From migmatites to crustal granites: Pb–Pb isotopic system of feldspars of partial melting products,Northern Ladoga region,Fennoscandinavian Shield

The isotopic–geochemical features of late and postorogenic granites of the S type and ambient migmatites are studied within the Russian part of the Svecofennian orogen of the Fennoscandinavian Shield. The spatial association of leucosomes of migmatites and granites of the S type and their similar petro- and geochemistry and distribution of Pb isotopes are evidence of the genetic similarity of their parental melts. The Borodinskoe pluton has a more primitive ²⁰⁶Pb/²⁰⁷Pb ratio, which indicates the presence of upper and U-poor lower crustal material in the source of granitic magmas. This conclusion is supported by the ?_Nt(t) lower value of granites of this pluton relative to those of other plutons of the region.     

The evolution of the fluid phase during the crystallization of granite types: Salmi pluton,Karelia, Russia

Summary Two main geochemiscl types of granites are distingushed in the Salmi pluton: 1) ovoid biotite-hornblende granites, 2) non-ovoid biotite granites. The first one is characterized by higher CO₂, CO and CH₄ concentrations. The second type is rich in fluorine and shows similarities with rare metal Phanerozoic granites. Both granite types began to crystallize when P_f, < P_tot, but non-ovoid granites, which crystallized in a wider temperature range, reached conditions P_f, > PO_tot at the final stage. The mole fraction of carbon group gases (CO₂, CO and CH₄) decreases and that of H₂O increases in all granites from early crystallizing minerals to those of late crystallization.Compositional differences between ovoid biotite-hornblende and non-ovoid biotite granites are due to differences in the protolith composition.

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Die Evolution der fluiden Phase während der Kristallisation von Graniten, Salmi Pluton, Karelia, Russland

Zusammenfassung Zwei geochemisch charakterisierte Granittypen können innerhalb des Salmi Plutons unterschieden werden: 1) ein ovoidaler Biotit-Hornblende-Granit, und 2) ein nichtovoidaler Biotit-Granit. Der erste Typ ist durch höhere Konzentrationen von CO₂, CO und CH₄ charakterisiert; der zweite Granittyp ist reich an Fluor und zeigt Ähnlichkeiten mit phanerozoischen Graniten, die seltene Metalle führen. Beide Granittypen beginnen bei P_fl, < P_tot, zu kristallisieren, nicht-ovoidale Granite jedoch, deren Kristallisation in einem weiteren Temperaturbereich abläuft, erreichen im Finalstadium der Kristallisation P_fl > P_tot,-Bedingungen. In allen Graniten sinkt die Molfraktion der Kohlenstoffgasgruppe (CO₂, CO und CH₄) bei gleichzeitigem Anstieg von H₂O, wenn man frühe Kristallisationsphasen mit späten vergleicht.Die Unterschiede in der Zusammensetzung zwischen den ovoidalen und nichtovoidalen Graniten sind auf Unterschiede in der Protolith-Zusammensetzung zurückzuführen.

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Behavior of apatite in granitic melts derived from partial melting of muscovite in metasedimentary sources

Fluid-absent and fluid-fluxed melting of muscovite in metasedimentary sources are two types of crustal anatexis to produce the Himalaya Cenozoic leucogranites. Apatite grains separated from melts derived from the two types of parting melting have different geochemical compositions. The leucogranites derived from fluid-fluxed melting have relict apatite grains and magmatic crystallized apatite grains, by contrast, there are only crystallized apatite grains in the leucogranites derived from fluid-absent melting. Moreover, apatite grains crystallized from fluid-fluxed melting of muscovite contain higher Sr, but lower Th and LREE than those from fluid-absent melting of muscovite, which could be controlled by the distribution of partitioning coefficient (D_Ap/Melt) between apatite and leucogranite. D_Ap/Melt in granites derived from fluid-absent melting is higher than those from fluid-fluxed melting. So, not only SiO₂ and A/CNK, but also types of crustal anatexis are sensitive to trace element partition coefficients for apatite. In addition, due to being not susceptible to alteration, apatite has a high potential to yield information about petrogenetic processes that are invisible at the whole-rock scale and thus is a useful tool as a petrogenetic indicator.©2021 China Geology Editorial Office.     

Thermochronological models for the evolution of A-type leucogranites in the Neoproterozoic collisional orogen of the Yenisei Ridge

Results of complex geological, petrological, geochemical, and isotope-geochronological studies of Neoproterozoic postcollisional A-type granites of the Glushikha complex, Yenisei Ridge, are presented, as well as results of mathematical modeling. The localization, sizes, and depths of formation of magmatic bodies and the physicochemical conditions of the formation of granite intrusions and their magmatic sources are considered. The research is focused on the modeling of the thermal history of the formation and subsequent cooling of granites in the collision orogen. The modeling of heat transfer during the acid-magma intrusion was performed by the example of the Lendakha and Glushikha leucogranite plutons. With the combined methods of the modeling of heat transfer and the behavior of K/Ar isotopic system, the models for leucogranite pluton cooling have been verified for the first time. The time of formation and cooling of granite bodies is estimated, and a generalized geodynamic model for the formation of the Glushikha postcollisional A-type leucogranites is proposed.     

Geochemistry, geochronology and mineralisation potential of the granites in the Central Iberian Zone: The Jalama batholith

The Jalama batholith (Spain and Portugal) is one of the numerous granites of the Central Iberian Zone with Sn- and W-associated mineralisation. On the basis of petrographical and geochemical characterisation three types of granite have been distinguished: inhomogeneous granitoids, porphyrytic granites and leucogranites, all of these being peraluminous and subalkaline. All the granites correspond to S-type granites. The field data, the petrography and lack of geochemical affinity relationships of the leucogranites with the remaining granites indicate that their geneses correspond to an independent magma batch and superimposed fractional crystallisation process. The granitic units show subparallel REE patterns. There is a decrease in total REE and an increase in the negative Eu anomaly from the inhomogeneous granitoids to leucogranites. Some leucogranites show relatively low contents of Sn and W almost certainly due to segregation in the magma of a melt rich in water carrying Sn-W. These elements are concentrated in the water phase, which eventually gives rise to Sn-W-associated mineralisation.The ages obtained by means of a whole-rock Rb-Sr isochron for the granites mainly indicate an early intrusion of the inhomogeneous granitoids (319±10 Ma), followed in time by porphyrytic granites (279±9 Ma), which can be associated to the late-post-kinematic granites within the third Variscan deformation phase (D₃).Apart from the average Sn content, the variations of trace elements, principally Sr, Ba, Rb, Th and P, establish that the porphyritic granites and the inhomogeneous granitoids will be barren granites while the leucogranites and the subfacies at the margin of the porphyritic granites correspond to granites with mineralisation potential. It is precisely in these granites of the Jálama batholith that the Sn-W mineralisation is located, for which the criteria utilised has been demonstrated to be effective.     

Geochemistry of lepidolitic granitoids from the Mungutiyn Tsagaan Durulj occurrence (central Mongolia)

We studied the geologic position, geodynamic setting, petrology, and geochemistry of veined lepidolitic granitoids from the Mungutiyn Tsagaan Durulj (MTD) occurrence (central Mongolia), found within the area of Mesozoic intraplate rare-metal magmatism. It has been established that their trace-element enrichment resulted from the intense effect of fluids rich in F, K, Li, Rb, Cs, Sn, Be, and W, which arrived from a deep magma chamber of rare-metal granitic melts, on leucogranites with originally weak rare-metal mineralization. Very high contents of F, rare alkali metals, Sn, Be, and W, characteristic of MTD granitoids, are close only to those in greisens of rare-metal granites and topaz-lepidolite-albitic pegmatites. The difference from the greisens in each case might be due to the features of the original rocks. The difference between the greisenized MTD leucogranites and the topaz-lepidolite-albitic pegmatites is more radical: Along with evident petrographic distinctions, it includes an evolution trend toward the albite norm decrease, not typical of Li–F igneous rocks; rock shearing and gneissosity, which must have contributed to their chemical transformation according to this trend; and stably lower contents of Nb and Ta (trace elements which usually accumulate during crystallization fractionation of F–Li granitic melts and are poorly soluble in magmatic fluids). The greisenized MTD granitoids are not only high-grade rare-metal ores of Li, Rb, F, and Sn but are also regarded as an indicator of a deep concealed pluton of rare-metal granites.     

中国南天山晚石炭世—早二叠世花岗质侵入岩的岩石成因与地壳增生

晚石炭世—早二叠世在中亚南天山造山带形成了大量的花岗质侵入岩.中国境内这些岩体以晚石炭世Ⅰ型花岗岩、早二叠世Ⅰ型和S型花岗岩以及最晚期的A型花岗岩为代表.不同类型的岩石在源区特征和岩浆形成的温压条件上存在一定的差异,而这些差异性反映了该时期内构造环境的演化过程.本文选取铁列克岩体、盲起苏岩体、英买来岩体、川乌鲁杂岩体、...     

Generation and emplacement of shear-related highly mobile crustal melts: the synkinematic leucogranites from the Variscan Tormes Dome, Western Spain

The Tormes dome consists of S-type granites that intruded into Ordovician augen gneisses and Neoproterozoic–Lower Cambrian metapelites/metagreywackes at different extents of migmatization. S-type granites are mainly equigranular two-mica granites, occurring as: (1) enclave-laden subvertical feeder dykes, (2) small external sill-like bodies with size and shape relations indicative for self-similar pluton growth, and (3) as large pluton bodies, emplaced at higher levels than the external ones. These magmas were highly mobile as it is inferred from the high contents of fluxing components, the disintegration and alignment of pelitic xenoliths in feeder dykes and at the bottom of some sill-like bodies. Field relations relate this 311?Ma magmatism (U–Pb monazite) to the regional shearing of the D₃ Variscan event. Partial melting modeling and the relatively high estimated liquidus temperatures indicate biotite-dehydration partial melting (800–840°C and 400–650?MPa) rather than water-fluxed melting, implying that there was no partial melting triggered by externally derived fluids in the shear zones. Instead, the subvertical shear zones favored extraction of melts that formed during the regional migmatization event around 320?Ma. Nd isotope variation among the granites might reflect disequilibrium partial melting or different protoliths. Mass-balance and trace element partial melting modeling strongly suggest two kinds of fertile crustal protoliths: augen gneisses and metapelites. Slight compositional variation among the leucogranites does not reflect different extent of protolith melting but is related to a small amount of fractional crystallization (<13% for the equigranular granites), which is generally more pronounced in shallower batholitic leucogranites than in the small and homogeneous sill-like bodies. The lower extent of fractional crystallization and the higher-pressure emplacement conditions of the sill-like bodies support a more restricted movement through the crust than for batholitic leucogranites.     

Petrology,geochronology and Sr–Nd isotopic geochemistry of the Konso pluton,south-western Ethiopia: implications for transition from convergence to extension in the Mozambique Belt

Granites were shown to be excellent geochronological, structural and geodynamic markers. Among several generations of granites described in the Neoproterozoic of Ethiopia, we studied the post-tectonic Konso pluton to characterise the post-Pan-African evolution of the Mozambique Belt (MB) of southern Ethiopia. The Konso pluton is a composite intrusion of slightly peraluminous and ferro-potassic, bt (biotite)–leucogranites, bt–hbl (hornblende)–granites and subordinate coeval metaluminous monzodiorites, intruded into high-grade gneiss–migmatite associations of the MB. The whole suite displays chemical features of A-type granites. It is LIL- and HFS-elements enriched with Y/Nb and Yb/Ta1.2. The granites and leucogranites show non-fractionated to fractionated REE patterns [(La/Yb)_N=0.3–9.4] with strong negative Eu anomalies. The monzodiorites show fractionated REE patterns [(La/Yb)_N=5.5–7.4] with negligible negative Eu anomaly. The low initial (⁸⁷Sr/⁸⁶Sr)₄₅₀ ratios (0.70113–0.70441) and positive Nd₍₄₅₀₎ values (+1.8 to +3.3) suggest an isotopically primitive source. The Konso granites are likely to be derived from a basaltic parent, with minor contamination by crustal material with high Y/Nb and low Sr initial isotopic ratios. Age of pluton emplacement is constrained by a Rb–Sr isochron and zircon U–Pb data at 449±2 Ma. The Konso pluton is, therefore, the witness of an Ordovician A-type magmatic event, which marks a change from convergence, related to the Pan-African collision, to extension in the Mozambique Belt of southern Ethiopia.     

Sources and formation conditions of Early Proterozoic granitoids from the southwestern margin of the Siberian craton

Three stages of Early Proterozoic granitoid magmatism were distinguished in the southwestern margin of the Siberian craton: (1) syncollisional, including the formation of migmatites and granites in the border zone of the Tarak massif; (2) postorogenic, postcollisional, comprising numerous granitoid plutons of diverse composition; and (3) intraplate, corresponding to the development of potassic granitoids in the Podporog massif. Rocks of three petrological and geochemical types (S, I, and A) were found in the granitoid massifs. The S-type granites are characterized by the presence of aluminous minerals (garnet and cordierite), and their trace element distribution patterns and Nd isotopic parameters are similar to those of the country paragneisses and migmatites. Their formation was related to melting under varying H₂O activity of aluminous and garnet—biotite gneisses at P ≥ 5 kbar and T < 850°C with a variable degree of melt separation from the residual phases. The I-type tonalites and dioritoids show low relative iron content, high concentrations of CaO and Sr, fractionated REE distribution patterns with (La/Yb)_n = 11–42, and variable depletion of heavy REE. Their parental melts were derived at T ≥ 850°C and P > 10 and P < 10 kbar, respectively. According to isotopic data, their formation was related to melting of a Late Archean crustal (tonalite-diorite-gneiss) source with a contribution of juvenile material ranging from 25–55% (tonalites of the Podporog massif) to 50–70% (dioritoids of the Uda pluton). The most common A-type granitoids show high relative iron content; high concentration of high-field-strength elements, Th, and light and heavy REE; and a distinct negative Eu anomaly. Their primary melts were derived at low H₂O activity and T ≥ 950°C. The Nd isotopic composition of the granitoids suggests contributions to the magma formation processes from ancient (Early and Late Archean) crustal (tonalite-diorite-gneiss) sources and a juvenile mantle material. The contribution of the latter increases from 0–35% in the granites of the Podporog and Tarak massifs to 40–50% for the rocks of the Uda and Shumikha plutons. The main factors responsible for the diversity of petrological and geochemical types of granitoids in collisional environments are the existence of various fertile sources in the section of the thickened crust of the collisional orogen, variations in magma generation conditions $(\alpha _{H_2 O} , T, and P)$ during sequential stages of granite formation, and the varying fraction of juvenile mantle material in the source region of granitoid melts.     

The Cornubian Batholith: an Example of Magmatic Fractionation on a Crustal Scale

Abstract. The Cornubian Batholith comprises six major and several smaller bodies of S‐type granite in southwestern England. These late‐Variscan granites comprise two‐mica granites, and much less abundant Li‐mica granites that are restricted to one of the major bodies (St Austell) and smaller bodies. Some of these intrusive rocks are associated with major Sn mineralization. This paper is concerned with the geochemistry of the two‐mica granites, which are felsic, strongly peraluminous, and have a high total alkali content and low Na:K. Rocks with very similar compositions to these granites occur elsewhere, including the Variscan granites of continental Europe, and in southeastern Australia. In detail all of the major plutons of this batholith have distinctive compositions, except for Bodmin Moor and Carnmenellis which cannot be discriminated from each other compositionally. A comparison with experimental data shows that the granites attained their major element composition under conditions of crystal‐liquid equilibrium, with the final melt being saturated in H₂O, at temperatures close to 770d?C and pressures about 50 MPa. That temperature estimate is in good agreement with values obtained from zircon saturation thermometry. The specific minimum‐temperature composition excludes the possibility of widespread transfer of elements during hydrothermal alteration. Minor elements that are relatively very abundant are Li, B, Cs and U, while F, Ga, Ge, Rb, Sn, Ta, W and Tl are quite abundant and P is high for felsic rocks. Sr, Ba, and the trace transition metals Sc to Zn, are low, but not as low as they commonly are in very felsic granites. These trace element abundances, and the EL₂O‐saturation, resulted from the fractional crystallization of a melt derived by the partial melting of feldspathic greywackes in the crust. The Cornubian granites have compositions very similar to the more felsic rocks of the Koetong Suite of southeastern Australia, where a full range of granites formed at the various stages of magmatic fractionation postulated for the Cornubian granites, can be observed. The operation of fractional crystallization in the Cornubian granites is confirmed by the high P abundances in the feldspars, with P contents of the plagioclase crystals correlating with Ab‐con‐tent Most of the granites represent solidified melt compositions but within the Dartmoor pluton there is a significant component of granites that are cumulative, shown by their higher Ca contents. The Cornubian plutons define areas of high heat flow, of a magnitude which requires that fractionated magmas were transported laterally from their sources and concentrated in the exposed plutons. The generation of these granite plutons therefore involved magmatic fractionation during the stages of partial melting, removal of unmelted material from that melt, and fractional crystallization. During the later stages of those processes, movement of those magmas occurred on a crustal scale.     

Significance of selective crystal entrainment and differential crystal-melt separation in petrogenesis of granites from the Tongbai orogen

Partial melting has been shown to be an important mechanism for intracrustal differentiation and granite petrogenesis. However, a series of compositional differences between granitic melt from experiments and natural granites indicate that the processes of crustal differentiation are complex. To shed light on factors that control the processes of crustal differentiation, and then the compositions of granitic magma, a combined study of petrology and geochemistry was carried out for granites (in the forms of granitic veins and parautochthonous granite) from a granulite terrane in the Tongbai orogen, China. These granites are characterized by high SiO₂ (>72 wt%) and low FeO and MgO (<4 wt%) with low Na₂O/K₂O ratios (<0.7). Minerals in these granites show variable microstructures and compositions. Phase equilibrium modelling using P–T pseudosections shows that neither anatectic melts nor fractionated melts match the compositions of the target granites, challenging the conventional paradigm that granites are the crystallized product of pure granitic melts. Based on the microstructural features of minerals in the granites, and a comparison of their compositions with crystallized minerals from anatectic melts and minerals in granulites, the minerals in these granitoids are considered to have three origins. The first is entrained garnets, which show comparable compositions with those in host granulites. The second is early crystallized mineral from melts, which include large plagioclase and K-feldspar (with high Ca contents) crystals as well as a part of biotite whose compositions can be reproduced by crystallization of the anatectic melts. The compositions of other minerals such as small grained plagioclase, K-feldspar and anorthoclase in the granites with low Ca contents are not well reconstructed, so they are considered as the third origin of crystallized products of fractionated melts. The results of mass balance calculation show that the compositions of these granites can be produced by mixing between different proportions of crystallized minerals and fractionated melts with variable amounts of entrained minerals. However, the calculated modal proportions of different crystallized minerals (plagioclase, K-feldspar, biotite and quartz) in the granites are significantly different from those predicted by melt crystallization modelling. Specifically, some rocks have lower modes of biotite and plagioclase, whereas others show lower K-feldspar modes than those produced by melt crystallization. This indicates that the crystallized minerals would be differentially separated from the primary magmas to form the evolved magmas that produce these granites. Therefore, the crystal entrainment and differential melt-crystal separation make important contributions to the composition of the target granites. Compared with leucogranites worldwide, the target granites show comparable compositions. As such, the leucogranites may form through the crystal fractionation of primary granitic magmas at different extents in addition to variable degrees of partial melting.     

The geochemistry and petrogenetic relationships of two granites and their inclusions in the Keimoes Suite of the Namaqua mobile belt,South Africa

The Colston and Straussburg plutons consist of two dissimilar granites belonging to the Proterozoic (1100–1200 Ma) Keimoes Suite along the eastern margin of the Namaqua mobile belt. The intrusives and their enclaves were investigated to establish their genetic relationships. The peraluminous Colston granite exhibits S-type characteristics while the Strausaburg intrusive shows marked similarity with I-type granites. One set of quartz-rich melanocratic inclusions are present in the Colston granite. The corresponding melanocratic enclaves in the Straussburg pluton are comprised of a porphyritic type and a non-porphyritic type, while leucocratic inclusions are also abundant.Field relationships, mineralogical and chemicál compositions as well as REE-patterns, point to a strong genetic relationship between the granites and their enclaves. Genetic models involving fractional crystallization, wall-rock assimilation, two-magma mixing, and minimum melt-restite mobilisation, were considered to explain the nature and origin of the inclusions and the host granites, and the observed REE-characteristics make most of the models unlikely. It is concluded that the quartz-rich melanocratic inclusions in both plutons formed as products of partial batch melting from a common source, possibly a basic or intermediate gneiss or granulite, under relatively high XCO₂ conditions. After the intrusion and consolidation of the first melts, water-undersaturated granitic magmas intruded as a secondstage, incorporating the first melt products as melanocratic inclusions. The different crystallization conditions of the melanocratic inclusions and the host granites are highlighted by the difference in chemical composition of the biotites, as for instance illustrated in Ti-Al diagrams. The biotite is accompanied by hornblende in all the rock types with the exception of the Colston granite and the leucocratic inclusions of the Straussburg granite.The leucocratic enclaves in the Straussburg granite are interpreted as depleted restite material which formed at a pressure near 5 kbar, and which was transported to the surface by the granite magma. When the compositions of the granitic rocks are compared with the experimental results for the haplogranitic (Ab-Or-An-Q) system, they prove to be quite near the expected minimum melt compositions for a total pressure of 5 kbar.     

东蒙地区燕山期三类成矿岩体地质地球化学特征

根据东蒙地区广泛发育的中生代燕山期岩体的成矿特征，将其成矿岩体分成三种类型。它们分别是铜成矿岩体、铅锌成矿岩体和锡成矿岩体。通过对三种成矿岩体的岩石学、稀土元素和微量元素的分析研究，认为铜成矿岩体具有明显的幔源和壳源双重特征，为燕山早期岩浆演化的结果；锡成矿岩体为燕山晚期岩浆演化的产物，具有壳源特点；铅锌成矿岩体的地质特征处于铜成矿岩体和锡成矿岩体的过渡。     

Phase equilibria of a fluorine-rich leucogranite from the St. Austell pluton,Cornwall

Highly evolved leucogranitic rocks in the St. Austell pluton, Cornwall, of Hercynian age, contain accessory muscovite, topaz and fluorite. We have studied the H₂O-saturated melting behavior of one representative sample. Its solidus and liquidus pass through the points 663 and 725°C, respectively, at 1 kbar, 640 and 665°C at 2 kbar, 610 and 717°C at 4 kbar and 608 and 700+°C at 8 kbar. Plagioclase is on the liquidus at low pressure and topaz is on the liquidus at 4 kbar: The fluorite is consumed in the formation of the first-formed liquid. Calcium can partition into an evolved granitic melt if complexed by fluorine. The fluorite appears to be largely primary in fresh fluorite granite at St. Austell and not to reflect the albitization of oligoclase in the surrounding biotite granite. Such fluorine-rich leucogranites can be expected to be of subsolvus character.     

青海大黑山钨矿黑云二长花岗岩的锆石U-Pb同位素定年及岩石地球化学特征

大黑山钨矿位于祁连山加里东造山带,其形成与宝库河黑云二长花岗岩密切相关。黑云二长花岗岩锆石LA-ICPMS U-Pb测年结果显示其形成年龄为:450.2±2.8Ma,为加里东期岩浆活动的产物。地球化学数据显示,宝库河黑云二长花岗岩富硅(SiO2含量为73.03%～74.18%)、富钾(K2O/Na2O为1.13～1.94,K2O+Na2O含量为7.25%～8.51%)、铝过饱和(A/CNK为1.04～1.12),为过铝质钙碱性-高钾钙碱性花岗岩。P2O5含量低(0.03%～0.08%),且具有随SiO2含量的增长呈现负增长的趋势。稀土含量低,Eu明显负异常,LREE分异强烈,HREE分异不明显。微量元素蛛网图中Th、U、Pb、Zr、Hf呈现明显的正异常,Ba、Sr、Ta、Nb、P、Ti呈现负异常,为I型花岗岩。结合对区域动力地质背景的分析,表明宝库河黑云二长花岗岩形成于活动大陆边缘,由地壳物质熔融并结晶形成。     

Sm-Nd systematics and petrology of postorogenic granitoids in the northern Baltic Shield

In the northern part of the Baltic Shield, quartz diorites, diorites, and monzodiorites compose massifs of postorogenic granites, in which younger granite phases are restricted to their central parts, and dike rocks (aplites, pegmatites, and granite porphyries) occur in the apical parts. The rocks of the Litsa-Araguba Complex (which is located in the northwestern part of the Kola Peninsula and was examined most thoroughly) compose seven intrusions 850 km² in total area, which were formed in mesoabyssal and hypabyssal depth facies. The massifs consist of quartz diorites and monzodiorites dated at 1774 ± 9 Ma, diorites, diorite porphyries, and lamprophyres, which are distinguished as phase 1. The porphyritic and equigranular granites, granodiorites, quartz monzonites, granites, alaskites and related vein leucogranites, pegmatites, and granite porphyries of phases 2 (main), 3, and 4 have an age of 1772–1762 Ma. Data obtained on the Sm-Nd systematics of the rocks indicate that their ?_Nd(1765) values are close to those for rocks of phases 1, 2, and 3 (from ?6.8 to ?8.8) and vary from ?5.0 to ?11.9 for the leucocratic granites of phase 4. The model age values are, respectively, 2.37–2.62 and 2.58–3.23 Ga. These data suggest that the parental melts were of anatectic genesis and were produced by the melting of mostly metasomatically altered garnet granulites from the lower crust. The leucogranites and alaskites of phase 4, which occur as relatively thin bodies in the rocks of the Archean Complex penetrated by the Kola Superdeep Borehole, were derived from a Neoarchean sialic source or produced by the contamination of the parental melts with the material of the Late Archean upper crust. The SHRIMP-II zircon age of the lower crustal migmatized garnet granulites lies within the range of 1831 ± 23 to 1392 ± 21 Ma in the concordia plot. All dates of the rocks are characterized by a unimodal distribution with most values lying within the range of 1650–1800 Ma and approximated by a discordia with T₁ = 1750 ± 30 Ma, MSWD = 3.1. This age value can be interpreted as an averaged age of the lower crustal granitization and corresponds, within the errors, to the age of postorogenic granite intrusions in the upper crust.     

安徽铜陵沙滩脚矿田中酸性侵入岩成因及构造意义

安徽省铜陵地区是中国著名的以矽卡岩和斑岩型矿床为主的铜-金多金属矿集区,区内广泛产出的中酸性侵入岩与成矿关系十分密切。沙滩脚矿田位于该矿集区的东部,出露沙滩脚、桂花冲和姚家岭岩体及其不同规模、不同矿化类型的铜、金、锌等矿床,岩体对成矿起了重要的控制作用。本文在前人研究的基础上,对该矿田内的沙滩脚、姚家岭、桂花冲3个岩体进行了详细的岩石学、地球化学和锆石U-Pb年代学研究,以期查明沙滩脚矿田中酸性侵入岩的成因及成岩构造环境。岩石地球化学分析表明,3个岩体具有准铝质特征,均属于高钾钙碱性I型花岗岩类,轻稀土富集,重稀土亏损,具有弱的负Eu异常,富集Rb、Th等元素,亏损Nb、Ta等高场强元素。姚家岭岩体的锆石U-Pb年龄为140.4~140.9 Ma,沙滩脚岩体形成时代相对较早（141.4~144.1 Ma）,桂花冲岩体形成相对较晚（138.3Ma）。结合区域地质背景,笔者认为沙滩脚矿田的这些岩体形成于早白垩世伸展环境,是由来自于富集地幔的分异的碱性玄武质岩浆与地壳易熔组分部分熔融形成的花岗质岩浆混合后分期侵位形成的。     

Petrogenesis and geodynamic setting of the Triassic granitoid plutons in West Qinling,China: insights from LA-ICP-MS zircon U–Pb ages,Lu–Hf isotope signatures and geochemical characteristics of the Zhongchuan pluton

West Qinling is one of the most important parts of the Qinling orogenic belt and includes acidic–intermediate plutons and many types of ore deposits. In this article, we collected geochemical and geochronological data for the Triassic granitoid plutons of West Qinling and found that nearly all plutons share the similar features with the Zhongchuan pluton. We present new laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages, major and trace element geochemistry, and zircon Hf isotope systematics for the granites of the Zhongchuan pluton to elucidate the evolution of granitoid plutons in West Qinling during the Triassic. LA-ICP-MS zircon U–Pb dating indicates that the Xujiaba and Guandigou units formed at 220.1 ± 1.2 and 215.9 ± 0.85 Ma, respectively, reflecting the time of the Late Triassic. The rocks of the Zhongchuan pluton are metaluminous to weakly peraluminous and have a high-K calc-alkaline to shoshonite series with high SiO₂ (63.59–76.22%) and low P₂O₅ (0–0.2%) concentrations, a high K₂O/Na₂O ratio (1.18–17.92), a high differentiation index (78.45–93.04) and a medium A/CNK ratio (0.98–1.69). The zircon Hf isotope dating indicates that the Xujiaba and Guandigou units have an inhomogeneous ε_Hf(t) (?4.425 to 1.067 for Xujiaba and ?4.920 to 2.042 for Guandigou) and two-stage Hf model ages (1123–1531 Ma for Xujiaba and 1115–2342 Ma for Guandigou). The geochemical and isotopic data imply that the granites of each unit share the same origin. They probably derived from the partial melt of metagreywackes and then mixed with the mantle-derived magma. Based on the regional geological history, petrographic characteristics and new geochemical and isotopic data of the Zhongchuan pluton, we suggest that the Triassic magma was derived from the partial melts of metagreywackes and was influenced by the mantle-derived melt during the collision of the Yangtze and Qinling plates.     

Single Zircon LA-ICP-MS U-Pb Dating of the Guandimiao and Wawutang Granitic Plutons in Hunan, South China and Its Petrogenetic Significance

1 Introduction The South China Block (SCB), located between the Qinling-Dabie and Songma Indosinian sutures, experienced successively two important tectonic movements during the Mesozoic, i.e. the Indosinian movement (early Mesozoic) and the Yanshanian movement (late Mesozoic). Therefore, the generally accepted viewpoint is that the key geological problems during the Mesozoic are essentially the dynamics and material expression of these two tectonic movements in South China (Chen et al.…