Aegirine Syenite Research Articles

Petrogenesis of the Early Cretaceous Hongshan Complex in the Southern Taihang Mountains: Constraints from Element Geochemistry, Zircon U-Pb Geochronology and Hf Isotopes

The Hongshan complex, located in the southern part of the Taihang Mountains in the central part of the North China Craton, consists of syenite stocks (including fine-grained biotite aegirine syenite, medium-grained aegirine gabbro syenite, coarse-grained aegirine gabbro syenite, syenite pegmatite, and biotite syenite porphyry), with monzo-diorite and monzo-gabbro dikes. This paper presents zircon U-Pb ages and Hf isotope data and whole-rock geochemical data from the Hongshan complex. LA–ICP-MS zircon U–Pb age from the fine-grained biotite aegirine syenite, monzo-diorite, and monzo-gabbro are 129.3 ± 2.0 Ma, 124.8 ± 1.3 Ma, and 124.1 ± 0.9 Ma, respectively, indicating their emplacement in the Early Cretaceous when the North China Craton was extensively reactivated. The monzo-diorite and monzo-gabbro have low SiO2 contents (48.94–57.75 wt%), total alkali contents (5.2–9.4 wt%), and εHf (t) values of −22.3 to −18.4 and are enriched in MgO (4.0–8.2 wt%), Al2O3 (14.3–15.8 wt%), light rare earth elements (LREEs) and large ion lithophile elements (LILEs). Interpretation of elemental and isotopic data suggests that the magma of monzo-diorite and monzo-gabbro were derived from partial melting of the enriched lithospheric mantle metasomatized by slab-derived hydrous fluids. Syenites with high alkali (K2O + Na2O = 9.4–13.0 wt%) and Sr contents (356–1737 ppm) and low Yb contents (0.94–2.65 ppm) are enriched in Al (Al2O3 = 16.4–19.1 wt%), but depleted in MgO (0.09–2.56 w%), Cr (Avg = 7.16 ppm), Co (Avg = 6.85 ppm) and Ni (Avg = 9.79 ppm), showing the geochemical features of adakitic rocks associated with thickened lower crust. Combining zircon 176Hf/177Hf ratios of 0.282176 to 0.282359, εHf(t) values of −18.3 to −11.8 and εNd (t) values of −11.1 to −8.2, we conclude that the syenite magma was derived from the mixing of the thickened lower crust and the enriched lithospheric mantle magma. These magma processes were controlled by Paleo-Pacific plate subduction and resulted in the destruction and thinning of the central North China Craton.

Geochronology and mineralogy of the Weishan carbonatite in Shandong province, eastern China

The Weishan REE deposit is located at the eastern part of North China Craton (NCC), western Shandong Province. The REE-bearing carbonatite occur as veins associated with aegirine syenite. LA-ICP-MS bastnaesite Th-Pb ages (129 Ma) of the Weishan carbonatite show that the carbonatite formed contemporary with the aegirine syenite. Based on the petrographic and geochemical characteristics of calcite, the REE-bearing carbonatite mainly consists of Generation-1 igneous calcite (G-1 calcite) with a small amount of Generation-2 hydrothermal calcite (G-2 calcite). Furthermore, the Weishan apatite is characterized by high Sr, LREE and low Y contents, and the carbonatite is rich in Sr, Ba and LREE contents. The δ13CV-PDB (−6.5‰ to −7.9‰) and δ13OV-SMOW (8.48‰–9.67‰) values are similar to those of primary, mantle-derived carbonatites. The above research supports that the carbonatite of the Weishan REE deposit is igneous carbonatite. Besides, the high Sr/Y, Th/U, Sr and Ba of the apatite indicate that the magma source of the Weishan REE deposit was enriched lithospheric mantle, which have suffered the fluid metasomatism. Taken together with the Mesozoic tectono-magmatic activities, the NW and NWW subduction of Izanagi plate along with lithosphere delamination and thinning of the North China plate support the formation of the Weishan REE deposit. Accordingly, the mineralization model of the Weishan REE deposit was concluded: The spatial-temporal relationships coupled with rare and trace element characteristics for both carbonatite and syenite suggest that the carbonatite melt was separated from the CO2-rich silicate melt by liquid immiscibility. The G-1 calcites were crystallized from the carbonatite melt, which made the residual melt rich in rare earth elements. Due to the common origin of G-1 and G-2 calcites, the REE-rich magmatic hydrothermal was subsequently separated from the melt. After that, large numbers of rare earth minerals were produced from the magmatic hydrothermal stage.

Petrology and Geochemistry of Igneous Rocks in Zarinkamar Area, NE of Shahrood, Iran

Zarinkamar area is located in northeast of Shahrood, northeast of Iran, between latitudes of 36°37’ - 36°42’ and longitudes of 55°07’ - 55°12’. Different types of igneous rocks have an outcrop on the region. Intrusive igneous rocks include a type of syenite with aegirine pyroxene and the other includes quartz from 5 to 20 percent. Moreover, aegirine syenite, ordinary syenite, and quartz syenite have been injected into Karaj Formation with an age of middle to early Eocene. Also, some parts of trachyte magma have given rise to produce trachyte outcrops after passing the crust and current flows. Studying major and rare elements shows that a magma separation has been caused by separation smelting or a crystal separation. These magmas are alkaline and shoshonites and they have been originated in a continental rift. The magma of Zarinkamar region has been combined with acidic continent crust as it rose to the surface. High amount of Th, and Rb and low amount of Ti, P, Sr, and Ba can prove this hypothesis.

Photoluminescence of baratovite and katayamalite

The photoluminescence (PL) and optical excitation spectra of baratovite in aegirine syenite from Dara-i-Pioz, Tien Shan Mts., Tajikistan and katayamalite in aegirine syenite from Iwagi Islet, Ehime, Japan were obtained at 300 and 80 K. Under short wave (253.7 nm) ultraviolet light, baratovite and katayamalite exhibited bright blue-white luminescence. The PL spectrum of baratovite at 300 K consisted of a wide band with a peak at approximately 406 nm and a full width at half maximum (FWHM) of approximately 6.32k cm−1. The excitation spectrum of the blue-white luminescence from baratovite at 300 K consisted of a prominent band with a peak at approximately 250 nm. The PL and excitation spectra of katayamalite were similar to those of baratovite. The luminescence from these minerals was attributed to the intrinsic luminescence from the TiO6 center.

Geochronology and geochemistry of the Fangcheng Neoproterozoic alkali-syenites in East Qinling orogen and its geodynamic implications

Finding of Neoproterozoic syenites at Fangcheng in the northern Qinling region of the East Qinling orogen provides an important constraint on timing of tectonic transformation to extensional regime. The alkaline pluton consists mainly of nepheline syenite, aegirine syenite, and alkali-feldspar syenite. The syenites are of intermediate (SiO2 = 54%–62%), rich in alkali (K2O+Na2O = 12%–15%), aluminum (Al2O3 = 16.81%–23.26%) and large ion lithophile elements (LILE), without any obvious Nb, Ta, Zr, and Hf anomalies. The Fangcheng syenites are geochemically characterized by relative enrichment of LREE, minor differentiation of HREE, significant negative Eu anomalies (Eu = 0.13–0.23), less negative eNd(t) values of −1.37 to −3.90, young Nd model ages of 1364 to 1569 Ma, and high zircon saturation temperatures of 915 to 1044°C. The syenitic magmas probably originated from small proportion melting of upper mantle in an extensional regime of intraplate-anorogenic tectonic setting, and have been slightly contaminated by crustal materials during ascending and/or emplacement. LA-ICP-MS zircon U-Pb dating yields ages of 844.3±1.6 Ma (MSWD = 0.86), suggesting that the Fangcheng alkaline syenites formed in the early Neoproterozoic. They are the oldest Neoproterozoic alkaline rocks ever recognized in the Qinling orogen as well as in South China. This implies that the tectonic regime of the Qinling region would have transformed from post-collisional stretch to intraplate-anorogenic extension no later than 844 Ma.

Palaeomagnetism of the Early to Mid-Ordovician Salala igneous ring complex, Red Sea Hills, Sudan

SUMMARY Palaeomagnetic samples were collected from the Early to Mid-Ordovician igneous ring complex at Salala, northern Red Sea Hills, Sudan. Detailed demagnetization experiments on 114 samples from 17 sites yield two distinct groups of characteristic directions of the natural remanent magnetization. Component ‘A’, predominant in samples from the quartz syenitic central part and minor ring dyke of the complex, displays rather high blocking temperatures, well above 600°C and is presumably carried by haematite. The direction of this component (Dec/Inc = 1°/+37°) is virtually identical with the direction of the present day Earth's magnetic field at the sampling locality (Dec/Inc = 0°/ +37°). Mixed polarities of ‘A’ magnetization strongly suggest a Recent/pre-Brunhes age of this component, and the effects of long-term weathering and low-temperature oxidation. Component ‘B’, pointing to the southeast and upward, has been identified in seven sites from the major ring dyke, composed of aegirine syenite. Maximum blocking temperatures of this component do not exceed 580°C and, together with the results of rock magnetic and optical examinations, are indicative of primary magnetite as the carrier of the characteristic magnetization. The mean direction (Dec/Inc = 124°/-50°, α95 = 9.2, k= 44.1) differs significantly from component ‘A’ and is thought to be primary and representative for the direction of the Earth's magnetic field during emplacement and cooling of the ring complex in Mid-Ordovician times. The resulting palaeomagnetic pole (40°N, 30°W, dp= 8, dm= 12), situated off the coast of West Africa, plots very close to a cluster of Ordovician palaeomagnetic poles from Africa. These poles have not been integrated into the majority of the various apparent polar wander paths for Gondwana but this new result re-enforces their correctness. The application of recently revised rotation parameters for eastern Gondwana significantly reduces the longitudinal gap between the African data and that from eastern Gondwana (particularly Australia) for the Ordovician.

Geology and uranium-thorium mineral deposits of the Bokan Mountain Granite Complex, southeastern Alaska

The Bokan Mountain (Kendrick Bay) uranium-thorium deposits are associated with a Late Jurassic peralkaline granite ring-dike complex. The uranium-thorium deposits form pipe-like bodies along contacts, or occur as pods in en echelon northwest-striking shear zones. The host intrusive is a multiphased body consisting mainly of riebeckite granite porphyry and subordinately of pegmatite-aplite, aegirine granite porphyry, and eight other lesser rock types; the ore is closely associated with an albitized aegirine syenite. The ore consists of thorium and rare earth-rich rock containing uranothorite, uraninite, and generally less than 2% of sulfide species. About 100,000 tons (89,000 t) of ore have been mined at an average grade of about 1% U 3O 8 and nearly 3% ThO 2, mainly from the Ross-Adams pipe. The pipe itself lies along the contact of aegirine syenite and aegirine granite porphyry; it is as much as 24 m across and was mined along strike for over 300 m. The ore in shear zones occurs in lenses as much as 3 m thick and 30 m in strike length. Wallrock alteration within and adjacent to orebodies consists of pervasive hydrothermal albite and lesser amounts of chlorite, fluorite, calcite, quartz, sericite, and tourmaline. Hematite is present in the outer-distal parts of the ore zones. The minerals produced to date occur within the outer annular zone of the Bokan Granite Complex in which aegirine is present as the major alkali ferro-magnesian mineral. Ore emplacement occurred during the first subsidence event in association with devolatilization of the magma chamber. The pod-like ore zones appear to have formed during regional faulting synchronous with magma crystallization and subsequent hydrothermal events. Subsequent magma crystallization yielded riebeckite granites that were depleted in U and Th. Filling temperatures in ore stage fluid inclusions within quartz range from 320 to 331°C with pressure corrections increasing the temperature of formation to 420°C or higher, depending on dissolved gas content. Sulfur isotopic analyses on pyrite, galena, sphalerite and pyrrhotite indicate disequilibrium, but δ 34S H 2S is estimated at 7.6‰. Carbon and oxygen isotopic analyses on ore stage calcite yield δ 18O H 2O of 6.8 to 8.1‰ and δ 13C ΣC of −4.3 to −7.0‰. The oxygen and carbon isotopic data support a magmatic origin for the calcite and associated thorium-uranium deposits.

Katayamalite, a new Ca-Li-Ti silicate mineral from Iwagi Islet, Southwest Japan.

Katayamalite occurs as a fine-grained accessory mineral amounting to 0.3–0.5 percent by volume in the aegirine syenite from Iwagi Islet, Ehime Prefecture, Southwest Japan. It coexists usually with albite, aegirine and pectolite. To the naked eye, katayamalite is white in color and phosphorescent to the ultraviolet rays. Striation white, luster vitreous. Hardness (Mohs) 3.5–4.0. Specific gravity 2.899 (calc), 2.91 (meas.). (001) cleavage is perfect. In thin section it is colorless with strong absorption. α=1.670, β=1.671, γ=1.677, γ−α=0.007, 2V(+)=ca. 32°.Chemical analysis shows SiO2 52.31, TiO2 10.99, Fe2O3 0.29, MnO 0.22, Li2O 3.25, CaO 28.25, Na2O 0.22, K2O 2.89, H2O 1.21, F 0.34, –O=F2 0.14, total 99.83%, corresponding ideally to (K, Na)Li3Ca7(Ti, Fe+3, Mn)2[Si6O18]2(0H, F)2 with Z=4.Katayamalite is triclinic with a0=9.721, b0=16.923, c0=19.942A, α=91.43°, β=104.15°, γ=89.94°, Space group C1. The strongest lines in X-ray powder data are 3.23 (100) (006·0-44), 3.06 (30) (2-43), 2.943 (30) (-3-14·3-11·-153), 2.898 (30) (-2-44·2-42), 2.417 (30) (008), 1.933 (40) (00.10).Katayamalite resembles baratovite (Dusmatov et al., 1975) both structurally and also chemically, but it is distinguished from the latter by the difference in crystal system and unit cell parameters. Dominance of OH over F and lacking of Zr replacing Ti are another chemical features of katayamalite.The name katayamalite is given for the mineralogist, Emeritus Professor Nobuo Katayama.

Petrology and petrogenesis of the Bokan Granite Complex, southeastern Alaska

The Bokan Granite Complex is a peralka-line ring-dike complex emplaced into marine shales, volcanic flows and tuffs, and plutonic rocks. Mineralogically and chemically, the Complex is composed of I-type granites. Aegirine- and riebeckite-bearing granite aplites, porphyries, and pegmatites comprise twelve distinct intrusive episodes. The aegirine-bearing rocks occur in an outer annular zone formed during early crystallization. Subsequent rocks are riebeckite-bearing, due to devolatilization of the magma chamber during a collapse-ring-dike emplacement event. Early crystallization of alkali feldspar occurred during magma ascension from a lower crustal-upper mantle source. At shallow depths, subsolvus crystallization allowed microcline and albite to dominate. Local bodies of aegirine syenite were formed during the early collapse-ring-dike emplacement, in response to the magma devolatilization. The riebeckite granites reflect lower Po2 and possibly declining peralkalinity. The granitic rocks at Bokan all exhibit Na2O contents greater than K2O. Lithophile elements are concentrated in all the rocks, especially in zones where hydrothermal albite and chlorite formed. Rb/Sr ratios increase in progressively younger rocks in the Complex. Agpaitic ratios vary from 0.92 to 2.08 for the granitic rocks.

Sugilite, a new silicate mineral from Iwagi Islet, Southwest Japan

Sugilite occurs as an essential mineral amounting to 3–8 percent by volume in aegirine syenite from Iwagi Islet, Ehime Prefecture. It is associated with albite, aegirine, pectolite and a Ca-K-Ti silicate (a still to be identified mineral). Sugilite is light brownish yellow, luster vitreous, streak white. Symmetry hexagonal. Cleavage 0001 weak. Hardness 6–61/2. Specific gravity 2.802 (calc.), 2.74 (meas.).Under the microscope, it is uniaxial negative with e=1.607, ω=1.610, ω−e=0.003, and colorless.Estimated chemical composition is SiO2 71.38, TiO2 0.51, A12O3 2.97, Fe2O3 12.76, FeO 0.19, Li2O 3.14, Na2O 4.37, K2O 3.76, H2O(+) 0.81, H2O(−) 0.12, total 100.01%, corresponding ideally to (K, Na)((H2O), Na)2(Fe3+, Na, Ti, Fe2+)2(Li, Al, Fe3+)3(Si12O30) with Z=2.The unit cell dimensions are a0=10.007(2), c0=14.000(2)A. Space group D26h−P6⁄mcc. X-ray powder data resemble those for sodgianite, milarite, osumilite, merrihueite, roedderite and brannockite.It is clear from the above-cited data that sugilite has milarite-type structure and resembles sodgianite and brannockite in containing lithium in tetrahedral site, but it is distinguished by a high content of ferric iron in 6-coordination.The name is given in honour of the late Professor Ken-ichi Sugi (1901-1948), who first found the occurrence of this mineral with Mr. M. Kutsuna.

“Aegirine syenite” from Iwaki I., Ehime Pref. Japan. Dedicated to the memory of the late prolsessor K. Sugi

“Aegirine syenite” from Iwaki I., Ehime Pref. Japan. Dedicated to the memory of the late prolsessor K. Sugi