Geochemistry and petrogenesis of the Kolah-Ghazi granitoid assemblage, south of Esfahan

پترولوژی، شیمی کانیها و محیط تکتونوماگمایی سنگهای آتشفشانی شمال شرق فرمهین (شمال اراک)

Introduction In the east and northeast of Sanandaj in the Qorveh-Bijar-Takab axis, there are series of basaltic composition volcanoes with Quaternary age. The study area is part of the Sanandaj-Sirjan zone and is located between 47°52' and 47°57' E longitudes and 35°26 and '35°30' N latitudes. Due to the location of the volcanic cone on Pliocene clastic sediments and Quaternary travertine, the age of these volcanoes is considered to be Quaternary. The cones mostly consist of low scoria, ash, volcanic bombs, lapilli deposits and basaltic lava (Moein Vaziri and Aminsobhani, 1985). Petrological and geochemical studies have been carried out to evaluate Quaternary magmatism in the area and to determine the nature of the lithological characteristics, such as the evaluation of source rocks and magma type, degree of partial melting and the tectonic setting of Ghezel Ghaleh rocks (Moein Vaziri, 1997). Simplified geological map of the study area is characterized by ER-Mapper software. Materials and methods In the course of field studies in the region, 40 samples were taken, 30 thin sections were prepared and polished. XRD analyses were performed on some whole rock samples. All major, minor and trace elements were assessed by ICP-MS at Lab Weft Laboratory in Australia. Results Based on the classification of structural zones, the area is located in the Sanandaj-Sirjan zone, hundred kilometers away from the main Zagros thrust along the NW-SE direction. After early Cimmerian orogeny, andesitic volcanic activity took place (Moein Vaziri and Aminsobhani, 1985). A major secondary mineral in these rocks is iddingsite, formed by hydration and oxidation of the olivine (Shelley, 1993). According to SiO2 against Na2O + K2O (TAS) diagram (Irvine and Baragar , 1971) and cationic R1 and R2 diagram (De La Roche et el., 1980), volcanic rocks of the area indicate alkaline series. Discussion To obtain more information on the tectonic setting of these rocks, the Zr/Y-Zr diagram by Pierce (Pearce and Norry, 1979) as well as Nb/Y versus Ti/Y diagram of Pierce (Pearce and Cann, 1973), show that alkali basalt rocks in the study area are fitted in the field of within plate basalts. To determine the genesis of rocks from melting curve of Aldanmaz and Colleagues (Aldanmaz et al., 2006) based on changes in REE (La on Sm/Yb), the samples show approximately 1 to 5% partial melting of garnet lherzolites. The spider diagrams indicate that the studied rocks are enriched in LREE and LILE, depleted in HFSE with no Eu anomaly, Cs, Sr, and Pb positive anomalies which are the characteristics of alkaline magmas and high concentrations of incompatible elements and alkaline elements in the lava, implying the melting of the lower part of the mantle source. Light rare earth elements, are incompatible with the primary crystallized phases such as olivine, clinopyroxene and plagioclase, consequently focused increasingly during phase crystallization and fractionation in the remaining fluid (Hirschman, 1998). Conclusions Based on microscopic and geochemical data, these rocks are alkali basalt, basanite and tephrite. The rocks contain olivine, pyroxene, feldspar, and minerals such as iddingsite, opaque and secondary minerals, calcite with porphyritic texture and microlitic and glassy matrix, vesicular and some glomeroporphyritic, vitrophyric and amygdaloidal textures. Most minerals have undulose extinction which indicates mantle deformation. Geochemical data for the rocks indicate high-K alkaline characteristic of the primary magma. The spider diagrams indicate that the studied rocks are enriched in LREE and LILE, depleted in HFSE with no negative Eu anomaly, positive anomalies of Cs, Sr, Pb which are characteristics of alkaline magmas. These rocks are produced by partial melting of garnet-lherzolite rich under lithospheric mantle. Based on tectonomagmatic diagrams, they are within plate basalts and by magmatic series graphs are alkali basalts. Microscopic evidence such as disequilibrium textures in the minerals (zoned state, solution and twinning) shows a magmatic contamination in mixing volcanic mass. References Aldanmaz, E., Koprubasi, N.O., Gurer, F., Kaymakci, N. and Gournaud, A., 2006. geochemical constraints on the Cenozoic, OIB-type alkaline volcanic rocks of NW Turkey: implications for mantle sources and melting processes. Lithos, 86 (1–2) pp. 50–76. De La Roche, H., Leterrier, J., Grand claude, P. and Marchel, M., 1980. A classification of volcanic and plutonic rocks using R1-R2 diagrams and major elements, it’s relationships with current nomenclature. Chemical Geology, 29(1-4): 183–210. Hirschman, M., 1998. Origin of the transgressive granophyres in the layered series of the Skaergaard intrusion, East Greenland. In: D.J. Geist and C.M. White (Editors.). Journal of Volcanology and Geothermal Research, 52(1-3): 185–207. Irvine, T.N. and Baragar, W.R.A., 1971. A guide to chemical classification of the common volcanic rocks. Canadian Journal of Earth Sciences, 5(8): 448– 523. Moein Vaziri, H., 1997. The history of magmatism in Iran. Tehran University Press, Tehran, 440 pp. (in Persian) Moein Vaziri, H. and Aminsobhani, A., 1985. Study of young volcanic region being involved in –Qorveh- Takab. Tehran University Press, Tehran, 350 pp. (in Persian) Pearce, J.A. and Cann, J.R., 1973. Tectonic setting of basaltic volcanic rocks determind using traceelements analysis. Earth and Planetary Science Letters, 19(2): 290– 300. Pearce, J.A. and Norry, M.J., 1979. Petrogenetic implications of Ti, Zr, Y and Nb variation in volcanic rocks. Contributions to Mineralogy and Petrology, 69(1): 33– 47. Shelley, D. (Translated by Mohamadzadeh, F.), 1993. Igneous and metamorphic rocks under the microscope, classification, textures, microstructures and mineral preferred-orientations. Chapman and Hall, Unwin, London, 445 pp.

ژئوشیمی ایزوتوپ های Rb-Sr و Nd-Sm و پتروژنز دایک های بازیک کوههای میشو (شمال غرب ایران)

Petrology, geochemistry, and Sr, Nd isotopes of mantle xenolith in Nghia Dan alkaline basalt (West Nghe An): implications for lithospheric mantle characteristics beneath the region

THE GENESIS OF PYROXENITE-RICH PERIDOTITE AT CABO ORTEGAL (NW SPAIN). INFERENCES FROM GEOCHEMICAL, MINERAL AND PB-SR ISOTOPIC DATA

Geochemistry, origin and anatexis temperature of monzogranite formation in Mount Khalaj (Mashhad, Iran)

The Barro Vermelho Fe-Ti ore body is located 12 km east of the town of Custodia and 320 km west of the city of Recife in the State of Pernambuco (PE), Northeast Brazil. It is part of many enclave entrained within granitic to tonalitic orthogneisses that constitute the basement of the Proterozoic Pajeu-Paraiba foldbelt in the Borborema Province. The field relationships, petrographic features, geochemistry and U/Pb data on zircons suggest that the gneisses of granitic composition formed at 2.01 Ga by migmatization of the 2.44 Ga old tonalites. Many decimetric to metric and a few hectometric metamorphosed enclaves of anorthosite, gabbro to gabbronorite, banded diorite to gabbroic amphibolites, calc-silicate rocks and trondhjemites are randomly distributed within the orthogneisses. The Fe-Ti ore body occurs as an almost concordant tabular massive unit, 0.8 m thick and 60 m to 80 m long, enclosed in gabbro-anorthosite, banded amphibolite and trondhjemite that together form a hectometric mega-enclave within the orthogneisses. Some apophysis of the ore body, formed by martitized magnetite and illmenite, crosscut the mafic wallrock. The banded amphibolite enclosing the ore body are identical to those found as synplutonic dykes and enclaves in the tonalitic orthogneisses, while the gabbroanorthosite are similar to those found as xenoliths in the orthogneisses. Petrographic features, variation diagrams, and trace element and REE distribution patterns strongly suggest that the gabbro-anorthosites, gabbronorites, trondhjemites, and banded amphibolites as enclaves are differentiation products of a tholeiitic magma of oceanic affinity or originated by the melting of a crustal slab composed of volcanic arc tholeiites. The metagabbronorites appear to represent the most primitive magma from which the anorthosites are interpreted to have formed by fractional crystallization of plagioclase while the protholiths of amphibolites may have crystallized from the residual melt. The ore body may represent the most evolved melt of this suite.

The mafic enclaves from Mesozoic intermediate-acid magmatic rocks, widely developed along Fujian coast, are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy, and geochemistry of granites and mafic microgranular enclaves (MMEs) in Langqi Island are studied to provide new information for tracing crust-mantle interaction. The zircon U-Pb dating results show that the Langqi rocks were formed at ~101 Ma, which are metaluminous, enriched in silica and high-K calc-alkaline I-type granites. The enclaves have a typical magmatic structure, which is characterized by magma mixing between high-temperature basic magma and low-temperature acidic magma through injecting. The enclaves and host granites show a tendency to mixed major and trace elements, displaying a clear-cut contact relationship, which is indicative of coeval magmatism. The genesis of Langqi rocks is related to the extensional setting caused by the subduction of Paleo-Pacific Plate, and they are the results of mixing of subduction-related metasomatized mantle-derived mafic and induced crustal-melted granitic magma originating from partial melting of the crustal material.

Concentrations of major and trace elements in soil profiles developed over granites across a climosequence in northeastern Brazil

The Kasian volcanic body is located in the eastern margin of the Zagros thrust belt, close to the Sanandaj-Sirjan metamorphic zone. These volcanic rocks are mainly composed of andesite and andesite-basalt rocks with porphyritic, hypocrystalline porphyritic, hyalo-porphyritic and hyalo-microlitic porphyritic textures. Analyses of the distributions of major, rare earth and trace elements reveal a tholeiitic nature and evidence such as enrichment of Pb and LILE (e.g., U, Rb, Ba), depletion in HFSE (e.g., Nb, Ti, Y), slight enrichment of LREE relative to HREE and trace elements discrimination plots reveal island arc affinity for the Kasian volcanic rocks. Some characteristics like, low Nd/Pb and Ce/Pb values (average 8.76 and 12.70, respectively), high U values and low Nb/U ratios (average 3.52) indicate enrichment of mantle wedge by contribution of slab-derived fluids during dehydration of subducting slab of Neo-Tethys oceanic lithosphere. Moreover, the results show these volcanic rocks to have fractionated as they ascended to higher crustal levels. The results of this study are consistent with the new tectonic scenario for the Sanandaj-Sirjan zone, which suggests that during ocean–ocean subduction (from Jurassic to Cretaceous) an immature island arc developed before the closure of Neo-Tethys ocean.

The Dam Feliciano Belt is a Pan-African mobile belt from the Ribeira orogen of southern Brazil. A detailed field and geochemical traverse along the BR392 road section between Pelotas and Caҫapava do Sul identifies two major tectonic domains; the Pelotas Batholith and the Santana Metamorphic Belt, striking NNE-SSW parallel to the major foliation of the belts. The two belts are separated by a Triassic basin with flat lying red beds and interbedded andesites and rhyolites. The Santana Metamorphic Belt is a NW-verging fold belt with a metamorphosed shelf sequence of quartzites, marbles and graphitic schists and a polydeformed Lower Proterozic gneissic basement deformed during the Pan-African orogeny. Detailed mapping recognized four phases of deformation in the basement gneisses, three of which are recorded in the basement schists and cover sequence. There is also evidence of late NE-verging thrusting post-dating the formation unmetamorphosed Paleozoic sediments. Late extension caused NW-SE and NE-SW normal faulting. Metamorphism occurred contemporaneously with D2 and 03, and PT conditions for peak: metamorphism have been calculated as 8.6Kb and 600°C within the basement schists corresponding to garnet growth during D3 deformation. Three phases of granite intrusion are recognized in the Santana Metamorphic Belt The Santana Granite (8oom.y.) represents the first phase intruding the basement and it is folded by 02 and 03. The Campinas Granite (500m.y.) has a D3 foliation and the Caҫapava Granite (474m.y.) is post-tectonic and intrudes the NW portion of the Santana Metamorphic Belt The Pelotas Batholith is almost entirely composed of granitoids of Pan-African age (600- 4S0m.y.). Both D2 and D3 are recognized in the batholith. A two fold subdivision based on geochemical and field criteria distinguishes the following categories of granitoid; foliated granitoids and unfoliated granites. Geochemically all granitoids of the two belts have a strong crustal signature. The foliated granitoids of the Pelotas Batholith (600-550m.y.) are metaluminous, calkalkaline granodiorites, and have volcanic arc characteristics with Sr initial ratios between 0.708 and 0.710 and model ages in the range of 1.6-1.4b.y. The unfoliated granites (500-450m.y.) of the Pelotas Batholith are slightly peraluminous and their field relations, trace element and isotopic data suggest a post-collision setting for their formation. Their higher Sr initial ratios (0.710-0.770), Nd model ages of 1.2-1.1b.y. and high source Rb/Sr, support the proposal that they are melts of the migmatized granodiorites. The Canguҫu Red Granite and the Capao do Leao Granite are also unfoliated but appear to be geochemically distinct from the other unfoliated granites. They have high Fe/Mg, Rb/Sr and Rb/Ba ratios, flat rare earth element patterns and negative europium anomalies, all suggestive of A-type granites. From isotopic studies, the Canguҫu Granite has very high Sr initial ratios of 0.750 to 0.81 and old model ages of 2.0-3.0b.y. In the Santana Metamorphic Belt, the foliated Santana Granite has a more depleted trace element chemistry than foliated granites of the Pelotas Batholith and an earlier emplacement age of 8oom.y. Trace element and isotope modelling suggest it to be a melt of the basement gneisses. The Campinas Granite is strongly peraluminous with high Rb/Sr, Rb/Ba and Sm/Nd and initial ratios between 0.780 and 0.820 and model ages of 2.0 b.y. suggesting that it is a crustal melt from a pelitic source. The unfoliated Caҫapava Granite of the Santana Metamorphic Belt has low Rb/Ba, a low Sr initial ratio (0.705) and high model age (2.5b.y.) suggesting it is a lower crustal melt. The unfoliated Encruzilhada Granite is fault bounded and outcrops between the two belts. It is distinctive from granitoids of both belts in terms of its trace element and isotopic characteristics which suggest that it formed from a basaltic source in a within plate tectonic setting. There appears to be no systematic change in geochemistry with distance along the cross-section and any changes appear to be temporal. Combined Sr and Nd isotope studies suggest that the Pan-African Ribeira orogen represents a period of crustal reworking rather than crustal growth and in this respect resembles the Damara orogen of Namibia which is dominated by crustal reworking, in contrast to the rapid crustal growth observed in the Arabian shield.

Tantalum–(niobium–tin) mineralisation in African pegmatites and rare metal granites: Constraints from Ta–Nb oxide mineralogy, geochemistry and U–Pb geochronology

The Xintianling tungsten deposit is a super-large deposit in the Nanling tungsten–tin mineralization belt, which is genetically associated with the early-stage hornblende-biotite monzonitic granite of Qitianling pluton. The orebodies predominantly occur as veins and lenses within skarn rocks between Xintianling granite and limestone (Shidengzi group). In this work, whole-rock major and trace elements and zircon U–Pb ages of the Xintianling granite were studied in an attempt to investigate the geochronological framework, petrogenesis, tectonism, and metallogenesis with regard to the deposit. The petrographic and geochemical analyses indicated that the Xintianling granite consists of three intrusive units of medium- and coarse-grained biotite granite, fine-grained biotite granite, and granite porphyry, of which the biotite granite was strongly associated with mineralization. Biotite granite rocks are highly K-calc-alkaline and weakly peraluminous, with A/CNK ratios ranging from 0.99 to 1.05. Late-granite porphyry is aluminum-supersaturated with a high evolution degree, whose geochemical characteristics suggest that it is either an I- or S-type granite. LA-ICP-MS zircon U-Pb dating revealed that medium- and coarse-grained biotite granite (162.3 ± 1.2 Ma, MSWD = 1.3), fine-grained biotite granite (161.8 ± 1.3 Ma, MSWD = 1.8), and granite porphyry (154.3 ± 1.6 Ma, MSWD = 2.4) formed in the late Jurassic. The emplacement of the Qitianling A-type granite and associated tungsten-tin polymetallic mineralization is a continuous evolution process, and they are products of the large-scale mineralization of the Nanling in the middle–late Jurassic (150–160 Ma). Under the tectonic setting of the Mesozoic lithospheric extension, asthenosphere upwelling along deep-fault, intensive mantle–crust interaction processes probably provide not only the high heat flow, but also partly mantle-derived material for large-scale W-Sn-polymetallic mineralization in this area.

New analyses of 131 samples of A-type (alkaline or anorogenic) granites substantiate previously recognized chemical features, namely high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr. Good discrimination can be obtained between A-type granites and most orogenic granites (M-, I and S-types) on plots employing Ga/Al, various major element ratios and Y, Ce, Nb and Zr. These discrimination diagrams are thought to be relatively insensitive to moderate degrees of alteration. A-type granites generally do not exhibit evidence of being strongly differentiated, and within individual suites can show a transition from strongly alkaline varieties toward subalkaline compositions. Highly fractionated, felsic I- and S-type granites can have Ga/Al ratios and some major and trace element values which overlap those of typical A-type granites. A-type granites probably result mainly from partial melting of F and/or Cl enriched dry, granulitic residue remaining in the lower crust after extraction of an orogenic granite. Such melts are only moderately and locally modified by metasomatism or crystal fractionation. A-type melts occurred world-wide throughout geological time in a variety of tectonic settings and do not necessarily indicate an anorogenic or rifting environment.

Mobilization and redistribution of major and trace elements in two weathering profiles developed on serpentinites in the Lomié ultramafic complex, South-East Cameroon