Sodic-calcic Amphibole Research Articles

Mineral chemistry and P–T conditions of the winchite-bearing metabasic rocks in the NE edge of the Menderes Massif (Western Türkiye)

The Menderes massif is a large metamorphic crystalline complex located in western Turkey. The massif consists of late Neoproterozoic basement (core) rocks and Palaeozoic - Cenozoic cover units that have undergone by high- and low-grade polyphase metamorphisms. Palaeozoic to Mesozoic cover units cropped out in the NE edge of the massif (east of Sivaslı) are overlaid tectonically by upper Cretaceous meta-ophiolitic rocks. The meta-ophiolitic unit comprises blocks mainly of metabasalt, metagabbro, metadiorite and metaultramafite within an intensively sheared serpentinite matrix. It also includes blocks of epidote-actinolite-schist and tremolite-actinolite-schist, which originated from basic rocks, as well as chlorite schist blocks, which originated from ultramafic rocks. Sodic-calcic amphiboles recorded in the samples of metabasalt block taken from the marble-metabasalt block boundary, at the tectonic contact where the meta-ophiolitic rocks overlap the underlying marble sequence. Sodic-calcic amphiboles were classified into winchite and ferri-winchite with relatively homogeneous TSi (7.35–8.01 a.p.f.u.), and XMg (0.69–0.80) values. P-T conditions were estimated to be around 300–400 °C and 5–6 kb based on the mineral chemical analyses of the sodic-calcic amphiboles. According to these values, the NE edge of the Menderes Massif must have undergone metamorphism under a medium-pressure (MP) greenschist facies.

Ferro-chloro-winchite in Northwest Africa (NWA) 998 apatite-hosted melt inclusion: New insights into the nakhlite parent melt

Melt inclusions are of major significance because they can constrain the volatile abundances in magmas. Here, we report the discovery of the first melt inclusion in a martian apatite containing the first chloro-amphibole reported in Northwest Africa (NWA) 998, a sample that crystallized early from the nakhlite-source. The amphibole is also the first sodic-calcic amphibole in a nakhlite, identified as ferro-chloro-winchite (4.75 wt% Cl) by FIB-TEM. The melt inclusion is present in a euhedral, cumulus apatite grain (Cl/F = 2.11) and is surrounded by a shell of voids. Evidence indicates that the melt inclusion remained as a closed system although syn- and post-entrapment processes may have modified the chemical composition of the original trapped melt. The inclusion also contains Fe-rich, Ca-poor pyroxene and a residual silicate melt consisting of pyroxene and interstitial K-rich glass. Additionally, Cl-enriched apatite is present within the boundaries of the melt inclusion. This apatite could result from cracking of host-apatite during contraction of the melt inclusion glass or represent daughter apatite crystallizing on the walls of the inclusion. Given that Cl-enrichments are found in the host apatite outside the melt inclusion, it is inferred that a later, fluid alteration event locally modified the composition of the apatite in and/or around the melt inclusion. The calculated bulk composition of the melt inclusion is generally consistent with previous work in other nakhlites. Prior to this study, Cl-rich amphiboles have only been found within olivine- and pyroxene-hosted melt inclusions in the later-formed nakhlites. The present study thus demonstrates that (i) the nakhlites record magmatic mixing with a Cl-rich exogenous component that is absent within olivine-hosted melt inclusions in the chassignites, (ii) Cl-rich amphiboles were able to crystallize from the earliest nakhlite parent melt, and (iii) the presence of a Cl-rich fluid was not required to stabilize chloro-amphiboles. We also conclude that magmatic martian amphiboles likely stabilized at lower pressures (and temperatures) than terrestrial amphiboles due to their higher Cl contents.

Mineralogical and geochemical characteristics of the Sedemte Prestola potassic alkaline pluton

The Sedemte Prestola pluton is an intermediate to acid plutonic body of Variscan age (308.7 ± 9.1 Ma). Despite its small size, several petrographic varieties are present: syenites, quartzsyentes and granites. It is composed of potassium feldspar, quartz, sodic-calcic amphibole; biotite, when present, is often rimmed by amphibole or strongly altered; zircon, titanite, apatite and ilmenite are the accessory phases. The rocks display pronounced potassic character with up to 10.4 wt% K2O, peralkaline tendency, and significant trace element enrichment for REE, Zr, Th, U, and Ba. The rocks also show enriched isotopic characteristic with 87/86Sri between 0.7107 and 0.7111, and 143/144Ndi between 0.51193 and 0.51182. The geochemical features of the Sedemte Prestola pluton imply orogenic geodynamic setting of formation as a product of more primitive magma fractionation. Isotopic characteristics and high LILE, Th and U contents support the derivation from enriched mantle source – phlogopite-bearing peridotites in the spinel stability field.

Resurfacing of deeply buried oceanic crust in Naga Hills Ophiolite, North-East India: Petrofabric, microstructure and seismic properties

We have studied the microstructure, texture and seismic anisotropy of a foliated blueschist-eclogite rock in the Naga Hills Ophiolite (NHO) complex, North-East India. The rock is composed essentially of omphacite, sodic amphibole (glaucophane), sodic-calcic amphibole (barroisite), phengite, and garnet, and represents oceanic crust that experienced Neo-Tethyan subduction and metamorphism before it resurfaced and accreted in the ophiolite. Omphacite and glaucophane show weak shape preferred orientation (SPO), while phengite displays a strong SPO. The Crystallographic Preferred Orientation (CPO) of omphacite is characterized by the [001]-axes gridle within the foliation, and the (010)-poles concentrated sub-perpendicular to the foliation. For glaucophane, the [001] axis aligns parallel to lineation and the [100] axis and (110) pole plunge perpendicular to foliation. These CPOs correspond to SL-type fabrics, related to plane strain deformation geometry. Based on our analysis, we propose that the observed texture had developed from plastic deformation through dislocation creep. Employing the textural data, we have presented the seismic anisotropies of the individual minerals, blueschist-eclogite domains and discussed their contributions in the bulk-rock anisotropy. The calculated bulk-rock seismic anisotropies, AVP and AVS, of the rock are 12.8% and 8.1%, respectively, which correlate with the observed seismic anisotropy of the subducting oceanic crust.

Petrogenesis and tectonic setting of the Cambrian Kharly alkaline–carbonatite complex (Sangilen Plateau, Southern Siberia): Implications for the Early Paleozoic evolution of magmatism in the western Central Asian Orogenic Belt

The Cambrian Kharly alkaline plutonic complex composed mainly of foidolite and nepheline syenite makes up a small intrusive field in the Sangilen Plateau in Tuva (southern Siberia). The rocks show large ranges of major oxides (38–58 wt% SiO2; 1–18 wt% Na2O + K2O; 11–28 wt% Al2O3; 1.5–20 wt% CaO; 0.1–8 wt% MgO; 2–12 wt% Fe2O3) controlled by variable percentages of minerals: clinopyroxenes, calcic amphiboles, micas, nepheline and feldspars. Alkaline rocks are cut by carbonatite veins composed of predominant calcite coexisting with femic minerals (10–15% of aegirine-ferrosalite-hedenbergite, sodic-calcic amphiboles, ferrobiotite, Ti-garnet), Na–K feldspar and nepheline (up to 15–20%), fluorapatite (up to 20–25%), Sr-apatite, and accessory carbocernaite, titanite, Ti-magnetite and ilmenite. Carbonatites (4057–8859 ppm Sr, 426–1901 ppm Ba (Sr/Ba ≥ 2), 290–980 ppm REE + Y, 2 to 100 ppm Zr, and 0.5 to 15 ppm Nb) possibly originated at high (≥500–650 °C) temperatures as a result of liquid immiscibility. The isotope systematics of rocks and minerals (εNd(t) from ~2.9 to 6.5; 207Pb/206Pbin = 0.89; 208Pb/206Pbin = 2.15; 87Sr/86Sr(t) = 0.70567–0.70733, δ18OV-SMOW ≈ 7.2–19.5‰, and δ13CV-PDB from −6.0 to −1.4‰) suggest mixing of PREMA and EM 1 material during magma generation and crustal contamination of the evolving melts. The rocks bear signatures of interaction with “magmatic-equilibrated” fluids or heated meteoric waters. LILE/HFSE ratios indicate mixed magma sources that involved the material of IAB and OIB, as well as a crustal component, possibly, due to interaction of a mantle plume with rock complexes on the active continental margin.

Mafic whole-rock geochemistry and neodymium isotopes, Green Mountain and Rowe/Prospect Rock slices, Vermont Appalachians

Mafic rocks containing sodic-calcic amphibole in the Green Mountain slice (GMS) and Rowe/Prospect Rock slice (R/PRS), Vermont Appalachians were originally subalkaline basalts emplaced as melts during Neoproterozoic rifting of Rodinia that led to the formation of the Iapetus Ocean basin. Relatively high degrees of partial melting of asthenosphere that was highly depleted in incompatible elements produced R/PRS magma(s), which may have been contaminated locally by continental crust and/or fluids. Trace element chemistry suggests that mafic bodies from different locations in the R/PRS may be fractionated magmatic equivalents. Mafic rocks in the GMS formed from magmas produced by relatively low degrees of partial melting of mantle that was relatively enriched in incompatible elements compared to depleted mantle. These enriched melts may have been derived from a plume and/or enriched lithospheric components, potentially continental crust, embedded in depleted upper mantle. A depleted mantle signature preserved locally in the GMS probably reflects increasing asthenospheric input during crustal thinning, opposed to crustal or fluid contamination. Whole-rock minor and trace element data from the GMS and R/PRS are distinct from analyses of glaucophane schist from the Tillotson Peak Complex in northern Vermont, which may be exhumed Iapetan ocean floor. Exhumed mafic rocks in the GMS and R/PRS were formed as lower plate melts prior to relatively high pressure subduction zone metamorphism, providing evidence for subduction of the Laurentian margin, not subduction erosion. Low pressure greenschist facies mafic rocks that occur structurally between the GMS and R/PRS were sourced from depleted or highly depleted mantle in a supra-subduction zone environment, potentially a forearc or backarc basin; an ophiolitic origin is equivocal. Geochemical and isotopic data and interpretations are compatible with rift-related tectonomagmatic models for the peri-Laurentian realm of the northern Appalachians.

Electron probe microanalysis of Fe2+/ΣFe ratios in calcic and sodic-calcic amphibole and biotite using the flank method

We present an analytical approach to determine the Fe2+/ΣFe ratio in amphiboles and biotites using electron probe microanalysis (EPMA). The “flank method” applied in this study is based on the fact that FeL line spectra show different peak position and intensity for Fe2+ and Fe3+, which is associated with a resonant process involving both X-ray absorption and emission. The flank positions for Lα and Lβ, which correspond to sites with minimal Fe3+L3 absorption and maximal Fe2+L2 absorption respectively, are determined based on the L-line spectra difference of two Fe-rich ferric and ferrous garnet endmembers, i.e. andradite and almandine. Spectra intensities measured at the Lα and Lβ flank positions for selected amphibole and biotite references can be quantitatively correlated with their Fe2+ weight contents by a linear relation: Lβ/Lα = a + b*Fe2+, in which a and b are constants calibrated upon reference materials. It is emphasized that the constants a and b may vary significantly for different mineral groups and analytical conditions. Thus, a calibration is necessary for each analytical session. Our tests show that the potential beam damage during EPMA that may induce oxidation of the measured material can be minimized by using a large beam size (e.g., 20 μm). The Fe2+/ΣFe ratios determined using the EPMA flank method in collected natural calcic and sodic-calcic amphiboles (FeOT = 2.4–12.7 wt%, Fe2+/ΣFe = 0.45–75) and biotites (FeOT = 4.3-28.2 wt%, Fe2+/ΣFe = 0.67–0.87) are consistent within an error of ±0.1 with the data obtained from the colorimetric wet chemistry method. The EPMA flank method has the potential to be widely applied for accurate in-situ determination of Fe oxidation states in a wide range of minerals, provided that references are available.

The Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean: Further evidence from the Barleik subduction-related metamorphic complex in the West Junggar region, NW China

In this study, we present new evidence from the Barleik subduction-related metamorphic complex in the southern West Junggar region, northwestern China, for the Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean. The Barleik metamorphic complex is mainly composed of blueschist and amphibolite blocks within an ophiolitic mélange and their protoliths are calc-alkaline andesite and alkali and tholeiitic basalts. The calc-alkaline andesite has a zircon U–Pb age of 502±2Ma, obtained from magmatic cores of zircon grains, and shares geochemical features similar to the 515–485Ma intra-oceanic arc magmatic rocks in the West Junggar region. By contrast, the alkali and tholeiitic basalts have trace element features similar to ocean island and enriched mid-ocean ridge basalts, respectively. Rutile and sodic–calcic amphibole from the amphibolite have a U–Pb age of 502±25Ma and a 40Ar/39Ar age of ∼504Ma, respectively, which are in good agreement within errors with a 40Ar/39Ar age of 492±4Ma for phengite from the blueschist. These metamorphic ages of ∼500Ma are interpreted to represent the timing of Pacific-type subduction-related metamorphism and are also compatible with ages of the oldest supra-subduction zone ophiolites (531–512Ma) and intra-oceanic arc plutons (515–485Ma) in the southern West Junggar region. Being one of the oldest subduction-related metamorphic complexes (509–490Ma) in the southern Central Asian Orogenic Belt, the Barleik metamorphic complex, together with the oldest arc plutons, definitely indicate the initial intra-oceanic subduction in the southern Paleo-Asian Ocean at least in the Early Cambrian.

Petrogenesis of Late Permian silicic rocks of Tu Le basin and Phan Si Pan uplift (NW Vietnam) and their association with the Emeishan large igneous province

Major and trace elements and whole rock Sr–Nd isotope data of Late Permian silicic plutonic and volcanic rocks from the Phan Si Pan–Tu Le region in NW Vietnam were collected in order to establish their petrogenetic relationship with the magmatic rocks of the Song Da zone (NW Vietnam) and the alkaline silicic rocks of the Panxi area of the Emeishan large igneous province (ELIP) in SW China. The granites and rhyolites have geochemical characteristics of anorogenic granites (e.g. high Fe# and high Ga/Al) and are further subdivided based on mineralogy. The Phu Sa Phin and Muong Hum granites contain sodic to sodic–calcic amphiboles and sodic pyroxene, while the Phan Si Pan granite does not. The Phu Sa Phin and Muong Hum granites occasionally show peralkaline to metaluminous compositions, while the Phan Si Pan granites and the Tu Le rhyolites have metaluminous to peraluminous compositions. The chondrite-normalized REE patterns [(La/Yb)N=3.6–51.3, (Gd/Yb)N=1.4–3.4] and the primitive mantle-normalized spidergrams (enrichment in high field strength elements) are similar to those of the Song Da silicic rocks and the Panzhihua and Taihe granites in the Panxi area. Rhyolite-MELTS modeling suggest that the silicic magmas were likely generated by fractionation of the Song Da high-Ti basalts. The εNd(t) values range from weakly negative to moderately positive values (−2.2 to +2.2), suggesting the silicic rocks may be assimilated by basement rocks during magma emplacement. Permian magmatic rocks in the Phan Si Pan–Tu Le region are petrologically, geochemically and geochronologically comparable to those of the inner zone of ELIP. Although Permian lithospheric mantle and lower crustal structure of the Phan Si Pan–Tu Le region may be destroyed by a lithospheric removal in response to Cenozoic India–Eurasia collision, our results along with recent geophysical analyses in NW Vietnam suggest that the upper to middle crust of Phan Si Pan–Tu Le region represent a remnant upper to middle crust of inner zone of ELIP.

Single zircon Hf–O isotope constraints on the origin of A-type granites from the Jabal Al-Hassir ring complex, Saudi Arabia

The Jabal Al-Hassir ring complex in the southern Arabian Shield is an alkaline granite complex comprising an inner core of biotite granite that outwardly becomes a porphyritic sodic-calcic amphibole (ferrobarroisite–katophorite) granite. A combined study of mineral chemistry and single zircon Hf–O zircon isotope analyses was carried out to infer the magma sources of the Neoproterozoic post-collisional A-type granitoids in Saudi Arabia. The granitic rocks show high positive initial ɛHf(t) values of +7.0 to +10.3 and δ18O values of +5.8‰ to +7.4‰ that are consistent with melting of a juvenile crustal protolith that was formed during the Neoproterozoic assembly of the Arabian-Nubian Shield (ANS). Crustal-model ages (Hf-tNC) of 0.71–0.94Ga indicate minor contribution from an older continental crust in the formation of the Jabal Al-Hassir granitic rocks (crystallization age=620±3Ma), but any such component is likely to be Neoproterozoic in age. Temperature and oxygen fugacity (ƒO2) estimates suggested that the Jabal Al-Hassir A-type granite magma was generated at high temperature (820–1050°C) and low ƒO2. Geochemical characteristics (e.g., low ƒO2), geochronological data, and Hf and O isotope compositions, indicate that the magmas of the Neoproterozoic A-type granites of the Jabal Al-Hassir ring complex were likely generated by crustal partial melting of a juvenile Neoproterozoic lower crustal tholeiitic rocks, following collision between East and West Gondwana in the final stages of the evolution of the Arabian Shield.

Widespread hydrothermal alteration minerals in the fine‐grained matrices of the Tieschitz unequilibrated ordinary chondrite

AbstractMineralogic, textural, and compositional studies of black and white matrices in the unequilibrated ordinary chondrite Tieschitz (H/L, 3.6) show, for the first time in an ordinary chondrite, the presence of widespread, randomly distributed geode‐like voids and veins. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies show that these voids and veins are partially or completely filled by sodic–calcic amphiboles (winchite and barroisite). The occurrence of amphiboles provides unequivocal evidence of the involvement of fluids in the metamorphic evolution of the parent body of Tieschitz. The presence of amphiboles as the main hydrous phases, rather than phyllosilicates, indicates that aqueous fluids were present at or close to the peak of thermal metamorphism, rather than during the waning stages of the cooling history of the parent body. In addition, ferrous olivine crystals, in association with the amphibole, also establish an important link between thermal metamorphism and hydrous phases formed at high temperatures. Mineralogic and textural evidence suggests that the white matrix and amphibole formed contemporaneously from the same hydrous fluid, prior to the formation of ferrous olivine crystals. Additionally, a dark inclusion identified in the host chondrite has mineralogic, petrologic, and bulk chemical characteristics that are similar to the black matrix of host Tieschitz, suggesting that this dark inclusion was emplaced before or during parent body metamorphism.

Geochemical variation of amphiboles in A-type granites as an indicator of complex magmatic systems: Wentworth pluton, Nova Scotia, Canada

The Wentworth pluton is the most complex intrusion among a series of A-type granitic plutons, emplaced along an active shear zone in the Cobequid Highlands of Nova Scotia during the latest Devonian–earliest Carboniferous. This pluton consists of A-type granites of different generations and a large gabbroic body. Among all late Paleozoic plutons in the Cobequid Highlands, only the Wentworth granites contain both primary calcic (edenite, hornblende) and sodic amphiboles (arfvedsonite). Whole-rock, and mineral chemical data were examined along with estimated magmatic parameters, such as temperature, emplacement pressure, oxygen fugacity and volatile contents, in order to understand the geological factors responsible for this mineralogical variation. The granites with calcic amphiboles show systematically lower εNd values, magmatic temperatures, and F-in-melt contents and appear geochemically less evolved, compared to the granites with the sodic amphiboles. All granites, however, appear geochemically homogeneous with limited evidence of fractionation. Specific chemical differences between these two types of granites indicate the presence of two coeval but distinct granitic systems in the Wentworth pluton. The granites with the calcic amphiboles were formed from a geochemically less evolved, hydrous, relatively calcic melt, whereas the granites with sodic amphiboles were emplaced at structurally deeper levels and were derived from a relatively drier sodic melt, which had a larger mantle component and was enriched in fluorine. Coexistence of these two magmas is indicated by the presence of interstitial sodic–calcic amphiboles in a late granitic dyke. This study provides evidence that in A-type granites, where fractional crystallization is limited, extreme variation in the type of amphibole can be the result of a very complex magmatic history.

The discovery of blueschist-facies rock in Airgin Sum area, Erenhot, Inner Mongolia and its tectonic significance

Blueschist has been discovered in melange of the early-middle Paleozoic Orogenic Belt in Airgin Sum area, Erenhot. Mineral chemistry analysis reveals that the blue-amphibole belongs to sodic-calcic and sodic amphiboles in this rock. The sodic-calcic amphibole can be divided into magnesiokatophorite, winchite and barroisite, while all the sodic amphiboles are magnesioriebeckite. Our research indicates that the temperature and pressure of blueschist-facies metamorphism were about 400-450℃ and 0.7-1.0 GPa, respectively, which suggests a high-pressure, low-temperature metamorphic condition. The discovery of the blueschist-facies rock indicates that the early-middle Paleozoic Orogenic Belt extends 200 km to the west and the suture between North China Plate and South Mongolia Microcontinent is located from Airgin Sum to Sunid Zuoqi.

MAFIC MINERALS OF THE ALKALINE PEGMATITES IN THE LARVIK PLUTONIC COMPLEX, OSLO RIFT, SOUTHERN NORWAY

The major and trace element geochemistry of mafic silicate minerals from alkaline pegmatites within the 10 ring sections of the Larvik plutonic complex, Oslo rift, southern Norway, have been studied to shed light on the complex evolutionary history of the pegmatites. Pyroxene compositions plot within the aegirine-diopside-hedenbergite ternary diagram, trending from the 50-50% Di-Hd tie line towards the 100% Ae endmember. Primary magmatic diopside and hedenbergite with minor aegirine occur primarily within miaskitic to low agpaitic pegmatites, with compositions ranging from Ae 3 Di 45 Hd 51 to Ae 89 Di 5 Hd 6 , whereas aegirine and aegirine-augite are the primary magmatic clinopyroxenes in agpaitic pegmatites, with compositions ranging from Ae 31 Di 27 Hd 42 to Ae 90 Di 6 Hd 4 . Secondary clinopyroxene, after amphibole or as a hydrothermal phase within fractures and vugs, is dominantly aegirine, with compositions ranging from Ae 59 Di 16 Hd 25 to Ae 99 Di 1 Hd 0 . Primary amphibole compositions are dominantly calcic (edenite, ferro-edenite, hastingsite, magnesio-hastingsite, pargasite, and ferro-pargasite), with less common late-stage sodic-calcic amphiboles (katophorite, magnesio-katophorite, ferro-richterite, and taramite); sodic amphiboles (ferro-ferri-nyboite, ferri-nyboite) are only observed in agpaitic pegmatites. All early pegmatite mafic minerals in low agpaitic pegmatites have negative Eu anomalies (Eu/Eu* = 0.16–0.26), positive Ce anomalies, and low Nb/Ta N and Y/Ho N ratios. Sodic mafic silicates in highly agpaitic pegmatites are HREE-enriched, with Ce/Yb N = 0.22–0.58 compared to Ce/Yb N > 1 for all other primary mafic phases, are strongly depleted in MREE, and have only slightly negative Eu anomalies (Eu/Eu* = 0.66–0.75). On the basis of major and trace element geochemistry, it can be concluded that miaskitic and alkaline pegmatites in Ring Sections 1–8 within the Larvik complex have been derived from the same parental melt, whereas pegmatites in Ring Sections 9 and 10 have a distinct geochemical signature, suggesting a separate source.

Geochemistry and petrogenesis of the Ediacaran post-collisional Jabal Al-Hassir ring complex, Southern Arabian Shield, Saudi Arabia

The Jabal Al-Hassir ring complex is located between latitudes 19°21′ and 19°42′N, and longitudes 42°55′ and 4312′E, Southern Arabian Shield. It is an alkaline to highly fractionated calc-alkaline granite complex consisting of an inner core of biotite granite followed outward by porphyritic sodic-calcic amphibole (ferrobarroisite) granite. U–Pb zircon geochronology indicates that the Jabal Al-Hassir ring complex was emplaced at ca. 620Ma. The granites display highly fractionated geochemical features (i.e., Eu/Eu*=0.05–0.35; enrichment of K, Rb, Th, U, Zr, Hf, Y and REE; depletion of Ta, Nb, Ba, Sr, P, Eu, and Ti). Jabal Al-Hassir granites are post-collisional plutonic rocks and contain abundant microcline perthite and sodic-calcic amphibole, sharing the petrological and chemical features of A2-type granites. Sri values range from 0.70241 to 0.70424, are similar to those expected for magmas extracted from a Neoproterozoic depleted source and much lower than what would be expected, if there was minor involvement of pre-Neoproterozoic continental crust. The geochemical characteristics indicate that their magma was most plausibly represented by partial melting of juvenile lower crust following the collision between East and West Gondwana at the final stage of the Arabian Shield evolution. The data presented in this study are therefore consistent with an intraplate, post-collisional magmatism formed at the beginning of a transition from convergent to extensional tectonics.

The Sabzevar blueschists of the North-Central Iranian micro-continent as remnants of the Neotethys-related oceanic crust subduction

The Sabzevar ophiolites mark the Neotethys suture in east-north-central Iran. The Sabzevar metamorphic rocks, as part of the Cretaceous Sabzevar ophiolitic complex, consist of blueschist, amphibolite and greenschist. The Sabzevar blueschists contain sodic amphibole, epidote, phengite, calcite ± omphacite ± quartz. The epidote amphibolite is composed of sodic-calcic amphibole, epidote, albite, phengite, quartz ± omphacite, ilmenite and titanite. The greenschist contains chlorite, plagioclase and pyrite, as main minerals. Thermobarometry of a blueschist yields a pressure of 13–15.5 kbar at temperatures of 420–500 °C. Peak metamorphic temperature/depth ratios were low (~12 °C/km), consistent with metamorphism in a subduction zone. The presence of epidote in the blueschist shows that the rocks were metamorphosed entirely within the epidote stability field. Amphibole schist samples experienced pressures of 5–7 kbar and temperatures between 450 and 550 °C. The presence of chlorite, actinolite, biotite and titanite indicate greenschist facies metamorphism. Chlorite, albite and biotite replacing garnet or glaucophane suggests temperatures of >300 °C for greenschist facies. The formation of high-pressure metamorphic rocks is related to north-east-dipping subduction of the Neotethys oceanic crust and subsequent closure during lower Eocene between the Central Iranian Micro-continent and Eurasia (North Iran).

40Ar/39Ar geochronology constraints on the formation age of Myanmar jadeitite

The jadeitite that occurs in Myanmar is one of the largest and most important jadeite deposits in the world. However, the formation age of the Myanmar jadeitite remains poorly constrained. Here, we conduct an integrated study using petrology and 40Ar/39Ar geochronology to analyze the Myanmar jadeitite. Petrological observations show that the studied jadeitite consists mainly of jadeite minor sodic–calcic amphibole and analcime and that the jadeitite was cut by late amphibole rock consisting of sodic amphibole and minor chlorite. 40Ar/39Ar laser stepwise heating dating of jadeite from the jadeitite yielded a plateau age of 123.9±3.4Ma, the sodic–calcic amphibole associated with jadeite yielded a plateau age of 134.8±1.4Ma, and the sodic amphibole of late amphibole rock yielded a plateau age of 92.7±1.2Ma. These results indicate that the studied jadeitite was formed during the early Cretaceous from (135Ma) high-pressure (HP) metasomatism and then experienced a late Cretaceous (93Ma) HP metasomatism. Combining our results with previous studies using petrography and geochronology, we suggest that the formation process of Myanmar jadeitite involved multistages of metasomatism.

Mineralogy of jadeitite and related rocks from Myanmar: a review with new data

The jadeitite from Myanmar is the most important commercial source on Earth, and its mineralogy perhaps the most diverse. More than thirty mineral species, including jadeite, omphacite, kosmochlor, Cr-bearing jadeite-omphacite, albite, celsian, banalsite, hyalophane, nyboite, eckermannite, magnesiokatophorite, glaucophane, richterite, winchite, analcime, natrolite, thomsonite-Ca, pectolite, vesuvianite, titanite, grossular, uvarovite, allanite, phlogopite, cymrite, zircon, graphite, quartz, diaspore, kaolinite, pyrite, galena, chromite, and ilmenite have been documented from these jadeitites and related rocks, which we review and update. Phlogopite, natrolite, thomsonite-Sr, titanite and ilmenite are newly reported here. Amphiboles, kosmochlor and omphacite formed closely related to the paragenetic sequence in the presence of jadeite; however, uvarovite is formed by replacement of chromite and does not require the presence of jadeite. At least two stages of jadeitization have been identified for Myanmar jadeitite. Late-stage zeolites, pectolite and hyalophane, banalsite, titanite and some celsian formed at lower P and T . The spectrum of minerals in Myanmar jadeitite indicates that the jadeite-forming fluids were rich in Na, Al, Ba, Sr, and Ca. Moreover, the variety of replacement textures suggests that most rocks in the serpentinite melanges were subject to infiltration and potential replacement by jadeitite or reaction with jadeitite. Serpentinite was replaced by sodic to sodic-calcic amphibole, chromite in ultramafic rock by kosmochlor and Cr-bearing jadeite, and the clinopyroxene in mafic rock by omphacite. Relict ilmenite replaced by titanite in omphacitite is evidence for metasomatism of mafic rock. Sodium-rich fluids were likely dominant throughout jadeitite crystallization and metasomatic reactions. A general mineralogical comparison of jadeitites world-wide indicates both similarities and distinctions; these could be used for interpreting sources of the jadeite jade, particularly in archaeology.

Structural evolution of the Dayman dome metamorphic core complex, eastern Papua New Guinea

Research Article| November 01, 2011 Structural evolution of the Dayman dome metamorphic core complex, eastern Papua New Guinea Nathan R. Daczko; Nathan R. Daczko † 1Geochemical Evolution and Metallogeny of Continents Australian Research Council (GEMOC ARC) National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Sydney, Australia †E-mail: nathan.daczko@mq.edu.au Search for other works by this author on: GSW Google Scholar Peter Caffi; Peter Caffi 1Geochemical Evolution and Metallogeny of Continents Australian Research Council (GEMOC ARC) National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Sydney, Australia Search for other works by this author on: GSW Google Scholar Paul Mann Paul Mann § 2Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78758-4445, USA §Current address: Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204-5007; pmann@uh.edu Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (11-12): 2335–2351. https://doi.org/10.1130/B30326.1 Article history received: 07 May 2010 rev-recd: 13 Oct 2010 accepted: 21 Oct 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Nathan R. Daczko, Peter Caffi, Paul Mann; Structural evolution of the Dayman dome metamorphic core complex, eastern Papua New Guinea. GSA Bulletin 2011;; 123 (11-12): 2335–2351. doi: https://doi.org/10.1130/B30326.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A shallow-dipping ductile mylonitic shear zone and concordant brittle detachment fault (Mai'iu fault) together make up the dominant geological structure that controls the orientation of dip slopes on the flanks of Mount Dayman, eastern Papuan Peninsula, Papua New Guinea. The dip slopes dip in all directions from the peak of Mount Dayman and form a domed landform that is much less dissected by streams compared to the adjacent Mount Suckling domed landform. The orientation of megacorrugations on the domed surface of Mount Dayman (footwall) is consistent with NNE-directed transport of the hanging-wall block, which is composed of low-grade undifferentiated volcanic and sedimentary rocks and minor ultramafic rocks. Though previously documented as a thrust surface, the geometry and style of structures and map relations presented in this study indicate an extensional origin for the domed mylonitic foliation (S1) and mineral elongation lineation (L1). The field relationships are consistent with the domed landform comprising the core of a metamorphic core complex. Observations of dominantly NNE-trending regional lineaments in aerial photography and Shuttle Radar Topography Mission (SRTM) data correlate with detailed field analysis of mineral elongation lineations (L1) in the main metamorphic core complex–bounding shear zone. Field relationships show a crosscutting sequence of structures that includes: (1) ductile S2 folia with ESE-plunging blue sodic-calcic amphibole mineral elongation lineations; (2) narrow, steeply dipping ductile D2 shear zones; and (3) semibrittle to brittle fault zones. S-C′ fabrics, asymmetric strain shadows around porphyroclasts, and fault drag indicate a top-down-to-the-NNE sense of shear for most structures. Kinematic vorticity analysis of the highest-grade ductile deformation indicates a kinematic vorticity number (Wk) between 0.34 and 0.56, suggesting general shear for the early stage of deformation (D1). The NNE-directed lineaments and L1 mineral elongation lineations are consistent with the Australia-Woodlark Eulerian pole for periods between the early Pliocene (3.6 Ma) and Pleistocene (0.52 Ma). This observation is consistent with ca. 3.3 Ma granite and monzonite intrusions that cut the mylonitic fabrics and limit the age of the mylonitic fabrics to older than 3.3 Ma on Mount Suckling. A SE-dipping sedimentary sequence (Gwoira Conglomerate) characterizes part of the hanging wall of the metamorphic core complex. Petrography of the clasts within the sedimentary rocks indicates that metabasite rocks were the dominant source. The unit is in fault contact with the metabasite footwall across prehnite-bearing D3 brittle fault zones. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structural evolution of the Dayman dome metamorphic core complex, eastern Papua New Guinea

Research Article| November 01, 2011 Structural evolution of the Dayman dome metamorphic core complex, eastern Papua New Guinea Nathan R. Daczko; Nathan R. Daczko † 1Geochemical Evolution and Metallogeny of Continents Australian Research Council (GEMOC ARC) National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Sydney, Australia †E-mail: nathan.daczko@mq.edu.au Search for other works by this author on: GSW Google Scholar Peter Caffi; Peter Caffi 1Geochemical Evolution and Metallogeny of Continents Australian Research Council (GEMOC ARC) National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Sydney, Australia Search for other works by this author on: GSW Google Scholar Paul Mann Paul Mann § 2Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78758-4445, USA §Current address: Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204-5007; pmann@uh.edu Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (11-12): 2335–2351. https://doi.org/10.1130/B30326.1 Article history received: 07 May 2010 rev-recd: 13 Oct 2010 accepted: 21 Oct 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Nathan R. Daczko, Peter Caffi, Paul Mann; Structural evolution of the Dayman dome metamorphic core complex, eastern Papua New Guinea. GSA Bulletin 2011;; 123 (11-12): 2335–2351. doi: https://doi.org/10.1130/B30326.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A shallow-dipping ductile mylonitic shear zone and concordant brittle detachment fault (Mai'iu fault) together make up the dominant geological structure that controls the orientation of dip slopes on the flanks of Mount Dayman, eastern Papuan Peninsula, Papua New Guinea. The dip slopes dip in all directions from the peak of Mount Dayman and form a domed landform that is much less dissected by streams compared to the adjacent Mount Suckling domed landform. The orientation of megacorrugations on the domed surface of Mount Dayman (footwall) is consistent with NNE-directed transport of the hanging-wall block, which is composed of low-grade undifferentiated volcanic and sedimentary rocks and minor ultramafic rocks. Though previously documented as a thrust surface, the geometry and style of structures and map relations presented in this study indicate an extensional origin for the domed mylonitic foliation (S1) and mineral elongation lineation (L1). The field relationships are consistent with the domed landform comprising the core of a metamorphic core complex. Observations of dominantly NNE-trending regional lineaments in aerial photography and Shuttle Radar Topography Mission (SRTM) data correlate with detailed field analysis of mineral elongation lineations (L1) in the main metamorphic core complex–bounding shear zone. Field relationships show a crosscutting sequence of structures that includes: (1) ductile S2 folia with ESE-plunging blue sodic-calcic amphibole mineral elongation lineations; (2) narrow, steeply dipping ductile D2 shear zones; and (3) semibrittle to brittle fault zones. S-C′ fabrics, asymmetric strain shadows around porphyroclasts, and fault drag indicate a top-down-to-the-NNE sense of shear for most structures. Kinematic vorticity analysis of the highest-grade ductile deformation indicates a kinematic vorticity number (Wk) between 0.34 and 0.56, suggesting general shear for the early stage of deformation (D1). The NNE-directed lineaments and L1 mineral elongation lineations are consistent with the Australia-Woodlark Eulerian pole for periods between the early Pliocene (3.6 Ma) and Pleistocene (0.52 Ma). This observation is consistent with ca. 3.3 Ma granite and monzonite intrusions that cut the mylonitic fabrics and limit the age of the mylonitic fabrics to older than 3.3 Ma on Mount Suckling. A SE-dipping sedimentary sequence (Gwoira Conglomerate) characterizes part of the hanging wall of the metamorphic core complex. Petrography of the clasts within the sedimentary rocks indicates that metabasite rocks were the dominant source. The unit is in fault contact with the metabasite footwall across prehnite-bearing D3 brittle fault zones. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.