Generation Of Granites Research Articles

Petrogenesis of Ta-Nb mineralization related Early Cretaceous Lingshan granite complex, Jiangxi Province, southeast China: Constraints from geochronology, whole-rock and in-situ mineral geochemistry, and Nd-Hf isotopic compositions

The Lingshan granite complex, located in the northeast part of the Qin-Hang Belt, Jiangxi Province, southeast China, has produced the largest Ta-Nb deposits in China, i.e., the Huangshan Nb-Ta and Songshugang Ta-Nb-(W-Sn) deposits. This complex is spatially a ring-like multiphase batholith, and comprises a series of granitic rocks from the central to marginal units. Mafic microgranular enclaves (MMEs) occur only in the central unit. Geochronologic results show that the magmatic activities at Lingshan district took place at Early Cretaceous, with similar emplacement ages (133–134 Ma) between the central and marginal units. The Lingshan granites are metaluminous to weakly peraluminous (most A/CNK < 1.1), and display typical A-type affinity. However, the whole-rock REE contents and Zr/Hf and (La/Yb)N ratios exhibit an abnormal increase from the central to marginal units. The Li, Rb and Cs elements of biotite as well as the Zr/Hf ratios of zircon do not exhibit a continuous enrichment trend from the central towards marginal granites. All these features suggest that the generation of Lingshan granites is more complex than the fractional crystallization from a single parental magma. Alternatively, a crystal mush model could be applied to better interpret the geochemical and isotopic contrasts between different granite phases. The marginal granites were likely formed by later crystallization events after the rejuvenation and extraction from the crystal mush reservoirs, while the central granites were formed from the residual crystal-rich mush with a relatively low terminal porosity. Moreover, the Nb and Ta contents of biotite exhibit a gradual enrichment with increasing fluorine contents in the marginal granites. The enrichment of lithium and fluorine in the granitic melt can significantly promote the proportion of non-bridging oxygens (NBOs) for coordinating Nb and Ta in the melt, further enhancing the solubility of columbite and tantalite, and eventually causing the Nb and Ta elements either incorporate into the mineral lattice of micas in the early marginal granites or form columbite-group minerals in the pegmatite/altered granite. In summary, we propose that the Ta-Nb enrichment event in the Lingshan district is spatially and genetically related to the extensive fractionation evolution from central to marginal units.

Mixing of cognate magmas as a process for producing high-silica granites: Insights from Guanmenshan Complex in Liaodong Peninsula, China

Ascertaining how high-silica granites form is important for understanding why Earth has a high-silica continental crust and how the composition of the continental crust has evolved through time. This study presents a systematic dataset for the petrology, mineralogy, geochronology, and geochemistry of the granite porphyries and related microgranular enclaves and diabases from the Early Cretaceous Guanmenshan Complex (126–123 Ma) in Liaodong Peninsula, North China Craton, to reveal the complex, multi-stage, magmatic evolution in a shallow silicic magma system prior to and during emplacement of high-silica granites. Zircons from the granite porphyries and microgranular enclaves can be classified into two groups: those with dark-CL cores surrounded by light-CL rims, and those comprising entirely light-CL domains, without dark-CL cores. Our results indicate that dark-CL zircon domains with high Th (46–579 ppm), U (120–1274 ppm), and Hf (6709–12,493 ppm) contents and low Ti contents (1.52–7.85 ppm) and Ti-in-zircon temperatures (TTiZ = 622–751 °C) formed from highly evolved magmas, whereas light-CL zircon domains with low Th (14–157 ppm), U (24–236 ppm), and Hf (4749–10,474 ppm) contents and high Ti contents (7.59–29.36 ppm) and Ti-in-zircon temperatures (TTiZ = 748–885 °C) formed from low evolved magmas. These characteristics, combined with the similar UPb ages and Hf isotopic compositions of the dark-CL zircon cores and light-CL zircon domains and insignificant intra- or inter-grain (87Sr/86Sr)i variations of plagioclase from the granite porphyries and microgranular enclaves, reflect mixing between two cognate magma batches with contrasting evolved signatures. This study presents a model in which the highly evolved magmas were derived from initial interstitial melts that were extracted from a crystal mush leaving behind residual cumulates, whereas the less evolved magmas were the products of re-melting of the cognate cumulates. The diabases likely represent the mafic recharge magma that contributed necessary heat but limited mass to remobilize the cumulate mush, inducing the internal self-mixing and formation of the hybrid high-silica magmas. Feeder-dyke related emplacement of the hybrid magma generated more mafic rocks that became incorporated and dispersed into the high-silica granite porphyries as cognate microgranular enclaves. Our results lend new insights into the important role of cognate magma mixing induced by mafic recharge in generation of high-silica granites.

ZIRCONS FROM ROCKS OF THE MURZINKA-ADUI METAMORPHIC COMPLEX: GEOCHEMISTRY, THERMOMETRY, POLYCHRONISM, AND GENETIC CONSEQUENCES

Transformation of the oceanic crust into the continental one in orogenic belts is an important problem in petrological studies. In the paleocontinental sector of the Urals, a key object for tracing the stages of metamorphism and investigating the origin of anatectic granites is the Murzinka-Adui metamorphic complex. We have analyzed trace elements in zircons and established their genesis, sources, crystallization conditions, and stages of metamorphic events and granite generation in this complex. Zircons compositions were determined by the LA-ICP-MS method. Temperatures were calculated from Ti contents in the zircons. We distinguish three geochemical types of zircons, which differ in the ratios of light and heavy REE, U, Th, Ti, Y and show different values of Ce- and Eu-anomalies and Zr/Hf ratios, which are indicative of different crystallization conditions, as follows. Type I: minimal total LREE content; clear negative Eu- and Ce- anomalies; features of magmatic genesis; crystallization temperatures from 629 to 782 °C. Type II: higher contents of Ti, La, and LREE; low Ce-anomaly; assumed crystallization from highly fluidized melts or solutions. Type III: low positive Eu-anomaly; high REE content; low Th/U-ratio; zircons are assumed to originate from a specific fluidized melt with a high Eu-concentration. Ancient relict zircons (2300–330 Ma) in gneisses and granites show features of magma genesis and belong to types I and II. Such grains were possibly inherited from granitoid sources with different SiO2 contents and different degrees of metamorphism. Based on the geological and petrogeochemical features and zircon geochemistry of the Murzinka-Adui complex, there are grounds to conclude that the material composing this complex was generated from the sialic crust. The main stages of metamorphism and/or granite generation, which are traceable from the changes in types and compositions of the zircons, are dated at 1639, 380–370, 330, and 276–246 Ma. Thus, transformation of the oceanic crust into the continental one was a long-term and complicated process, and, as a result, the thickness of the sialic crust is increased in the study area.

The production of granitic magmas through crustal anatexis at convergent plate boundaries

Granite petrogenesis is associated with the formation and evolution of continental crust along convergent plate boundaries. While magmatic processes such as partial melting and fractional crystallization result in the compositional diversity of granites, the nature of magma sources is related to tectonic settings of granite generation. Although granites consist predominantly of magmatic minerals, they generally contain small amounts of peritectic and residual minerals. This results in the compositional difference between natural granites and experimental melts. In addition to the fractional crystallization of mantle-derived mafic magmas for the generation of granites during accretionary orogeny, a wide range of crustal rocks can be partially melted to form granites in both accretionary and collisional orogens. In the latter case, metasedimentary and metaigneous crustal sources lead to the dichotomy of S- and I-type granites. Geochemically, granites with negative εNd(t) and εHf(t) values are certainly derived from reworking of the ancient crust. On the other hand, granites with positive εNd(t) and εHf(t) values may be produced either by reworking of the juvenile crust or by fractional crystallization of asthenospheric mantle-derived magmas at actively convergent plate boundaries. In this case, major and trace elements may be of use in distinguishing between the crustal and mantle contributions. Granite, migmatite and granulite generally form lithological associations at previously converged plate boundaries, with migmatitic domes as the major component of metamorphic core complexes. Their formation is related to extensional heating subsequent to thinning of the thickened mantle lithosphere. As soon as the thickened lithospheric mantle was foundered into the asthenospheric mantle, it makes the space for asthenospheric upwelling to induce active rifting along the thinned lithosphere. This provides an external heat source for anatectic metamorphism at high thermal gradients, marking the tectonic transition in the property of orogenic systems into the rifting stage. Therefore, the active rifting is spatially and temporally dictated by thinning of the orogenic mantle lithosphere, and its operation is a geodynamic mechanism for crustal anatexis at convergent plate boundaries. Consequently, the lithospheric thickness has a profound effect on crustal anatexis for granitic magmatism, which is considerably later than plate convergence.

Migmatite rheology of crustal catazone: An example from theSSEpart of T. Sundupalle granite‐greenstone terrain, Eastern Dharwar Craton, India

The southern basement of the Cuddapah Basin comprises the Dharwar Batholith and greenstone belt complex. Granitoids of the batholith exhibit extensive variation in terms of geomorphology, age, mineralogy, and micro/meso scale structures. The eastern part of Dharwar Craton along 13°50′ to 14°8′N latitude and 78°45′ to 79°05′E longitude was studied to enlighten the rheological influence on crustal evolution. Frequent occurrences of migmatites of restricted dimension are observed in the south of 14°10′N latitude. The granite‐migmatite contacts are not sharp in general. Different types of migmatite complex and their relationships with granitoids as well as older country rocks represent an exhumed segment of the crustal catazone. The widespread group of migmatitic rocks are classified in a composite manner on the basis of morphology and structure. Furthermore, genetic implication vis‐a‐vis anatexis history is also evaluated. Static and dynamic modes of migmatites are recognized with reference to geothermal gradient and tectonics. Based on the degree of anatexis, two categories of migmatites are identified in the field, that is, metatexites and diatexites. In addition, metatexites are classified into four sub‐types (viz, patch, dilatant, net, and stromatic) and diatexites are also sub‐divided into two categories (viz, schollen or raft and schlieren). The hybrid nature of migmatitic rocks with both metamorphic and igneous characteristics are used to analyse pre‐ and post‐anatectic events. The preserved evidences of partial melting are marked as leucocratic patches. In situ stagnation of the melt or subsequent separation from the remaining solid provides different morphology of static mode. Importance of dihedral angle at solid–liquid contacts is also considered in the present context to describe the grain boundary penetration by partial melt. Folds, veins, and boudins of different styles and generations played significant role in dynamic mode migmatitization. The syn‐ and post‐metamorphic deformation events and granite melt generation from migmatites are schematically defined. Spatial and temporal relationships of schist‐gneiss‐migmatites of both static as well as dynamic mode reveal initiation of the crustal development by vertical accretion of ultramafic‐mafic lava and TTG. Cyclic partial remelting of the metabasic lava and TTG and underplating led to development of the lithospheric plate. Later upwelling material at convergent plate and associated heat transfer led to generation of granitic magma. The established prograde and retrograde cycle of metamorphism were possibly interrupted by crustal reworking events. This study confirms about the crustal catazone segment (with &gt;15 km depth and &gt;500°C) in which physical processes control generation, segregation, ascent, and emplacement of juvenile granite from migmatites.

Generation of Cretaceous high-silica granite by complementary crystal accumulation and silicic melt extraction in the coastal region of southeastern China

Abstract It is generally hypothesized that high-silica (SiO2 &amp;gt; 75 wt%) granite (HSG) originates from crystal fractionation in the shallow crust. Yet, identifying the complementary cumulate residue of HSG within plutons remains difficult. In this work, we examine the genetic links between the porphyritic monzogranite and HSG (including porphyritic granite, monzogranite, and alkali feldspar granite) from the coastal area of southeastern China using detailed zircon U-Pb ages, trace elements, Hf-O isotopes, and whole-rock geochemistry and Nd-Hf isotopic compositions. Zircon U-Pb ages indicate that the porphyritic monzogranite and HSG are coeval (ca. 96–99 Ma). The HSG and porphyritic monzogranite have similar formation ages within analytic error, identical mineral assemblages, similar Nd-Hf isotopic compositions, and consistent variations in their zircon compositions (i.e., Eu/Eu*, Zr/Hf, and Sm/Yb), which suggests that their parental magma came from a common silicic magma reservoir and that the lithological differences are the result of melt extraction processes. The porphyritic monzogranite has relatively high SiO2 (70.0–73.4 wt%), Ba (718–1070 ppm), and Sr (493–657 ppm) contents, low K2O and Rb concentrations and low Rb/Sr ratios (0.1–0.2), and it displays weak Eu anomalies (Eu/Eu* = 0.57–0.90). Together with the petrographic features of the porphyritic monzogranite, these geochemical variations indicate that the porphyritic monzongranite is the residual silicic cumulate of the crystal mush column. The HSG (SiO2 = 75.0–78.4) has variable Rb/Sr ratios (2–490) and very low Sr (1–109 ppm) and Ba (9–323 ppm) contents. Zircon from the HSG and porphyritic monzogranite overlap in Eu/Eu*, Zr/Hf, and Sm/Yb ratios and Hf contents; however, some zircon from the HSG show very low Eu/Eu* (&amp;lt;0.1) and Zr/Hf ratios. These features suggest that the HSG represents the high-silica melt that was extracted from a crystal-rich mush. The injection of mantle-derived hotter mafic magma into the mush column and the exsolution of F/Cl−-enriched volatiles (or fluids) from the interstitial melt rejuvenated the pre-existing highly crystalline mush. Subsequent extraction and upward migration of silicic melt resulting from compaction of the mush column formed the HSG at shallow crustal levels, which left the complementary crystal residue solidified as porphyritic monzogranite at the bottom.

Characterisation and geodynamic setting of the 1 Ga granitoids of the Karagwe-Ankole belt (KAB), Rwanda

The Karagwe-Ankole belt (KAB) is a poorly understood deformation belt in the Great Lakes area of Central Africa, with several hypotheses put forward to explain the emplacement of the various generations of granites. The youngest generation of granites (G4; 1000 Ma) are spatially associated with Sn-W-Ta ore deposits, and are considered as the parental granites. The paragenesis of these mineral resources have been extensively scrutinised, but the geodynamic context and characterisation of these parental granites has been neglected. Tectonic models for the formation of this plutonic suite range from an intra-cratonic to full-scale continent–continent collision setting.In this study, the G4 intrusive suite of the KAB granites, are characterised based on whole-rock geochemical analysis and U-Pb zircon dating.Two main populations of U-Pb zircon ages are identified in the G4 granites at 1370–1420 Ma and 950–1020 Ma. The older population is attributed to inheritance of the bimodal magmatic Kibaran event, while the younger population is ascribed to the new crystallisation. G4 granites contain xenocrystic zircon, indicating inheritance of older granites or basement rocks. G4 granites are, however, much more differentiated compared to older Kibaran granites, containing higher K and Rb and lower Ca, Sr and Ba concentrations, which implicates recycling of older crustal material. The variable geochemistry, as well as the different proportions of xenocrystic zircons in the different granite bodies, suggest melting was highly localised and derived from a highly heterogeneous source region, for which an intracontinental setting is favoured. The Th/U ratios of the parental granites are lower than 0.1, which would suggest a metamorphic origin of the granites. Together with the low luminescence signal of these zircons an anatectic origin of the melt is considered, implying that the parental granites could be considered more like migmatites rather than actual granites formed by fractionation out of large magma chambers.

The role of mantle and the ancient continental crust in the generation of post-collisional high-K calc-alkaline and alkaline granites, with main reference to the Arabian-Nubian Shield

Continental-scaled magmatic activity occurs after the end of collision-orogenic stages of the Wilson cycle. This post-collisional magmatism is widely exhibited, from 635 to 540 Ma, in a series of large Neoproterozoic (Pan-African) orogenic belts throughout North Africa. Special reference is given to the Arabian-Nubian Shield (ANS) and the LATEA metacraton (Tuareg shield). For comparison, two Late Paleozoic-Early Mesozoic transcontinental belts, the Variscan in Western Europe and the east Central Asian Orogenic Belt, are briefly discussed. Two main types of consecutive magmatic suites characterize the Late Neoproterozoic (Ediacaran) and Late Paleozoic-Early Triassic (Variscan) post-collisional magmatic events despite their different formation age and geographic location: (a) Early post-collisional suites composed of dominant HKCA monzogranite, with secondary quartz monzonite, granodiorite, and related high-K calc-alkaline gabbro, diorite; (b) Late post-collisional to intra-continental suites of Alk syenogranite, alkali feldspar granite and quartz syenite, in places with Na-rich pyroxene and amphibole; volcanic activity and numerous dike swarms are abundant. The mafic rocks related to Alk granite suites are monzogabbro and monzonite (shoshonitic series). Granitoids of the same type, HKCA or Alk, are very similar in mineral and chemical composition throughout the belts and in different belts. This similarity is observed in regions with very distinct types of crust, e.g. the dominant juvenile oceanic island arc crust in the ANS, and Archean-Paleoproterozoic continental crust in the LATEA metacraton. The isotope U-Sr-Nd-Hf-O signatures suggest that HKCA granite magmas in these regions were produced from different crustal sources with varying contribution of mantle-derived basic materials to the granitoid magma generation. For HKCA granites, a model of crustal anatexis, accompanied with a limited influx of H2O, K, LILE, HFSE from underplated basalt magmas (convective diffusion in the contact of silicic and mafic liquids) is suggested. The most likely model of the Alk silicic magma generation is partial melting of related mantle-derived mafic rocks (monzogabbro, monzonite in the lower crust. Data on the enhanced temperature of A-type silicic magmas, more than 1000 °C, suggest that magma-generation could occur even at the depth of uppermost lithospheric mantle.

The importance of sequential partial melting and fractional crystallization in the generation of syn-D3 Variscan two-mica granites from the Carrazeda de Ansiães area, northern Portugal

In the Carrazeda de Ansiães region, northern Portugal, a mesozonal granitic suite intruded Precambrian to Ordovician metasedimentary rocks during the late kinematic stages of the Variscan orogeny. In this multiphase granitic complex, consisting of ten granite types, the youngest group of two-mica granites (G7–G10) was emplaced between 318 ± 1 Ma and 316.2 ± 0.7 Ma, as determined by ID-TIMS U–Pb on zircon and monazite. Granite types G7–G9 were affected by the third phase of deformation (D3) before they were completely crystallized, as indicated by their internal NW–SE magmatic foliation concordant with the regional structures. The granite type G10 shows some distinctive textural features, showing a strong brittle deformation, probably due to its preferential emplacement in late NNE-SSW fault zones. Granites G7–G9 have equal or higher amounts of muscovite than biotite and contain surmicaceous enclaves, xenoliths, “schlieren”, and, more rarely, microgranular enclaves. The muscovite-dominant granite G10 does not contain enclaves. These Variscan granites are peraluminous, with ASI ranging between 1.22 and 1.39 and normative corundum of 2.79–4.39%, having the characteristics of S-type granites. In fact, the enrichment in LREE relatively to HREE, the negative Eu anomalies, and similar mean values of (87Sr/86Sr)i, εNdt and δ18O for G7 (0.7156 ± 0.0005; − 8.5; 11.49 ‰) and G8 (0.7155 ± 0.0007; − 8.4; 11.39 ‰) show that these two granite types resulted from sequential partial melting of the same metasedimentary material, where granite G8 would have derived from a higher degree of partial melting than G7. Granites G8–G10 and their minerals show a fractionation trend that is confirmed by modeling of major and trace elements. The subparallel REE patterns and the decreasing REE contents within the differentiation series, the Rb–Sr isochron for G8, G9 and G10 (315.5 ± 5.4 Ma; MSWD = 1.3) and the relatively uniform εNdt and δ18O data suggest that fractional crystallization was the main mechanism, which would have lasted less than 1 Ma. The tin-bearing granites G7 and G10 have ≥ 20 ppm Sn, but the main quartz veins containing cassiterite and wolframite cut granite G10, which contains 31 ppm Sn. Fractional crystallization was responsible for the increase in Sn content in granites from the G8–G10 series and their micas.

Generation of syn-collisional S-type granites in collision zones: An example from the Late Triassic Tanggula Batholith in northern Tibet

Mechanisms of syn-collision magma generation are unclear due to the uncertainty in defining the term collision. We address this issue by presenting detailed petrographic, chronological, and geochemical data for the Tanggula Batholith located immediately to the north of the Longmu Tso–Shuanghu suture zone (LSSZ) in northern Tibet. Zircon LA–ICPMS U–Pb dating suggests that the Tanggula Batholith was emplaced at 235–226 Ma. Samples from the batholith show variable SiO2 of 66.6–80.6 wt% and are characterized by high normative corundum (1.09–4.35 wt%) and high aluminum saturation index (A/CNK = 1.05–1.40). These samples exhibit high initial 87Sr/86Sr (0.7165–0.7214), negative whole-rock εNd(t) (−10.1 to −8.5), εHf(t) (−8.7 to −6.3), enriched Pb isotope compositions, and variable zircon εHf(t) values (−29.9 to +5.6), as well as variable zircon δ18O value (6.90–9.22‰). These signatures are characteristic of S-type granites, and were derived from anataxis of metasedimentary rocks from the Qiangtang Terrane with input from mantle-derived components. We propose that the Tanggula Batholith was emplaced in a syn-collisional setting following closure of the Longmu Tso–Shuanghu Ocean along a north dipping subduction zone based on: the timing of high-pressure, low-temperature metamorphism at 244–221 Ma marking collision between Southern and Northern Qiangtang; the timing of exhumation of metamorphic rocks at ~223–204 Ma; and, bimodal volcanism (225–202 Ma) associated with slab breakoff at 220–215 Ma.

Nature and (in-)coherent metamorphic evolution of subducted continental crust in the Neoproterozoic accretionary collage of SW Mongolia

In continental subduction complexes minor volumes of high-pressure mafic rocks (eclogites) often co-exist with much more abundant felsic (granitic) and metasedimentary rocks, which are vital for resolving the origin and metamorphic evolution of subducted continental crust. In SW Mongolia, the Alag Khadny eclogite-bearing accretionary complex (AKC) is assumed to represent either a remnant of oceanic slab, or a continental margin, subducted in the Early Cambrian. Here we present geochronological, geochemical and petrological evidence of subduction records for the three major types of lithologies that host mafic eclogites, including Mesoproterozoic and Neoproterozoic granitic basement and overlying Neoproterozoic continental-margin sediments. Variably deformed, ferroan and peraluminous metagranitoids compose a major part of AKC and are interlayered with eclogites in its southern and eastern margins. They have geochemical features of post-collisional/intraplate high-K calc-alkaline granites. LA-ICP-MS U-Pb zircon geochronology of three distinct metagranite samples show uniform protolith crystallization ages of ca. 0.96 Ga and uncertain re-crystallization in the Late Neoproterozoic or Early Paleozoic metamorphic event, whereas abundant zircon inheritance indicates older, Mesoproterozoic to Paleoproterozoic crustal substrate during granite generation. The existence of Mesoproterozoic crust is highlighted by finding of distinct metagranitoids with the U-Pb zircon crystallization age of ca. 1.6 Ga. Hafnium isotope signatures (TDMC 2.88–1.85 Ga) of zircons from all lithologies preserved the evidence of reworked Neoarchean to Paleoproterozoic crust, similar to that of the Baidrag block (southern Mongolia), for both Mesoproterozoic and Neoproterozoic rocks. Regardless of the specific lithology, the rocks display indicators of high-pressure metamorphic re-equilibration, including garnet (XCa up to 0.65) + epidote + phengite (Si p.f.u. up to 3.56) ± rutile assemblage in metagranitoids, garnet + phengite (Si p.f.u. up to 3.42) in quartz-rich semi-pelites and garnet + phengite (Si p.f.u. up to 3.39) + medium-Mg chloritoid (XMg up to 0.25) + kyanite + rutile in metapelites. Corresponding P-T conditions recovered from different lithologies reveal incoherent subduction of rocks, which could be shallow for granitic basement (1.1–1.4 GPa and 600–670 °C) and clastic metasediments (1.4–1.6 GPa, 570–620 °C), but deeper for metapelites (2.1–2.3 GPa, 500–570 °C). consistent with that of eclogites, The combined data show that the Alag Khadny complex represents a remnant of a rifted Mesoproterozoic to Neoproterozoic (ca. 1.6–0.96 Ga) continental margin consequently metamorphosed under HP conditions during Late Neoproterozoic–Early Cambrian evolution of the southern Central Asian Orogenic Belt. Acquired P-T estimates imply that high-pressure metagranitoids and metasedimentary rocks equilibrated at different depths, but most likely shared a common subduction-related metamorphic evolution.

Origin of the late Paleoproterozoic low-δ18O A-type granites on the southern margin of the North China Craton and their geodynamic mechanism

A-type granites with 18O-depletion signatures are rather enigmatic as regards not only their typology and petrogenesis but also their rock-forming geodynamic mechanism. Here we report a suite of late Paleoproterozoic low-δ18O A-type granites from the Longwangzhuang pluton on the southern margin of the North China Craton. SIMS zircon U-Pb dating showed that the Longwangzhuang pluton was emplaced at 1613 ± 4 Ma. Combined with previous data, it is clear that the mineral components of Longwangzhuang granites are variable and consist of perthite, quartz, plagioclase, biotite and amphibole (calcic hastingsite, ferroedenite, and sodic ferrogedrite). Geochemically, they are metaluminous to peraluminous and have high alkali contents (K2O + Na2O > 8.76 wt%, K2O/Na2O > 1), FeOt/(FeOt + MgO) (>0.95) ratios, Zr + Nb + Ce + Y (>993 ppm) contents, and 10000 Ga/Al (>4.31) ratios, resembling A-type granites. In-situ oxygen isotope analysis displayed low zircon δ18O values between 4.0‰ and 4.9‰ with a weighted average of 4.4‰. Based on the Archean two-stage zircon Hf and whole-rock Nd model ages coupled with the low (La/Yb)CN ratios, negative anomalies of Eu and Sr, and high Zr saturation temperatures, and the presence of low pressures (3.3–5.7 kbar) amphiboles, the Longwangzhuang A-type granites were generated by “self-cannibalizing” pre-existing low-δ18O old rocks (i.e., the Taihua Complex) and emplaced at shallow depth. Combined with regional geological observations (i.e., coeval tuffites), a passive rift setting was the most plausible explanation for the generation of the late Paleoproterozoic low δ18O A-type granites on the southern margin of the North China Craton. Such a rifting could likely have lasted at least till 1.6 Ga.

The role of melting on the geochemical evolution and isotopic variability of an anatectic complex in the Iberian Variscides

The genesis and evolution of migmatite-granite terranes usually involve several complex petrological and geochemical processes that leave their imprint on elemental and isotopic signatures. In this paper, we assess the role of melting reactions on the genesis of the variscan Figueira de Castelo Rodrigo-Lumbrales Anatectic Complex (FCR-LAC) in the Central Iberian Zone that culminated in the generation of abundant S-type granites. At odds with the proposed for several anatectic complexes elsewhere, here we demonstrate that no isotopic (Sr-Nd-Hf-Pb) disequilibrium occurred in the FCR-LAC, either in the transitions from metatexites to diatexites nor to granites. However, variable contribution of the source minerals generated batches of melts characterized by distinct parent/daughter ratios, which explain the significant heterogeneity of present-day isotopic signatures. While Rb/Sr ratios and the Pb budget of the successively generated lithotypes were mainly controlled by major minerals such as muscovite, K-feldspar and plagioclase, the accessory phases played a major control on the Sm/Nd and Lu/Hf ratios. Our study also demonstrates the existence of two distinct diatexite groups produced by different melting reactions. Type-1 diatexites, having high Rb contents and fractionated HREE, are geochemically akin to the associated S-type granites. They were produced by dehydration-melting of muscovite with production of peritectic K-feldspar, sillimanite and melt. The less abundant type-2 diatexites required influx of external fluids for melting, which consumed more plagioclase than muscovite.Isotopic data reveal the existence of two groups with distinct initial compositions (εNd320 = −5.05 to −6.03 and εHf320 = −3.42 to −4.45 vs. εNd320 = −7.30 to −8.89 and εHf320 = −6.45 to −8.47), both composed of metatexites, diatexites and granites, due to source heterogeneity. The main source of the anatectic complex was the metasedimentary Neoproterozoic – lower Cambrian Douro-Beiras Supergroup, with minor contribution of Ordovician, Ollo de Sapo magmatic rocks.

Charnockites from Carajás Province, SE Amazonian Craton (Brazil): Petrogenetic constraints and intensive crystallization parameters

The gabbronorite-charnockite-granite series rocks in the Carajás Province consist of three granitoid varieties: orthopyroxene granodiorite, clinopyroxene monzogranite and amphibole monzogranite; gabbronorites are spatially associated. They occur as a NE-SW-elongated pluton with minor E-W-oriented lenses. In general, the planar fabrics are defined by a NE-SW to E-W trend and steep dip (70–85°) restricted to shear zones. The main mafic phases are pyroxene and amphibole. Biotite is annite with magmatic and subalkaline signature. Plagioclase includes labradorite and andesine. Amphibole thermometers estimates vary from 713 to 800 °C and 765–809 °C in the granitoids and gabbronorite, respectively. Pyroxenes gave higher temperatures of 1194–1573 °C. The pressures were 190–310 MPa during emplacement. The presence of primary magnetite together with geochemical and amphibole-biotite chemical data argues that the studied rocks have crystallized under oxidized conditions (NNO ± 0.5 and NNO +1). The H2O contents are estimated as higher than 4%. The gabbronorite-charnockite-granite series has magnesian affinity, calc-alkaline to high-K calcic-alkaline trends and metaluminous character. The magnesian and oxidized character is inherited from the source, which was likely extracted from a depleted mantle (low HFSE contents). Geochemical modeling shows that the orthopyroxene granodiorite originated by fractional crystallization from a magma akin to the gabbronorite. Water activity was high in the monzogranites, and hydration had an important role in the magmatic evolution of the gabbronorite-charnockite-granite series. The emplacement of these rocks was controlled by a translithospheric-scale shear zone acting as a preexisting conduit for the migration of mantle-derived magmas to epizonal levels (7.0–10.5 km) in a sinistral transpressive regime in a post-collisional setting. Deep crustal levels favor crystallization of orthopyroxene-bearing rocks (poor water conditions), while at shallower crustal levels fluids tend to be dominant in the magma, leading to the generation of amphibole-bearing granite.

Spatiotemporal distribution, geological characteristics and metallogenic mechanism of tungsten and tin deposits in China: An overview

Tungsten and tin are important strategic and critical mineral resources, as well as one of China’s most abundant mineral resources. Their distribution is mainly concentrated in the South China block, followed by the Kunlun-Qilian-Qinling-Dabie orogenic belt, the Tianshan-Xingmeng orogenic belt, and the Tibet-Sanjiang orogenic belt. The tungsten and tin resources in South China are mainly concentrated in the Nanling tungsten-tin metallogenic belt, the northern Jiangxi-southern Anhui tungsten metallogenic belt, the Youjiang-Guibei tin metallogenic belt, and the southeast coastal tungsten-tin metallogenic belt. The formation of tungsten and tin deposits in China spans a large period of time, from Proterozoic to Cenozoic, but the Mesozoic Yanshanian mineralization is the most important. There are five main types of primary tungsten-tin deposits in China, namely, porphyry, greisen, skarn, quartz vein, and cassiterite-sulfide. In addition, there are also other types such as altered granite, hydrothermal breccia, and low-temperature hydrothermal vein. Many tungsten-tin deposits are often not of a single genetic type, and multiple mineralization types commonly co-exist in a deposit. Most of the granitoids associated with tungsten mineralization are thought to be S-type granite derived from partial melting of continental crustal materials, while the granitoids associated with tin deposits include I-type and A-type in addition to the S-type granite. Crust-mantle interaction plays an important role in generation of the Sn-bearing granites. Nd-Hf isotope studies show that beside the Sn-bearing granites, some W-bearing granites also have mantle-derived contributions. Whether it is W-bearing or Sn-bearing granite, a highly evolved feature is often more favorable for mineralization. The composite granitoids in South China are closely related to multiple tungsten-tin mineralization. Many tungsten and tin deposits in China are often co-produced with mineralization of other rare metals. According to the combination of ore elements, they mainly include the following three types: W-(Sn)-Be (including Sn-Be), W-(Sn)-Nb-a (including Sn-Nb-Ta), and Sn-Li-Rb-Nb-Ta. All of them are closely related to highly evolved peraluminous granites. The source of ore-forming fluids in most tungsten-tin deposits is closely related to magmatic hydrothermal activity, and some deposits also have characteristics of multi-source fluids. The temperature and salinity of ore-forming fluids vary widely, and the composition of the fluid system is also complex in many cases. Oxygen fugacity plays an important role in the transportation and precipitation of tin, but such an effect on tungsten is still in debate. The formation of many tungsten-tin deposits is generally controlled by a number of factors, such as temperature dropping, fluid mixing, fluid immiscibility, fluid boiling, and water-rock interaction.

Origin of peraluminous A-type granites from appropriate sources at moderate to low pressures and high temperatures

Four Triassic plutons from South China exhibit compositional features of S-type granites (high A/CNK values, enriched Sr–Nd isotopic compositions and high zircon δ18O values), but also of A-type granites (alkali-rich and ferroan compositions, high Zr + Nb + Ce + Y contents and high Ga/Al ratios). The S-type-like features suggest a metasedimentary source. However, the exact anatectic processes are poorly known. Here, phase equilibrium modelling on the melting of five representative metasedimentary rocks with contrasting compositions at 0.4–1.2 GPa and FMQ − 1 to FMQ + 1 indicate that the most likely source should have a composition of Mg#<52, A/CNK>1.14, K2O/Na2O<1.90, and K2O + Na2O>5. Two Neoproterozoic volcanic-sedimentary rocks adjacent to the PAGs have compositions that match these requirements, and modelled melts at P≤0.8 GPa and T≥850 °C match the main compositional variables of the plutons. This study highlights that source composition and anatectic P–T conditions are the main factors controlling the generation of peraluminous A-type granites.

Petrogenesis and geodynamic implications of two episodes of Permian and Triassic high-silica granitoids in the Chinese Altai, Central Asian Orogenic Belt

Tectonic transition from post-collision to intraplate settings is a crucial process in orogenic belts. To characterize such a transition in the Chinese Altai, we conduct an integrated study on Permian to Triassic granitoids. Zircon U–Pb dating reveals that the granitoids can be subdivided into two stages: early Permian (291–286 Ma) and late Triassic (216–209 Ma). Granitoids of both two stages exhibit high SiO2, low Mg#, low Cr and Ni contents, and variable Sr–Nd–Hf isotopes, all of which indicate a multiple crustal origin. Generally, the Triassic granitoids have similar εNd(t) but relatively higher εHf(t) values than those of the Permian granitoids. Moreover, the Triassic granitoids possess relatively higher ASI and more variable Al2O3/TiO2, CaO/Na2O, Rb/Sr and Rb/Ba values than those of the Permian granitoids, suggesting that the Triassic magmatic sources were much variable and complicated with higher proportions of sediments. By integrating regional data, two magmatic peaks at Permian and Triassic can also be recognized. From early Permian to Triassic, the SiO2, Na2O + K2O and Th contents, ASI and 87Sr/86Sr, Al2O3/TiO2, Rb/Sr and Rb/Ba values for the felsic rocks gradually increase, implying more and more strongly reworking of continental crust. Also, the Rb, Y + Nb and Yb + Ta concentrations for felsic rocks progressively increase from early Permian to Triassic, demonstrating a geodynamic evolution from syn/post-collision to intraplate settings. Furthermore, we propose that the post-collision and intraplate tectonism, especially the latter, could facilitate the generation of high-silica granites, which drive maturation of continental crust in accretionary orogenic belts.

Mineral chemistry using for evaluation of the Esmaeilabad granite generation in the Posht-e-Badam area (Central- East Iranian Microcontinent)

Mineral chemistry using for evaluation of the Esmaeilabad granite generation in the Posht-e-Badam area (Central- East Iranian Microcontinent)

Origin of cordierite-bearing monzogranites from the southern Central Iberian Zone – Inferences from the zoned Sierra Bermeja Pluton (Extremadura, Spain)

Voluminous peraluminous (biotite, biotite–cordierite and cordierite–muscovite-bearing) granitic plutons were emplaced in the southern part of the Central Iberian Zone (Iberian Massif) during the waning stages of the Variscan Orogeny. The role of the mantle and the nature of the crustal sources involved in the generation of these remarkable granites are still a matter of discussion. To address these issues, a detailed study of the Sierra Bermeja Pluton, a ~60 km2 cordierite-bearing monzogranite intrusion representative of the regional Nisa–Alburquerque–Los Pedroches Magmatic Alignment, has been carried out. This pluton was formed by an inward sequence of three distinct but near contemporaneous magma pulses: Outer Unit (OU), Middle Unit (MU) and Inner Unit (IU). The nested pluton is cut by a number of syn-plutonic vaugneritic dykes, while lamprophyres were distinctly later.The age of the Pluton has been established at ca. 306 Ma (309 ± 3 to 304 ± 3 Ma) by LA-ICP-MS U–Pb dating of zircon and monazite. The peraluminosity (A/CNK = 1.01–1.33) and P2O5 contents (0.19–0.35 wt%) of the monzogranitic units increase inwards (OU → MU → IU). This is accompanied by an overall decrease in TiO2, MgO, CaO, and FeOt, and most trace-elements, including REE. The three units display similarly low 87Sr/86Sr306Ma ratios (0.7033–0.7046) but decreasing εNd306Ma (OU: ~ −2.7, MU: ~ −3.8, IU: −7.5 to −4.7). Vaugneritic rocks have homogeneous composition with similar 87Sr/86Sr306Ma ratios (~0.7043) to those of the monzogranites but higher εNd306Ma (~ +1.1) values. Whole-rock geochemical data imply a partial melting of mainly Cambro–Ordovician felsic metaigneous rocks (OU) with increasing proportion of Neoproterozoic–Lower Cambrian metasediments of the Schist–Greywacke Complex (MU) that formed, almost exclusively, the source of the IU. Thermobarometric data suggest that melting processes progressed upward through the geological record and magma emplacement took place at <3 kbar, with crystallization temperatures of 710–810 °C. Geochemical modelling implies that each monzogranitic unit could have evolved independently at the emplacement level by a 20–26% fractional crystallization of a mineral assemblage constituted by Kfs + Pl > Bt >> Ap + Mnz + Xtm. The present results could be extensible to other cordierite-bearing granites of the southern Central Iberian Zone although forthcoming experimental work and detailed comparisons are required to confirm such extrapolation.

From migmatite to magma - crustal melting and generation of granite in the Camboriú Complex, south Brazil

Partial melting of continental crust and granite genesis were investigated in the Camboriú region, south Brazil. Structural geology and geochemistry were used in order to characterize the link between the high Ba-Sr Itapema Granite (IG) and the syntectonic melting of orthogneisses and amphibolites of the Camboriú Complex (CC). The IG is a sheet-like intrusive body of biotite monzogranite to granodiorite with large amount of migmatitic amphibolite and gneiss xenoliths, and a well-developed magmatic foliation concordant with the main gneissic banding. Discordant, m-thick granitic dykes which crosscut the migmatitic sequence and transport magma and xenoliths to feed the IG main body mark the transition from the migmatitic to the magmatic system within the complex. Whole-rock geochemical data reveal important contamination and assimilation processes of xenoliths during IG magmatic flow which give rise to different facies and geochemical signatures. The generation of the IG is an example of a continuous exposure from source to sink formed through a continuous and efficient deformation-driven melting/extraction/transport system generated during coeval folding and anatexis of the CC metamorphic sequence.