A comparative electron microprobe study of “Aeginetan” wares with potential raw material sources from Aegina,Methana, and Poros,Greece

Qualitative stylistic evidence from ceramic vessels and limited petrographic analysis suggested that a distinctive group of ceramics with visible inclusions of biotite (Gold Mica Fabric) was produced on the island of Aegina, Greece, during the Middle Helladic and Late Helladic I periods. To quantitatively evaluate this provenance, we sampled all potential source rocks on Aegina, Methana, and Poros. Electron microprobe analysis of amphibole in these samples revealed that each of these volcanic centers has its own unique mineralogical signature. Comparative analyses of amphibole in Zerner's original stylistic “Gold Mica Fabric” type sample with the reference samples reveal that two sherds are Aeginetan. Three additional sherds from this sample may have a non‐Aeginetan provenance, probably from a back‐arc setting outside the Saronic Gulf. These results suggest that the hypothesis of a single source production site for Aeginetan Ware should be reexamined. © 2002 Wiley Periodicals, Inc.     

An electron microprobe study of P645/T390: Evidence for an Early Helladic III Lerna–Aegina connection

Middle Helladic Aeginetan Ware is widely distributed throughout the Aegean. It is characterized by a “gold mica or volcanic ash” fabric and is abundant at Lerna on the Argive plain, Greece, in the Middle Helladic and Late Helladic I periods. A group of Early Helladic III ceramics at Lerna includes P645/T390, which also has a volcanic fabric. We have sampled all the major rock types of the separate volcanic episodes on Aegina, Methana, and Poros and analyzed the constituent minerals with the electron microprobe. These analyses provide a reference standard against which the mineralogy of P645/T390 and other potential Aeginetan wares can be compared. The compositions of amphibole, clinopyroxene, plagioclase, and biotite in P645/T390 are identical to the same minerals in dacites on Aegina, suggesting an origin on that island. Compositional mismatches with the minerals of Methana and Poros indicated the ceramic was not manufactured at these locations. This narrow‐necked jar represents the earliest occurrence of Aeginetan Ware on mainland Greece that has been confirmed by a quantitative method. © 2002 Wiley Periodicals, Inc.     

The source of raw materials for Roman pottery from Leptiminus,Tunisia

Leptiminus, a Roman port city on the west coast of Tunisia, North Africa, exported olive oil and a garum fish paste to Rome. Excavations have uncovered many facilities including kilns and a potter's workshop, indicating an extensive ceramic industry. The vessels, manufactured at Leptiminus, included African red‐slip fineware, coarseware, and amphorae. A petrographic study of pottery sherds showed them to contain very similar temper, rounded aeolian sand grains and limestone, but varying in proportions to produce different textures. An investigation of the source of raw materials for the pottery found three distinct types of clay within a 50 km radius of Leptiminus: grey Miocene, brown Pliocene, and green Late Pliocene clay. Statistical analysis of trace element compositions, using induced neutron activation, of clays and sherds showed that the Pliocene brown clay was used to create all types of pottery. The specific clay horizon, used in Roman times, has apparently been removed by quarrying. However, a lateral continuation of this bed was found 7 m beneath the Leptiminus site 290. © 2002 Wiley Periodicals, Inc.     

Provenance of sand temper in Hohokam Ceramics,Arizona

Sand temper compositions of regionally distinct Hohokam pottery sherds were determined by detailed point counts using sedimentary petrographic methods. Different temper compositions from different sites were compared with maps of sand composition zones within the geographic range of the pottery in order to establish the probable provenance of each sherd. A number of probable instances of intraregional pottery exchange were identified. The larger number of sand sources in undecorated vs. decorated pottery at each site suggests that undecorated pottery was made in more places than decorated vessels, and may have been traded differently as well. Petrographic analysis of temper is a useful method for studying exchange of homogeneous pottery in geologically diverse areas, and for investigating prehistoric Hohokam interaction in the Tucson and Red Rock Basins on a scale not possible with traditional archaeological techniques.     

The Serra da Graciosa A-type Granites and Syenites, southern Brazil. Part 3: Magmatic evolution and post-magmatic breakdown of amphiboles of the alkaline association

Amphiboles are the main mafic minerals in most metaluminous to peralkaline alkali-feldspar granites and syenites, and they usually preserve an important record of the compositional evolution of the melts from which they crystallize. In the alkaline association of the Serra da Graciosa A-type Granites and Syenites (southern Brazil), amphibole compositions span a large range, including calcic, sodic–calcic, and sodic amphiboles. Calcic amphiboles are typically observed in the metaluminous rocks, while sodic amphiboles are characteristic of the more strongly peralkaline rocks; sodic–calcic amphiboles are found in intermediate varieties. Compositional variations record the differentiation trends within two petrographic series of the alkaline association. The overall evolution of amphibole compositions is similar in both: they reveal a progressive increase in Na and Fe³⁺ with differentiation (increase in alkalinity of the magmas), a characteristic shared by undersaturated peralkaline (or agpaitic) differentiation trends. In detail, however, the evolutions of the amphibole compositions in the two series are distinct. In Alkaline series 1, the cores of the crystals form a continuum from calcic to sodic compositions, with the exception of a small compositional gap within the sodic–calcic amphiboles. The rims, however, show compositions that diverge from this main trend; this divergence results from increasing amounts of the oxy-amphibole component, and reflects more oxidizing conditions at the final stages of magmatic crystallization. In Alkaline series 2, these oxidation trends are much more subtle and a reverse trend is observed in the sodic amphiboles. Sodic–calcic amphiboles are in several cases replaced by intergrowths of post-magmatic sodic amphibole and Al-poor (“tetrasilicic”) biotite.     

Geochemistry of hydrothermally influenced sediments off Methana (western Hellenic volcanic arc)

Surface sediment samples from near-shore shallow water as well as deeper water locations N and NE of the island of Methana were investigated geochemically. Shallow water samples from Thiafi Bay reveal up to 38-fold enrichment of As, associated with elevated contents of Sb, Fe and Zn. Deeper water samples NE of Methana show moderate Mn enrichment accompanied with elevated trace metal concentrations of As and, in some samples, Cd and Cu. In an area, where small mounds of possible hydrothermal origin were observed on the sea floor, fine-grained Fe-rich sediment was sampled with enrichment of typical hydrothermal trace elements As, P and Sb. Element enrichment in the investigated areas off Methana corresponds in terms of absolute concentrations and element suite to comparable hydrothermally influenced sediments from other locations of the Hellenic volcanic arc. The region between Methana peninsula and Aegina Island is not marked by vigorous hydrothermal activity, but localised enrichments of Fe and/or Mn, As, Sb as well as associated trace elements typically found in hydrothermally influenced sediments were identified.     

Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes: a case study from Ciomadul volcano (SE Carpathians)

Ciomadul is the youngest volcano in the Carpathian–Pannonian region produced crystal-rich high-K dacites that contain abundant amphibole phenocrysts. The amphiboles in the studied dacites are characterized by large variety of zoning patterns, textures, and a wide range of compositions (e.g., 6.4–15 wt% Al₂O₃, 79–821 ppm Sr) often in thin-section scale and even in single crystals. Two amphibole populations were observed in the dacite: low-Al hornblendes represent a cold (<800 °C) silicic crystal mush, whereas the high-Al pargasites crystallized in a hot (>900 °C) mafic magma. Amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage (~8–12 km). This was also the place where the erupted dacitic magma was formed during the remobilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple-zoned and composite amphiboles. This includes reheating (by ~200 °C) and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population (including pargasites). Breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes, suggesting that pre-eruptive heating and mixing could take place within days or weeks before the eruption. The decompression rim of pargasites suggests around 12 days of magma ascent in the conduit. Several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the Ciomadul, but in our dacite the two amphibole population can be found even in a single crystal (composite amphiboles). Our study indicates that high-Al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone; thus, they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes. The simple-zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the Al-tschermak substitution can be recognized, suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation.     

Mineralogy of New Caledonian metamorphic rocks

The chemistry and phase relations of calcic and sodic amphiboles in the Ouégoa blueschists are investigated. The first appearance of sodic amphiboles is controlled by bulkrock chemistry. Sodic amphibole appears first in weakly-metamorphosed pumpellyite metabasalts prior to the crystallization of lawsonite but does not crystallize in pelitic schists until the middle of the lawsonite zone; sodic amphibole continues as an apparently stable phase in rocks of all bulk compositions into, and throughout, the highest-grade rocks in the district. Calcic amphibole is widespread in metabasalts of the lawsonite and epidote zones and also occurs in metasediments of appropriate composition. Coexisting pairs of calcic and sodic amphiboles are common in metabasalts but they have also been found in some metasediments. A grunerite-riebeckite pair is described.Electron-probe analyses of 120 amphiboles from representative rock-types are presented in graphical form. Sodic amphiboles show an increased Mg/(Mg+Fe) ratio with increasing metamorphic grade. Sodic amphiboles in pelitic schists are ferroglaucophane in the lawsonite zone and crossite and glaucophane in the epidote zone. Sodic amphiboles in metabasalts are iron-rich crossites in weakly-metamorphosed rocks and more-magnesian crossites and glaucophanes in the lawsonite and epidote zones. The abrupt increase in Mg/(Mg+Fe) ratio in sodic amphiboles at the epidote isograd is attributed to the crystallization of epidote and almandine which take the place of lawsonite and spessartine of the lawsonite zone. Calcic amphiboles are fibrous actinolites in the lawsonite zone and grade with increasing Al and Na/Ca ratio into prismatic blue-green hornblendes (barroisites) in the upper epidote zone. In calcic amphiboles, increasing metamorphic grade effects the coupled substitution of (Na+Al) for (Ca+Mg) and a small increases in Fe/Mg ratio; octahedrally and tetrahedrally coordinated Al increases in an approximately 11 ratio. Both the calcic and the sodic amphiboles show an increase in A-site occupancy with increasing metamorphic grade. In two-amphibole assemblages Ti, Mn and K are concentrated in the calcic amphibole.The textural and chemical relations between coexisting calcic and sodic amphiboles are discussed. If the calcic and sodic amphiboles are an equilibrium pair then the data collected from the Ouégoa amphiboles gives a picture of a very asymmetric solvus in the system glaucophane-actinolite-hornblende, i.e. steep-sided to glaucophane and with a gentle slope to the calcic amphibole field; there is no indication of any termination of the solvus under the pressure-temperature conditions of crystallization of the Ouégoa schists.     

The crystallization of pyroxenes and amphiboles in some alkaline rocks and the presence of a pyroxene compositional gap

Ca- and Na-rich pyroxene-amphibole compositions and textures from a range of felsic alkaline rocks have been studied in detail. The data indicate that in a single sample, when amphibole crystallizes, a gap is observed between Ca- and Na-rich pyroxene compositions. This break in composition is analogous to Aoki's (1964) immiscibility gap between Ca-and Na-rich pyroxenes and can be overlooked when considering pyroxene compositions from a suite of rocks. The role of volatiles in governing the stability and composition of amphiboles is discussed. The presence of late crystallizing Na-rich pyroxene is related to the development of peralkinity in the late-stage melts.On extrusion, many alkaline rocks lose their volatiles and amphibole is absent. In these rocks complete zoning from Ca-rich to Na-rich pyroxene compositions are observed within the one sample.     

The Serra da Graciosa A-type Granites and Syenites, southern Brazil: Part 2: Petrographic and mineralogical evolution of the alkaline and aluminous associations

The Serra da Graciosa Granites and Syenites comprise five distinct plutons in the Brasiliano/Pan-African Graciosa A-type Province, southern Brazil. Six petrographic series can be identified in these plutons: (1) Alkaline series 1, composed of amphibole-bearing alkali feldspar syenites with varied mafic mineralogy and quartz contents, from alkali feldspar syenites with calcic amphibole, clinopyroxene, olivine and allanite to alkali feldspar quartz syenites with sodic–calcic amphibole and chevkinite–perrierite and to alkali feldspar granites with sodic amphibole; (2) Alkaline series 2, characterized by amphibole-bearing alkali feldspar granites, with limited modal variations but amphibole compositions also varying from calcic to sodic; (3) Alkaline series 3, of limited occurrence, which includes alkali feldspar syenites with olivine and clinopyroxene and no amphibole; (4) Aluminous series 1, of widespread occurrence, with various petrographic facies of biotite granites with amphibole; (5) Aluminous series 2, characterized by alkali feldspar granites with biotite and only minor amphibole; (6) Monzodiorites, typically with biotite, calcic amphibole and augitic clinopyroxene, partially mingled with granitic magmas. The mafic minerals present are, in general, Fe-rich with correspondingly low Mg and Al contents. In Alkaline series 1, amphiboles crystallized in progressively more oxidizing and alkaline conditions, while in Alkaline series 2, the initial conditions were somewhat more oxidizing and shifted to reducing in the final stages. In Aluminous series 1 and Aluminous series 2, amphiboles are calcic and comparatively homogeneous. The amphiboles in the monzodioritic rocks, while also homogeneous, are more Mg-rich and show compositions quite distinct from the calcic varieties in the other associations, and this is also the case for clinopyroxene. Mg# in biotite decreases from the monzodioritic rocks to Aluminous series 1 and further to Aluminous series 2. Contrasting evolution of the various associations suggests that several coeval magmatic series are present in the Serra da Graciosa granites.     

中国夕卡岩矿床中的角闪石

文章综合分析研究了中国21个夕卡岩矿床中的130个角闪石的成分分析数据。根据夕卡岩类型及其伴生金属矿化的不同，把角闪石分为4大类：钙夕卡岩中的角闪石多属钙角闪石，包括绿钙闪石、铁角闪石、镁绿钙闪石、铁浅闪石、阳起石、铁阳起石、铁镁钙闪石和铁韭闪石等；镁夕卡岩中的角闪石以透闪石为主，局部有浅闪石或韭闪石；锰质夕卡岩中的角闪石有锰质阳起石、锰质透闪石、锰直闪石和锰镁闪石；碱质夕卡岩中的角闪石属钠-钙角闪石或钠角闪石类，包括钠透闪石、镁亚铁钠闪石、亚铁钠闪石、镁铝钠闪石和镁钠闪石。碳酸盐围岩和有关侵入岩的成分对角闪石的类型、成分及其伴生金属矿化起重要的作用。     

内蒙古文圪气镁铁-超镁铁质杂岩体中环带角闪石矿物学特征及成因

内蒙古文圪气镁铁-超镁铁杂岩体主要由辉石岩和角闪石岩组成,普遍发育角闪石环带的角闪石岩位于岩体南部,呈伟晶结构,主要由角闪石(>95%)和磷灰石(3%～5%)组成。选取环带较明显的两个角闪石样品,采用EMPA和LA-ICPMS分别做主量和微量成分剖面,环带角闪石边部为铁韭闪石,核部为韭闪石。从核部到边部,SiO2、MgO、Na2O含量逐渐降低,Al2O3、TiO2、FeOT、K2O和碱金属(Na2O+K2O)逐渐升高。中稀土、重稀土元素和Sc最大值位于核部,最小值位于边部;轻稀土元素、高场强元素、大离子亲石元素及过渡金属元素最大值位于幔边部,最小值位于核部,反映了核部氧逸度较高、温度和压力较低,边部氧逸度较低、温度和压力较高,是两期不同成分、温度、压力和氧逸度岩浆结晶的表现,并且角闪石岩受到后期高氧逸度低温热液的改造。环带角闪石的形成机理与文圪气岩体中铂族元素矿化过程相吻合。文圪气岩体与华北地台北缘中泥盆世镁铁质-超镁铁质岩具有相同的岩石组成、成因和构造背景,环带角闪石具有幔源角闪石特点,核部平均温度大于732℃,边部大于770℃,核、边部温度均小于950℃,结晶压力≤272 MPa,结晶深度≤12.4km。环带角闪石的结晶过程可能与文圪气岩体中铂族元素的成矿过程类似。     

Calcic amphiboles in calc-alkaline and alkaline magmas: thermobarometric and chemometric empirical equations valid up to 1,130°C and 2.2 GPa

The following article presents constraints of the stability of Mg-rich (Mg/(Mg + Fe²⁺) > 0.5) calcic amphibole in both calc-alkaline and alkaline magmas, testing of previous thermobarometers, and formulation of new empirical equations that take into consideration a large amount of literature data (e.g. more than one thousand amphibole compositions among experimental and natural crystals). Particular care has been taken in choosing a large number of natural amphiboles and selecting quality experimental data from literature. The final database of experimental data, composed of 61 amphiboles synthesized in the ranges of 800–1,130°C and 130–2,200 MPa, indicates that amphibole crystallization occurs in a horn-like P–T stability field limited by two increasing curves (i.e. the thermal stability and an upper limit), which should start to bend back to higher pressures. Among calcic amphiboles, magnesiohornblendes and tschermakitic pargasites are only found in equilibrium with calc-alkaline melts and crystallize at relatively shallow conditions (P up to ~1 GPa). Kaersutite and pargasite are species almost exclusively found in alkaline igneous products, while magnesiohastingsite is equally distributed in calc-alkaline and alkaline rocks. The reliability of previous amphibole applications was checked using the selected experimental database. The results of this testing indicate that none of the previous thermobarometers can be successfully used to estimate the P, T and fO₂ in a wide range of amphibole crystallization conditions. Multivariate least-square analyses of experimental amphibole compositions and physico-chemical parameters allowed us to achieve a new thermobarometric model that gives reasonably low uncertainties (T ± 23.5°C, P ± 11.5%, H₂O_melt ± 0.78wt%) for calc-alkaline and alkaline magmas in a wide range of P–T conditions (up to 1,130°C and 2,200 MPa) and ∆NNO values (±0.37 log units) up to 500 MPa. The ^AK-^[4]Al relation in amphibole can be readily used to distinguish crystals of calc-alkaline liquids from those of alkaline magmas. In addition, several chemometric equations allowing to estimate the anhydrous composition of the melts in equilibrium with amphiboles of calc-alkaline magmas were derived.     

Pliocene clays from Aegina (Greece): Reference material for chemical provenance studies on bronze age pottery from the Island

Normally, the use of clays as reference materials in chemical provenance studies of ancient ceramics is complicated due to the original clay paste processing. The primary mixing and/or refining of raw materials during pottery production makes a straightforward comparison of archaeological ceramics with extant geological materials difficult if not impossible in many cases. However, in the case of Pliocene clays from Aegina (Greece), which were examined chemically and mineralogically and compared with Bronze Age pottery produced on the island, a successful exception can be presented. The chemical composition of a large group of Aeginetan pottery resembles the chemical composition of clays from a deposit in close vicinity to the main Bronze Age settlement of the island. Clays from specific outcrops exhibit considerable chemical and mineralogical homogeneity, and the suitability of those clays for pottery production apparently made substantial clay paste processing unnecessary. © 2004 Wiley Periodicals, Inc.     

The petrology of a complex sodic and sodic–calcic amphibole association and its implications for the metasomatic processes in the jadeitite area in northwestern Myanmar,formerly Burma

In the Myanmar jadeitite area of Pharkan, amphibole felses occur between jadeitites and serpentinized dunites. These so-called amphibole fels boundary zones were studied optically and by electron microprobe, and found to include the six amphibole species magnesiokatophorite (Mg-kat), nyböite (Nyb), eckermannite (Eck), glaucophane (Gln), richterite (Rich) and winchite (Win). In most samples, the two main amphibole species Mg-kat and Eck coexist with amphiboles containing variable amounts of components of the remaining four species, as well as with the clinopyroxenes jadeite (Jd), omphacite (Omp) and kosmochlor (Ko). However, Mg-kat, Nyb and Eck are also present as separate phases as well as in zoned porphyroblasts with Mg-kat in the core, Nyb in the inner rims, and Eck in the outer rims. The analytical data on such zoned amphiboles reveal that the chemistry changes from core to inner rim by virtue of the substitution NaAlCa _-1Mg _-1 (glaucophane vector), and from the inner to the outer rim along MgSiAl _-1Al _-1 (tschermak vector). The overall substitution from core to outer rim is, therefore, along NaSiCa _-1Al _-1 (plagioclase vector). Based on the Si content, three groups can be distinguished within Eck: Eck coexisting with Nyb has low Si contents of <7.6 a.p.f.u., Eck rimming Nyb has higher Si contents of 7.6–8.0 a.p.f.u., and fine-grained Eck in the matrix has Si contents of 7.9–8.0 a.p.f.u. Plotting the amphibole analyses in a compositional volume with the axes (Na+K) in A, Na in M(4), and tetrahedral Si shows that three groups of amphibole compositions can be distinguished, one being subdivided into three subsets. Group A contains Rich and Mg-kat, B comprises of Win and Gln, whereas the subsets C can be defined as follows: C1: high-Na amphiboles with low tetrahedral Si; these are mainly amphiboles from the Eck field but overlap with the two fields of Gln and Win; C2: high-Na and low-Si Ecks overlapping to high-Si Nybs; this group is midway between Eck and Nyb end members; C3: high-Na Mg-kats. Textural observations indicate three stages of sodic and sodic–calcic amphibole growth: stage 1 are amphiboles of group A (Mg-kat+Rich), stage 2 are amphiboles of group C2 (Nyb+Eck with Si<7.6 a.p.f.u.), and stage 3 are amphiboles of groups C1 and B (Eck with Si>7.6 a.p.f.u., +Gln+Win). Based on the subdivision into the compositional groups A–C, the only hint to a miscibility gap is provided by the large gap in the (Na+K) content on the A site which may point to a possible solvus in the system Eck–Win. Overall, the amphiboles investigated here show discontinuities in their growth compositions, rather than miscibility gaps. Textural observations suggest amphibole formation during fluid infiltration in the contact zone between the jadeitite bodies and the surrounding peridotite under high-pressure conditions (>1.0 GPa) and rather low temperatures of about 250–370 °C. Based on compositional trends within the amphiboles as well as phase-equilibrium constraints between amphibole and coexisting pyroxene solid solutions, the chemical composition of zoned amphibole porphyroblasts indicates two growth episodes—increasing pressures from stage 1 to stage 2 lead to the formation of Nyb from Mg-kat, and subsequently decreasing pressures lead to the formation of stage 3 Eck from Rich.     

Experimental modal metasomatism of a spinel lherzolite and the production of amphibole-bearing peridotite

Experiments have been done which simulate the modal metasomatism of spinel lherzolite by partial melts of the subducted slab. The experiments were designed so that the metasomatizing melts were generated during the experiments by partial melting of a slab analog (basaltic composition amphibolite). The melts are thought to be representative of hybridizing melts in that they are derived by high-pressure partial melting under conditions appropriate to a hot slab geotherm. During the experiments, the melts infiltrate into and metasomatize a model depleted peridotite. Chemical modifications to minerals in the peridotite are of the same nature and extent as those found in naturally metasomatized spinel lherzolites. Modal metasomatism produced pargasitic amphiboles in runs at 1.5 GPa and in all but the highest temperature run at 2.0 GPa. The amphiboles are indistinguishable from amphiboles found in amphibole-bearing peridotites from supra-subduction zone environments. Systematic variations in amphibole composition suggest that the melt infiltration process in the experiments involved continuous modification of the composition of the infiltrating melt as observed around inferred quenched melt (i.c., amphibolite or amphibolite/clinopyroxenite) veins in xenoliths and massif peridotites. The compositions of the initial and final mineral phases in the experiments and those of the metasomatizing melts are used to derive amphibole formation reactions at 1.5 and 2.0 GPa that are similar in form to those inferred in studies of natural amphibole-bearing peridotites. The metasomatism reactions show that the extent of amphibole formation in peridotite at 1.5 and 2.0 GPa will, in general, be limited by clinopyroxene and spinel abundance.     

In situ major and trace element analysis of amphiboles in quartz monzodiorite porphyry from the Tonglvshan Cu–Fe (Au) deposit,Hubei Province,China: insights into magma evolution and related mineralization

The Tonglvshan deposit is the largest Cu–Fe (Au) skarn deposit in the Edong district, which is located in the westernmost part of the Middle and Lower Yangtze River metallogenic belt, China. In this study, we performed a detailed in situ analysis of major and trace elements in amphiboles from the ore-related Tonglvshan quartz monzodiorite porphyry using electron microprobe (EMPA) analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Two distinct populations of amphiboles, which can be distinguished by their aluminum content, are found in the quartz monzodiorite porphyry. The low-aluminum (Low-Al) amphiboles are subhedral or anhedral and formed at 46.3–73.5 MPa and 713–763 °C. In contrast, the high-aluminum (High-Al) amphiboles are euhedral and formed at 88–165 MPa and 778–854 °C. Some euhedral amphiboles are partially or completely replaced by Low-Al amphibole. The compositions of parental melts in equilibrium with the High-Al amphibole (Melt 1) and Low-Al amphibole (Melt 2) were computed by applying solid/liquid partition coefficients. This modeling shows that magma in equilibrium with High-Al amphibole (Melt 1) underwent 40% fractional crystallization of amphibole, plagioclase and apatite at a depth of ~5 km to evolve to magma in equilibrium with Low-Al amphibole (Melt 2). Copper enrichment occurred in the magma after undergoing fractional crystallization. The magma had a high oxygen fugacity, increasing from NNO + 1 (Melt 1) through NNO + 2 to HM (Melt 2), which could have prevented the loss of Cu (and possibly Au) to sulfide minerals during crystallization. Finally, the evolved magma intruded to shallower depths, where it presumably exsolved aqueous ore-forming fluids. Therefore, the large Cu–Fe–Au reserves of the Tonglvshan deposit can likely be attributed to a combination of controlling factors, including high oxygen fugacity, fractional crystallization, fluid exsolution, and a shallow emplacement depth.     

Petrography and geologic provenance of sand tempers in prehistoric potsherds from Fiji and Vanuatu,South Pacific

Indigenous sand tempers in prehistoric potsherds from Fiji, Vanuatu, and neighboring islands of the eastern Solomon outliers and northern Melanesian borderland have diverse compositions reflecting the varied geology of different islands in patterns controlled by regional geotectonic relations. Mineralogical compositions of noncalcareous temper sands reflect the nature of the bedrock sources on different islands. Temper analysis indicates that the ceramic assemblages recovered from most archaeological sites within the region were made locally or nearby, but also documents interisland ceramic transfer in widely varying volumes over distances as much as several hundred kilometers. Contrasts in island geology allow exotic wares to be identified without ambiguity but to varying degrees of specificity in terms of islands of origin. Rare sherds of New Caledonian wares have been collected in prehistoric context from several islands in Vanuatu, but there is as yet no temper evidence for prehistoric ceramic transfer between Vanuatu and Fiji. © 2001 John Wiley & Sons, Inc.     

Amphibole zoning in the Garland Peak Syenite,Red Hill complex,New Hampshire: camptonitic parental magmas and differentiation to silica-oversaturated syenites

The Garland Peak Syenite (GPS) of the Red Hill complex, New Hampshire, consists predominantly of amphibole, oligoclase, perthite, and quartz; amphiboles have homogeneous kaersutite cores with strongly zoned rims ranging in composition from pargasite to hastingsite to hornblende. The thin section scale association of kaersutite, an amphibole that typically crystallizes in silica-undersaturated magmas, with quartz suggests that the GPS magma experienced substanital changes in magmatic composition, including silica activity, during its crystallization history. Kaersutite-bearing camptonites are also associated with the Red Hill complex. The camptonite amphiboles are very similar in composition to the core kaersutites in the GPS, suggesting that the earliest GPS liquid may have had camptonitic affinities. In order to elucidate the process where-by silica-undersaturated magmas differentiate to saturation, amphiboles in these rocks were analyzed by electron and ion microprobe techniques. Amphiboles show a progressive increase in REE abundances from the camptonites to the GPS kaersutite cores to the GPS pargasite/hastingsite/hornblende rims. The systematic change in REE concentrations, and the variations in V, Ti, Sr versus Zr, Eu/Eu⁰ and La/Yb versus Ce, suggest a possible differentiation relationship for the amphiboles and imply that the GPS was derived from magmas similar to camptonites. Rimward depletions in Sr, Ti, V, and Eu/Eu⁰, and the increase in La/Yb values suggest that parental camptonites fractionated plagioclase, magnetite, and amphibole to produce the silica-oversaturated GPS. Bulk-rock modelling agrees with the trace element record preserved in the amphiboles, that plagioclase, magnetite, and amphibole fractionation caused silica saturation. Minor pegmatitic patches occur in the GPS. Ferrohornblendes in the pegmatites have REE abundances distinct from the other GPS amphiboles, and this difference may be due to open system processes.     

Thin section petrography of northern Lesser Antilles ceramics

Thin sections from 44 sherds representing eight prehistoric sites on four islands (Barbuda, Montserrat, Anguilla, St. Martin) in the northern Lesser Antilles (West Indies) were examined using a petrographic microscope. Point counting distinguished three temper associations: (1) exclusively volcanic,(2) volcanic and carbonate, and (3) volcanic, carbonate, and grog. Exclusively volcanic or dominantly volcanic (with low carbonate) temper associations occur in all Saladoid and many post-Saladoid sherds, with plagioclase feld-spar and volcanic rock fragments being most abundant. Thin sections with significant carbonate content or with grog were restricted to post-Saladoid sherds from Barbuda and to a lesser extent Anguilla. the presence of volcanic grains in sherds from the limestone islands of Barbuda and Anguilla indicates that volcanic islands in the region served as sources of pottery (or volcanic temper) for these two islands.