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1.
The Sandaowanzi (>22t Au) and Beidagou (>5t Au) tellurium–gold deposits are located in the northeastern Central Asian Orogenic Belt (Heilongjiang Province, NE China). The ore-hosting volcanic rocks unconformably overly monzogranite and were intruded by adakitic granodiorite. In this study, we report new-age, geochemical, and Sr–Nd–Pb isotopic data to elucidate the genetic link between the igneous rocks and the Te–Au mineralization. New-age data indicate that local magmatism occurred in the Early Jurassic (ca. 177.2 Ma) and Early Cretaceous (ca. 118.7 ? 122.0 Ma). Geochemically, the igneous rocks are enriched in LREEs, Pb, K, and U, and depleted in Nb, P, and Ti, showing calc-alkaline affinity. The Early Jurassic monzogranite rocks are featured by 87Sr/86Sr = 0.7111?0.7118; εNd(t) = ?4.6 to ?4.7; 206Pb/204Pb = 18.098?18.102, 207Pb/204Pb = 15.558?15.580, and 208Pb/204Pb = 37.781?37.928, whereas the Early Cretaceous adakitic granodiorite contains: 87Sr/86Sr = 0.7071?0.7073; εNd(t) = ? 3.4 to ?3.2; 206Pb/204Pb = 17.991?18.080, 207Pb/204Pb = 15.483?15.508, and 208Pb/204Pb = 37.938?37.985. Initial isotopic ratios for the Early Cretaceous volcanic rocks: 87Sr/86Sr = 0.7061?0.7087; εNd(t) = ? 3.6 to ?2.9; 206Pb/204Pb = 18.136?18.199, 207Pb/204Pb = 15.512?15.628, and 208Pb/204Pb = 38.064?38.155. The pyrite, chalcopyrite, and telluride grains yielded δ34S of ?6.52 ‰ to 2.13 ‰ (mean = ? 0.82 ‰) and δ13CPDB of the calcite samples are in the range of ?6.64 ‰ to ?5.24 ‰, implying the ore materials were derived from mantle. The geochemical and isotopic results indicate that primary melts of Late Mesozoic magmatic rocks have features by partial melting of the continental crust. The adakitic rocks may have been the products of the thickened lower crustal delamination and the subsequent asthenospheric upwelling during the intra-continental extension in NE China. Regionally, intrusive activity and molybdenum mineralization during the Jurassic was affected by subduction setting, whereas gold mineralization was controlled by the Early Cretaceous tectonothermal events associated with a superposition extension.  相似文献   

2.
ABSTRACT

Volcanic rocks in the Hala’alate and Aladeyikesai formations, which are composed of basaltic andesite and pyroxene andesite, are widespread in Hala’alate Mountain, West Junggar, Northwest China. These rocks (plagioclase + clinopyroxene/olivine) formed in the late Carboniferous and show a remarkable geochemical affinity with typical sanukitoids with oversaturated SiO2 (52.9–56.9 wt.%) and high MgO (3.47–6.88 wt.%, Mg# >48) contents. They also exhibit a narrow range of Sr-Nd-Pb isotopes within (87Sr/86Sr)i = 0.7037–0.7041, εNd(t) = 4.4–6.2, 206Pb/204Pb = 18.22–18.41, 207Pb/204Pb = 15.48–15.52, 208Pb/204Pb = 37.99–38.30. Hala’alate Formation volcanic rocks are similar to the sanukitoids of Karamay, with high Sr (633.5–970.1 ppm), Ba (268.7–796.3 ppm), and Sr/Y (61.34–84.28), formed by partial melting of the mantle metasomatized by slab-derived adakitic melts. In contrast, Aladeyikesai Formation volcanic rocks show some affinity with sanukitoids of the Hatu area and the Setouchi Volcanic Belt, with low Sr (442.2–508.7 ppm), Ba (199.2–485.1 ppm), and Sr/Y (25.03–30.28), generated by the partial melting of subducting sediments. Identification of late Carboniferous sanukitoids in Hala’alate Mountain provides important constraints on the closing time of the remnant ocean basin in West Junggar, and implies that multi-stage subduction–accretionary orogeny plays a crucial role in the evolution and growth of the continental crust in the Central Asian Orogenic Belt.  相似文献   

3.
《International Geology Review》2012,54(16):1964-1983
Extensive magmatism occurred in southeast China during Late Jurassic time, forming large-scale granitic and volcanic rocks associated with non-ferrous, rare earth and rare, radioactive metal deposits. The Shuikoushan Pb–Zn–Au orefield is a typical example located in Hunan Province. This study reports LA-ICP-MS zircon U–Pb ages, whole-rock chemistry, and Sr–Nd–Pb isotopic compositions, and in situ Hf isotopic geochemistry of zircons from the Laomengshan rhyodacite in the Shuikoushan Pb–Zn–Au orefield. Zircon U–Pb dating yields a weighted average age of 156.7 ± 1.6 Ma for the intrusion of the rhyodacite. The rhyodacite samples are mainly shoshonitic series, having metaluminous to weakly peraluminous A/CNK values ranging from 0.96 to 1.09, with moderately high magnesium content (Mg# = 42.4–47.5). Samples display high (87Sr/86Sr)i values (0.71165–0.71176), low εNd(T) values (?10.7 to ?10.3), old Nd model ages (TDM = 1.73–1.86 Ga), and relatively homogeneous Pb isotopic compositions [(206Pb/204Pb)i = 18.365–18.412, (207Pb/204Pb)i = 15.663–15.680, and (208Pb/204Pb)i = 38.625–38.666]. The zircons exhibit enriched εHf(T) values (?16.22 to ?9.86) and old two-stage Hf model ages (TDM2 = 1.82–2.22 Ga). All the above data indicate that the Laomengshan rhyodacite originated from melting Palaeoproterozoic basement, perhaps contaminated by subordinate mantle melts. Intense extension and thinning of the continental lithosphere during Late Jurassic time resulted in melting of upwelling asthenosphere, and mafic mantle melts interacted with and melted Palaeoproterozoic lower crust, thus forming the Laomengshan rhyodacite.  相似文献   

4.
The Jurassic magmatic and volcanic rocks are widespread along the west central Lhasa subterrane. However, the petrogenesis of these rocks is poorly understood because of lacking high-quality geochronology and geochemical data. Here, we present new zircon U–Pb age and Hf isotopic data, whole-rock geochemical and Sr–Nd–Pb isotopic data for the Songduole and Qiangnong plutons in Geji area. LA-ICP-MS dating of zircon yield crystallization ages of 172.1 ± 1.9 and 155.9 ± 1.2 Ma for the Songduole and Qiangnong plutons, respectively. Geochemically, Songduole and Qiangnong granodiorite are characterized by high MgO (2.63–3.49 wt%), high Mg# (49–50), and low TiO2 (0.48–0.57 wt%). Besides, all rocks show metaluminous, calc-alkaline signatures, with strong depletion of Nb, Ta, and Ti, enrichment of large-ion lithophile (e.g. Rb, Th, K), and a negative correlation between SiO2 and P2O5. All these features are indicative of arc-related I-type magmatism. Five samples from the Songduole granodiorite have whole rock (87Sr/86Sr)i of 0.71207–0.71257, εNd(t) values of ?15.1 to ?13.9, zircon εHf(t) values of ?17.4 to ?10.5, (206Pb/204Pb)t ratios of 18.402–18.854, (207Pb/204Pb)t ratios of 15.660–15.736, and (208Pb/204Pb)t ratios of 38.436–39.208. Samples from the Qiangnong granodiorite have (87Sr/86Sr)i of 0.71230–0.71252, εNd(t) values of ?15.1 to ?14.2, zircon εHf(t) values of ?12.6 to ?6.4, (206Pb/204Pb)t ratios of 18.688–18.766, (207Pb/204Pb)t ratios of 15.696–15.717, and (208Pb/204Pb)t ratios of 38.546–39.083. These geochemical signatures indicate that the two plutons most likely originated from partial melting of the ancient Lhasa lower crust with obvious inputs of mantle-derived melts. Combined with regional geology, our results indicate that the Jurassic magmatism in the west central Lhasa subterrane most likely resulted from the southward subduction of the Bangong Ocean lithosphere beneath the central Lhasa terrane.  相似文献   

5.
The Dexing porphyry copper deposit, part of the circum-Pacific porphyry copper ore belt, is the largest porphyry copper deposit in China. We present new LA–ICP–MS zircon U–Pb and molybdenite Re–Os dating, bulk-rock elemental and Sr–Nd–Pb isotopic as well as in situ zircon Hf isotopic geochemistry for these ore-bearing porphyries, in an attempt to better constrain their petrogenesis. LA–ICP–MS zircon U–Pb dating shows that the Dexing porphyries were emplaced in the early Middle Jurassic (～171 Ma); molybdenite Re–Os dating indicates that the associated Cu–Mo mineralization was contemporaneous (～171 Ma) with the igneous intrusion. The rocks are mainly high-K calc-alkaline and show adakitic affinities, including high Sr and low Y and Yb contents, high Sr/Y and La/Yb ratios, and high Mg# (higher than pure crustal melts). These porphyries have initial 87Sr/86Sr ratios of 0.7044?0.7047, ?Nd(T) values of –1.5 to?+0.6, and ?Hf(T) (in situ zircon) values of?+2.6 to?+4.6. They show unusually radiogenic Pb isotopic compositions with initial 206Pb/204Pb ratios up to 18.41 and 207Pb/204Pb up to 15.61. These isotopic compositions are distinctly different from either Pacific MORB or Yangtze lower crust but are similar to the subducting sediments in the western Pacific trenches. Detailed elemental and isotopic data suggest that the Dexing porphyries were emplaced in a continental arc setting coupled with westward subduction of the palaeo-Pacific plate. Partial melting involved the subducted slab (mainly the overlying sediments), with generated melts interacting with the lithospheric mantle wedge, thereby forming the investigated high-K calc-alkaline porphyry magmas.  相似文献   

6.
We conducted geochemical and isotopic studies on the Oligocene–Miocene Niyasar plutonic suite in the central Urumieh–Dokhtar magmatic belt, in order better to understand the magma sources and tectonic implications. The Niyasar plutonic suite comprises early Eocene microdiorite, early Oligocene dioritic sills, and middle Miocene tonalite + quartzdiorite and minor diorite assemblages. All samples show a medium-K calc-alkaline, metaluminous affinity and have similar geochemical features, including strong enrichment of large-ion lithophile elements (LILEs, e.g. Rb, Ba, Sr), enrichment of light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs, e.g. Nb, Ta, Ti, P). The chondrite-normalized rare earth element (REE) patterns of microdiorite and dioritic sills are slightly fractionated [(La/Yb)n = 1.1–4] and display weak Eu anomalies (Eu/Eu* = 0.72–1.1). Isotopic data for these mafic mantle-derived rocks display ISr = 0.70604–0.70813, ?Nd (microdiorite: 50 Ma and dioritic sills: 35 Ma, respectively) = +1.6 and ?0.4, TDM = 1.3 Ga, and lead isotopic ratios are (206Pb/204Pb) = 18.62–18.57, (207Pb/204Pb) = 15.61–15.66, and (208Pb/204Pb) = 38.65–38.69. The middle Miocene granitoids (18 Ma) are also characterized by relatively high REE and minor Eu anomalies (Eu/Eu* = 0.77–0.98) and have uniform initial 87Sr/86Sr (0.7065–0.7082), a range of initial Nd isotopic ratios [?Nd(T)] varying from ?2.3 to ?3.7, and Pb isotopic composition (206Pb/204Pb) = 18.67–18.94, (207Pb/204Pb) = 15.63–15.71, and (208Pb/204Pb) = 38.73–39.01. Geochemical and isotopic evidence for these Eocene–Ologocene mafic rocks suggests that the magmas originated from lithospheric mantle with a large involvement of EMII component during subduction of the Neotethyan ocean slab beneath the Central Iranian plate, and were significantly affected by crustal contamination. Geochemical and isotopic data of the middle Miocene granitoids rule out a purely crustal-derived magma genesis, and suggest a mixed mantle–crustal [MASH (melting, assimilation, storage, and homogenization)] origin in a post-collision extensional setting. Sr–Nd isotope modelling shows that the generation of these magmas involved ～60% to 70% of a lower crustal-derived melt and ～30% to 40% of subcontinental lithospheric mantle. All Niyasar plutons exhibit transitional geochemical features, indicating that involvement of an EMII component in the subcontinental mantle and also continental crust beneath the Urumieh–Dokhtar magmatic belt increased from early Eocene to middle Miocene time.  相似文献   

7.
《International Geology Review》2012,54(10):1220-1238
Recently, many Mo deposits genetically related to emplacement of Early Cretaceous granites have been found in the Dabie–Qinling belt. A typical intrusion that combines magmatism and metallogenesis, the Bao'anzhai granite, yields a zircon 238U–206Pb age of 123.2 ± 1.1 Ma and a molybdenite Re–Os isochron age of 122.5 ± 2.7 Ma. This granite is characterized by high silica and alkali, but low Mg, Fe, and Ca. It is enriched with light rare earth elements (REEs) and large-ion lithophile elements (LILEs, Rb, K, Th, U) but depleted of heavy REEs, high field strength elements (HFSEs, Nb, Ta, Ti, and Y), and Sr. This high-K granite has medium initial 87Sr/86Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [(206Pb/204Pb)i, 16.423–16.699; (207Pb/204Pb)i, 15.285–15.345; (208Pb/204Pb)i, 37.335–37.633], and is characterized by low ?Nd(t) and ?Hf(t) values (?14.92 to??14.22 and??21.67 to??19.19, respectively). These data indicate that this pluton is a high-K calc-alkaline fractionated I-type granitite. It was generated by partial melting of the Yangtze lower crust, which is probably similar to Neoproterozoic TTG-like magmatic rocks at the north Yangtze Block under a non-thickened lower crust environment (<35 km). The ores also have low radiogenic Pb isotopes (206Pb/204Pb, 16.592–17.674; 207Pb/204Pb, 15.300–15.476; 208Pb/204Pb, 37.419–37.911) and low Re content in molybdenite (5.693–10.970 ppm), suggesting a crustal magmatic source for the metallogenic minerals in the Mo deposit.  相似文献   

8.
TPost-orogenic intrusive complexes from the Sulu belt of eastern China consist of pyroxene monzonites and dioritic porphyrites. We report new U–Pb zircon ages, geochemical data, and Sr–Nd–Pb isotopic data for these rocks. Laser ablation-inductively coupled plasma-mass spectrometry U–Pb zircon analyses yielded a weighted mean 206Pb/238U age of 127.4 ± 1.2 Ma for dioritic porphyrites, consistent with crystallization ages (126 Ma) of the associated pyroxene monzonites. The intrusive complexes are characterized by enrichment in light rare earth elements and large ion lithophile elements (i.e. Rb, Ba, Pb, and Th) and depletion in heavy rare earth elements and high field strength elements (i.e. Nb, Ta, P, and Ti), high (87Sr/86Sr)i ranging from 0.7083 to 0.7093, low ?Nd(t) values from ?14.6 to ? 19.2, 206Pb/204Pb = 16.65–17.18, 207Pb/204Pb = 15.33–15.54, and 208Pb/204Pb = 36.83–38.29. Results suggest that these intermediate plutons were derived from different sources. The primary magma-derived pyroxene monzonites resulted from partial melting of enriched mantle hybridized by melts of foundered lower crustal eclogitic materials before magma generation. In contrast, the parental magma of the dioritic porphyrites was derived from partial melting of mafic lower crust beneath the Wulian region induced by the underplating of basaltic magmas. The intrusive complexes may have been generated by subsequent fractionation of clinopyroxene, potassium feldspar, plagioclase, biotite, hornblende, ilmenite, and rutile. Neither was affected by crustal contamination. Combined with previous studies, these findings provide evidence that a Neoproterozoic batholith lies beneath the Wulian region.  相似文献   

9.
《International Geology Review》2012,54(13):1626-1640
Dolerite dike swarms are widespread across the North China Craton (NCC) of Hebei Province (China) and Inner Mongolia. Here, we report new geochemical, Sr–Nd–Pb isotope, and U–Pb zircon ages for representative samples of these dikes. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb analysis yielded consistent Permian ages of 274.8 ± 2.9 and 275.0 ± 4.5 Ma for zircons extracted from two dikes. The dolerites have highly variable compositions (SiO2 = 46.99–56.18 wt.%, TiO2 = 1.27–2.39 wt.%, Al2O3 = 14.42–16.20 wt.%, MgO = 5.18–7.75 wt.%, Fe2O3 = 8.03–13.52 wt.%, CaO = 5.18–9.75 wt.%, Na2O = 2.46–3.79 wt.%, K2O = 0.26–2.35 wt.%, and P2O5 = 0.18–0.37 wt.%) and are light rare earth element (LREE) and large ion lithophile element (LILE, e.g. Rb, Ba, and K, and Pb in sample SXG1-9) enriched, and Th and high field strength element (HFSE, e.g. Nb and Ta in sample SXG1-9, and Ti) depleted. The mafic dikes have relatively uniform (87Sr/86Sr)i values from 0.7031 to 0.7048, (206Pb/204Pb)i from 17.77 to 17.976, (207Pb/204Pb)i from 15.50 to 15.52, (208Pb/204Pb)i from 37.95 to 38.03, and positive ?Nd(t) (3.6–7.3), and variable neodymium model ages (TDM1 = 0.75–0.99 Ga, TDM2 = 0.34–0.74 Ga). These data suggest that the dike magmas were derived from partial melting of a depleted region of the asthenospheric mantle, and that they fractionated olivine, pyroxene, plagioclase, K-feldspar, and Ti-bearing phases without undergoing significant crustal contamination. These mafic dikes within the NCC formed during a period of crustal thinning in response to extension after Permian collision between the NCC and the Siberian Block.  相似文献   

10.
Alkaline intrusions in the eastern Shandong Province consist of quartz monzonite and granite. U-Pb zircon ages, geochemical data, and Sr-Nd-Pb isotopic data for these rocks are reported in the present paper. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon analyses yielded consistent ages ranging from 114.3?±?0.3 to 122.3?±?0.4 Ma for six samples of the felsic rocks. The felsic rocks are characterised by a wide range of chemical compositions (SiO2?=?55.14–77.63 wt. %, MgO?=?0.09–4.64 wt. %, Fe2O3?=?0.56–7.6 wt. %, CaO?=?0.40–5.2 wt. %), light rare earth elements (LREEs) and large ion lithophile elements (LILEs) (i.e., Rb, Pb, U) enrichment, as well as significant rare earth elements (HREEs) and heavy field strength (HFSEs) (Nb, Ta, P and Ti) depletion, various and high (87Sr/86Sr) i ranging from 0.7066 to 0.7087, low ε Nd (t) values from ?14.1 to ?17.1, high neodymium model ages (TDM1?=?1.56–2.38Ga, TDM2?=?2.02–2.25Ga), 206Pb/204Pb?=?17.12–17.16, 207Pb/204Pb?=?15.44–15.51, and 208Pb/204Pb?=?37.55–37.72. The results suggested that these rocks were derived from an enriched crustal source. In addition, the alkaline rocks also evolved as the result of the fractionation of potassium feldspar, plagioclase, +/? ilmenite or rutile and apatite. However, the alkaline rocks were not affected by crustal contamination. Moreover, the generation of the alkaline rocks can be attributed to the structural collapse of the Sulu organic belt due to various processes.  相似文献   

11.
ABSTRACT

Late Jurassic ultramafic lamprophyre (UML) sills and dikes occur as 3 km-long intrusions within the allochthonous Whara Formation of the Batain nappes, eastern Oman. The sills and dikes comprise macrocrystic phlogopite and spinel-bearing aillikite and damtjernite. Aillikite is a light grey, massive fine-grained tuffaceous rock with euhedral laths of mica, while damtjernite is a dark grey, medium- to coarse-grained rock with abundant pelletal lapilli and globular segregationary textures. Both lithologies are composed of calcite, phlogopite, apatite, magnetite, spinel, diopside, and richterite. Orthoclase occurs only within damtjernite. The rocks are strongly silica undersaturated (17.6–33.7 wt.% SiO2), with low MgO (4.7–10.2 wt. %) and high Al2O3 (3.5–8.6 wt.%). The aillikites are distinguished from the damtjernites by their lower SiO2, Al2O3, and Na2O abundances, and their higher MgO, CaO, and P2O5 contents. The rare earth element (REE) patterns of both rock types are similar and show strong light REE (LREE) enrichment. Both are enriched in Ba, Th, U, Nb, and Ta, with normalized concentrations of up to 1000 times those of primitive mantle. Relative depletions are apparent for high REE (HREE), K, Rb, Pb, Sr, P, Zr, and Hf. The rocks have initial 87Sr/86Sr ratios of 0.70435–0.70646, whereas initial 143Nd/144Nd ratios vary between 0 · 512603 and 0 · 512716 (εNdi 2.6–3.2). Pb isotopic ratios are more varied among the aillikites and damtjernites: 208Pb/204Pbi = 38.97–39.39 and 207Pb/204Pbi = 15.35–15.58, 206Pb/204Pbi = 18.08–18.96. The abundance of phlogopite, apatite, and rutile and enrichment in LREEs, Ba, Th, U, Nb, and Ta in the Sal UMLs suggest metasomatic enrichment of these rocks following a low degree of partial melting of a depleted source region. Ar–Ar age dating of phlogopite macrocrysts from the aillikites and damtjernites (154 and162 Ma, respectively) correlates with large-scale tectonic events recorded in the proto-Indian Ocean at 140–160 Ma.  相似文献   

12.
ABSTRACT

Zircon U–Pb ages, major element and trace element compositions, and Sr, Nd, and Pb isotopic compositions for late Mesozoic granites from the southern Jiaodong Peninsula (eastern China) were determined. Ages for the Wulianshan, Xiaozhushan, and Dazhushan plutons are 119.1–122.3, 114.2, and 108.9 Ma, respectively. Major and trace element characteristics show that these granitic rocks belong to alkaline, A-type granites formed in an extensional setting. Trace element compositions show strong, variable negative anomalies in Ba, K, P and Ti, and positive anomalies in Rb, Th, U, Pb, Ce, Zr, and Hf, which are typical characteristics of A-type granites. Variable Sr and Nd isotopic compositions, 87Sr/86Sr(i) = 0.70540–0.7071 and εNd(t) = ?14.5 to ?20.9. Whole-rock Pb isotopic compositions have the following ranges, (206Pb/204Pb)t = 15.707–16.561, (207Pb/204Pb)t = 15.376–16.462, and (208Pb/204Pb)t = 36.324 to 37.064. Isotopic modelling indicates an origin that lies between mantle tapped by Cenozoic basalts around the Tan-Lu megafault and lower continental crust (LCC), and which can be explained by mixing of 11–18% mantle and 82–89% LCC. Based on new and compiled data, we suggest that the southern Jiaodong Peninsula, as well as the Laoshan area, was in a regional extensional setting of an orogenic belt during 106–126 Ma. The granitic rocks may be the result of late Mesozoic lithospheric thinning and decratonization (i.e. late Mesozoic craton destruction event occurring throughout eastern China).  相似文献   

13.
The Acigöl rhyolite field erupted the most recent high-silica rhyolites within the Cappadocian Volcanic Province of central Anatolia, Turkey. It comprises two sequences of domes and pyroclastic rocks with eruption ages of ~150–200 ka (eastern group) and ~20–25 ka (western group). Compositionally, the eastern rhyolite group lavas are less evolved (SiO2 = 74–76 wt%), whereas the western group has higher silica abundance (SiO2 = ~77 wt%) with extremely depleted feldspar-compatible trace elements. Within each group, compositional variability is small and 143Nd/144Nd (0.51257–0.51265) and Pb isotope compositions (206Pb/204Pb = 18.87–18.88, 207Pb/204Pb = 15.65–15.67 and 208Pb/204Pb = 38.94–38.98) are homogeneous. The western group rhyolites have δ18O(zircon) overlapping mantle values (5.7 ± 0.2‰), whereas eastern group rhyolites are enriched in δ18O by ~0.5‰, consistent with a tendency to lower εNd values. By contrast, western group rhyolites have markedly more radiogenic 87Sr/86Sr ratios (0.7065–0.7091) compared to those of the eastern group (0.7059–0.7065). The presence of angular granitic xenoliths and a correlation between hydration (based on loss on ignition data) and 87Sr/86Sr in the western lavas, however, indicates that Sr was added during the eruption or post-eruption alteration. Isotope constraints preclude the possibility that the rhyolite magmas formed by partial melting of any known regional crystalline basement rocks. Basalts and andesites erupted in the periphery of the Acigöl field are characterised by 87Sr/86Sr ratios between 0.7040 and 0.7053, 143Nd/144Nd = 0.51259–0.51300, 206Pb/204Pb = 18.85–18.87, 207Pb/204Pb = 15.646–15.655, 208Pb/204Pb = 38.90–38.97. The isotopic and trace element data favour an origin of the rhyolites by mixing of basaltic/andesitic magmas with minor amounts of crustal melts and followed by extensive fractional crystallization.  相似文献   

14.
<正>The Nadingcuo high-K calc-alkaline rocks mainly composed of trachyte and trachyandesite are the largest outcrop area of volcanic rocks in southern Qiangtang terrane in the Tibetan plateau. However,their exact source and peterogenesis are still debated.~(40)Ar-~(39)Ar and LAM-ICPMS zircon U-Pb isotopic dating confirm that these rocks erupted in Eocene.In addition,the Nadingcuo volcanic rocks are characterized by high Sr/Y content ratios,similar with the adakite derived from partial melting of oceanic crust.They can be further classified as high Mg~#(Mg~#=48-57) and low Mg~# (Mg~#=33-42) subtypes.The Nadingcuo adakitic rocks have relatively low(~(87)Sr/~(86)Sr)_i and highε_(Nd)(t), showing a trend of similarity to the Dongcuo ophiolite present in the Bangong-Nujiang oceanic crust. Simple modeling indicates that the Nadingcuo adakitic rocks are a mix resulting from the basalt of Bangong-Nujiang Ocean with 10%-20%crustal material of Lhasa terrane.On these bases we suggest that the low Mg~# Nadingcuo adakitic rocks are the product of partial melting of remnant oceanic crust with small sediment,and the high Mg~# rocks are the result of reaction between rising melt of remnant oceanic crust with subducted sediment and mantle wedge.Therefore,the origin of Nadingcuo adakitic rocks may be related to intracontinental subduction triggered by collision of India-Asia during Cenozoic.  相似文献   

15.
The newly discovered Zhunuo porphyry Cu-Mo-Au deposit is located in the western part of the Gangdese porphyry copper belt in southern Tibet, SW China. The granitoid plutons in the Zhunuo region are composed of quartz diorite porphyry, diorite porphyry, granodiorite porphyry, biotite monzogranite and quartz porphyry. The quartz diorite porphyry yielded zircon U-Pb ages of 51.9±0.7 Ma(Eocene) using LA-ICP-MS, whereas the diorite porphyry, granodiorite porphyry, biotite monzogranite and quartz porphyry yielded ages ranging from 16.2±0.2 to 14.0±0.2 Ma(Miocene). CuMo-Au mineralization is mainly hosted in the Miocene granodiorite porphyry. Samples from all granitoid plutons have geochemical compositions consistent with high-K calc-alkaline series magmatism. The samples display highly fractionated light rare-earth element(REE) distributions and heavy REE distributions with weakly negative Eu anomalies on chondrite-normalized REE patterns. The trace element distributions exhibit positive anomalies for large-ion lithophile elements(Rb, K, U, Th and Pb) and negative anomalies for high-field-strength elements(Nb and Ti) relative to primitive mantlenormalized values. The Eocene quartz diorite porphyry yielded εNd(t) values ranging from-3.6 to-5.2,(~(87)Sr/~(86)Sr)i values in the range 0.7046–0.7063 and initial radiogenic Pb isotopic compositions with ranges of 18.599–18.657 ~(206)Pb/~(204)Pb, 15.642–15.673 ~(207)Pb/~(204)Pb and 38.956–39.199 ~(208)Pb/~(204)Pb. In contrast, the Miocene granitoid plutons yielded ε_(Nd)(t) values ranging from-6.1 to-7.3 and(87Sr/86Sr)i values in the range 0.7071–0.7078 with similar Pb isotopic compositions to the Eocene quart diorite. The Sr-Nd-Pb isotopic compositions of the rocks are consistent with formation from magma containing a component of remelted ancient crust. Zircon grains from the Eocene quartz diorite have ε_(Hf)(t) values ranging from-5.2 to +0.9 and two-stage Hf model ages ranging from 1.07 to 1.46 Ga, while zircon grains from the Miocene granitoid plutons have ε_(Hf)(t) values from-9.9 to +4.2 and two-stage Hf model ages ranging from 1.05–1.73 Ga, indicating that the ancient crustal component likely derives from Paleo- to Mesoproterozoic basement. This source is distinct from that of most porphyry Cu-Mo-Au deposits in the eastern part of the Gangdese porphyry copper belt, which likely originated from juvenile crust. We therefore consider melting of ancient crustal basement to have contributed significantly to the formation Miocene porphyry Cu-Mo-Au deposits in the western part of the Gangdese porphyry copper belt.  相似文献   

16.
We investigate the geology of Altar North (Cu–Au) and Quebrada de la Mina (Au) porphyry deposits located in San Juan Province (Argentina), close to the large Altar porphyry copper deposit (995 Mt, 0.35% Cu, 0.083 g/t Au), to present constraints on the magmatic processes that occurred in the parental magma chambers of these magmatic-hydrothermal systems. Altar North deposit comprises a plagioclase-amphibole-phyric dacite intrusion (Altar North barren porphyry) and a plagioclase-amphibole-biotite-phyric dacite stock (Altar North mineralized porphyry, 11.98 ± 0.19 Ma). In Quebrada de la Mina, a plagioclase-amphibole-biotite-quartz-phyric dacite stock (QDM porphyry, 11.91 ± 0.33 Ma) crops out. High Sr/Y ratios (92–142) and amphibole compositions of Altar North barren and QDM porphyries reflect high magmatic oxidation states (fO2 = NNO +1.1 to +1.6) and high fH2O conditions in their magmas. Zones and rims enriched in anorthite (An37–48), SrO (0.22–0.33 wt.%) and FeO (0.21–0.37 wt.%) in plagioclase phenocrysts are evidences of magmatic recharge processes in the magma chambers. Altar North and Quebrada de la Mina intrusions have relatively homogeneous isotopic compositions (87Sr/86Sr(t) = 0.70450–0.70466, εNd(t) = +0.2 to +1.2) consistent with mixed mantle and crust contributions in their magmas. Higher Pb isotopes ratios (207Pb/204Pb = 15.6276–15.6294) of these intrusions compared to other porphyries of the district, reflect an increase in the assimilation of high radiogenic Pb components in the magmas. Ages of zircon xenocrysts (297, 210, 204, 69 Ma) revealed that the magmas have experienced assimilation of Miocene, Cretaceous, Triassic and Carboniferous crustal rocks.Fluids that precipitated sulfides in the Altar deposit may have remobilized Pb from the host rocks, as indicated by the ore minerals being more radiogenic (207Pb/204Pb = 15.6243–15.6269) than their host intrusions. Au/Cu ratio in Altar porphyries (average Au/Cu ratio of 0.14 × 10?4 by weight in Altar Central) is higher than in the giant Miocene porphyry deposits located to the south: Los Pelambres, Río Blanco and Los Bronces (Chile) and Pachón (Argentina). We suggest that the increase in Au content in the porphyries of this region could be linked to the assimilation of high radiogenic Pb components in the magmas within these long-lived maturation systems.  相似文献   

17.
The Wangjiazhuang porphyry–breccia Cu(–Mo) deposit is located in the Zouping volcanic basin, western Shandong Province. Seven molybdenite samples yield a Re–Os weighted mean age of 127.8 ± 0.7 Ma (2σ), which is identical within error to the zircon weighted mean 206Pb/238U age of 128.3 ± 1.3 Ma (2σ) determined for quartz monzonite samples. The host rock is characterized by high concentrations of K2O (4.26–4.53 wt.%), Na2O (4.97–5.76 wt.%), LILEs and LREEs, and high Mg# (> 40), and low concentrations of HFSEs and HREEs, with K2O/Na2O ratios of 0.76–0.88. The quartz monzonite also has high Sr/Y (69.9–112.5) and (La/Yb)N (22.0–30.0) ratios, similar to adakitic rocks worldwide. Relatively low initial 87Sr/86Sr ratios (0.70549–0.70556), high εNd(t) values (2.58–3.06), high radiogenic Pb [(206Pb/204Pb)i = 18.3424–18.4606, (207Pb/204Pb)i = 15.5692–15.5985, (208Pb/204Pb)i = 38.1714–38.2734] and high zircon εHf(t) values (− 2.1 to + 4.3) indicate that the magma was likely derived from the partial melting of subducted oceanic crust which then reacted with the peridotitic mantle wedge. Both the breccia and porphyry ores have a narrow range of δ34S (− 4.8 to + 2.1‰) and Pb isotopic compositions (206Pb/204Pb = 18.295–18.402, 207Pb/204Pb = 15.551–15.573, and 208Pb/204Pb = 38.215–38.331), suggesting that the ore metals were extracted primarily from the quartz monzonite or similar source. Subduction of the Paleo-Pacific slab during the Early Cretaceous resulted in the formation of the Wangjiazhuang quartz monzonite and associated Cu(–Mo) deposit in western Shandong Province.  相似文献   

18.
The Dongguashan Cu-Au deposit located in the eastern portion of the Tongling mining district, the Lower Yangtze River Metallogenic Belt (LYRB), Eastern China is a typical one associated with the Qingshanjiao quartz monzodiorite, including porphyry, skarn, and stratabound ores. In order to constrain the petrogenesis of the intrusive rocks and associated Cu-Au mineralization, detailed analyses of the zircon geochronology and geochemistry, whole-rock geochemistry and Sr-Nd-Pb isotopes, and zircon Lu-Hf isotopes were performed. Magmatic zircons from quartz monzodiorite yield U-Pb ages of 136–138 Ma, revealing their formation ages of early Cretaceous. Geochemical characteristics of the quartz monzodiorites (SiO2 = 63.6–66.2 wt%, high Sr, low Y and Yb concentrations) discriminate their adakitic affinity. They are enriched in LILE and LREE, depleted in HFSE and HREE, and has no or slightly negative Eu anomalies. These geochemical characteristics indicate that the monzodiorites may be primarily derived from the magma mixing of mantle- and LCC-derived melts. The relatively low εNd(t) values (−11.7 to −10.7) and high (87Sr/86Sr)i ratios (0.7075 to 0.7078) may be plausibly interpreted by contamination of enriched mantle materials and/or continental crust. The high radiogenic Pb isotopes with (206Pb/204Pb)i = 17.98–18.09, (207Pb/204Pb)i = 15.51–15.53, and (208Pb/204Pb)i = 38.18–38.26 plot in the field of MORB, near the intersection of EM-1 and EM-2, and are considerably different from those of the upper and lower continental crust and the Dabie adakites, which exclude major contamination from the continental crust. Ti-in-zircon temperatures and calculated Ce4+/Ce3+ values fall within the field between MH and FMQ. The results indicate that the intrusive rocks and associated large-scale Cu-Au mineralization in the Dongguashan deposit are resulted from the magma mixing of mantle- and LCC-derived melts. in a lower magma temperature, yet higher fO2 and water content environment.  相似文献   

19.
An isotopic study was systemically carried out on the granitic complex, diorite-porphyrite, ores and ore minerals of the 103 Ma Xiaoxinancha gold-rich copper deposit in Jilin province to determine the geodynamic model of diagenesis and metallogenesis. Results show that the initial Nd and Sr isotopic compositions of the granitic complex are in the range of 0.70425–0.70505 for (87Sr/86Sr)i , 0.51243–0.51264 for INd, and –1.31 to +2.64 for εNd(t); those of the diorite-porphyrite are in the range from 0.70438–0.70448 for (87Sr/86Sr)i, 0.51259–0.51261 for INd, and +1.56 to +2.09 for εNd(t). For ores and sulfides, the (87Sr/86Sr)i , INd, and εNd(t) values are in the range from 0.70440–0.70805, 0.51259–0.51279 and +1.72 to +5.56, respectively. The Pb isotopic ratios of the granitic complex range from 18.2992–18.6636 for 206Pb/204Pb, from 15.5343–15.5660 for 207Pb/204Pb, and from 38.1640–38.5657 for 208Pb/204Pb. For diorite-porphyrite, the isotopic ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 18.3919, 15.5794 and 38.3566, respectively, whereas those of the ores and ore sulfides vary from 18.2275–18.3770 for 206Pb/204Pb, from 15.5555–15.5934 for 207Pb/204Pb and from 38.1318–38.3131 for 208Pb/204Pb. The results indicate that the mineralization was correlated to the formation and evolution of the granitic complex and the diorite-porphyrite. Combining with the reported data in petrologic characteristics, elemental geochemistry and chronology, conclusions can be drawn that the geodynamic settings of diagenesis and metallogenesis of this deposit were consistent with the subduction of the Izanagi oceanic plate during the Early Cretaceous. The diorite-porphyrite was formed by the emplacement of the adakitic magma triggered by partial melting of the enriched mantle, which originated from the derivative continental lithospheric mantle metasomatized by dehydration fluids from the subducting oceanic crust. The granitic complex was produced by fractional crystallization of the mixture between the adakitic magma and the high-K calc-alkaline acidic magma, which were generated by the remelting of the lower crust in the course of intraplate upwelling of the adakitic magma. The ore-bearing fluid reservoir convened in a late stage of the evolution of the mixed magma chamber.  相似文献   

20.
To better understand the evolution of the South China Craton (SCC), we have determined the geochronological and geochemical compositions of newly recognized Grenville-aged metabasalts in the Shennongjia region of the northern Yangtze block. LA-ICP-MS U-Pb dating of zircons indicates that the metabasalts formed at 1063 ± 16 Ma. The rocks are calc-alkaline, are characterized by SiO2 contents (50.50 to 55.62 wt.%), and have moderate-to-high MgO contents (7.25–9.60 wt.%). They display light rare earth element enrichment ((La/Yb)N = 7.0–9.8) with slightly negative Eu anomalies (Eu/Eu* = 0.82–0.90) and have pronounced depletion in high-field strength elements as well as positive Pb anomalies in the primitive mantle-normalized trace element pattern. They possess high initial Sr isotopic ratios of 0.7092–0.7107, large negative εNd(t) values of ?12.1 to ?11.0, and a relatively narrow range of initial Pb isotope ratios (206Pb/204Pb = 16.503–17.019, 207Pb/204Pb = 15.259–15.452, and 208Pb/204Pb = 36.169–36.994). These isotopic characteristics are typical of basalts derived from an EM2 source region and suggest a subcontinental lithospheric mantle source that was metasomatized by subducted components (fluids and melts). Integrating our new data with documented igneous and metamorphic events during late Mesoproterozoic to early Neoproterozoic time in the region and western segments of the Yangtze block, we suggest that the Shennongjia area might be a microcontinent that was independent of the continental nucleus of the Yangtze block and was accreted to the Yangtze block at the end of Mesoproterozoic time. This study thus argues against the traditional view that the SCC was formed simply by Yangtze–Cathaysia collision and supports a hypothesis in which the Yangtze block was a collage of microcontinents accreted during the Grenvillian period accompanying the assembly of the Rodinia supercontinent.  相似文献   

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