首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
《China Geology》2021,4(4):658-672
The Paleoproterozoic tectonic evolution of the Bangweulu Block has long been controversial. Paleoproterozoic granites consisting of the basement complex of the Bangweulu Block are widely exposed in northeastern Zambia, and they are the critical media for studying the tectonic evolution of the Bangweulu Block. This study systematically investigated the petrography, zircon U-Pb chronology, and petrogeochemistry of the granitoid extensively exposed in the Lunte area, northeastern Zambia. The results show that the granitoid in the area formed during 2051±13–2009±20 Ma as a result of Paleoproterozoic magmatic events. Geochemical data show that the granites in the area mainly include syenogranites and monzogranites of high-K calc-alkaline series and are characterized by high SiO2 content (72.68% –73.78%) and K2O/Na2O ratio (1.82–2.29). The presence of garnets, the high aluminum saturation index (A/CNK is 1.13–1.21), and the 1.27%–1.95% of corundum molecules jointly indicate that granites in the Lunte area are S-type granites. Rare earth elements in all samples show a rightward inclination and noticeably negative Eu-anomalies (δEu = 0.16–0.40) and are relatively rich in light rare earth elements. Furthermore, the granites are rich in large ion lithophile elements such as Rb, Th, U, and K and are depleted in Ba, Sr, and high field strength elements such as Ta and Nb. In addition, they bear low contents of Cr (6.31×10−6–10.8×10−6), Ni (2.87×10−6–4.76×10−6), and Co (2.62×10−6–3.96×10−6). These data lead to the conclusion that the source rocks are meta-sedimentary rocks. Combining the above results and the study of regional tectonic evolution, the authors suggest that granitoid in the Lunte area were formed in a tectonic environment corresponding to the collision between the Tanzania Craton and the Bangweulu Block. The magmatic activities in this period may be related to the assembly of the Columbia supercontinent.©2021 China Geology Editorial Office.  相似文献   

2.
Whole rock elemental and Sr–Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810–580 Ma), and is dominated by crust-derived relatively low-T (850–750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative εNdt (−8 to −10) and highest mg# (30–40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96–1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595–580 Ma) plutons have a spread of compositions from biotite granites with SiO2 as low as ∼65% (e.g., Itapeti, Mauá, Sabaúna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO2). εNdT are characteristically negative (−12 to −18), with corresponding Nd TDM indicating sources with Paleoproterozoic mean crustal ages (2.0–2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative εNdt, highest 87Sr/86Srt (0.714–0.717) and lowest 208Pb/206Pb and 207Pb/206Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd–Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Mauá granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The Ediacaran granites are coeval with profuse granite magmatism attributed to continental arc magmatism in northern Ribeira and Araçuaí belts. However, their evolved compositions with low mg# and dominantly peraluminous character are unlike those of magmatic arc granites, and they are more likely products of post-collisional magmatism or correspond to an inner belt of crust-derived granites.  相似文献   

3.
Available cores of porphyritic granite and aplitic granite from the Diyanqinamu porphyry Mo deposit in the north central Great Xing’an Range presented an opportunity to examine and analyze Mesozoic igneous rocks far from the Paleo-Pacific subduction zone. The Diyanqinamu granites are highly fractionated I-type, distinguished from the M-, A- or S-type granite by: high SiO2, and Rb; low Zr, Nb, Y, and Ce; low Fe2O3total/MgO and (K2O + Na2O)/CaO ratios; low alumina saturation index (<1.1); low initial ISr ratios (0.70137–0.70451); positive εNd(t) values (2.37–3.77); and negative correlation between P2O5 and SiO2. The aplitic granites were generated by fractional crystallization of the porphyritic granite, as evidenced by: spatial proximity; consistent zircon U–Pb ages (156 Ma) within error; correlations between other oxides and SiO2 in Haker diagrams; low Ba, Sr, Nb, P, Ti, Eu; linear relationship in both (La/Yb)N vs. La and Sr vs. Ba diagrams; and, decreasing LREE and ∑REE with increasing SiO2. The Diyanqinamu granites have young depleted-mantle two-stage model ages (avg. TDM2 = 660 Ma) similar to those of most Mesozoic voluminous felsic magmas in northeastern China, and were likely sourced from pre-existent crustal components both “old” and juvenile that had been juxtaposed during the tectonic evolution of the Paleo-Asian Ocean. These granites project in the transitional field from syn-collision to post-collision tectonic settings on tectonic discrimination diagrams, implying emplacement in an extensional environment. Extensional volcanism and basin formation in the Great Xing’an Range region in Late Jurassic is coeval with the Diyanqinamu granites, demonstrating that post-orogenic lithospheric extension related to the closure of the Mongol-Okhotsk Ocean was the main driving force for Late Jurassic magmatism in this region.  相似文献   

4.
Biotite granites and muscovite-bearing granites are dominant rock types of the widespread granites in SE China. However, their petrogenesis has been enigmatic. A combined study of zircon U–Pb dating and Lu–Hf isotopes, whole-rock element geochemistry and Sr–Nd–O isotopes was performed for three late Mesozoic granitic plutons (Xinfengjie, Jiangbei and Dabu) in central Jiangxi province, SE China. All the plutons are composed of biotite granites and muscovite-bearing granites that have been poorly investigated previously. The new data not only allow us to assess their sources and magma evolution processes, but also helps us to better understand the genetic link to the large-scale polymetallic mineralization in SE China. LA-ICP-MS zircon U–Pb dating shows that three plutons were emplaced in the Late Jurassic (159–148 Ma) and that the muscovite-bearing granites are almost contemporaneous with the biotite granites. The biotite granites have SiO2 contents of 70.3–74.4 wt% and are weakly to strongly peraluminous with ASI from 1.00 to 1.26, and show a general decrease in ASI with increasing SiO2. They have relatively high zircon saturation temperatures (T Zr = 707–817 °C, most > 745 °C) and show a general decrease in T Zr with increasing SiO2. They have high initial 87Sr/86Sr ratios (0.7136 to 0.7166) and high δ18O values (9.1–12.8‰, most > 9.5‰) and clearly negative ε Nd (T) (? 9.5 to ? 11.8) and ε Hf (T) (in situ zircon) (? 13.1 to ? 13.5). The muscovite-bearing granites have high SiO2 contents (74.7–78.2 wt%). They are also weakly to strongly peraluminous with ASI of 1.04–1.18 but show a general increase in ASI with increasing SiO2. They have relatively low T Zr (671–764 °C, most < 745 °C) and also show a general decrease in T Zr with increasing SiO2. The muscovite-bearing granites have high Rb (up to 810 ppm) and high (K2O + Na2O)/CaO (up to 270), Rb/Sr (up to 42) and Rb/Ba (up to 30) as well as low K/Rb (< 150, down to 50), Zr/Hf (< 24, down to 11) and Nb/Ta (< 6, down to 2). They show similar Nd–O–Hf isotopic compositions to the biotite granites with ε Nd (T) of ? 8.7 to ? 12.0, δ18O of 8.7–13.0‰ (most > 9.5‰) and ε Hf (T) (in situ zircon) of ? 11.3 to ? 13.1. Geochemical data suggest the origin of the biotite granites and muscovite-bearing granites as follows: Partial melting of Precambrian metasedimentary rocks (mainly two-mica schist) in the lower crust at temperatures of ca. 820 °C generated the melts of the less felsic biotite granites. Such primary crustal melts underwent biotite-dominant fractionation crystallization, forming the felsic biotite granites. Progressive plagioclase-dominant fractionation crystallization from the evolved biotite granites produced the more felsic muscovite-bearing granites. Thus, the biotite granites belong to the S-type whereas the muscovite-bearing granites are highly fractionated S-type granites. We further suggest that during the formation of the muscovite-bearing granites the fractional crystallization was accompanied by fluid fractionation and most likely the addition of internally derived mineralizing fluids. That is why the large-scale polymetallic mineralization is closely related to the muscovite-bearing granites rather than biotite granites in SE China. This is important to further understand the source and origin of biotite granites and muscovite-bearing granites in SE China even worldwide.  相似文献   

5.
Widespread in the Wuyi Mountain area of eastern Jiangxi are petrochemically peraluminous granites and they are characterized as being high in silica (SiO2 > 75% ) and highly alkaline (ALK=6.9% -7.5%) with K2O > Na2O and rather high ratios of FeOT/MgO (11.3-17.9). The rocks have low contents of CaO, MgO, TiO2 and P2 O5. The granites are enriched in REE (ΣREE =210.3 - 496. 8 μg/g) with remarkable negative Eu anomalies, but depleted in Eu, Ba, Sr, V, Co, and Ni, with 10000 x Ga/Al ratios, varying from 6. 1 to 9. 8. It is clear that these granites are obviously different from the I- and S-type granites, but are quite similar to those typical A-type granites such as aluminous A-type granites in the coastal areas of Fujian Province. State Geological Survey Project: supported by the Regional Geological Survey Project (No: 20001300002091 ) on the basis of the maps (scale 1: 250000) of Jingdezheng City, Nanchang City and Shangrao City.  相似文献   

6.
《Precambrian Research》1987,37(4):267-286
Two major phases of granitic magmatism occurred in the Daniels Range, represented by the late Proterozoic Wilson Plutonic Complex and the Cambro-Ordovician Granite Harbour Intrusives. Both groups were derived from sedimentary protoliths (S-type), compositionally similar to the country rocks (Rennick Schist), although minor I-type (igneous-derived) intrusives are also present. New UPb zircon data indicate minimum emplacement ages of 652−20+17and 634−27+20 for Wilson Complex intrusives, and that the metasedimentary source rocks include a considerably older, possibly Archaean, component. Chemical data for the S-type granitoids show that neither restite unmixing nor fractional crystallisation can explain the observed variation trends, and different degrees, and possibly conditions, of melting of heterogeneous source materials were apparently important. The source of the Granite Harbour Intrusives was chemically (and isotopically) distinct from that of the Wilson intrusives. Although both groups have some chemical affinities with tin granites, they do not show the extreme fractionation of such granites, possibly because they represent low to intermediate levels of the intrusions.  相似文献   

7.
S-type granites are typical features of collisional orogenic belts and could provide insights into the tectonic process associated with the final phase of orogeny. The East Qinling Orogen, one of significant segments in the Central China Orogen, witnessed complex tectonic evolution during the Late Mesozoic. The rare S-type granites in this orogen can be used as important proxies to understand the Late Mesozoic tectonic processes. Although a few previous studies suggested that the Huangbeiling pluton in the East Qinling Orogen might be S-type granite, detailed studies are lacking. Thus, we report the results from a systematic petrological, whole-rock geochemical and zircon U-Pb-Lu-Hf isotopic studies on the Huangbeiling pluton, with a view to constrain the timing of magmatism, petrogenetic evolution and genetic type, and to evaluate the implications for Late Mesozoic tectonic evolution of the East Qinling Orogen. Zircon U-Pb analysis yield 206Pb/238U spot ages in the range of 156.7–132.2 Ma, with weighted 206Pb/238U mean ages varying from 146.8 to 141.9 Ma, suggesting the Huangbeiling pluton formed during the Late Jurassic to Early Cretaceous. Zircon Lu-Hf isotopic data show negative εHf(t) values of ?21.5 to ?14.9 and two-stage Hf model ages of 2546–2131 Ma, which are correlated with the Neoarchean to Paleoproterozoic (3.0–2.1 Ga) meta-sedimentary rocks from nearby Taihua Group, indicating that the magma was sourced from reworked ancient crustal components involving meta-sedimentary rocks. Whole-rock geochemical data display enrichment of LREEs, Pb, Hf and Y as well as depletion in HREEs, Ba and HFSEs (e.g., Ta, P, Ti), with weakly negative Eu anomalies. The Huangbeiling granitoids are identified as S-type granites, which generated through partial melting of lower-middle crust and upper crustal fractional crystallization in syn-collisional settings. In conjunction with published information related to the tectonic evolution of the East Qinling Orogen, we propose that the Late Mesozoic Huangbeiling S-type granites might response to the complex tectonic evolution related to extensional tectonics induced by multi-directional (intra-continental) subductions from the Yangtze and North China Cratons as well as the Paleo-Pacific Plate during the Late Mesozoic.  相似文献   

8.
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   

9.
The Dahongliutan granitic pluton consists of two-mica granites and is located in the eastern part of the Western Kunlun Orogen, northwestern Tibetan Plateau. Zircon separates from the pluton yield a SIMS U–Pb age of 217.5 ± 2.8 Ma. Rocks from the pluton contain relatively high and uniform SiO2 (72.32–73.48 wt%) and total alkalis (Na2O + K2O = 8.07–8.67 wt%) and are peraluminous and high-K calc-alkaline to shoshonitic in composition. The Dahongliutan granites are relatively depleted in the high-field-strength elements and the heavy rare earth elements (HREEs) and have relatively high Rb, and low Ba and Sr concentrations. They contain low total rare earth element (REE) concentrations. The light REEs are strongly enriched relative to the HREEs, with (La/Yb)N values of 28.56–37.01. The εNd(t) values range from ?10.6 to ?8.8, and (87Sr/86Sr)i = 0.7142–0.7210. Zircons from the pluton yield εHf(t) values of ?13.8 to ?1.6, and δ18O = 10.5–11.6‰. Petrographic and geochemical features of the pluton indicate that the granites are S-type and were derived from parting melting of a mixture of metasedimentary and minor metaigneous sources in the middle–lower crust. Magmatic differentiation was dominated by the fractional crystallization of plagioclase, K-feldspar, muscovite, biotite, and accessory monazite, allanite, and Fe–Ti oxides. Regional granitoids were emplaced in the Early-to-Middle Triassic. Other younger granitoids, with ages of 240–200 Ma, are mostly I-type in character and were likely derived from multiple types of source rock, suggesting the source was heterogeneous Triassic crust. Such a scenario is consistent with their formation in a post-collisional setting. Our new data, combined with other geological evidence, suggest that the collision between the Tianshuihai and southern Kunlun terranes occurred between ca. 250 and 240 Ma, resulting in the closure of the Palaeo-Tethys. Post-collisional tectono-magmatic events may have occurred between 240 and 200 Ma.  相似文献   

10.
Whole-rock major and trace element and Sr-Nd isotopic data, together with zircon LA ICPMS in-situ U-Pb and Hf isotopic data of the syenites and granites in the Tengchong Block are reported in order to understand their petrogenesis and tectonic implications. Zircon U-Pb data gives the emplacement ages of ca. 115.3±0.9 Ma for syenites and 115.7±0.8 Ma for granites, respectively. The syenites are characterized by low SiO_2 content(62.01–63.03 wt%) and notably high Na_2O content(7.04–7.24 wt%) and Na_2O/K_2O ratios(2.02–2.10), low MgO, Fe_2O_3 T and TiO_2, enrichment of LILEs(large-ion lithophile element) such as Rb, Th, U, K, and Pb) and obvious depletion HFSE(high field strength element; e.g. Nb, Ta, P, and Ti) with clearly negative Eu anomalies(d Eu=0.53–0.56). They also display significant negative whole-rock εNd(t) values of-6.8 and zircon εHf(t) values(-9.11 to-0.27, but one is +5.30) and high initial ~(87) Sr/~(86) Sr=0.713013. Based on the data obtained in this study, we suggest that the ca. 115.3 Ma syenites were possibly derived from a sodium-rich continental crustal source, and the fractionation of some ferro-magnesian mineral and plagioclase might occur during the evolution of magma. The granites have high SiO_2 content(71.35–74.47 wt%), metaluminous to peraluminous, low Rb/Ba, Rb/Sr, and Al_2O_3/(MgO+FeOT+TiO_2) ratios and moderate(Al_2O_3+MgO+FeOT+TiO_2) content. They show low initial ~(87) Sr/~(86) Sr(0.703408 to 0.704241) and εNd(t) values(-3.8 to-3.5), plotted into the evolutionary trend between basalts and lower crust. Hence, we suggest that the granites were derived from the melting of mixing sources in the ancient continental crust involving some metabasaltic materials and predominated metasedimentary greywackes. Together with data in the literatures, we infer that the Early Cretaceous magmatism in the Tengchong block was dominated by magmas generated by the partial melting of ancient crustal material, which represent the products that associated to the closure of Bangong-Nujiang Meso-Tethys.  相似文献   

11.
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   

12.
《International Geology Review》2012,54(12):1445-1461
We present zircon U–Pb ages, Hf isotopes, and whole-rock geochemistry of the Xiaochuan gneissic granite intrusion, SE China, to constrain its petrogenesis and provide insights into early crustal evolution of the Cathaysia Block. LA-ICP-MS zircon U–Pb dating of a representative sample yields a weighted mean 206Pb/207Pb age of 1839 ±16 Ma, interpreted as the emplacement age of the Xiaochuan granite. Zircons have ?Hf(t) values ranging from –8.1 to 2.7 and T DM2 model ages from 2.23 to 3.03 Ga. The granites are strongly peraluminious (A/CNK = 1.14–1.41), with relatively high FeOt, TiO2, and CaO/Na2O, and low CaO, Al2O3/TiO2, and Rb/Sr values. In addition, they show strongly negative Ba, Sr, Nb, and Ta and positive Th and Pb anomalies in the primitive mantle-normalized spider diagram, similar to other Cathaysia Palaeoproterozoic S-type granites. The geochemical and Hf isotopic signatures suggest that the Xiaochuan gneissic granites were generated by partial melting of Archaean crustal materials in an intraplate extensional setting. Our results, combined with existing geochronological data, further demonstrate that the Wuyishan terrane is underlain by Palaeoproterozoic crystalline basement.  相似文献   

13.
The Hashitu molybdenum deposit is located in the southern part of the Great Hinggan Range,NE China.Molybdenum mineralization is hosted by and genetically associated with monzogranite and porphyritic syenogranite.Sr-Nd-Pb isotopes of the intrusions show that the porphyritic syenogranite has initial~(87)Sr/~(86)Sr ratios of 0.70418-0.70952,ε_(Nd)(t)values of 1.3 to 2.1(t=143Ma),~(206)Pb/~(204)Pb ratios of 19.191-19.573,~(207)Pb/~(204)Pb ratios of 15.551-15.572,and~(208)Pb/~(204)Pb ratios of38.826-39.143.The monzogranite has initial~(87)Sr/~(86)Sr ratios of 0.70293-0.71305,ε_(Nd)(t)values of 1.1 to2.0(t=147 Ma),~(206)Pb/~(204)Pb ratios of 19.507-20.075,~(207)Pb/~(204)Pb ratios of 15.564-15.596,and~(208)Pb/~(204)Pb ratios of 39.012-39.599.The calculated Nd model ages(T_(DM))for monzogranite and porphyritic syenogranite range from 866 to 1121 Ma and 795 to 1020 Ma,respectively.The granitic rocks in the Hashitu area have the same isotope range as granites in the southern parts of the Great Hinggan Range.The isotope composition indicates that these granites are derived from the partial melting of a juvenile lower crust originating from a depleted mantle with minor contamination by ancient continental crust.The integrating our results with published data and the Late Mesozoic regional tectonic setting of the region suggest that the granites in the Hashitu area formed in an intra-continent extensional setting,and they are related to the thinning of the thickened lithosphere and upwelling of the asthenosphere.  相似文献   

14.
We report geochronological, geochemical and isotopic data for the Mesozoic Shangshuiquan granite from the northern margin of the North China craton. The granite is highly fractionated, with SiO2 > 74%. Occurrence of annitic biotite, high contents of alkalis (K2O + Na2O), Rb, Y, Nb and heavy rare earth elements, high FeOt/MgO, low contents of CaO, Al2O3, Ba, and Sr, and large negative Eu anomalies, makes it indistinguishable from typical A-type granites. A mantle-derived origin for the rocks of the granite is not favored because their high initial 87Sr/86Sr (≥0.706) and low εNd (t) (<−15) are completely different from either those of the lithospheric or asthenospheric mantle. In fact, their Sr–Nd isotopes fall within the range of Sr–Nd isotopic compositions of the Archean granulite terrains and are comparable to those of Mesozoic crustal-derived I-type granitoids in the region. Therefore, the Shangshuiquan granite is considered to be dominantly derived from partial melting of the ancient lower crust. Its parental magmas prove to be similar to I-type magmas and to have undergone extensive fractionation during its ascent. This is supported by the fact that some of the nearby Hannuoba feldspar-rich granulite xenoliths can be indeed regarded as the early cumulates in terms of their mineralogy, chemistry, Sr–Nd isotopes and zircon U–Pb ages and Hf isotopes. It is furthermore argued that some of highly fractionated granites worldwide, especially those with A-type characteristics and lacking close relationship with unfractionated rocks, may in fact be fractionated I-type granites. This suggestion can explain their close temporal and spatial associations as well as similar Sr–Nd isotopes with I-type granites. Our study also sheds new light on the petrogenesis of deep crustal xenoliths.  相似文献   

15.
The aim of this article is to examine the geochemistry and geochronology of the Cadomian Mishu granites from northwest Iran, in order to elucidate petrogenesis and their role in the evolution of the Cadomian crust of Iran. The Mishu granites mainly consist of two-mica granites associated with scarce outcrops of tonalite, amphibole granodiorite, and diorite. Leucogranitic dikes locally crosscut the Mishu granites. Two-mica granites show S-type characteristics whereas amphibole granodiorite, tonalities, and diorites have I-type signatures. The I-type granites show enrichment in large-ion lithophile elements (e.g. Rb, Ba and K) and depletion in high field strength elements (e.g. Nb, Ti and Ta). These characteristics show that these granites have been formed along an ancient, fossilized subduction zone. The S-type granites have high K, Rb, Cs (and other large ion lithophile elements) contents, resembling collision-related granites. U–Pb zircon dating of the Mishu rocks yielded 238U/206Pb crystallization ages of ca. 550 Ma. Moreover, Rb–Sr errorchron shows an early Ediacaran age (547 ± 84 Ma) for the Mishu igneous rocks. The two-mica granites (S-type granites) show high 87Sr/86Sr(i) ratios, ranging from 0.7068 to 0.7095. Their ?Nd values change between ?4.2 and ?4.6. Amphibole granitoids and diorites (I-type granites) are characterized by relatively low 87Sr/86Sr(i) ratios (0.7048–0.7079) and higher values of ?Nd (?0.8 to ?4.2). Leucogranitic dikes have quite juvenile signature, with ?Nd values ranging from +1.1 to +1.4 and Nd model ages (TDM) from 1.1 to 1.2 Ga. The isotopic data suggests interaction of juvenile, mantle-derived melts with old continental crust to be the main factor for the generation of the Mishu granites. Interaction with older continental crust is also confirmed by the presence of abundant inherited zircon cores. The liquid-line of descend in the Harker diagrams suggests fractional crystallization was also a predominant mechanism during evolution of the Mishu I-type granites. The zircon U–Pb ages, whole rock trace elements, and Sr–Nd isotope data strongly indicate the similarities between the Mishu Cadomian granites with other late Neoproterozoic–early Cambrian (600–520 Ma) granites across Iran and the surrounding areas such as Turkey and Iberia. The generation of the Mishu I-type granites could be related to the subduction of the Proto-Tethyan Ocean during Cadomian orogeny, through interaction between juvenile melts and old (Mesoproterozoic or Archaean) continental crust. The S-type granites are related to the pooling of the basaltic melts within the middle–upper parts of the thick continental crust and then partial melting of that crust.  相似文献   

16.
《International Geology Review》2012,54(15):1877-1888
The Hai Van granitoid complex constitutes an important part of the Indosinian batholith of the northern Kontum massif in central Vietnam. The Kontum massif is a key region for understanding the palaeo-Tethyan accretionary history and the crustal evolution of the Indochina terrane. In this study, zircon U–Pb ages and geochemical data on the Hai Van complex are reported to shed more light on these geological processes. Zircon U–Pb isotopic analyses of six representative samples by the LA-ICP-MS technique show that granitoids from this complex crystallized between 242 and 224 Ma, indicating a prolonged period of magmatism in a late orogenic stage. Rocks from the Hai Van complex have S-type geochemical characteristics with high SiO2, Na2O + K2O, and Zr contents as well as typical S-type minerals such as cordierite and muscovite. Trace elements of the samples are depleted in Ba, Nb, P, Sr, and Ti and enriched in Rb, K, Th, U, and Pb. Negative Eu-anomalies indicate feldspar fractionation during magma crystallization. The Hai Van granitoids exhibit Nd–Hf isotopic features similar to Proterozoic rocks exposed in South China, with low initial ?Hf and initial ?Nd values and two-stage Hf model ages of 1.9–1.7 Ga. It is suggested that during the palaeo-Tethyan orogeny, central Vietnam experienced strong early Mesozoic magmatism that originated from partial melting of crustal material similar in composition to the basement of the South China block.  相似文献   

17.
《International Geology Review》2012,54(15):1823-1841
ABSTRACT

The Song Ma zone in Northwestern Vietnam is considered as a suture of the South China and Indochina blocks, and plays an important role in understanding the tectonic evolution in Southeast Asia and surrounding areas. Granitic rocks of the Muong Lat complex are distributed in the Song Ma suture, consisting mainly of monzogranite and granodiorite. The rocks are sub-alkaline in affinity with high K contents and characteristics of S-type granite. They have high SiO2, total Na2O + K2O, and Zr contents and high aluminium saturation index values (0.97 to 1.29 with an average of 1.14). All these geochemical signatures, together with high (87Sr/86Sr)i ratios (0.71391 to 0.74568), and low whole rock εNd(t) and zircon εHf(t) values (?13.1 to ?9.4) suggested an origin from partial melting of crustal source rocks. Primitive mantle normalized trace element contents exhibit positive anomalies of Rb, Th, U and Pb, but negative anomalies of Nb, Ta, and Ti, indicating a collision-related environment. The depleted Nd and Hf zircon model ages from investigated samples, in combination with inherited zircon ages, suggest the existence of Precambrian basement in the study region. S-type granites of the late Permian-early Triassic (the Muong Lat, Phia Bioc and Hai Van complexes) in Vietnam were formed by the subduction-collision of the South China and Indochina blocks.  相似文献   

18.
Palaeozoic rapakivi granites occur in the western segment of the China Central Orogenic System. Exhibiting typical rapakivi texture, these granites contain magmatic microgranular enclaves of intermediate compositions. SHRIMP zircon U–Pb ages for the granites and enclaves are 433 ± 5 Ma and 433 ± 3 Ma, respectively. The rapakivi granites are magnesian to ferroan, calc-alkalic to alkalic, and are characterized by high FeOt/(FeOt + MgO) (0.74–0.91) and Ga/Al ratios, and SiO2, Na2O + K2O and rare earth element (apart from Eu) contents, but low CaO, Ba, and Sr contents. These are typical A-type granite geochemical features. The granites and enclaves exhibit a uniform decrease in TiO2, CaO, Na2O, K2O, FeO, and MgO with increasing SiO2, and both lithologies have similar trace element patterns. Whole-rock ?Nd(t) values vary from??9.2 to??8.7 for the granites and from??9.0 to??8.4 for the enclaves, but zircon ?Hf(t) values vary more widely from??5.8 to??0.2 and??4.6 to +5.1, respectively. Our data suggest that the granites and enclaves have crystallized from different magmas. The granites appear to have been derived from old continental crust, whereas the enclaves required a source having a juvenile component. The spherical shape and undeformed nature of the granites and their geochemical characteristics, coupled with the (ultra)-high pressure metamorphism and evolution of Palaeozoic granitoid magmatism in the North Qaidam orogen, indicate that the rapakivi granites were generated in a post-collisional setting. These rocks are therefore an example of Palaeozoic rapakivi granites emplaced in a post-collisional, extensional orogenic setting.  相似文献   

19.
The Cretaceous granites of Mianning, located in the northern Panxi region, were emplaced after collision of the Tibetan Plateau and Yangtze Block. These granites have very high K2O + Na2O, Ga, Zr, Nb, Y, REE (except Eu), and very low MgO, CaO, P2O5, and Sr contents relative to M-, I- or S-type granites. Based on the chemical discrimination criteria of Whalen et al . [Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, distribution and petrogenesis. Contributions to Mineralogy and Petrology 95, 407–419], most of them are A-type granites. Moreover, the granites plot in the range of post-collision granites and belong to the A2 type. Elevated initial Sr isotopic ratios (>0.72) suggest their derivation dominantly from a crustal source. These features are consistent with granite formation in a post-orogenic setting, such as after subduction or collision between of the Tibetan Plateau and Yangtze Block. In addition, the granites are characterized by low abundances of Ba, Sr, P, Ti, and Eu, positive correlation between Ba and Eu anomalies, and negative correlation between Rb and K/Rb. Plots of Rb vs. Sr suggest that fractional crystallization affected the final compositions of these granites after melting from a dominantly crustal source. From the late Proterozoic to late Mesozoic, the crustal composition, compared to that of the mantle, appears to have increased in the Panxi region. While the mantle component played an important part in the generation of Cretaceous granites in southeastern China, its influence was relatively minor in the Panxi region. Thus, there was a significant difference in mantle evolution between southeastern China and the Panxi region, which led to different metallogenic processes.  相似文献   

20.
The Shalair area, which is located in northeastern Iraq, is considered to be part of the northern Sanandaj-Sirjan Zone (SaSZ) and contains several granitoid bodies. One of these bodies, the Mishao porphyritic-granite (MG), was crystallized at 111.6?±?2.4 Ma, based on its zircon U-Pb age. Its geochemical characteristics suggest that the MG rocks are calc-alkaline, peraluminous, I-type granites with microgranular mafic enclaves. They are enriched in SiO2, Na2O, Al2O3 and Zr and depleted in MgO, Fe2O3, Nb and Ti; in contrast, the enclave sample records lower SiO2 content and higher contents of MgO and Fe2O3. These rocks show an enrichment of LREE relative to HREE, and pronounced negative Eu anomalies implying feldspar fractionation. The isotopic and geochemical characteristics of the MG samples suggest that these rocks are evolved through fractional crystallization. In the La/Nb-Nb diagram and Sm/Nd ratios, the MG rocks and the enclave samples exhibit strong evidence for crustal contamination. The MG rocks record high initial 87Sr/86Sr (0.70625–0.70740) and low 143Nd/144Nd(i) (0.51235–0.51274) ratios. These Sr-Nd isotopic data, combined with the presence of high Th/U and Rb/Sr ratios and significant depletions of Nb, Ta and Ti, show a relation of these bodies to an active continental margin regime. Based on the age and geochemical data of the MG, this study presents new information about the occurrence of Middle Cretaceous magmatic activities, which are related to the active continental margins in the SaSZ that run parallel to the Zagros Fold-Thrust Belt.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号