixed with depleted mantle materials. (2) Early Cretaceous granodiorites with low εNd(t) and εHf(t) values of − 8.92 and − 4.91 with Nd and Hf model ages of 1.41 Ga and 1.49 Ga, respectively. These rocks have high initial 87Sr/86Sr (0.711992) and lower crustal Pb values, suggesting that they were derived from Mesoproterozoic amphibolites with tholeiitic signature, leaving behind granulite residue at the lower crust. (3) Early Late Cretaceous granites with low εNd(t) and εHf(t) values of − 9.58 and − 4.61 with Nd and Hf model ages of 1.43 Ga and 1.57 Ga, respectively. These rocks have high initial 87Sr/86Sr (0.713045) and lower crustal Pb isotopic values. These rocks were generated from the partial melting of Mesoproterozoic metapelitic sources resulting from the delamination of thickened lithosphere, following the closure of the Bangong–Nujiang Ocean and collision of the Lhasa–Qiangtang blocks. (4) Late Cretaceous to Paleogene granitic gneisses with low εNd(t) and εHf(t) values of − 4.41 to − 10 and − 5.95 to − 8.71, Nd model ages ranging from 1.08 Ga to 1.43 Ga, and Hf model ages from 1.53 Ga to 1.67 Ga, respectively. These rocks show high initial 87Sr/86Sr (0.713201 and 714662) and lower crustal Pb values. The data suggest that these rocks are likely related to the eastward subduction of the Neo-Tethyan Oceanic slab, which induced partial melting of Mesoproterozoic lower crustal metagreywacke. The results presented in this study from the Gaoligong belt offer important insights on the evolution of the Proto-Tethyan, Bangong–Nujiang, and Neo-Tethyan oceans in the southeastern margin of the Tibetan Plateau. 相似文献
18.
Miguel Tupinambá Monica Heilbron Claudio Valeriano Rubem Porto Júnior Fátima Blanco de Dios Nuno Machado Luiz Guilherme do Eirado Silva Júlio Cesar Horta de Almeida 《Gondwana Research》2012,21(2-3):422-438
The ca. 790–600 Ma Rio Negro Complex (RNC) of the Ribeira belt (Brazil) consists of a plutonic portion of a magmatic arc built by the E-vergent subduction of the ESE border of the São Francisco paleoplate during the amalgamation of Western Gondwana.The plutonic series comprises low- to medium-K granitoids (ca. 790–620 Ma) and high-K granitoids and shoshonite rocks (ca. 610–605). The age span of 185 m.y. is suggestive of a long history of arc-related magmatism, continuously or not in time. The Nd isotopic signatures of the RNC consist of εNd(t) ratios from ? 3 to + 5 for the medium-K series shoshonite series and from ? 14 to ? 3 for the younger high-K group. This time-dependent trend of Nd isotopes is indicative of progressive maturity of the arc over time. The same evolution is indicated by Sr data, as the medium-K rocks have 87Sr/86Sr initial ratios < 0.705 while the high-K rocks yield values between 0.705 and 0.710. The predominance of intermediate rocks over mafic ones suggests an initial intra-oceanic to transitional stage, possibly developed in a distal portion of a passive margin, such as the Japanese arc, evolving to a more developed, differentiated felsic rock associations.The role of transform fault zones, such as the Luanda shear zone, is emphasized in order to explain the consumption of a wide oceanic plate in the inner portion of Western Gondwana. 相似文献
19.
Post-collisional, potassic magmatic rocks widely distributed in the eastern Lhasa terrane provide significant information for comprehensive understanding of geodynamic processes of northward subduction of the Indian lithosphere and uplift of the Tibetan Plateau. A combined dataset of whole-rock major and trace elements, Sr–Nd–Pb isotopes, and in situ zircon U–Pb dating and Hf–O isotopic analyses are presented for the Yangying potassic volcanic rocks (YPVR) in the eastern part of the Lhasa terrane, South Tibet. These volcanic rocks consist of trachytes, which are characterized by high K2O (5.46–9.30 wt.%), SiO2 (61.34–68.62 wt.%) and Al2O3 (15.06–17.36 wt.%), and relatively low MgO (0.47–2.80 wt.%) and FeOt (1.70–4.90 wt.%). Chondrite-normalized rare earth elements (REE) patterns display clearly negative Eu anomalies. Primitive mantle-normalized incompatible trace elements diagrams exhibit strong enrichment in large ion lithophile elements (LILE) relative to high field strength elements (HFSE) and display significantly negative Nb–Ta–Ti anomalies. Initial isotopic compositions indicate relatively radiogenic Sr [(87Sr/86Sr)i = 0.711978–0.712090)] and unradiogenic Nd [(143Nd/144Nd)i = 0.512121–0.512148]. Combined with their Pb isotopic compositions [(206Pb/204Pb)i = 18.615–18.774, (207Pb/204Pb)i = 15.708–15.793, (208Pb/204Pb)i = 39.274–39.355)], these data are consistent with the involvement of component from subducted continental crustal sediment in their source region. The whole-rock Sr–Nd–Pb isotopic compositions exhibit linear trends between enriched mantle-derived mafic ultrapotassic magmas and relatively depleted crustal contaminants from the Lhasa terrane. The enrichment of the upper mantle below South Tibet is considered to result from the addition of components derived from subducted Indian continental crust to depleted MORB-source mantle during northward underthrusting of the Indian continental lithosphere beneath the Lhasa terrane since India–Asia collision at ~ 55 Ma. Secondary Ion Mass Spectrometry (SIMS) U–Pb zircon analyses yield the eruptive ages of 10.61 ± 0.10 Ma and 10.70 ± 0.18 Ma (weighted mean ages). Zircon Hf isotope compositions [ƐHf(t) = −4.79 to −0.17], combined with zircon O isotope ratios (5.51–7.22‰), imply an addition of crustal material in their petrogenesis. Clinopyroxene-liquid thermobarometer reveals pressure (2.5–4.1 kbar) and temperature (1029.4–1082.9 °C) of clinopyroxene crystallization, suggesting that depth of the magma chamber was 11.6–16.4 km. Energy-constrained assimilation and fractional crystallization (EC–AFC) model calculation indicates depth of assimilation and fractional crystallization in the region of 14.40–18.75 km underneath the Lhasa terrane, which is in consistent with depth of the magma chamber as suggested by clinopyroxene-liquid thermobarometer. Based on the whole-rock major and trace elements and Sr–Nd–Pb isotope compositions, combined with EC–AFC modeling simulations and zircon Hf–O isotope data, we propose that the YPVR resulted from assimilation and fractional crystallization (AFC) process of the K-rich mafic primitive magmas, which were caused by partial melting of the Indian continental subduction-induced mélange rocks. 相似文献
20.
《Gondwana Research》2014,25(1):401-419
This study reports new zircon U–Pb and Hf isotopes and whole-rock elemental and Sr–Nd isotopic data for the gneissic granite and leucogranite from the Nabang metamorphic zone, Yingjiang area (West Yunnan, SW China). The metamorphosed granitoids crystallized during the early Eocene (~ 55–50 Ma) with zircons showing εHf(t) values from + 11 to − 5.3 and crustal model ages of 1.5 to 0.42 Ga, comparable to those of coeval I-type granitoids from the Gangdese batholith, southern Lhasa. The rocks are characterized by metaluminous and weakly peraluminous hornblende-bearing gneissic granites with A/CNK = 0.95–1.09, Na2O > K2O, coupled with low initial Sr isotopic values of 0.7049–0.7070 and high εNd(t) values from + 1.1 to − 7.1. The rocks were derived from crustal materials involving ancient upper crust/sedimentary and juvenile mantle-derived rocks. Together with available data from nearby regions, it is proposed that the early Eocene granitoids in the Nabang and Tengliang area can be correlated to the Gangdese granitoids and represent the southeastward continuation of the magmatic arc resulting from the Neotethyan subduction in southern Tibet. The petrogenesis of early Eocene granitoids in western Yunnan was probably related to the rollback of the subducting Neotethyan slab that caused the remelting of the crustal materials newly modified by the underplated basaltic magma. 相似文献