Quartz Monzodiorite Research Articles

Underplating generated A- and I-type granitoids of the East Junggar from the lower and the upper oceanic crust with mixing of mafic magma: Insights from integrated zircon U–Pb ages, petrography, geochemistry and Nd–Sr–Hf isotopes

Whole rock major and trace element, Nd–Sr and zircon Hf isotopic compositions and secondary-ion mass spectrometry zircon U–Pb ages of eleven granitoid intrusions and dioritic rocks from the East Junggar (NW China) were analyzed in this study. The East Junggar granitoids were emplaced during terminal Early to Late Carboniferous (325–301Ma) following volcanic eruption of the Batamayi Formation. Zircons from the East Junggar granitoids yielded 210 concordant 206Pb/238U ages which are all younger than 334Ma and exhibit εHf(t) values distinctly higher than Devonian arc volcanic-rocks. Seismic P-wave velocities of deep crust of the East Junggar proper resemble those of oceanic crust (OC). These characteristics suggest absence of volcanic rock and volcano-sedimentary rock of Devonian and Early Carboniferous from the source region. The East Junggar granitoids show εNd(t) and initial 87Sr/86Sr values substantially overlapping those of the Armantai ophiolite in the area. The Early Paleozoic OC with seamount-like composition as the Zhaheba–Armantai ophiolites remained in the lower crust and formed main source rock of the East Junggar granitoids. Based on petrography and geochemistry, the East Junggar granitoids are classified into peralkaline A-type in the northern subarea, I-type (I1 and I2 subgroups) mainly in the north and A-type in the south of the southern subarea. The perthitic or argillated core and oligoclasic rim with an argillated boundary of feldspar phenocrysts and inclusion of perthites or its overgrowth by matrix plagioclase, in the monzogranites (northern subarea), suggest mixing of peralkaline granitic magma with mafic magma. In the north of the southern subarea, the presence of magmatic microdioritic enclaves (MMEs) in the I1 subgroup granitoids, transfer of plagioclase phenocrysts and hornblendes between host granodiorite and the MME across the boundary and a prominent resorption surface in the plagioclase phenocrysts indicate mixing of crustal magma (I2 subgroup granitoids) with mafic magma. Magma mixing shifted (87Sr/86Sr)i of the I1 subgroup granitoids towards the mantle array. Two generations of hornblende with zonal distribution and similar mineral and geochemical compositions of quartz monzodiorite and hosted MME with unfractionated rare earth elements (REE) suggest extended magma mixing with onset probably at or near source region. These observations imply concurrency of mantle input and the crustal melting and, hence, a causal relationship between underplating/intraplating and the lower OC/upper OC melting. The I-type granitoids experienced plagioclase and hornblende fractionations, whereas fractionated phases of the two groups of A-type granites were alkali feldspar and albite–oligoclase with significant involvement of F−-rich fluid. Granodioritic parent magmas of the I2 subgroup granitoids stemmed from the hydrous upper OC. Parent magmas of the two A-type groups possess syenogranitic or quartz syenitic compositions. The peralkaline A-type granites stemmed from the lower OC, whereas the A-type granites from dehydrated upper OC left behind after extensive partial melting and extraction of I-type granitoids. Based on comparison in the ternary system Mg2SiO4–CaAl2SiO6–SiO2, most of the Batamayi volcanic rocks with affinity to ocean-island basalts were derived from asthenospheric upwelling. The gabbro–dioritic rocks with higher light to heavy REE ratios stemmed from metasomatized lithospheric mantle. Both of the above mafic rocks contain subducted slab component.Loci of ponding of mafic magma and crustal melting migrated upward and southeastward from the lower OC in the northern subarea (yielding the peralkaline A-type granites) to the upper OC in the southern subarea. The latter evolved from hydrous (yielding the I-type granitoids in the north of the subarea) to dehydrated (yielding the A-type granites in the south of the subarea). Sequence of these events resulted in increasingly-later formation of the East Junggar granitoids southeastwards with an age span of ~20Ma. Minor contribution from Late Paleozoic OC to the source of the southern granitoid subarea caused the latter showing distinctly higher εNd(t) than the northern subarea. In conclusion, underplating caused OC remelting which, together with significant magma mixing, produced the East Junggar granitoids in a non-subduction zone environment.

Mesoproterozoic arc magmatism in SE India: Petrology, zircon U–Pb geochronology and Hf isotopes of the Bopudi felsic suite from Eastern Ghats Belt

The southern segment of the Eastern Ghats Mobile Belt (EGMB) in India was an active convergent margin during Mesoproterozoic, prior to the final collision in Neoproterozoic during the assembly of the Rodinia supercontinent. Here we present mineralogical, whole-rock geochemical, zircon U–Pb and Hf isotopic data from a granitoid suite in the Bopudi region in the EGGB. The granitoid complex comprises quartz monzodiorite with small stocks of rapakivi granites. The monzodiorite, locally porphyritic, contains K-feldspar megacrysts, plagioclase, quartz, biotite and ortho-amphibole. The presence of mantled ovoid megacrysts of alkali feldspar embaying early-formed quartz, and the presence of two generations of the phenocrystic phases in the rapakivi granites indicate features typical of rapakivi granites. The K-feldspar phenocrysts in the rapakivi granite are mantled by medium-grained aggregates of microcline (Ab7 Or93), which is compositionally equivalent to the rim of Kfs phenocryst and Pl (An23–24 Ab75). The geochemistry of both the granitoids shows arc-like features for REE and trace elements. LA-ICP-MS zircon analyses reveal 207Pb/206Pb ages of 1582 (MSWD=1.4) for the rapakivi granite 1605±3Ma (MSWD=3.9) for the monzodiorite. The zircons from all the granitoid samples show high REE contents, prominent HREE enrichment and a conspicuous negative Eu anomaly, suggesting a common melt source. The zircons from the monzodiorite have a limited variation in initial 176Hf/177Hf ratios of 0.28171–0.28188, with εHf(t) values of −2.2 to +2.8. Correspondingly, their two-stage Hf isotope model ages (TDM2) ranging from 2.15 to 2.47Ga probably suggest a mixed source for the magma involving melting of the Paleoproterozoic basement and injection of subduction-related juvenile magmas. The prominent Mesoproterozoic ages of these granitoids suggest subduction-related arc magmatism in a convergent margin setting associated with the amalgamation of the Columbia-derived fragments within the Neoproterozoic Rodinia assembly.

Neoarchean sanukitoid magmatism in the Kola region: Geological, petrochemical, geochronological, and isotopic-geochemical data

New geological, isotopic-geochronological, petrochemical, and isotopic geochemical data were obtained on the Porosozero and Kolmozero sanukitoid intrusions in the Kola region. The Porosozero differentiated intrusion was formed in four phases successively emplaced during approximately 60 Ma. Phase 1 consists of a gabbrodiorite-quartz monzodiorite-granodiorite-granite series. The zircon ages of granodiorite and quartz monzodiorite from the Porosozero are 2733 ± 6 and 2734 ± 4 Ma, respectively. Phase 2 of the intrusion comprises biotite leucogranites and aplite and leucoplagiogranite veins. The zircon age of the leucogranite is 2712 ± 6 Ma. Phase 3 consists of lamprophyre dikes of odinite-spessartite-vogesite composition. The emplacement age of the lamprophyres is constrained by the age of magmatic zircon from an odinite dike: 2680 ± 10 Ma. The age of the metasomatic zircon is 2629 ± 8 Ma. Phase 4 is composed of the youngest pegmatite veins. The Rb-Sr isochron age of the phase-1 rocks is 2724 ± 74 Ma. The zircon age of granitoids from the Kolmozero is 2736 ± 4 Ma. The rocks of the sanukitoid intrusions affiliate with the calc-alkaline series, have Mg# = 0.45−0.60, are enriched in Ba, Sr, K, P, and LREE, and contain elevated concentrations of Cr and Ni. Sm-Nd isotopic data on sanukitoids from both intrusions suggest that they were derived from a mantle source enriched in LILE and LREE and having ɛNd(2740) from +1.02 to +0.36. It was melted approximately 140 Ma after its origin [T(DM) = 2.9−2.8 Ga]. The rocks of the Porosozero and Kolmozero are proved to be similar to magmatic sanukitoid series of Archean and Phanerozoic age whose genesis was controlled by mantle-crustal interaction in suprasubduction environments at active continental margins. Elevated concentrations of Ag and Au in rocks from the Porosozero make it metallogenically promising in terms of precious metals.

پترولوژی، ژئوشیمی و کانی سازی سنگهای آتشفشانی ترشیری و توده های نفوذی و نیمه نفوذی همراه آنها در منطقه ارغش- قاسمآباد (شمالشرق ایران) با گرایشی ویژه به سن و منشأ گرانیت ها

منطقه ارغش- قاسم آباد در شمال‌شرق ایران و در حاشیه زون ساختاری سبزوار قرار دارد. رخنمونهای ترشیری شامل گرانیت و کوارتز مونزودیوریت پورفیری همراه با سنگهای آتشفشانی از نوع داسیت و آندزیت هستند. در منطقه مورد مطالعه، دایک‌هایی از نوع کوارتز گابرو و کوارتز مونزودیوریت، سنگهای قدیمی تر را مورد نفوذ قرار داده اند. گرانیت‌ها و سنگهای آتشفشانی، میزبان رگه های کوارتز-‌کلسیت طلا و آنتیموان دار هستند. رگه های کانی سازی عمدتا در اطراف دایک‌ها و در نیمه جنوبی منطقه دیده می شوند. مطالعات ژئوشیمیایی حاصل از این پژوهش نشان می دهد که گرانیت‌ها ماهیت کالک‌آلکالن پتاسیم بالا داشته، و از نوع گرانیتوئیدهای انتقالی بین دو نوع A و I هستند. سنگهای آتشفشانی نیز با ترکیب آداکیتی، سرشار از استرانسیم و باریم می‌باشند. دایک‌های منطقه مورد مطالعه، ویژگیهای سنگهای لامپروفیری را نشان می دهند. سن سنجی اورانیم- سرب بر روی زیرکن در گرانیت، سن 2/2 ± 4/55 میلیون سال (ائوسن زیرین) را نشان می دهد. نسبتهای 87Sr/86Sr و eNd اولیه در گرانیت‌ها به‌ترتیب 704142/0 و 84/5+ می-باشند. داده های نسبتهای ایزوتوپی 87Sr/86Sr اولیه، وجود ماگمایی با منشأ گوشته تهی‌شده را تأیید می کند. سن به‌دست آمده نشان می دهد کانی سازی طلا- آنتیموان از ائوسن زیرین جوانتر است. براساس شواهد صحرایی، ارتباط کانی سازی با دایک‌های لامپروفیری، بیش از ارتباط آن با سنگهای آداکیتی است.

Origin of Middle Cambrian and Late Silurian potassic granitoids from the western Kunlun orogen, northwest China: a magmatic response to the Proto-Tethys evolution

This paper presents new SHRIMP zircon U–Pb chronology, major and trace element, and Sr–Nd–Hf isotopic data of two Early Paleozoic granitic plutons (Yierba and North Kudi) from the western Kunlun orogen, in attempt to further constrain the Proto-Tethys evolution. SHRIMP zircon U–Pb dating shows that the Yierba pluton was emplaced in the Middle Cambrian (513 ± 7 Ma) and the North Kudi pluton was emplaced in the Late Silurian (420.6 ± 6.3 Ma). The Yierba pluton consists of quartz monzodiorite, quartz monzonite and granodiorite. These granitoids are metaluminous and potassic, with initial 87Sr/86Sr ratios of 0.7072–0.7096, eNd (T) of −0.2 to −1.6 and eHf (T) (in-situ zircon) of −1.2. Elemental and isotopic data suggest that they were formed by partial melting of subducted sediments, with subsequent melts interacting with the overlying mantle wedge in an oceanic island arc setting in response to the intra-oceanic subduction of Proto-Tethys. The North Kudi pluton consists of syenogranite and alkali-feldspar granite. These granites are metaluminous to weakly peraluminous and potassic. They show an affinity of A1 subtype granite, with initial 87Sr/86Sr ratios of 0.7077–0.7101, eNd (T) of −3.5 to −4.0 and eHf (T) (in-situ zircon) of −3.9. Elemental and isotopic data suggest that they were formed by partial melting of the Precambrian metamorphic basement at a shallow depth (<30 km) during the post-orogenic regime caused by Proto-Tethyan oceanic slab break-off. Our new data suggest that the subduction of the Proto-Tethyan oceanic crust was as early as Middle Cambrian (∼513 Ma) and the final closure of Proto-Tethys was not later than Late Silurian (∼421 Ma), most probably in Middle Silurian.

The magmatic record in the Arghash region (northeast Iran) and tectonic implications

The area of Arghash in northeast Iran, prominent for its gold mineralization, was newly mapped on a scale of 1:20,000 with particular attention to the occurring generations of igneous rocks. In addition, geochronological and geochemical investigations were carried out. The oldest geological unit is a late Precambrian, hornblende-bearing diorite pluton with low-K composition and primitive isotope signatures. This diorite (U–Pb zircon age 554 ± 6 Ma) is most likely a remnant from a Peri-Gondwana island-arc or back-arc basin. About one-third of the map area is interpreted as an Upper Cretaceous magmatic arc consisting of a volcanic and a plutonic part. The plutonic part is represented by a suite of hornblende-bearing medium-K, I-type granitoids (minor diorite, mainly quartz–monzodiorite and granodiorite) dated at 92.8 ± 1.3 Ma (U–Pb zircon age). The volcanic part comprises medium-K andesite, dacite and tuffitic rocks and must be at least slightly older, because it is locally affected by contact metamorphism through the hornblende–granitoids. The Upper Cretaceous arc magmatism in the Arghash Massif is probably related to the northward subduction of the Sabzevar oceanic basin, which holds a back-arc position behind the main Neotethys subduction front. Small occurrences of pillow basalts and sediments (sandstone, conglomerate, limestone) tectonically intercalated in the older volcanic series may be relics of earlier Cretaceous or even pre-Cretaceous rocks. In the early Cenozoic, the Cretaceous magmatic arc was intruded by bodies of felsic, weakly peraluminous granite (U–Pb zircon age 55.4 ± 2.3 Ma). Another strong pulse of magmatism followed slightly later in the Eocene, producing large masses of andesitic to dacitic volcanic rocks. The geochemistry of this prominent Eocene volcanism is very distinct, with a high-K signature and trace element contents similar to shoshonitic series (high P, Zr, Cr, Sr and Ba). High Sr/Y ratios feature affinities to adakite magmas. The Eocene magmatism in the Arghash Massif is interpreted as related to thermal anomalies in crust and mantle that developed when the Sabzevar subduction system collapsed. The youngest magmatic activities in the Arghash Massif are lamprophyres and small intrusions of quartz–monzodiorite porphyries, which cut through all other rocks including an Oligocene–Miocene conglomerate cover series.

Characteristics of Mineralizing Fluids of the Darreh‐Zerreshk and Ali‐Abad Porphyry Copper Deposits, Central Iran, Determined by Fluid Inclusion Microthermometry

AbstractThe Darreh‐Zereshk (DZ) and Ali‐Abad (AB) porphyry copper deposits are located in southwest of the Yazd city, central Iran. These deposits occur in granitoid intrusions, ranging in composition from quartz monzodiorite through granodiorite to granite. The ore‐hosting intrusions exhibit intense hydrofracturing that lead to the formation of quartz‐sulfide veinlets. Fluid inclusions in hydrothermal quartz in these deposits are classified as a mono‐phase vapor type (Type I), liquid‐rich two phase (liquid + vapor) type (Type IIA), vapor‐rich two phase (vapor + liquid) type (Type IIB), and multi‐phase (liquid + vapor + halite + sylvite + hematite + chalcopyrite and pyrite) type (Types III). Homogenization temperatures (Th) and salinity data are presented for fluid inclusions from hydrothermal quartz veinlets associated with potassic alteration and other varieties of hypogene mineralization. Ore precipitation occurred between 150° to &gt;600°C from low to very high salinity (1.1–73.9 wt% NaCl equivalent) aqueous fluids. Two stages of hydrothermal activity characterized are recognized; one which shows relatively high Th and lower salinity fluid (Type IIIa; Th(L‐V) &gt; Tm(NaCl)); and one which shows lower Th and higher salinity (Type IIIb; Th(L‐V) &lt; Tm(NaCl)). The high Th(L‐V) and salinities of Type IIIa inclusions are interpreted to represent the initial existence of a dense fluid of magmatic origin. The coexistence of Type IIIb, Type I and Type IIB fluid inclusions suggest that these inclusions resulted either from trapping of boiling fluids and/or represent two immiscible fluids. These processes probably occurred as the result of pressure fluctuations from lithostatic to hydrostatic conditions under a pressure of 200 to 300 bar. Dilution of these early fluids by meteoritic water resulted in lower temperatures and low to moderate salinity (&lt;20 wt% NaCl equiv.) fluids (Type IIA). Fluid inclusion analysis reveals that the hydrothermal fluid, which formed mineralized quartz veinlets in the rocks with potassic alteration, had temperatures of ∼500°C and salinity ∼50 wt% NaCl equiv. Cryogenic SEM‐EDS analyses of frozen and decrepitated ore‐bearing fluids trapped in the inclusions indicate the fluids were dominated with NaCl, and KCl with minor CaCl2.

New lunar meteorite Northwest Africa 2996: A window into farside lithologies and petrogenesis

AbstractThe Northwest Africa (NWA) 2996 meteorite is a lunar regolith breccia with a “mingled” bulk composition and slightly elevated incompatible element content. NWA 2996 is dominated by clasts of coarse‐grained noritic and troctolitic anorthosite containing calcic plagioclase (An#~98) and magnesian mafic minerals (Mg#~75), distinguishing it from Apollo ferroan anorthosites and magnesian‐suite rocks. This meteorite lacks basalt, and owes its mingled composition to a significant proportion of coarse‐grained mafic clasts. One group of mafic clasts has pyroxenes similar to anorthosites, but contains more sodic plagioclase (An#~94) distinguishing it as a separate lithology. Another group contains Mg‐rich, very low‐titanium pyroxenes, and could represent an intrusion parental to regional basalts. Other clasts include granophyric K‐feldspar, disaggregated phosphate‐bearing quartz monzodiorites, and alkali‐suite fragments (An#~65). These evolved lithics are a minor component, but contain minerals rich in incompatible elements. Several anorthosite clasts contain clusters of apatite, suggesting that the anorthosites either assimilated evolved rocks or were metasomatized by a liquid rich in incompatible elements. We used Lunar Prospector gamma‐ray spectrometer remote sensing data to show that NWA 2996 is most similar to regoliths in and around the South Pole Aitken (SPA) basin, peripheral regions of eastern mare, Nectaris, Crisium, and southern areas of Mare Humorum. However, the mineralogy of NWA 2996 is distinctive compared with Apollo and Luna mission samples, and is likely consistent with an origin near the SPA basin: anorthosite clasts could represent local crustal material, mafic clasts could represent intrusions beneath basalt flows, and apatite‐bearing rocks could carry the SPA KREEP signature.

Early Carboniferous (Viséan) emplacement of the collisional Kłodzko–Złoty Stok granitoids (Sudetes, SW Poland): constraints from geochemical data and zircon U–Pb ages

Sensitive high-resolution ion microprobe zircon U–Pb dating and geochemical data of igneous rocks from the composite Klodzko–Zloty Stok (KZS) Granite Pluton, Sudetic Block, indicate that the granitoids represent an Early Carboniferous Visean phase of Variscan metaluminous, high-K, I-type, syn-collisional granite magmatism within the Saxothuringian Zone of the Central European Variscides. Igneous zircon records hypabyssal magmatism that produced various granitoids and lamprophyre (spessartite) emplaced from ca. 340 to 331 Ma. The KZS granitoids have compositions ranging from granodiorite to monzonite, low A/CNK ratios (<1), and are associated with abundant mafic members. Most of them are alkaline, highly potassic, and moderately evolved. The major and trace element contents of the KZS granitoids suggest geochemical heterogeneity, and the hybrid nature of magmas derived from a range of sources in the middle crust, with a strong input of material from the upper mantle. Mixing of magmas of mantle origin with high-K material from partly melted continental crust was probably a more important factor than fractional crystallization, in controlling the evolution of the magmas. The mean Pb–U ages of the main population of igneous zircon from a quartz monzodiorite (Żelazno) and hornblende monzonite (Droszkow) are 340.2 ± 2.5 Ma and 339.5 ± 3.1 Ma, respectively. A slightly younger biotite-hornblende granodiorite from Chwalislaw, 336.7 ± 2.5 Ma, was cut by a spessartite dyke at 333.1 ± 3.1 Ma. This indicates that mafic magmas were immediately intruded into fractured, probably incompletely solidified, granodiorites. The lamprophyric dyke also contains igneous zircon of Neoproterozoic age, 566.3 ± 6.4 Ma, typical of the crust in the Saxothuringian Zone. Tonalite from Ptasznik Hill near Droszkow is of similar age to the spessartite, 331.5 ± 2.6 Ma. High REE contents in the tonalite and its igneous zircon indicate advanced differentiation of granitic magma, producing a more leucocratic melt associated with post-magmatic activity including abundant late crosscutting pegmatites and quartz veins, and contact metasomatic mineralization. The KZS granitoids have rather similar petrographic and geochemical characteristics to granitoids from other parts of the Central European Variscides, where a thickened orogenic root caused a substantial rise in crustal temperatures, producing granitoid magmas closely correlated with regional tectonic activity between the Saxothuringian and Brunovistulia Terranes at the NE margin of the Bohemian Massif.

Metallogeny in response to lithospheric thinning and craton destruction: Geochemistry and U–Pb zircon chronology of the Yixingzhai gold deposit, central North China Craton

Magmatism and associated metallogeny provide important constraints on geodynamic processes. The Hengshan terrain of northern Taihang Mountains located within the central North China Craton is well-known for several Mesozoic gold deposits. Here we investigate the Yixingzhai quartz vein-hosted gold deposit associated with the Sunzhuang quartz monzodiorite intrusive complex. We present U–Pb data on zircon grains from the monzodiorite which constrain the timing of emplacement of the pluton as ca.134Ma, coeval with the formation of Yixingzhai quartz vein gold deposit (at ca. 131Ma). The magmatism and metallogenesis during early Cretaceous in the Hengshan terrain are part of a major regional magmatic and metallogenic event in the Taihang Mountains and elsewhere in the North China Craton at ca. 130Ma ago. We characterize the zircon grains from the Sunzhuang quartz monzodiorite through morphology, internal structures and chemistry, and also present data from analyses of the chemistry (Co and Ni), and S–Pb–D–O isotopes of the minerals from the Yixingzhai gold deposit and Sunzhuang quartz monzodiorite. Our results reveal a lower crustal signature with mantle input for the source magma of the Sunzhuang Pluton. The magma was enriched in water and alkalis and shows a wide range of crystallization temperature (850–550°C, and mainly 650 to 700°C) under high oxygen fugacity. The ore minerals and the mineralizing fluids in the Yixingzhai gold deposit were derived from magma generated in the lower crust with additional input of mantle components. Our study links the gold metallogenesis with magmatism in the Hengshan terrain. Based on the new results reported in this study, and in conjunction with our interpretation of the ultra-broadband high-precision magnetotelluric sounding profile from the region, we suggest that the lithosphere beneath the Hengshan terrain was strongly thinned and decoupled between the crust and mantle in the early Cretaceous, and that the partly destructed lithosphere was largely preserved through the Cenozoic to present. The metallogenesis in the Hengshan terrain was closely related to the lithosphere thinning and crust–mantle decoupling in the North China Craton.

Late-orogenic Variscan magmatism: The case of quartz monzodiorite dykes from the Blanice Graben, southern Bohemia

Late-orogenic Variscan magmatism: The case of quartz monzodiorite dykes from the Blanice Graben, southern Bohemia

Mineral chemistry and geothermobarometry of Moshirabad pluton, Qorveh, Kurdistan, western Iran

AbstractThe Moshirabad pluton is located southwest of the Sanandaj–Sirjan Metamorphic Belt, Qorveh, western Iran. The pluton is composed of diorite, monzodiorite, quartz diorite, quartz monzodiorite, tonalite, granodiorite, granite, aplite, and pegmatite. In this study 31 samples from various rocks were chosen for whole‐rock analyses and 15 samples from different lithologies were chosen for mineral chemical studies. The compositions of minerals are used to describe the nature of magma and estimate the pressure and temperature at which the Moshirabad pluton was emplaced. Feldspar compositions are near the binary systems in which plagioclase compositions range from An5 to An53 and alkali‐feldspar compositions range from Or91 to Or97. Mafic minerals in the plutonic rocks are biotite and hornblende. Based on the composition of biotites and whole‐rock chemistry, the Moshirabad pluton formed from a calc‐alkaline magma. Amphiboles are calcic amphiboles (magnesio‐hornblende or edenite). Temperatures of crystallization, calculated with the hornblende–plagioclase thermometer, range 550–750°C. These temperatures indicate that plutonic rocks have undergone some retrogressive changes in their mineral compositions. Aluminum‐in‐hornblende geobarometry indicates that the Moshirabad pluton was emplaced at pressures of 2.3–6.0 kbar, equal to depths of 7–20 km, but with consideration of regional geology, lower pressures than the above pressure range are more probable. Alteration of amphiboles can be the reason for some overestimation of pressures.

Petrology, geochemistry and geotectonic environment of the Alvand Intrusive Complex, Hamedan, Iran

The Alvand Intrusive Complex is located near Hamedan (Iran) and crops out over an area 400km2 intruding the Sanandaj-Sirjan plutono-metamorphic belt. The emplacement age of the AIC is constrained to Upper to Middle Jurassic, based on U–Pb zircon geochronogic data. This complex consists of granites (monzogranite and syenogranite), leucocratic granitoids (leucocratic tonalite, leucocratic granodiorite, and leucocratic quartz monzodiorite), mesocratic granitoids (tonalite, granodiorite, and quartz diorites), and abundant aplitic and pegmatitic dikes. The sequence of intrusion is as follows gabbro-diorites→mesocratic granitoids→granites and aplites and pegmatites associated with granites →leucocratic granitoids, based on emplacement relationships. Geochemically, this complex is metaluminous (ACNK=0.87) to peraluminous (ACNK=1.15). The mineralogical, lithological, and geochemical studies along with field observations indicate that the Alvand granites have S-type characteristics, leucocratic granitoids are arc-related I-type intrusions, mesocratic granitoids (tonalite and quartz diorites) possess transitional H-type features and granodiorites have S-type attributes. This complex has petrochemical characteristics that span the high K calc-alkaline and calc-alkaline series and displays the geochemical characteristics typical of magmatic arc intrusions related to an active continental margin. Depletion in Ti, Nb, Ta, Zr, Hf, Y, and HREE and enrichment in K, Rb, Cs, Th, and LREE are consistent with an arc setting associated with the subduction of Neo-Tethyan oceanic crust beneath the Sanandaj-Sirjan zone.

Geology, Geochemistry, and Geochronology of the Fenghuangshan Skarn‐type Copper Deposit in the Tongling Ore Cluster, Anhui Province, East China

Abstract:The Fenghuangshan skarn‐type Cu deposit, Tongling Ore Cluster, Anhui Province, is an important component in the Middle—Lower Yangtze River ore‐forming belt. To better understand magmatism and its relationship to mineralization, we investigated geochemical features, ore‐forming fluids, and geochronology of the Xinwuli intrusion and the related Fenghuangshan Cu deposit. Lithogeochemical characteristics show that the Xinwuli quartz monzodiorite is formed by mixing magma derived from upper mantle alkaline basalt that has been contaminated by crust materials. C, H and O isotopes indicate that ore‐forming fluids mainly come from the magma, with minor amounts of meteoric fluids involved at the late stage. S and Pb isotopic components indicate that ore‐forming materials are derived from the mantle. Molybdenite Re—Os isotopic dating yields Re—Os model ages ranging from 139.1±2.4 Ma to 142.0±2.2 Ma, with an isochronal age of 141.1±1.4 Ma, which is consistent with sensitive, high‐resolution ion microprobe (SHRIMP) zircon U—Pb ages of quartz monzodiorite and granodiorite in the mining area. Dating analysis yields ages from 136.0±2.0 Ma to 143.0±2.4 Ma for the quartz monzodiorite (a weighted average of 139.4±1.2 Ma) and ages from 136.7±2.0 Ma to 145.3±2.4 Ma for granodiorite (a weighted average of 141.0±1.1 Ma).

Early Cretaceous dioritic rocks in the Tongling region, eastern China: Implications for the tectonic settings

The Tongling district in the Lower Yangtze River belt is one of the most important Cu-polymetal producers in China. Copper–Au deposits in the region are closely related to Early Cretaceous dioritic intrusions, which can be classified into three rock associations: pyroxene diorite–pyroxene monzodiorite, quartz diorite–quartz monzodiorite and granodiorite. The dioritic rock series (SiO2=54.6–64.5wt.%) are calc-alkaline, with high Al2O3 (>15.4wt.%), Ba (Ba>700ppm) and Sr concentrations (~920ppm in average), and low Y and Yb concentrations, all of which are typical for adakite. Geochemical characteristics suggest that the Tongling adakitic rocks are genetically related to slab melting and subsequent interaction with the mantle, likely during a ridge subduction along the Lower Yangtze River Belt in the Early Cretaceous. Geothermometers show high formation temperatures of 800–900°C, which is consistent with interaction with the asthenosphere mantle as indicated. The relatively low εNd(t) values (−11.2 to −16.7) and high (87Sr/86Sr)i ratios (0.7067 to 0.7095) may be plausibly interpreted by contamination of enriched mantle materials and/or continental crust. The Tongling dioritic rocks are characterized by high radiogenic Pb isotopes with (206Pb/204Pb)i=17.80–18.56, (207Pb/204Pb)i=15.46–15.60, and (208Pb/204Pb)i=37.92–38.48, which mostly plot in the field of MORB, near the intersection of EM-1 and EM-2, and are clearly different from those of the upper and lower continental crust and Dabie adakites. These exclude major contamination from the continental crust. Given that eastern China has both EM-1 and EM-2 types of enriched mantle, whereas the Tongling region is located near the transition from EM-1 to EM-2, the enriched Sr–Nd isotopic characteristics of Tongling adakites are best explained by slab melts with assimilation of enriched mantle components.

Modification of a Palaeoproterozoic porphyry-like system: Integration of structural, geochemical, petrographic, and fluid inclusion data from the Aitik Cu–Au–Ag deposit, northern Sweden

The Aitik Cu–Au–Ag deposit in the Gällivare area in northern Sweden is Sweden's largest sulphide mine with an annual production of 35Mt of ore, and the biggest open pit operation in northern Europe. It is proposed in the present study that the Aitik deposit represents a Palaeoproterozoic, strongly metamorphosed porphyry copper deposit that was affected ca. 100Ma later by a regional IOCG-type hydrothermal event. Consequently, the Aitik deposit might represent a mixed ore system where an early copper mineralisation of porphyry type has been overprinted by later regional IOCG mineralisation.Several attempts have previously been made to genetically classify the Aitik Cu–Au–Ag deposit as a distinct ore type. New geochemical, petrographic, structural, and fluid inclusion results combined with published data have provided the opportunity to present new ideas on the genesis and evolution of the Aitik Cu–Au–Ag deposit. The emplacement of a ca. 1.9Ga quartz monzodiorite that host the ore at Aitik was related to subduction processes and volcanic arc formation, and synchronous with quartz vein stockwork formation and porphyry copper mineralisation. Highly saline aqueous (38wt.% NaCl) fluid inclusions in the stockwork veins suggest entrapment at 300°C and a pressure of nearly 3kbar, a high pressure for a typical porphyry copper ore, but consistent with conditions at associated deep root zones of intrusion-related magmatic–hydrothermal systems. The highly saline fluid formed disseminated and vein-type ore of mainly chalcopyrite and pyrite within comagmatic volcaniclastic rocks, and caused potassic alteration (biotite, microcline) of the host rocks. The early porphyry copper mineralising event was followed, and largely overprinted, by CO2 and aqueous medium- to high-salinity (16–57wt.% salts) fluids related to a ca. 1.8Ga tectonic and metamorphic event (peak conditions 500–600°C and 4–5kbar). Extensive deformation of rocks and redistribution of metals occurred. Magnetite enrichment locally found within late veins, and late amphibole–scapolite and K feldspar alterations within the deposit, are some of the features at Aitik implying that aqueous fluids responsible for IOCG-mineralisation (200–500°C and ~1kbar) and extensive Na–Ca alteration in the region during the 1.8Ga tectonic event also affected the Aitik rocks, possibly leading to addition of copper±gold.

SKARN GOLD MINERALIZATION AT THE GEODO MINE, SOUTH KOREA

The Geodo Bi-Te–bearing skarn deposit is located in the Taebaeksan mining district, South Korea. Both endoskarn and exoskarn are associated with the Cretaceous Eopyeong granitoids, which consist of magnetite-bearing oxidized (Fe 2 O 3 /FeO > 0.4) quartz monzodiorite to monzodiorite. Gold in the Geodo Mine occurs in a retrograde alteration stage within a garnet-rich proximal zone. Skarn minerals associated with gold ore include Fe-rich garnet (Ad 57–95 Gr 1–41 ) and a wide range of clinopyroxene (Hd 20–100 Di 0–79 ) compositions, broadly similar to those of typical gold-bearing skarn deposits. The paragenetic stages of the Bi- and Te-bearing skarn in the Geodo Mine consist of early calc-silicate alteration followed by three mineralization stages: Fe oxide, Cu rich, and Au rich. The Fe oxide and Cu-rich stages were deposited at higher temperatures than the Au-rich stage, based on mineral assemblage stabilities. Gold in Au-rich ores from the Geodo Mine occurs as native gold, ranging from 5 to 400 μ m in diameter, and is closely related to the Bi- and Te-bearing minerals bismuthinite and tetradymite, which at Geodo tend to be strongly enriched in Bi and depleted in S compared to ideal compositions. This association of gold with bismuthinite and tetradymite suggests that gold was deposited at relatively low temperatures, consistent with fluid inclusion studies on calcite that indicate that the gold was deposited from fluids ranging from 181° to 281°C and 8.0 to 10.9 wt % NaCl equiv, and with chlorite geothermometry indicating a range of 198° to 211°C. The presence of significant amounts of Bi- and Te-bearing minerals associated with Au suggests that liquid bismuth may have acted as a collector, increasing the concentration of gold.

A geochemical study of syn-subduction and post-collisional granitoids at Muzhaerte River in the Southwest Tianshan UHP belt, NW China

A combined study of zircon U–Pb ages and Lu–Hf isotopes, whole-rock elements and Sr–Nd isotopes was carried out for two granitic intrusions at Changawuzi and Alasan in Muzhaerte River of Southwest Tianshan (NW China). SHRIMP zircon U–Pb dating gave two 206Pb/238U ages of 333±3Ma and 326±3Ma for the Changawuzi pluton. LA-ICP-MS zircon U–Pb dating yielded two 206Pb/238U ages of 293±3Ma and 294±2.2Ma for the Alasan pluton. The two groups of ages predate and postdate the UHP metamorphic event at 320–305Ma in this region, respectively, registering to syn-subduction and post-collisional magmatism. The Changawuzi pluton is composed of gneissic porphyritic tonalite and garnet-bearing gneissic granitoids, having SiO2 of 55.1–64.5wt.%, K2O+Na2O of 2.58–5.07wt.%, MgO of 2.07–4.32wt.%, and Al2O3 of 17.4–19.9wt.% with A/CNK ratios of 0.99 to 1.27. They show arc-like geochemical affinity, with enrichment of LILE (K, Rb, Sr and Ba) and depletion of HFSE (Nb, Ta and Ti) and P, and moderate initial 87Sr/86Sr ratios of 0.7062–0.7071 and neutral εNd(t) values of −1.5 to 1.6. Except for one zircon with a negative εHf(t) value of −3.5, the others have positive εHf(t) values of 2.5–11.4 and single-stage Hf model ages of 509 to 869Ma. The Changawuzi pluton would be formed by partial melting of possible juvenile arc-derived rocks with minor involvement of ancient continental rocks during subduction of the paleo-South Tianshan oceanic crust and subsequent arc–continent collision. The Alasan pluton consists of medium-grained and porphyritic granitoids. The medium-grained granitoids are composed of granodiorite, quartz monzodiorite and quartz monzonite, displaying SiO2 of 59.37–65.49wt.%, K2O+Na2O of 6.24–8.2wt.% and MgO of 1.45–3.06wt.%, with A/CNK ratios of 0.87–1.04. They have relatively high initial 87Sr/86Sr ratios of 0.7082–0.7103, negative εNd(t) values of −5.9 to −5.6 and negative εHf(t) values of −4.5 to −1.1. The porphyritic granitoids consist of granite, granodiorite and quartz monzonite, with relatively high SiO2 (65.94–75.27wt.%) and K2O+Na2O (7.55–9.13wt.%), low MgO (0.18–1.22wt.%), and A/CNK ratios of 0.82–1.11. They also have relatively high initial 87Sr/86Sr ratios of 0.7073–0.7103, negative εNd(t) values of −6.0 to −0.5 and neutral εHf(t) values of −1.4 to 2.8. Both of them also display arc-like patterns of REE and trace element distribution. They belong to post-collisional granitoids and were produced by partial melting of the Paleo-Mesoproterozoic crust of obducted Central Tianshan block with minor involvement of juvenile crust. The geological occurrences of both the syn-subduction and post-collisional granitoids in this region suggest differential tectonic processes during the Late Paleozoic collision between the Tarim and Yili-Central Tianshan Blocks. It is inferred that slab breakoff occurred subsequent to the UHP metamorphism, resulting in partial melting of the subducted upper crust and the overlying lower crust and thus formation of voluminous granitoids like the Alasan pluton.

The nature and polygenetic origin of orbicular granodiorite in the Lower Castle Creek pluton, northern Sierra Nevada batholith, California

Mafic and granodioritic magmas mingled to produce a swarm of microdiorite enclaves in the granodiorite. The enclaves and rare hornfels inclusions were carried upward in an oval-shaped pipe, 30 m long and 15 m wide, probably as a gas-driven mass to a point where an H 2 O-rich, superheated felsic melt intruded the pipe and the enclave mass, and upon abrupt undercooling, deposited orbicular shells of tangentially oriented microcrystals of sodic plagioclase, quartz, K-feldspar, and biotite on 20% of the enclaves and inclusions now located only against the north margin of the pipe. The mass of orbicular and nonorbicular enclaves was then injected by a quartz monzodiorite magma that now comprises the matrix among the enclaves.

Magmatic differentiation in the calc-alkaline Khalkhab–Neshveh pluton, Central Iran

Geochemical and isotopic data (Sr, Nd) are presented for the Khalkhab–Neshveh pluton, an E-W elongated body of quartz monzogabbro, quartz monzodiorite, granodiorite and granite in the Urumieh–Dokhtar magmatic arc of Central Iran. The plutonic rocks are medium- to high-K, metaluminous, and I-type, with 52–71 wt.% SiO 2. The geochemistry shows smooth differentiation trends in which most major elements (except Al 2O 3, K 2O and Na 2O) are negatively correlated with SiO 2; K 2O, Ba, Rb, Ce, Nb, and Zr are positively correlated. Na 2O, Sr, Eu and Y follow curves that are not considered to represent simple mixing between mafic and felsic magmas, but reflect crystal fractionation of clinopyroxene, plagioclase and hornblende. Initial 87Sr/ 86Sr ratios (∼0.7047) and εNdt values (∼+3.0) are essentially constant, and the large volume of quartz monzogabbros compared to granites, as well as the lack of mafic enclaves in more evolved rocks, are also indicative of crystal fractionation rather than mixing of magmas from different sources. Clinopyroxene fractionation was the main control in the evolution of the magmas up to 55% SiO 2; hornblende took over from 55 wt.%, resulting in decreasing Dy/Yb with increasing silica content in the most siliceous rocks. Sr concentration increases up to 55% SiO 2, and then decreases together with CaO, Al 2O 3, Na 2O. Fractionation of opaque minerals and apatite throughout the sequence, and the continuous increase in K 2O and Ba vs. SiO 2 reflect the absence of significant fractionation of biotite and K-feldspar. Based on geochemical and isotope data, geophysics information and field studies, it seems that suturing of the Arabia and Iran plates caused the Khalkhab and Koush nousrat faults with left-lateral strike-slip in the Urumieh–Dokhtar region, and generated a purely tensional T space at 32° to the faults which was exploited by the emplacement of Khalkhab–Neshveh pluton.