Amphibole Granodiorites Research Articles

Redox conditions of formation of the Priiskovy massif rock and their metallogenic consequences (South Sikhote-Alin, Primorye)

The same Cenomanian (96.91 ± 0.88 and 96.5 ± 1.2 Ma) age of amphibole granodiorites of the magnetite and ilmenite series in the southern part of the Priiskovy massif has been established. Among the relatively homogeneous central ilmenite zone of the Sikhote-Alin orogenic belt, the local occurrence of magnetite rocks of the Priiskovy massif explains the distribution of deposits and ore occurrences of the studied site. All deposits and ore occurrences of tin within the boundaries of the Priiskovy massif are located in the zone of distribution of rocks of the ilmenite series (reducing conditions), and deposits and placers of gold and manifestations of polymetallic mineralization are located in the zone of rocks of the magnetite series (oxidizing conditions)

Crystal mush rejuvenation induced by heat and water transfer: Evidence from amphibole analyses in the Jialuhe Composite Pluton, East Kunlun Orogen, northern Tibet Plateau

Crystal mush rejuvenation is capable of magma differentiation, evolution, migration, and mixing and magma mixing may act as a trigger for crystal mush rejuvenation. The Jialuhe Composite Pluton in the eastern part of East Kunlun Orogen, northern Tibet Plateau, is a product of magma mixing that contains abundant mafic microgranular enclaves (MMEs) that often form dike–like clusters in the central parts of the pluton that is composed of porphyritic amphibole granodiorite containing medium– to coarse–grained amphibole crystals and fine–grained biotite, whereas the external zone consists of biotite granodiorite with dominant biotite accompanied by a small fraction of amphibole. Amphibole aggregate bands developed within the MMEs consist of densely packed amphibole megacrysts. We selected amphiboles from the MMEs, host rocks, and amphibole aggregate bands to study mush rejuvenation triggered by magma mingling. The amphibole megacrysts are euhedral and show zoning from cores to rims with decreasing in Si, Mg, and Na, and increasing in K, Al, Fe, and Ca. We have classified these amphibole megacrysts into three types according to their different rare earth element concentration zoning from cores to rims, which reflect recharge of dioritic magma and the final chemical equilibrium in the melt. The physicochemical crystallization conditions of the three types of amphibole megacrysts in the amphibole aggregate bands indicated that the temperature and oxygen fugacity decreased, while the pressure and water content in melt increased during amphibole crystallization. These results combined with petrography, suggest that injection of dioritic magma gave rise to the MMEs and transferred heat and water to the host granitic mush. This transference resulted in coarsening of amphiboles in the host mush, especially within the granodiorite patches encaged within the MMEs, where the coarsened amphiboles joined to forming the aggregate bands. Therefore, these bands are a good indicator of crystal mush rejuvenation caused by the combination of heat and introduction of water, but the rejuvenation process was limited and local. Recharge of mafic magma in transcrustal felsic mush systems could not rejuvenate the entire felsic magma reservoir, but only parts near the mafic magma recharge channel.

Petrogenesis of the Solanas gabbro-granodiorite intrusion, Sàrrabus (southeastern Sardinia, Italy): implications for Late Variscan magmatism

The igneous complex of Solanas is a small, composite calc-alkaline intrusion emplaced at ~ 300 Ma in the Sarrabus region (southeastern Sardinia), and consists of olivine gabbronorites, amphibole gabbros, microgabbros, quartz diorites, tonalites, amphibole granodiorites, and biotite granodiorites. Thermobarometry calculations indicate that the Solanas rocks were emplaced at mid-to-upper crustal levels (0.6–4.0 kbar). The intermediate and silicic rocks are metaluminous to weakly peraluminous and are enriched in large ion lithophile elements. The range in the initial Sr and Nd isotopic compositions is small throughout the intrusion despite a large range in silica contents (46.3–73.6 wt% SiO2). The isotopic signatures, mineralogy, and geochemistry suggest that the quartz diorites, tonalites, and granodiorites derived from fractional crystallisation and crustal contamination processes starting from different mafic parental magmas. The origin of tonalites and granodiorites is compatible with removal of plagioclase, hornblende, biotite, apatite and zircon starting from a quartz dioritic magma. The mafic rocks range in composition from primitive to relatively evolved (Mg# 49–70). The olivine gabbronorites and amphibole gabbros have petrographic and geochemical features of arc cumulates derived from different basaltic magmas. The microgabbros have geochemical characteristics similar to high-alumina basalts with fractionated rare-earth element patterns (LaN/YbN = 4.3–6.0), enrichment in large ion lithophile elements (e.g., Rb, Ba, U, and K) and depletion in Nb and Ta compared with the primitive mantle. These characteristics are consistent with partial melting of a mantle source that was enriched by subduction-related fluids.

Late Ediacaran crustal thickening in Iran: Geochemical and isotopic constraints from the ~550 Ma Mishu granitoids (northwest Iran)

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

Timescales and mechanisms of batholith construction: Constraints from zircon oxygen isotopes and geochronology of the late Variscan Serre Batholith (Calabria, southern Italy)

The late Variscan Serre Batholith in central Calabria represents the middle portion, c. 13-km-thick, of a tilted crustal section continuously exposed from lower-crustal granulites to upper-crustal phyllites. The batholith is zoned, consisting of several granitoid types that were emplaced at depths ranging from c. 23 to c. 6km. Deep, strongly foliated quartz diorites and tonalites were emplaced into migmatitic metapelites, the intermediate level granitoids are weakly foliated to unfoliated porphyritic granodiorites and monzogranites, and the shallowest bodies are two-mica granodiorites and granites, grading upward to biotite ± amphibole granodiorites, emplaced into paragneisses and phyllites. Five samples, representative of the main granitoid types in terms of both composition and emplacement depth, have been dated by SHRIMP. Zircon from a lower-crustal quartz diorite gave an emplacement age of 297.3±3.1Ma; two middle-crustal strongly peraluminous K-feldspar megacrystic granites were emplaced at 296.1±1.9Ma and 294.9±2.7Ma; a middle- to upper-crustal two-mica monzogranite was emplaced at 294.2±2.6Ma and finally, an upper-crustal weakly peraluminous granodiorite from the batholith roof was emplaced at 292.2±2.6Ma. These results are consistent with the development of the batholith by incremental multipulse overaccretion, each granitoid body being in a dominantly rigid state before intrusion of the next, with little or no possibility of magma mixing. The difference in age between the oldest and youngest granitoids, from the batholith floor and roof, respectively, is 5.1±4.0Ma, providing an upper limit of about 9Ma on the time taken for batholith construction. The presence in the c. 296–294Ma granitoids of c. 305–302Ma anatectic zircon with varied Th/U and oxygen isotope compositions indicates a time interval of 8–9Ma between incipient partial melting in the lower crust and magma emplacement in the middle crust. The emplacement of the first granitoid bodies into the top of the lower crust was controlled tectonically by the activation of a deep-seated shear zone. The shallowest granodiorites were emplaced during the waning stages of the shear zone activity, producing late- to post-tectonic contact metamorphism in the upper-crustal phyllites and mylonitic paragneisses.

Source-inherited compositional diversity in granite batholiths: The geochemical message of Late Paleozoic intrusive magmatism in central Calabria (southern Italy)

The Serre Batholith, in central Calabria, is a Late Paleozoic granitoid complex that makes up the middle portion, ca. 13km thick, of a continuous and nearly complete section of the continental crust. The batholith displays a large compositional variety, with granitoid rocks ranging with continuity from quartz diorite to syenogranite, a distinct group of leucotonalites also occur. The granitoids are on the whole magnesian and calcic to calc-alkalic, with only some of the more evolved rocks showing a ferroan calc-alkalic to alkali-calcic composition. Quartz diorites and tonalites are metaluminous to weakly peraluminous, while granodiorites and granites are weakly to strongly peraluminous, with two-mica porphyritic types being the only population with a genuine strongly peraluminous character. Fe*-number, MALI and ASI features highlight a strong affinity of the Serre Batholith rocks with Cordilleran granitoids, inherited from the compositions of the source rocks rather than reflecting the real tectonic environment of the magmas. Major trace element and existing Sr-Nd data are consistent with an origin of the Serre Batholith from the assembling of several batches of magmas with specific original compositions derived by fluid-absent melting of different crustal sources.Quartz diorites and tonalites originated from a metabasaltic magma source, whereas metagraywackes with various mafic and pelitic contents appear the most likely sources of weakly peraluminous granodiorites and strongly peraluminous granodiorites and granites. Biotite±amphibole granodiorites could also have been derived from mafic-intermediate metaigneous sources. Two-mica porphyritic leucogranites are the only rock types representing pure crustal melts, resulting from melting of mafic pelitic sources. The other granitoid compositions are too silica-poor and MgO+FeOt rich to represent pure melts, so they need to include other components, such as solid restitic/peritectic material entrained from the magma source.Mantle-derived magmas do not appear to have played a role in the geochemical diversity of the Serre Batholith granitoids; their inherited arc signature resulted from partial melting of crustal material of magmatic arc derivation, such as magnesian igneous rocks and sediments derived from their rapid erosion. This study suggests that post-collisional granitoid magmatism is likely not to be associated with the direct generation of new continental crust; all the granitoid rock types appear to represent recycled and reworked crustal material.

Triassic granitoids of the Qinling orogen, central China: Genetic relationship of enclaves and rapakivi-textured rocks

Granitoids varying in composition from biotite–amphibole granodiorite to monzogranite with rapakivi textures have recently been recognized in the Qinling orogen (central China). The granitoids are magnesian, calc-alkalic and metaluminous (A/CNK = 0.71–0.95). They contain many mafic to intermediate microgranular enclaves. The enclaves are quenched mafic melts in granitic host magma as evidenced by fine-grained sinuous margins against or transitional contacts with the host granitoids as well as disequilibrium textures and mineral assemblages. U–Pb zircon dating of the granitoids yields: 209 ± 2 Ma and 212 ± 2 Ma and the enclaves 210 ± 2 Ma and 211 ± 2 Ma, respectively. The host granitoids and enclaves show obvious silica gap but similar REE and trace element patterns. The whole-rock 87Sr/ 86Sr( t), ε Nd( t) and zircon ε Hf( t) values for the granitoids vary from 0.70516 to 0.70634, − 2.3 to − 4.4 and 0.7 to − 7.6, and for the enclaves from 0.70467 to 0.70600, − 1.1 to − 4.0, and 1.2 to − 8.8, respectively, showing overlapped ε Nd( t) and zircon ε Hf( t) values. All these suggest that the two magmatic systems represented by the host rock and enclave are probably derived from distinct sources with sufficient interaction, or common origin but underwent different degrees of crustal contamination. Mineralogical and geochemical data point to enclave dissolution in silicic magma as a major process accounting for the origin of the rapakivi texture. The possible bimodal magmatism suggested by the coeval granitoids and lamprophyre dykes, combined with the structural pattern, geochemical features and regional tectonics, suggest a post-collision setting for the Qinling rapakivi-textured granitoid plutons.

Calc-alkaline Arc I-type Granitoid Associated with S-type Granite in the Pan-African Belt of Eastern Anti-Atlas (Saghro and Ougnat, South Morocco)

The Sidi Flah and Ougnat inliers are located in the eastern Anti-Atlas antiform between the Anti-Atlas Major Fault (AAMF) and South Atlas Fault (SAF). They consist of many granitoid intrusions emplaced into Neoproterozoic metasedimentary rocks and surmounted by upper Neoproterozoic A-type granites. The Sidi Flah (Saghro) and Ougnat granitoids are part of the Neoproterozoic magmatic activity related to northwards subduction of an oceanic plate beneath the Saghro continental margin. They are post-orogenic I- and S-type granitoids related to the ending of the compressional deformation in this Pan-African belt. A petrographic, geochemical and zircon typology study leads us to subdivide these rocks into three magmatic groups: (1) a medium- to high-K calc-alkaline group formed by quartz diorites and amphibole granodiorites is found in both Sidi Flah and Ougnat inliers; (2) a high-K calc-alkaline group is present in Sidi Flah. These two groups have a (deeper and) hybrid mantle-crust origin; (3) a peraluminous group in Ougnat is linked to the post-collisional setting and has a shallow crustal source. On a primitive mantle-normalized trace-element diagram, almost all of these rocks show a significant Nb depletion relative to K and La, which is typical of the calc-alkaline magmatism from the subduction-zone environment. Absence of structural marks of thrusting upon the West African craton (WAC) of this arc system and the ophiolitic suite in Bou-Azzer, and the presence of Imiter muscovite-bearing granite as part of Pan-African belt do not support the localization of northern limit of WAC at the level of SAF.

Petrographic, Geochemical and Zircon Typology of Neoproterozoic Granitoids: Evidence of Continental Thickening in Saghro Arc (Eastern Anti-Atlas, Morocco)

Saghro is considered as a volcanic arc of the Neoproterozoic. The magmatic activity during this period is characterized by the emplacment of granitic plutons North-East from Bou-Azzer El Graara's suture zone. Sidi Flah-Bouskour buttonhole represents the near part of Saghro to this zone and Ougnat hills the far part. The buttonhole of Sidi Flah-Bouskour is cut by several successive granitic intrusions of Neoproterozoic. The earliest suite, composed of gabbro, quartz diorite and amphibole granodiorite constitute the Pan-African B1 phase related to pre- collision domain, and shows a calc-alkaline chemistry. The second phase includes the biotite granite of Bouskour which belong to the potassic calc-alkali suite emplaced during the Pan- African B2 phase in a syn-collisional environment. The granodioritic and granitic trends show separate evolution in CaO-Na,O-K,O diagram. Quartz diorite and amphibole granodiorite have moderate content of Sr (420-40ppm), Rb (133-88ppm), Cr (177-21ppm), Zr (131-67ppm) and V(470- 30ppm) and hight content of Ba (1156-368ppm). Garnet and biotite have low content of Sr (3lppm), Rb (104ppm), Cr (42ppm), V (93ppm), Zr (93ppm) and Ba (450ppm). REE normalised to MORB show that the Sidi Flah-Bouskour granitoids are enriched in LREE and LILE and relatively depleted in HFSE and Nb.The zircon populations of the quartz diorite and amphibole granodiorite show a strong frequency in the sub-type S17-18 with low @ index and high T index implying a temperature of 750 - 800°C. In addition to the T.E.T, the average points (0, T) placed in the (LA, 1.T) typological diagram permit to classify these rock into the hybrid granites domain which belong to the calc-alkali granodioritic affinity. The biotite granite shows zircon populations with dominance of the S19 sub-type implying high 0 index with apparition of the types P, D and J, and high T index. The average points (0, T) and the T.E.T. permit to classify the biotite granite among the hybrid granites implying a alkali-rich calc-alkali trend. Quartz diorite, amphibole granodiorite and garnet granite are emplaced in Ougnat hill, far separated from the suture zone. Petrographic, geochemical and zircon typology study of these rocks shows existence of two magmatic groups. The quartz diorite and the amphibole granodiorite represents a medium-K calc-alkaline trend and shows alkali enrichment (Bl). CaO-Na,O- KzO relationship shows that quartz diorite and granodiorite evolved separately from that of the garnet granite. Petrographic, mineralogical (zircon typology) and geochemical (overlap of garnet granite REE pattern on calculated crustal partial melt pattern) features of garnet granite are similar to those of crustal anatectic granites (B2). The occurrence of granodiorite very rich in biotite and mantled garnet grains identical to those in the crustal garnet granite indicates processes of assimilation and magma contamination during the emplacement of Ougnat granitoids. Biotite granite emplaced in Sidi Flah-Bouskour, adjacent to Saghro near the suture zone shows strong crustal participation and granitoids in Iknioun show high-K affinities. Away from the suture zone' in Ougnat' garnet granites of crustal origin occur. Isotopic data show variation of ENdi between biotite granite in Sidi Flah-Boukour (ENd= -1.8-2.4) and garnet granite in Ougnat (ENdi= -4.5). This is interpreted to indicate an increase in incorporation of crustal component while moving North-East. The contrast in isotopic data agree well with the spatial zonation observed in Saghro. This zonation might have evolved by crustal thickening toward the axis of Bou-Azzer El Graara's suture which is considered as a paleo-subduction zone during Neoproterozoic according to the model of Meen (1987).

Petrogénesis del plutón monzogranítico peralumínico de Santa Eufemia (Batolito de los Pedroches, Córdoba)

The Santa Eufemia pluton is part of the composite magmatic assoclatlon of Los Pedroches batholith, located in the southern branch of the Central Iberian Zone of the Hercynian orogenic belt of Spain. This high-Ievel postkynematic batholith consists of three main types of plutonic rocks: boitite±amphibole granodiorites, biotite-cordierite porphiritic monzogranites and cordierite leucogranites. The Santa Eufemia pluton consists of biotite-cordierite monzogranites, and in a lesser extent of cordierite leucogranites. Scarce enclaves of different type are found in the monzogranites, biotiteplagioclase- eordierite and fine grained porphiritic monzogranite enclaves being the most common. The petrographic, structural and geochemical (major and trace elements) data suggests a compiex evolutionary history of a metasedimentary-source monzogranitic magma with no genetical relationships with more basic magmas such as the one which is now represented by the granodiorite facies of the batholith. Non-minimum melt and reequilibrated source material (secondary restites) mixing during the ortomagmatic evolution of the magma accounts for the compositional heterogenities of the monzogranites. The ultimate product of this evolution is the segregation of a fluid-saturated residual liquid in the final level of intrusion of the magma, leading to the emplacement of leucogranite masses and dikes and the exsolution of a supercritical fluid phase related with the late magmatic recrystallization of sorne mineral phases (muscovite, albite, quartz, tourmaline, topaz), the geochemical removilization of sorne incompatible trace elements (Rb, Cs, Li, Be, Sn, Nb) due to fluid-rock interactions and the formation of periplutonic wolframite-arsenopyritequartz mineralizations.