Evidence For Magma Mixing Research Articles

Petrogenesis of microgranular enclaves in the A-type granitoid Krasnopol intrusion (Mazury Complex, northeastern Poland): Evidence of magma mixing

The origin of magmatic microgranular enclaves has been investigated in the Mesoproterozoic granitoid Krasnopol intrusion (1.5 Ga), part of the AMCG (anorthosite–mangerite–charnockite–granite) Mazury Complex in the East European Craton (NE Poland). The granitoids are ferroan and metaluminous, and display the typical characteristics of A-type granites, with high contents of Zr, Nb, Ga and rare earth elements (REEs). The enclaves are metaluminous and have a broad compositional range with two groups distinguished: silica-poor (45–50 wt% SiO2) and silica-rich (54 to 59 wt% SiO2), the latter overlapping in composition with the granitoid samples. The silica-poor enclaves are enriched in REEs compared to the silica-rich type, while the silica-rich enclaves exhibit trace-element patterns similar to those of the granitoids. Initial whole rock εNd values range between -3.8 and -4.0 for the granitoids and give a slightly wider range from -2.6 to -3.8 for the enclaves. The 87Sr/86Sr initial values vary from 0.7084 to 0.7138 for the granitoids and between 0.7052 and 0.7075 for the enclaves and indicate that the granitoids and enclaves are not isotopically identical. These may suggest that the two magmatic systems represented by the granitoid host rock and the enclaves, were probably derived from different sources, but with sufficient interaction, which led to a progressive change in the composition of the enclaves towards intermediate composition. We suggest that the mafic melts of the enclaves were generated at the base of the thickened crust through partial melting of the lower crustal source, with a significant contribution from mantle material. The increase in temperature resulted in anatexis of the lower crust and the formation of the granitoid parental magma.

A Mush-Facilitated Magma Mixing Process Revealed by Complex Zoning of Plagioclase in Mafic Magmatic Enclaves of the Early Cretaceous Sanguliu Granitic Pluton, East China

Abstract Mafic magmatic enclaves (MMEs) hosted in granitic plutons are ideal to investigate the role of mushes on magma mixing processes in crustal magma chambers. However, the petrographic evidence for mixing of magmas through infiltration and percolation in coexisting mushes and magmas is desired. Here, we describe complex zoning patterns of plagioclase in the MMEs hosted in the monzogranite of the Early Cretaceous Sanguliu pluton in East China to reveal a mush-facilitated magma mixing process. The MMEs appear as round to oval nodules about 10 to 20 cm in size and show diverse disequilibrium textures. Plagioclase in the MMEs can be identified as three populations (Plag1, Plag2, and Plag3) with distinct zoning patterns, anorthite contents (XAn) and initial Sr isotopic ratios (87Sr/86Sri). Plag1 is antecryst displaying normal zoning with An42–67 in the core and An20–36 in the mantle. The core of Plag1 shows coarse sieve texture with high-frequency oscillation in the margin, and the mantle displays resorption surface and patchy zoning. Plag2 is also antecryst with An23–66 in the core and An21–35 in the mantle. However, its core can be further recognized as Core I inside and Core II outside with distinctly different An23–43 and An44–66, respectively, showing reverse zoning. In addition, Core I contains aligned biotite inclusions and Core II shows sieve texture, resorption surface and patchy zoning. Amphibole inclusions are sporadically enclosed within Core I of Plag2 (Amp1) and mantles of Plag1 and Plag2 (Amp2), but rarely observed in Core II of Plag2. Plag3 is anhedral grain in the matrix and shows core-rim texture with An20–37 in the core. The three plagioclase populations all exhibit angular rims with resembling An9–22. Plag1 core and Plag2 Core II have (87Sr/86Sr)i (0.70920 to 0.71092) similar to the bulk (87Sr/86Sr)i of the mafic dykes intruding the Sanguliu pluton, and likely crystallized from basaltic andesitic magmas. In contrast, the rims of Plag1, Plag2, and Plag3 overall have (87Sr/86Sr)i (0.71391 to 0.71583) nearly identical to the (87Sr/86Sr)i of host monzogranite and the plagioclase in the monzogranite, likely crystallized from granitic magmas. The mantles of Plag1 and Plag2 and the core of Plag3 have (87Sr/86Sr)i (0.71141 to 0.71390) overlapping the (87Sr/86Sr)i of the MMEs, and may have crystallized from mixed melts. Calculation results based on amphibole thermobarometers show that Amp1 crystallized at ~775 °C and ~ 16 km depth, whereas Amp2 and the amphibole in the matrix of the MMEs and monzogranite crystallized at 730 to 744 °C and 8 to 9 km depth. We thus propose that the chemical and textural complexity of the three plagioclase populations in the MMEs can be attributed to that the MMEs may have come from a mushy hybrid layer that was developed through a molten granitic body being recharged by upwelling basaltic andesitic magma. Core I of Plag2 may have nucleated and grown from andesitic magma that was evolved from the basaltic andesitic magma from which the core of Plag1 and Core II of Plag2 crystallized. The two types of antecrystic plagioclase then may have experienced resorption and disequilibrium growth in the hybrid layer, and finally rimmed with ambient, evolved interstitial melt within mushy MMEs. This study shows that complex zoning patterns and compositions of plagioclase populations in the MMEs hosted in granitic plutons have important bearings on mush-facilitated magma mixing processes.

The ~1.1 Ga St. Ignace Island complex, Northern Ontario, Canada: Evidence for magma mixing and crustal melting in the generation of Midcontinent Rift-related bimodal magmas and implications for regional metallogeny

Abstract The St. Ignace Island complex in Northern Ontario is a package of dominantly felsic rocks emplaced within the upper portions of the Osler Volcanic rocks of the ~1.1 Ga Midcontinent Rift System. The Osler volcanic rocks are predominantly tholeiitic basalts intercalated with rare interflow sediments and rhyolites. The St. Ignace Island complex is a ~26 km2 stock with a felsic core of quartz-feldspar-phyric rhyolites and dacites and an outer ring of anorthosite and gabbro. Textures at a variety of scales within the rocks of the complex show clear evidence of the mingling and mixing of partially crystallized mafic and felsic liquids. Two multigrain (zircon/baddeleyite) fractions from a sample of the gabbro define a Discordia line with an upper intercept date of 1107±8.9 Ma. The core of the complex consists of dacites and rhyolites with similar REE abundances with negative Nb anomalies whereas the surrounding mafic rocks are gabbros to monzogabbros that are less LREE-enriched than the felsic rocks but with similar HREE. Felsic units have a narrow range of 87Sr/86Sri (0.7032-0.7045) and 143Nd/144Ndi (0.51051-0.51057) whereas the mafic end members have similar 87Sr/86Sri (0.7040-0.7061) but more radiogenic 143Nd/144Ndi (0.51067-0.51085). Very well-preserved silicate melt inclusions (MI), many completely glassy, were observed in quartz, clinopyroxene and some plagioclase phenocrysts from the complex. These represent some of the oldest unrecrystallized silicate melt inclusions described to date. Melt inclusions within quartz from the felsic volcanics are broadly rhyolitic in composition whereas MI from plagioclase in the mafic volcanics range from basalt to basaltic andesite; these felsic and mafic melt compositions are interpreted to represent the end-member liquids in the system and bulk rock analyses affirm mixtures of the two. Concentrations of Cu and Ag (in both mafic and felsic MI), and Mo (in felsic MI), are up to an order of magnitude higher in the mafic and felsic MI than in continental crust. Bulk rock metal concentrations are also significantly lower than in the MI, suggesting that the melt inclusions may preserve pre-eruptive metal tenors that were subsequently modified by sulfide saturation, degassing, or post-solidus hydrothermal alteration. The whole rock and MI geochemistry of the St. Ignace complex are broadly similar to the Central Osler Group and, given the broad similar ages, suggests they may have been derived from a similar mantle source, but distinct from the source of rhyolites in the Black Bay Peninsula. The negative Nb anomalies and negative εNd values for the St. Ignace complex are consistent with mixing with older continental crust during ascent and emplacement. The rocks of the St. Ignace Island complex likely formed as the result of emplacement of a large mafic magma chamber at the base of the Osler volcanic pile that triggered partial melting to generate the rhyolite end members. The felsic melts ascended to shallower levels in the crust where they mixed with mafic magmas derived directly from the deeper chamber. Generally, melt inclusions in the complex have very high Cu and Ag contents, similar to those observed in arc-related and extremely oxidized early rift-related rocks and may account for the world-class volcano-sediment-hosted Cu-(Ag) deposits within the rift and the presence of small porphyry-style deposits.

Potential flare-ups and lulls in the multi-stage magmatism of the Dom Feliciano belt, southern Brazil: Evidence from geochemistry and isotopic data

The genesis of Precambrian granitic batholiths related to supercontinent assembly is controversial, especially regarding their generating processes and tectonic settings. The present study focused on the Pelotas Batholith (Magmatic-arc domain) of the Dom Feliciano Belt, which comprises the southern segment of the Mantiqueira Province in southeastern South America. New U–Pb and Lu–Hf zircon data from plutonic rocks with evidence of magma mixing and mingling, as well as assimilation of wall rocks, suggest multi-stage magmatism related to flare-up episodes of intense magmatism, potentially triggered by changes in the tectonic setting. U–Pb zircon analyses yielded crystallization ages of granodioritic gneiss xenolith at 691.5 ± 7 Ma, microgranodiorite xenolith at 645.9 ± 3.7 Ma, host monzogranite at 634.4 ± 4.4 Ma, and intrusive syenogranite at 620.1 ± 4.7 Ma, all intruded by syenogranitic pegmatite at 606.9 ± 1.7 Ma. Other analyses were performed on calc-alkaline granite (633 ± 4 Ma) and peraluminous granite (609.6 ± 2.2 Ma). The Lu–Hf data highlights a model age interval ranging from 1.7 to 1.3 Ga with εNd values between −4 and 1, except for the pegmatite sample which also includes Paleoproterozoic and Archean model ages (3.3-1.6 Ga) and εNd values between −33 and −1. Furthermore, the acquired data, together with the gathered dataset Dom Feliciano Belt granites, emphasizes a contribution from slightly juvenile to crustal sources, with model ages ranging primarily from Statherian-Orosirian to Mesoproterozoic. Signature patterns are consistent with sources from African basement rocks.

Magma mixing affected the Late Triassic porphyry mineralization in the Yidun arc in SW China

The Yidun arc was formed by the westwards subduction of the Garze-Litang Ocean in the Late Triassic. It trends from near north to south. Many intermediate-acid intrusions became widely distributed in the Yidun arc during this period. Large to super-large porphyry-skarn deposits developed only in the southern Yidun arc, with no corresponding deposit in the northern part. It has been found that some mafic microgranular enclaves (MMEs) are exposed, and there is certain evidence of magma mixing in the Yidun arc in recent years. To clarify the relationship between widely developed magma mixing and metallogenic differences in the Yidun arc, the zircon U-Pb dating and geochemistry of quartz monzonite porphyry (QMP) and its MMEs in the Pulang super-large porphyry Cu deposit in southern Yidun have been carried out. Then, the granodiorite (GD, ore-barren) and MMEs of the Daocheng batholith in the middle and the Cuojiaoma batholith (ore-barren) in the north of the Yidun arc were compared. The results show that the oxygen fugacities of the Pulang QMP and MMEs are higher, and the MMEs are slightly higher than those of the QMP overall. The oxygen fugacity of MME in the Daocheng GD is slightly higher than that of FMQ, but it is still lower than that of QMP and MME in Pulang. That is, the magmatic oxygen fugacity of the Daocheng GD is lower than that of the Pulang QMP and MME. There are more magmas fractionated in the south than in the north of Yidun due to the difference in geological structure between the north and south. Therefore, the degree of magma mixing is gradually reduced in the Yidun arc from south to north (Pulang, Daocheng to Cuojiaoma), and the metallogenic potential is also higher in the south and lower in the north.

Geochronology and petrogenesis of granitoids and associated mafic enclaves from Ghohroud in the Urumieh–Dokhtar Magmatic Arc (Iran): Evidence for magma mixing during the closure of the Neotethyan Ocean

The Ghohroud granitoids (GG), containing mafic microgranular enclaves (MMEs) are located in the central part of the Urumieh‐Dokhtar Magmatic Arc (UDMA) in central Iran. They are associated with the subduction‐related magmatism in the Alpine‐Himalayan orogenic belt. The GG are comprised of a variety of intermediate and felsic rocks, including tonalite, granodiorite, granite, diorite porphyry and monzodiorite. The MMEs are gabbroic diorite and tonalite in composition and characterized by a fine‐grained hypidiomorphic microgranular texture with occasional chilled margins. They show rounded, sharp or irregular contact with the host granitoids. The occurrences of quartz, K‐feldspar and corroded plagioclase indicate that MMEs are the products of mixing between mantle and crust‐derived magmas. New ages of zircon U–Pb dating reveal that the GG in the Kashan area emplaced at ca. 19–17 Ma (Burdigalian). All the samples of MMEs and granitoid host rocks in this study are metaluminous and calc‐alkaline with I‐type affinities. They are enriched in light rare earth elements (LREEs) and show slight negative Eu anomalies (Eu/Eu* = 0.36–0.95). These features in a combination with the relative depletion in Nb, Ta, Ti and P, indicate the granitoids and MMEs are closely associated with subduction‐related magmas at an active continental margin. The host rocks yield relatively homogeneous isotopic compositions of initial 87Sr/86Sr ratios ranging from 0.706036 to 0.707055, εNd(t) values varying from −2.25 to 0.8, and the Nd model ages (TDM) vary in a limited range of 0.70–0.96 Ga. The MMEs show similar initial 87Sr/86Sr ratios (0.706420–0.707366), εNd(t) values (−1.32 to −0.27), TDM (0.68–1.09 Ga) and Pb isotopic compositions with host granitoids, which imply they attained isotopic equilibration during magma mingling and mixing. In combination with the petrographic, chemical and isotopic results, we suggest that the origin of MMEs and their host rocks were related to the interaction between crust‐derived melts and mantle‐derived mafic magmas. The magma‐mixing event possibly occurred during the transition from subduction to collision in the UDMA along with the closure of the Neotethyan ocean.

Multiple sources and multi-stage emplacement of the Esperança Granitic Complex and its relationship with the Patos – Campina Grande shear zone system, Borborema Province - NE Brazil

Expressive granitic magmatism and a complex system of transcurrent shear zones are the main features associated with the Ediacaran evolution of the Borborema Province (northeastern Brazil). Their petrogenesis and relationships with tectonic structures can provide important insights into lithospheric processes during the collisional to post-collisional stages of the Brasiliano Orogeny. The Esperança Complex is a NE-trending elongated granitic batholith with ca. 650 km2 comprising five plutons emplaced between the Patos and Campina Grande dextral shear zones in the central–eastern part of the Borborema Province. An integrated study of the complex was carried out using UPb zircon SHRIMP and LA-ICPMS geochronology, mineral and whole-rock geochemistry, and NdHf isotope geochemistry (whole-rock and zircon). The plutons are metaluminous to slightly peraluminous with geochemical and isotopic signature reflecting different sources. The Remigio and Areial plutons have Paleoproterozoic to Neoarchean Nd and Hf TDM model ages and strong negative εNd(t) (−15.29 to −16.71) and εHf (−12.20 to −21.03) values. Their geochemistry is compatible with derivation through partial melting of mafic to intermediate metaigneous sources like the Paleoproterozoic basement (Areial pluton) and metasedimentary sources (Remígio pluton). The Puxinanã, Serrote da Cobra and Pocinhos plutons show higher ɛNd (−5.90 to −7.35) and ɛHf (−2.83 to −6.91) values, and Statherian to Calymmian Nd and Hf TDM model ages, ranging from 1.4 to 1.7 Ga and from 1.6 to 1.8 Ga, respectively. They have geochemical affinity with A-type ferroan granites. The geochemical and isotopic signature are similar to those of Tonian orthogneiss that constitute part of the plutons' host rocks, suggesting derivation from Tonian crustal sources. Evidence of magma mixing and the presence of inherited zircon grains with ages like those of metasedimentary host rocks suggest contribution of the lithospheric mantle and sedimentary sources in different proportions in their petrogenesis. The reported data are compatible with building of the Esperança Complex by multiple intrusive events. The Pocinhos and Serrote da Cobra plutons are the oldest (~600 Ma) and their genesis is probably associated with heat input resulting from crustal thickening at the end of a long contractional period (ca. 630–600 Ma). The genesis of the Puxinanã and Areial plutons (~585 to 565 Ma) involved interactions of crustal and mantle mafic melts, with magma transport and emplacement controlled by the Campina Grande shear zone at the beginning of the transcurrent regime. The Remígio pluton is the youngest intrusion (~565 Ma) and its genesis can be related to a high geothermal gradient resulting from emplacement of the older plutons, possibly enhanced by strain heating related to displacement along the Patos shear zone.

Evidence for magma mixing during Triassic magmatism in West Qinling, China: Constraints from petrology, geochemistry, U–Pb zircon geochronology, and Sr–Nd–Hf isotopic of the Baguashan pluton

The West Qinling Orogen, which forms the western part of the Qinling Orogenic Belt, is characterized by the voluminous distribution of Triassic granitoids. Here, we investigate the Baguashan monzogranite which hosts numerous mafic microgranular enclaves (MMEs). We present zircon U–Pb–Hf and whole‐rock geochemical as well as Sr–Nd isotopic data of the monzogranites and MMEs with a view to gain insights on the petrogenesis and geodynamic setting. Zircon LA‐ICP‐MS U–Pb dating yields ages of 219.0 ± 1.7 Ma and 219.5 ± 1.6 Ma for the MMEs, and 214.2 ± 1.3 Ma for the host monzogranite, suggesting formation from coeval magmas. The host monzogranites show high SiO2, Rb, Ba, and Th contents, but low TiO2, MgO, P2O5 values, with A/CNK of <1.1. Zircon grains from monzogranites show εHf(t) values in the range of −6.3 to +3.2 with corresponding two‐stage Hf model ages (TDM2) of 1.39–2.25 Ga. The MMEs are mostly elliptical or spherical in shape and have lower SiO2 and Th contents, but higher MgO, TiO2, and CaO, and εHf(t) values ranging from −6.1 to +5.7 with TDM2 of 1.17–2.23 Ga. The Sr–Nd isotopic data for MMEs and monzogranites show (87Sr/86Sr)i ratios ranging from 0.7059 to 0.7069 and low εNd(t) values ranging from −6.07 to −4.18, suggesting a crustal origin. Based on the relatively homogeneous Sr–Nd–Hf isotopic compositions, we suggest that the MMEs represent magma mixing, and the mafic magma injected into the felsic magma chamber was probably derived by the reworking of mafic lower crust with a contribution of juvenile materials. We propose a model involving delamination of thickened lower crust below the West Qinling Orogen after the collision between the North China Block and the South China Block in the Late Triassic. Subsequently, the lower crust was partially melted by the heat input from the upwelling asthenosphere and produced the mafic magma. Partial melting of the ancient metamorphic rocks generated the granitic magma. The interaction of mafic and felsic magmas occurred within a post‐collisional tectonic setting in the Late Triassic.

Neoproterozoic high magmatic addition rate episode building a composite batholith in northeastern Brazil, and implications for the western Gondwana assembly

The composite Santana do Ipanema batholith is made up of several Cryogenian-Ediacaran granitic plutons in the Pernambuco-Alagoas (PEAL) Domain of the Borborema province, northeastern Brazil. The individual plutons in this batholith are high-K calc-alkalic to shoshonitic, metaluminous to peraluminous quartz syenites to granites that belong to magnetite-series and magnesian Cordilleran-type granitoids. They carry comagmatic microgranular mafic enclaves with evidence of magma mixing. Their chemical compositions overlap, and they exhibit enrichment in some incompatible and depletion in HFS elements, with variable initial 87Sr/86Sr ratios that range from 0.70511 to 0.71071. The εNd(0.6Ga) values cluster into two groups, in which plutons with ages ≥ 625 Ma exhibit slightly negative to slightly positive εNd values (average −1.6), in contrast with the younger plutons that have more negative ones (average −8.7), pointing out that mantle contribution to the source decreased with time, while recycled ancient crust augmented. Geochronological data from the literature indicate that the batholith has been constructed by continuous amalgamations of successive magma pulses via diking for ~30 m.y., with no large crystallization age gap among the plutons. A magma supply rate of 0.003 m3/year is estimated considering this batholith together with two other nearby composite batholiths of similar age in the PEAL Domain, and low volcanic-plutonic ratio. This rather high magmatic addition rate episode has been probably triggered by extensive and repeated basaltic underplating stalled in the lower crust in the magmatic arc formed during the convergence of the São Francisco craton and the Pernambuco-Alagoas block in the course of the western Gondwana amalgamation.

Spatiotemporal constraints on the western Cauaburi Belt tectonics – northwestern Amazon Craton, Brazil

ABSTRACT The study of Precambrian tectonics is an intricate task, demanding a holistic approach to take an accurate view of geologic history. Here we attempt to set up the overview of an Orosirian-Statherian continental arc in the northwestern Amazon Craton, the Cauaburi Belt. Field relations, petrological, geochemical, and geochronological data of calc-alkaline metagranitoids, high-grade metasedimentary rocks, and peraluminous metasyenogranites yielded new interpretations about its tectonic evolution. The record of intense and episodic calc-alkaline magmatism between ca. 1805 and 1759 Ma, assign to the Cauaburi Complex, with field evidence of magma mixing and lodgement in a compressional tectonic regime, suggest a continental arc as the tectonic setting. During the magmatic lulls, deformation and metamorphism increase, culminating with the partial fusion of the high-grade metasedimentary rocks of the Taiuaçu-Cauera Complex. This succession composes the precursor paleobasin, presenting maximum and minimum depositional ages of 1819 and 1794 Ma, and was a relevant source for the calc-alkaline magmatism. The geochronological record of a low-volume production of peraluminous crustal rocks (Igarapé Tocandira Granite), with crystallization age at ca. 1791 Ma and metamorphic age at ca. 1771 Ma, also highlights the time and effect of the magmatic lulls. The Cauaburi Belt structural framework follows a general E-W to ENE-WSW trend, expressed in the Paleoproterozoic rocks as syn-magmatic and solid-state deformation fabrics. Assuming that Columbia Supercontinent nucleus assembled in the late Orosirian, we interpret that this coeval continental arc developed at its border and followed a north-south shortening direction, at current orientation.

Petrology, geochemistry, and zircon U–Pb isotopes of Xintian Complex in Yanbian area, Northeast China: Evidence for magma mixing and geodynamics processes

Mixing/mingling of magmas is an important mode of magmatic evolution, crust–mantle interaction, and compositional exchanges, and the mafic microgranular enclaves (MMEs) in the host granites are commonly generated by the injection of hot mafic magmas into felsic reservoir at the crustal level. However, the exhaustion of most mafic melts causes the absence of the critical mantle marks after homogenization. The Xintian Complex in Yanbian area is composed of the gabbro diorite and granitic rocks enclosing the abundant MMEs, which likely provides the significant, but rare mantle end‐member information. On the basis of geochronology study, both MMEs (126.3 ± 1.2 Ma) and granodiorite (126.0 ± 2.0 Ma) were formed in the Early Cretaceous, which is coincident with the earlier emplacement of gabbro diorite (128.5 ± 1.0 Ma) within the errors. Geochemically, all of these distinguished phases have arc affinities related to subduction of oceanic slabs. Nevertheless, the dominant granodiorite rocks, typical high‐K calc‐alkaline I‐type granites, have the source of partial melting of mafic lower crust modified by subducted sediment melts, with additions of mafic melts as indicated by high Mg# values (48–56) and special textures (acicular apatite and re‐equilibrium plagioclase) of minerals in the hosted MMEs. In contrast, gabbro diorites are typical of calc‐alkaline affinities with deficit of the incompatible Zr and Hf, which were formed by re‐melting with low degree (3–10%) of mantle wedges metasomatized by subduction fluids with the crystallization of dominant pyroxene minerals. However, the MMEs is characterized by higher SiO2 (55.71–56.02 wt%), Cr (546–569 ppm), Ni (83.7–92.8 ppm), MgO (6.03–6.63 wt%), and heavy rare earth element (HREE) (546–569 ppm) with weak enrichment in Zr and Hf and lower (La/Yb)N values (17.98–20.93) compared to gabbro diorite. Therefore, the MMEs and host granodiorite are the products of heterogeneous mixing of weakly evolved mafic melts and subsolid felsic melts in the shallow storages, and this crust–mantle interaction is under a back‐arc extensional setting related to rollback of subducting palaeo‐Pacific slab.

Temporal change of Barujari Volcano magmatic process: Inferred from petrological study of erupted products since AD 1944

Barujari volcano is an active volcano located in Lombok Island Indonesia. The volcano is a part of post caldera stage of Rinjani volcano. The volcano shows strombolian to vulcanian type eruption and produces mainly lava with basaltic-andesitic composition (54-56 wt% SiO2). The volcano actively erupts several times during past 70 years. However, temporal change of its petrological characteristic has not been discussed. This paper discusses petrological changes in Barujari volcano erupted material through time from AD 1944 to 2015. Total 31 samples erupted from AD 1944, 1966, 1994, 2004, 2009, and 2015 are observed and analyzed with XRF method. Our study shows that most of samples can be classified into basaltic trachy-andesite with 53-56 wt% SiO2. All samples show nearly linear trend in harker diagram and shows no systematic change through time. However, AD 1966 shows curved trend and more silicic composition compared to other samples. We suggest that magma mixing with repeated injection of more mafic magma play an important role in producing most of basaltic-andesitic Barujari lava as suggested by linear trend of harker diagram and appearance of heterogeneity in groundmass. AD 1966 samples also contain evidence of magma mixing but curved trend does not suggest simple mixing processes. Appearance of olivine-poor samples in SiO2 rich AD 1966 samples might suggest more close system differentiation process that mixed with common Barujari products.

Zircon U–Pb geochronology, major-trace elements and Sr–Nd isotope geochemistry of Mashhad granodiorites (NE Iran) and their mafic microgranular enclaves: evidence for magma mixing and mingling

ABSTRACT Mashhad granitoids and associated mafic microgranular enclaves (MMEs), in NE Iran record late early Mesozoic magmatism, was related to the Palaeo-Tethys closure and Iran-Eurasia collision. These represent ideal rocks to explore magmatic processes associated with Late Triassic closure of the Palaeo-Tethyan ocean and post-collisional magmatism. In this study, new geochronological data, whole-rock geochemistry, and Sr–Nd isotope data are presented for Mashhad granitoids and MMEs. LA–ICP–MS U–Pb dating of zircon yields crystallization ages of 205.0 ± 1.3 Ma for the MMEs, indicating their formation during the Late Triassic. This age is similar to the host granitoids. Our results including the major and trace elements discrimination diagrams, in combination with field and petrographic observations (such as ellipsoidal MMEs with feldspar megacrysts, disequilibrium textures of plagioclase), as well as mineral chemistry, suggest that MMEs formed by mixing of mafic and felsic magmas. The host granodiorite is a felsic, high K calc-alkaline I-type granitoid, with SiO2 = 67.5–69.4 wt%, high K2O (2.4–4.2 wt%), and low Mg# (42.5–50.5). Normalized abundances of LREEs and LILEs are enriched relative to HREEs and HFSEs (e.g. Nb, Ti). Negative values of whole-rock εNd(t) (−3 to −2.3) from granitoids indicate that the precursor magma was generated by partial melting of enriched lithospheric mantle with some contributions from old lower continental crust. In the MMEs, SiO2 (53.4–58.2 wt%) is lower and Ni (3.9–49.7 ppm), Cr (0.8–93.9 ppm), Mg# (42.81–62.84), and εNd(t) (−2.3 to +1.4) are higher than those in the host granodiorite, suggesting a greater contribution of mantle-derived mafic melts in the genesis of MMEs.

Evolution of Magma Plumbing System in Miyakejima Volcano: Constraints From Melting Experiments

AbstractThe evolution of the magma plumbing system of Miyakejima volcano, an island arc basaltic volcano located on the volcanic front of the Izu arc, Japan, was investigated by combining (i) melting experiments of hydrous basaltic magma, (ii) analysis of melt inclusions in the volcanic rocks, and (iii) thermodynamic modeling using the thermodynamic program (MELTS) to understand the temporal evolution of the magma plumbing system. Basalts of the Ofunato Stage (10,000–4,000 year BP) show limited compositional variation without evidence of magma mixing, and seem to be parental to volcanic rocks of later stages. Hydrous melting experiments were conducted using the Ofunato Scoria (OFS), which represents the most undifferentiated basaltic magma during the past 10,000 years. The magma chamber conditions required to crystallize the phenocryst assemblage of the OFS were constrained to ~150 MPa, ~1100 °C, and ~3 wt% H2O in melt. The constrained H2O content is consistent with H2O content of olivine‐hosted melt inclusions in the OFS. Here we propose that a simple magma plumbing system existed beneath Miyakejima volcano during the Ofunato Stage, comprising a single magma chamber. The MELTS calculations show that andesites of the Tsubota Stage (4,000–2,500 year BP; representing the later part of the Ofunato Stage after a period of dormancy of 3,000 years), can be derived from the Ofunato basalts, provided that H2O content in magma is <1 wt%. The results of modeling indicate that a new magma chamber formed at a shallower depth after the Ofunato Stage, in which the differentiation of degassed basaltic magmas occurred.

Petrology, geochemistry, and zircon U–Pb–Hf isotopes of Late Triassic enclaves and host granitoids at the southeastern margin of the Songnen–Zhangguangcai Range Massif, Northeast China: Evidence for magma mixing during subduction of the Mudanjiang oceanic plate

We report zircon U–Pb ages and geochemistry (major and trace elements, mineral compositions, and Hf isotopic compositions) for the Hailin pluton in the southeastern Songnen–Zhangguangcai Range Massif, northeastern China, to constrain the role of magma mixing in its petrogenesis and to reconstruct the tectonic evolution of the Mudanjiang Ocean. Zircon U–Pb dating yields ages of 215 ± 1 Ma, 217 ± 1 Ma, and 219 ± 1 Ma for the host granitoids of the Hailin pluton, and 221 ± 1 Ma for mafic microgranular enclaves (MMEs) within the granitoids, indicating they were emplaced coevally. The host granitoids are characterized by 63.18–70.44 wt% SiO2 and 0.69–1.94 wt% MgO, and are depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti) and heavy rare earth elements (HREEs), and enriched in large ion lithophile elements (LILEs; e.g., Rb, Sr, and Ba) and light rare earth elements (LREEs). The zircons in the host granitoids yield two-stage model ages of 1058 Ma to 1770 Ma, together with εHf(t) values of −6.6 to +3.1. These results indicate that the host granitoid magmas were generated by partial melting of Mesoproterozoic lower crust contaminated by ancient crustal material. The MMEs have a restricted SiO2 range (47.61–57.4 wt%), high contents of Ni, Co, and Cr, and high Mg# values (42–54). They have higher Fe2O3T, MgO, Cr and Co contents than the host granitoids, as well as higher total rare earth element (REE) concentrations. Their REE patterns are sub-parallel to those of the host granitoids, characterized by enrichments in LILEs and LREEs, and depletions in HFSEs and HREEs. Zircons from two samples of the MMEs yield single-stage Hf model ages of 666–1077 Ma and εHf(t) values of −5.4 to +5.2. The geochemical characteristics of the MMEs are similar to those of the host granitoids, indicating crust-mantle interaction during their formation. The mafic magmas were derived from melting of depleted lithospheric mantle that had been metasomatized by slab-derived fluids. MMEs are common in the host granitoids and are characterized by irregular spheroidal shapes, with sharp, rounded, or irregular transitional contacts, acicular apatites, and plagioclase reverse zoning, suggesting the importance of magma mixing during petrogenesis. Our geochemical and isotopic data suggest that the Late Triassic Hailin pluton formed by the mixing of felsic and mafic magmas in an active continental margin setting, closely related to the westward subduction of the Mudanjiang oceanic plate beneath the Songnen–Zhangguangcai Range Massif.

Geochemistry, petrogenesis and tectonic setting of middle Eocene hypabyssal rocks of the Torud–Ahmad Abad magmatic belt: An implication for evolution of the northern branch of Neo-Tethys Ocean in Iran

The Torud–Ahmad Abad magmatic belt is located in the south-southeast of Shahrood (East of Semnan Province, NE Iran) and lies in the northern part of the Central Iran Structural Zone (CISZ), where a thick sequence of Paleocene to middle Eocene volcanic and volcanosedimentary rocks cropped out. This sequence was intruded by numerous dikes, hypabyssal igneous domes and one small gabbrodioritic intrusion, with compositions ranging from trachybasaltic andesite, trachyandesite, dacite, trachyte, gabbro, diorite and syenite. Various enclaves (cogentic and noncogenetic) with different composition, size and shape have been found in these domes and dikes. These enclaves are evidence of magma mixing and crustal contamination. Geochemically, the studied rocks exhibit a calc-alkaline to high potassium calc-alkaline affinity, and are enriched in LREE and LILE and depleted in HREE and HSFE. Other geochemical characteristics, such as a silica content varying between 59–63wt% and 51–59wt%, a Na2O content >3wt%, Al2O3 content>16wt%, Yb<1.8ppm, and Y<18ppm, make it possible to classify these rocks as high silica adakite in the Ahmad Abad region and low silica adakite in the Sahl-Razzeh region or at least, adakitic like rocks. Also, depletion of Nb and Ti, and high enrichment in Rb, Ba, K and Th, imply crustal contamination of the mentioned adakitic domes. The petrographical and geochemical evidence show that the magma forming of the high silica adakites has been originated from partial melting of the subducted oceanic slab of Neo-Tethys (Sabzevar–Darouneh branch) in amphibolite to eclogite facies and the low silica adakites formed by partial melting of the metasomatized or modified mantle wedge, above the subduction zone. Gabbroic to syenitic rocks are the products of fractional crystallization of basic magma which originated from a nearly non-modified mantle wedge above the subducted oceanic slab. U-Pb dating of the dacitic and andesitic rocks belong to hypabyssal rocks yielded age of 41.4±0.3Ma, and 35.5±0.2Ma respectively and consistent to Middle to Late Eocene.

Cogenetic origin of mafic microgranular enclaves in calc-alkaline granitoids: The Permian plutons in the northern North China Block

Mafic microgranular (microgranitoid) enclaves (MMEs) with fine-to medium-grain–size igneous microstructures are abundant in Permian granitoid plutons in the northern North China Block (NCB). They are mainly dioritic in composition with SiO 2 contents from 51.0 wt% to 62.7 wt% and are contiguous with their host granitoids (SiO 2 = 60.4–68.4 wt%). Their main mineral assemblage of plagioclase (oligoclase and andesine), hornblende, biotite, K-feldspar, and quartz is similar to that of their host granitoids but with different mineral proportions. Zircon laser ablation–inductively coupled plasma–mass spectrometer (LA-ICP-MS) U-Pb dating, hornblende-plagioclase thermobarometry, and Ti-in-zircon thermometry results show that the crystallization ages and pressure-temperature ( P-T ) conditions of the MMEs in each Permian granitoid pluton are very similar to those of their host granitoids, indicating simultaneous crystallization at the middle to upper crustal levels. Petrographical, geochemical, and Sr-Nd-Hf isotopic data show that the source areas of the Permian granitoid plutons in the northern NCB are temporally and spatially different and magma mixing was likely involved during formation of some granitoid plutons. However, the whole-rock Sr-Nd and zircon Hf isotopic compositions of the MMEs in each pluton are very similar to those of their host granitoids, indicating complete isotopic equilibration between the host granitoids and their enclaves. Combined with similar mineral assemblage and mineral chemistry between the MMEs and their host granitoids and absence of coeval mantle-derived rocks in or nearby the plutons, we confirm that the MMEs were crystallized from a coeval magma that gave rise to the host granitoids, and not by mixing and/or mingling between mantle-derived mafic and crustal-derived felsic magmas or by synplutonic injections of mafic magma into the host granitoid magma. We conclude that magma isotopic equilibration between host granitoids and their enclaves was achieved prior to emplacement and the magma mixing process during formation of some Permian granitoid plutons occurred mainly in the melting, assimilation, storage, and homogenization (MASH) zone in the lowermost crust or mantle-crust transition, not in the magma conduits or chambers at middle to upper crustal levels. A two-stage model that includes rapid cooling within the cogenetic host granitoid magma operating at pluton margins to form solid to sub-solid dioritic rocks and crystal accumulations of the host granitoid magma at the bottom of the pluton to form cumulates, and dioritic rocks and cumulates then fragmentated and interacted with progressive evolved host granitoid magma to change their shapes and orientations is proposed for origin of the MMEs in the Permian granitoid plutons in the northern NCB. This model may be more widely applicable to the generation of many MMEs in granitic rocks, especially where no direct evidence exists for the presence of mafic magmas coeval with granitoids and where there is a lack of isotopic contrast between hosts and enclaves. Our new results on origin of the enclaves in the granitoid plutons in the northern NCB show that some MMEs previously used as evidence for magma mixing and/or mingling are “autoliths (cognate xenoliths)” crystallized from the same magma as their host granitoids. There is an essential need for caution in using the MMEs as evidence for crustal-mantle interaction or mixing and/or mingling between crustal-derived felsic and mantle-derived mafic magmas during formation of granitic rocks, especially where no independent evidence is found for such a process. The role of MMEs in evaluating the mixing and/or mingling processes between crustal-derived felsic and mantle-derived mafic magmas has been much more likely overestimated by some previous studies and should be reconsidered. Instead, the MMEs in this origin can provide valuable information on emplacement mechanism and incremental growth of granitoid plutons in continental crust.

Geochemistry of lamprophyres in Karakaya (İscehisar, Afyon), Western Anatolia, Turkey

The geochemical characteristics of the volcanism, occured in the western Anatolia, display calc-alkaline (Oligocene-Lower Miocene) and alkaline (Upper Miocene-Pliocene) affinities. These two different volcanism have an important role to understand the geodynamic evolution of the western Anatolia during the Neogene time. The Karakaya lamprophyres, one of the products of these volcanism lying in the western Anatolia, comprises alkaline basaltic rocks extruded into the ignimbrites. Petrographically, they have mostly hyalopilitic, trachytic, intersertal, vitrophyric porphyritic, pilotaxitic and glomeroporphyritic texture. Olivine (mostly altered to iddingisite and resorbed by carbonate), clinopyroxene (diopside, augite) and phlogopite (partly transformed into Fe-Ti oxide) as phenocyrst phase, and apatite, quartz, garnet and opaque minerals as accessory phase defined. In some thin sections, quartz phenocrysts are surrounded by clinopyroxene needles that evulated as evidence of magma mixing. These lamprophyres are characterized by low concentrations of SiO2, TiO2 and total Fe2O3, high concentrations of Mg#, enriched in LREE and LILE but variably depleted in HFSE. In the total alkali silica diagram, Karakaya lamprophyres mainly plot in the fields of trachyandesite, basaltic trachyandesite. According to mineral chemistry results, olivines show normal zoning by increasing of CaO and decreasing of Fo contents from core to the rim. Pyroxenes are classified as diopside and augite compositions. The mica minerals are generally phlogopite The overall data about the petrograhic and mineral chemistry exhibit that these lamprophyres appear to derived by fractional crystallization of a magma mixing which formed by melting of the continental crust with effect of the uprising lithospheric mantle during in a extensional tectonic regime after the Middle Miocene.

Crystal Size Distribution of Pyroxenes from Aliabad andesite, Sagez- NW IRAN: Calculate of Resident Time Pyroxene in magma chamber and Evidence for magma mixing

Crystal Size Distribution of Pyroxenes from Aliabad andesite, Sagez- NW IRAN: Calculate of Resident Time Pyroxene in magma chamber and Evidence for magma mixing

Crystal Size Distribution of amphibole and plagioclase from Zanbil adakitic dacites, Urmia- Iran: Evidence for magma mixing and textural coarsening

Crystal Size Distribution of amphibole and plagioclase from Zanbil adakitic dacites, Urmia- Iran: Evidence for magma mixing and textural coarsening