Mantle-derived lherzolite xenoliths and megacrysts from Permo-Triassic dykes,Sunnhordland, western Norway

Permo-Triassic alkaline dykes in the Sunnhordland region contain angular inclusions of spinellherzolite composed of olivine (Fo_89.5), high-alumina pyroxenes, and Al₂O₃-rich spinel. Mineral chemistry suggests that the lherzolites represent mantle material which equilibrated at temperatures in the ranges 1050 to 1150°C, compatible with an oceanic geotherm. Megacrysts of augite and spinel are associated with the xenoliths, and have compositions which differ from analogous phases occurring both as phenocrysts and as xenolith constituents. Systematic chemical variations in the clinopyroxene megacrysts may reflect magmatic fractionation processes. Megacrysts may represent disaggregated parts of coarsely crystalline polymineralic assemblages precipitated at high pressures, and temperatures above that indicated by the xenoliths, with subsequent exsolution at temperatures of about 1060°C.     

Nickeliferous sulfides in xenoliths,olivine megacrysts and basaltic glass

The composition of olivine and nickeliferous sulfide inclusions from a selection of mafic and ultramafre rocks, xenoliths and megacrysts, including picritic basalts from Kilauea Volcano, Hawaii, kimberlite from Fayette County, Pennsylvania, and megacrysts from Mount Shasta, California are compared with the mean experimental value of the distribution coefficient for Ni/Fe exchange (K_D3=32). Only nine of the forty five olivipe/bulk-sulfide pairs investigated have compositions consistent with equilibration at high temperature, yielding calculated K_D3 values in the range 22 to 41. The remaining pairs have calculated K_D3 values which range from 0 to 19. Bulk-sulfides in disequilibrated assem-blages are consistently depleted in nickel and within both indivudual associations and individual petrographic sections they exhibit a wide variation in NiS content. The bulk copper contents of olivine-and groundmass-hosted sulfides from Kilauea Volcano range from 0.5 to 43 at%, and samples from the Kilauea Iki lava lake are more Fe-and Cu-rich and generally have lower K_D3 values than those from the eruption itself. As with magmatic Ni–Cu sulfide deposits, most nickeliferous sulfide inclusions in mantle-related rocks and xenoliths and in volcanic rocks do not have pristine early-magmatic bulk compositions, and it would seem to be premature to attribute these sulfides solely to either a mantle or an early-magnatic origin.     

Prehnite--Epidote Phase Relations in the Nordre Aputit?q and Kruuse Fjord Layered Gabbros, East Greenland

Layered gabbros at Nordre Aputit?q and Kruuse Fjord were emplacedduring extensional tectonism that led to the formation of theNorth Atlantic basin in the Early Tertiary. Sub-solidus reactionsbetween the gabbros and hydrothermal fluids formed superimposedalteration assemblages in fractures, cavities, and the adjacentgabbros. The earliest secondary minerals are Ca-Al amphibole+ clinopyroxene + biotite ? plagioclase that form thin veinsor porous pegmatitic masses. These minerals are crosscut, overgrownor partially replaced by one or more generations of prehniteand epidote bearing assemblages associated with filling of thefractures and cavities, and with extensive wall rock albitization. Wide variations in the partitioning of Fe³⁺ and Al between coexistingprehnite and epidote solid solutions occur in these alteredgabbros. The partitioning data define distinct clusters in termsof associated mineralogy and paragenetic relations. This, togetherwith prehnite and epidote compositions from active geothermalsystems, are used to evaluate the thermodynamic properties ofthe intercrystalline exchange reaction:When compared to thecompositions of prehnite and epidote in the Nordre Aputit?qand Kruuse Fjord intrusions, it is concluded that the latestand lowest temperature generations of prehnite and epidote displaydisequilibrium partitioning of Fe³⁺ and Al, manifested by theoccurrence of prehnite that is relatively enriched in Fe³⁺ Thermodynamic analysis of phase relations in the system Na₂O-CaO-Al₂O₃-Fe₂O₃-FeO-SiO₂-H₂O-HClis used to determine local equilibrium constraints on Fe³⁺-Alsubstitution in prehnite and epidote. It appears that parageneticand compositional relations of prehnite and epidote are sensitiveindicators of local fluctuations in fluid composition and temperature.The complex magmatic and structural history of the gabbros atNordre Aputit?q relative to Kruuse Fjord is considered to beresponsible for the differences in mineral paragenesis and compositionsof prehnite and epidote within these intrusions.     

安徽铜陵地区中生代幔源岩浆底侵作用——来自矿物巨晶和岩石包体的证据

安徽铜陵地区中生代的岩浆岩岩体中产有多种矿物巨晶和岩石包体。笔者对产于曹山辉石冈长玢岩和鸡冠石花岗闪长岩中的辉石和角闪石巨晶及其堆积岩或堆积晶进行了详细的岩相学和矿物化学研究，并在此基础上估算了矿物平衡结晶的温压条件，讨论了安徽铜陵地区中生代幔源岩浆底侵作用问题。研究表明，铜陵地区大约在140Ma以前发生了碱性橄榄玄武质岩浆的底侵作用，辉石巨晶和角闪石巨晶及其堆积晶是由底侵的碱性橄榄玄武质岩浆在28～33km深处的深位岩浆房中与下地壳发生同化混染作用形成的中基性岩浆经结晶分异作用形成的，而辉石堆积岩是由中基性岩浆在19～21km深处的浅位岩浆房中与中地壳的浅变质岩系发生同化混染作用形成的中性岩浆经结晶分异作用形成的。     

内蒙古集宁新生代玄武岩中橄榄岩包体和巨晶的发现及意义

内蒙古集宁新生代玄武岩产于华北克拉通北缘，属于广义的“汉诺坝玄武岩”。首次在三义堂附近的碱性玄武岩中发现了大量的橄榄岩包体、辉石和长石以及少量的含钛磁铁矿巨晶。包体主要是尖晶石二辉橄榄岩，造岩矿物为橄榄石＋斜方辉石＋单斜辉石＋尖晶石，辉石巨晶主要为透辉石和普通辉石，长石巨晶主要是歪长石和少量斜长石。1．5GPa条件下，尖晶石二辉橄榄岩样品所记录的平衡温度与汉诺坝相近，集中于950℃左右，大体上反映了华北克拉通北缘大陆岩石圈地幔尖晶石相部分的温度状态。单斜辉石巨晶的结晶温压大于幔源包体的平衡温压，表明巨晶的来源深度可能大于包体。包体的结构及矿物成分分析表明，这些包体是玄武质岩浆上升过程中偶然捕获岩石圈地幔的岩石碎块。二辉橄榄岩包体中橄榄石高Mg#值（89．5～91．7）和较高的NiO含量（0．29％～0．55％），暗示集宁玄武岩中的橄榄岩包体来自较高熔融程度的岩石圈地幔。     

Medium pressure crystallization of a monchiquitic magma — evidence from megacrysts of Drever''s block, Ubekendt Ejland, West Greenland

Megacrysts and polymineralic fragments of extraordinary diversity from a Tertiary monchiquitic dyke of Ubekendt Ejland comprise three groups: (1) Cr-diopside-fassaitic diopside + olivine, Fo_90.5?81.5 + CrAl spinels. (II) Fassaitic salite-ferrisalite + KTi-pargasite-ferropargasite + apatite + AlTi-magnetite, (III) Scapolite + hyalophane + potassium feldspar + nepheline + analcime. By comparison with mineralogy and phase relations in the host rock and experimental data from alkaline rocks the megacrysts are related to a sequence of crystallization from primitive monchiquitic to potassic phonolitic magmas rich in H₂O and CO₂ at 5–11 kb. Group I megacrysts formed at temperatures of 1300-1150°C and group II between ? bar at the latter temperature. High P_co2 may have stabilized the scapolite in the more evolved liquid and K-feldspar and nepheline began to crystallize at ca. 800°C possibly together with the ferrisalite.     

Petrology of high pressure clinopyroxenite series xenoliths,Mount Carmel,Israel

The Mount Carmel xenolith suite is composed of a series of garnet granulites of probable lower crustal origin, and a high pressure clinopyroxenite series. The clinopyroxenite series is petrologically diverse with the most common lithologies being garnet-clinopyroxenite, clinopyroxenite, garnet-amphibole-clinopyroxenite, amphibole-clinopyroxenite, amphibole-mica-clinopyroxenite plus megacrystalline nodules of clinopyroxene, garnet, amphibole and mica. Orthopyroxene is extremely rare (1 sample) and olivine is absent in the clinopyroxenite series xenoliths. The clinopyroxenite series is divided into three rock associations based on textures, mineralogy, mineral chemistry and equilibration temperatures: the metaclinopyroxenite, the magmatic garnet-clinopyroxenite and the amphibole-mica-clinopyroxenite associations. Many of the xenoliths contain late phases, largely amphibole, as microphenocrysts in glass and altered glass that was intruded into the xenoliths. Each of the three associations plus the late phases represents the crystallization products of one or more magma batchs. Garnet-clinopyroxene geothermometry and phase relations for alkaline basalts allow estimates of theP/T conditions of equilibration to be made for some of the xenoliths. The metaclinopyroxenites were equilibrated at 1.5–3 GPa and 990–1,115° and the magmatic garnet-clinopyroxenites were equilibrated at 2–3 GPa and 1,160–1,190°. The Mt. Carmel xenoliths are samples from the depth range 50–95 km and fall in the sampling gap between xenoliths typical of alkali basalts (d<60 km) and those typical of kimberlites (d> 90 km).     

The petrology of a melilitolite,melteigite, carbonatite and syenite ring dike system,in the Gardiner complex,East Greenland

The Tertiary Gardiner complex in East Greenland comprises ultramafic cumulates cut by dikes, ring dikes and cone sheets. One major ring dike is of melilite-rick rocks (melilitolites), and shows phase layering and cryptic layering with respect to melilite, perovskite and phologopite. The vertical variation in the assemblages through the ring dike is consistent with established fractionation trends in undersaturated melilite-bearing experimental systems. Related veins and dikes are: a) undersaturated rocks of the melteigite-ijolite-urtite/nepheline syenite suite, b) melanite-calcite veins and søvite dikes and sheets and c) coarse-grained magnetite-phlogopite-diopside-calcite pegmatites and dolomite rocks. It is proposed that a CO₂-bearing Ln-normative nephelinite liquid is parential to both melilitolites and related veins through a combination of fractional crystallization, liquid immiscibility and CO₂-metasomatism of dunite country rocks. Unlike other localities where melilitolites are attributed to metasomatic processes, the Gardiner melilitolites are magmatic.     

Fracture propagation associated with dike emplacement at the skaergaard intrusion,east Greenland

Extensive magmatic activity, including several episodes of dike emplacement, was associated with early Tertiary continental rifting in Eastern Greenland. Exposures of the Skaergaard intrusion host a large number of these dikes as well as a variety of hydrothermal veins. One vein set has a characteristic outcrop expression and is filled with silica-rich chlorites. Relative timing constraints as well as the distribution and geometric relations of these veins relative to the mafic dikes indicate that at least some of these fractures formed during the emplacement of the dikes that cut the intrusion. Calculations based on elastic theory permit modeling of dike geometries observed in the field and prediction of fracture geometries that could be associated with the inflation of these dikes. Extensional fractures may form in the area ahead of the dike termination for a variety of loading conditions. The predicted width to length ratio for the dike as well as the size of the predicted fracture zone increases with increasing magma pressure within the dike and/or increasing differential between the remote principal stresses. For dike geometries similar to those observed in the field, the predicted fracture zone is roughly elliptical in cross-section and is centered in front of the dike termination. The size of the zone perpendicular to the dike trend varies from less than one meter to several meters. Field observations indicate that dike-parallel fractures are locally offset normal to the dike margin by distances of a few centimeters to a few meters. Our analysis implies that at least some of these fractures initiated and propagated ahead of the dikes as they were emplaced. The cooling of these dikes initiated localized hydrothermal systems that formed the vein minerals currently filling the fractures.     

Ultra-depleted, shallow cratonic mantle beneath West Greenland: dunitic xenoliths from Ubekendt Ejland

Dunitic xenoliths from late Palaeogene, alkaline basalt flows on Ubekendt Ejland, West Greenland contain olivine with 100 × Mg/(Mg + Fe), or Mg#, between 92.0 and 93.7. Orthopyroxene has very low Al₂O₃ and CaO contents (0.024–1.639 and 0.062–0.275 wt%, respectively). Spinel has 100 × Cr/(Cr + Al), or Cr#, between 46.98 and 95.67. Clinopyroxene is absent. The osmium isotopic composition of olivine and spinel mineral separates shows a considerable span of ¹⁸⁷Os/¹⁸⁸Os values. The most unradiogenic ¹⁸⁷Os/¹⁸⁸Os value of 0.1046 corresponds to a Re-depletion age of ca. 3.3 Gy, while the most radiogenic value of 0.1336 is higher than present-day chondrite. The Os isotopic composition of the xenoliths is consistent with their origin as restites from a melt extraction event in the Archaean, followed by one or more subsequent metasomatic event(s). The high Cr# in spinel and low modal pyroxene of the Ubekendt Ejland xenoliths are similar to values of some highly depleted mantle peridotites from arc settings. However, highly depleted, arc-related peridotites have higher Cr# in spinel for a given proportion of modal olivine, compared to cratonic xenolith suites from Greenland, which instead form coherent trends with abyssal peridotites, dredged from modern mid-ocean ridges. This suggests that depleted cratonic harzburgites and dunites from shallow lithospheric mantle represent the residue from dry melting in the Archaean.     

Ultracataclasis, sintering, and frictional melting in pseudotachylytes from East Greenland

Large volumes of pseudotachylyte (an intrusive, fault-related rock interpreted to form by a combination of cataclasis and melting) occur in Tertiary normal faults and accommodation zones along 400 km of the East Greenland volcanic rifted margin. Analysis of representative pseudotachylyte samples reveals a wide range of mesoscopic and microscopic textures, mineralogies, and chemistries in the aphanitic pseudotachylyte matrix. Three distinct types of pseudotachylyte (referred to as angular, rounded and glassy) are identified based on these characteristics. Angular pseudotachylyte (found primarily in dike-like reservoir zones) is characterized by angular grains visible on all scales, with micron-scale fragments of mica and amphibole. Its matrix is enriched in Fe₂O₃, MgO, and TiO₂ relative to the host rock, with minor increases in CaO, K₂O, and small decreases in Na₂O. Rounded pseudotachylyte is found in reservoir zones, injection veins (pseudotachylyte-filled extension fractures), and fault veins (small faults with pseudotachylyte along their surfaces). It is characterized by smooth-surfaced, compacted grains on microscopic scales, and encloses rounded, interpenetrative lithic clasts on outcrop scale. Its matrix is enriched in Fe₂O₃, MgO, TiO₂, and Al₂O₃ relative to the host rock, with minor depletion in Na₂O and K₂O. Glassy pseudotachylyte is found primarily along fault surfaces. Its matrix is characterized by isotropic, conchoidally fractured material containing microscopic, strain-free amphibole phenocrysts, and is enriched in TiO₂, Al₂O₃, K₂O, Fe₂O₃, MgO, CaO, and Na₂O relative to the host rock. These observations suggest that angular pseudotachylyte was produced by cataclasis, with enrichment in metallic oxides resulting from preferential crushing of mechanically weak amphibole and mica minerals found in the gneissic host rock. Cataclasis and concomitant frictional heating resulted in the textural and chemical modification of angular pseudotachylyte by sintering or melting, producing rounded and glassy pseudotachylyte, respectively. Compositional and textural observations constrain the temperatures reached during frictional heating (700–900°C) which in turn delimit the amount of frictional heat imparted to the pseudotachylytes during slip. Our results suggest that the East Greenland pseudotachylytes formed during small seismic events along faults at shallow crustal levels. Consistent relative ages and widespread occurrence of pseudotachylyte-bearing faults in East Greenland suggest that widespread microseismicity accompanied the early development of this volcanic rifted margin.     

青岛地区晚白垩世基性脉岩中麻粒岩捕虏体的成分特征及其温压条件

青岛地区晚白垩世基性脉岩中含有两类麻粒岩捕虏体,富辉石麻粒岩和富长石麻粒岩.富辉石麻粒岩的主要矿物组合为Opx＋Cpx＋Pl,具有细粒变晶结构;富长石麻粒岩主要矿物组合为Pl＋OpX＋Cpx十Q或Pl＋Opx/Cpx＋Q,具有中粗粒粒状变晶结构.麻粒岩捕虏体中辉石的Mg#较低（＜66）,普通辉石具有富Na贫Ca的特征,与岩浆底侵作用形成的麻粒岩特征接近.二辉石温度计的计算结果显示这些麻粒岩捕虏体的麻粒岩相变质平衡温度在847～910℃之间.结合富长石麻粒岩的地质压力计的计算结果（0.99～1.17GPa）和地温梯度推测出的＂岩石学＂Moho面深度在33～36公里之间,与＂地震＂Moho面深度基本一致.麻粒岩捕虏体中普通辉石的矿物成分和该地区活跃的岩浆活动暗示青岛地区下地壳麻粒岩不同于典型的古老下地壳麻粒岩地体或捕虏体.他们的形成可能是华北克拉通古老麻粒岩与岩浆底侵作用相互作用的结果.     

Petrology of peridotite xenoliths in lamprophyre from Shingu,Southwestern Japan: Implications for origin of Fe-rich mantle peridotites

Summary Xenoliths of harzburgite, lherzolite, dunite and wehrlite (= Group I rocks) in lamprophyre dikes from Shingu are accompanied by large amounts of ultramafic-mafic xeno liths with Al- and Ti-rich clinopyroxene and/or kaersuite (websterite, clinopyroxenite, kaersutite rock, gabbro and anorthosite) (= Group II rocks). The latter rocks often crosscut the Group I rocks as veinlets, indicating that Group II rocks are younger. Although harzburgites and lherzolite from Shingu have ordinary modal compositions, the constituent minerals have extraordinary chemical characteristics; low Mg and Cr and high Ti, Al and Fe³⁺. Fo values of olivine range from 91 to 77. Cr/(Cr + Al) atomic ratios of spinel are lower than 0.5 even in harzburgites. Fe³⁺/(Cr+Al+Fe³⁺) atomic ratios of spinel are sometimes over 0.1. TiO₂ contents of clinopyroxene often exceed 0.5 wt%. These characteristics are revealed when Group I rocks are veined or selvaged by Group 11 rocks; chemical compositions of minerals in peridotites systematically change forwards the latter. This strongly suggests that injections of melts with alkali basaltic affinity which had precipitated Group 11 rocks resulted in diffusion metasomatism on the Group I rocks.It is likely that the metasomatized peridotites are widespread underneath the areas where alkali basalt magmatism had fluorished, such as southwestern Japan. Some of Fe-rich lherzolite and harzburgite xenoliths reported in the literature are possibly metasomatites.

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Petrologie von Peridotit-Xenolithen in Lamprophyren von Shingu, Südwest-Japan: Hinweise auf die Herkunft Fe-reicher Mantel-Peridotite

Zusammenfassung In lamprophyrischen Gängen von Shingu kommen Xenolithe von Harzburgit, Lherzolith, Dunit and Wehrlit (= Gesteinsgruppe I) vor. Sie werden von einer Vielzahl von ultramaf-isch-mafischen Xenolithen mit Al- and Ti-reichem Klinopyroxen and/oder Kaersutit (Websterit, Klinopyroxenit, Kaersutit-Gestein, Gabbro and Anorthosit) (=Gesteinsgruppe II) begleitet, die die Xenolithe der Gruppe I häufig gangförmig durchkreuzen, was auf ein jü ngeres Alter der Gesteinsgruppe II hinweist. Obwohl die Harzburgite and Lherzolithe von Shingu übliche modale Mineralbestände aufweisen, sind die Mineralchemismen außergewöhnlich: Niedrige Mg- and Cr- and hohe Ti-, Al- and Fe³⁺-Gehalte. Die Fo-Gehalte von Olivin reichen von 91 bis 77. Die Cr/(Cr+Al)-Atom-Verhältnisse der Spinelle sind kleiner als 0,5, sogar in den Harzburgiten; die Fe³⁺/(Cr+Al+Fe³⁺)-Atom-Verhaltnisse teilweise größer als 0,1. Der TiO₂-Gehalt im Klinopyroxen ist meist über 0,5 Gew.%. Diese Charakteristika zeigen sich dort, wo die Gesteinsgruppe II die Gesteinsgruppe I durchschlägt oder kontaktiert. Der Mineralchemismus in den Peridotiten ändert sich dabei systematisch. Es wird vermutet, daß Schmelzinjektionen mit alkali-basaltischer Affinität, von denen die Gesteinsgruppe II herstammt, eine Diffusions-Metasomatose der Gesteinsgruppe I verursacht hat.Es wird angenommen, daß metasomatisierte Peridotite an der Basis von alkali-basaltischem Magmatismus weft verbreitet sind, wie zum Beispiel in Südwest-Japan. Einige in der Literatur aufscheinende Fe-reiche Lherzolith- and Harzburgit-Xenolithe sind möglicherweise metasomatisch entstanden.

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With 6 Figures     

Early Holocene insect and plant remains from Jameson Land, East Greenland

Fluvial and deltaic sediments from Jameson Land in East Greenland contain the first record of the leaf beetle Phratora o f. polaris , not presently found in Greenland; the ground beetle Bembidion grapii , north of this species' present northern range limit; and the true bug Nysius gruenlandieus . In addition, there is a rather diverse flora. All of these records are in sediments of Early Holocene age. We suggest that most of these animals and plants immigrated to East Greenland in the Early Holocene by long-distance chance dispersal, mostly from northwest Europe. The environment was physiognomically similar to that of today, but Salix aretica and Cassiope tetragonu that are important dwarf shrubs today had not yet immigrated.     

A cummingtonite-porphyritic dacite with amphibole-rich xenoliths from the tertiary central volcano at Króksfjördur,NW Iceland

An instrusive dacite and a salic pumice, emplaced late in the evolution of the Miocene (c. 10 m.y.) Króksfjördur volcano, NW Iceland, contain a varied assemblage of xenolithic metaigneous rocks. Mineral and rock chemistry shows that the dacite is very similar to calc-alkaline salic rocks from the SW Pacific. It contains phenocrystic plagioclase, quartz, pyroxene, cummingtonite, hornblende, biotite, two oxides, apatite and zircon in a rhyolitic glass. The rock equilibrated at 700 to 750°C. P ～ 1.6 Kbar and P_H2O ～ 1 Kbar. The xenoliths are layered gabbros, granophyres and various fine-grained hornfelses and show that the dacite magma was residing within a gabbro intrusion capped by granophyre prior to the eruption. The hornfelses are amphibole-plagioclase, amphibole-pyroxene-plagioclase and pyroxene-plagioclase rocks formed during high-temperature metamorphism of basic dykes cutting the gabbro intrusion. The gabbros and hornfelses mostly record higher metamorphic temperatures (850–940°C) than the dacite, and indicate that they were equilibrated during the ascent of a magma body into a hydrous high-level region within the volcano. During a following thermal decline, the hydrated magma cooled to form the first cummingtonite-bearing low-T magma to be recorded from the ocean ridge systems.     

Composition and age of tertiary sills and dykes, Jameson Land Basin, East Greenland: relation to regional flood volcanism

The Paleozoic–Mesozoic Jameson Land Basin (East Greenland) is intruded by a sill complex and by a swarm of ESE trending dykes. Together with dykes of the inner Scoresby Sund fjord, they form a regional Early Tertiary intrusive complex located 200–400 km inland of the East Greenland rifted continental margin. Most of the intrusive rocks in the Jameson Land Basin are geochemically coherent and consist of evolved plagioclase–augite–olivine saturated, uncontaminated high-Ti basalt with 48.5–50.2 wt.% SiO₂, 2.2–3.2 wt.% TiO₂, 5.1–7.4 wt.% MgO, 9–17 ppm Nb and La/Yb_N=2.8–3.6. Minor tholeiitic rock types are: (a) low-Ti basalt (49.7 wt.% SiO₂, 1.7 wt.% TiO₂, 6.8 wt.% MgO, 2.6 ppm Nb and La/Yb_N=0.5) akin to oceanic basalts; (b) very-high-Ti basalt (48.6 wt.% SiO₂, 4.1 wt.% TiO₂, 5.1 wt.% MgO and 21 ppm Nb); and (c) plagioclase ultraphyric basalt. The tholeiitic dolerites are cut by alkali basalt (43.7–47.3 wt.% SiO₂, 4.1–5.1 wt.% TiO₂, 4.9–6.2 wt.% MgO, 29–46 ppm Nb and La/Yb_N=16–17) sills and dykes.Modelling of high-field-strength and rare-earth elements indicate that the high-Ti basalts formed from 6–10% melting of approximately equal proportions of garnet- and spinel-bearing mantle of slightly depleted composition beneath thick continental lithosphere. Conversely, dolerite intrusions and flood basalts of similar compositional kindred from adjacent but more rift-proximal occurrences in Northeast Greenland formed from shallower melting of dominantly spinel-bearing mantle beneath extended and thinned continental lithosphere. These variations in lithospheric thickness suggest the continent–ocean transition of the East Greenland rifted volcanic margin is sharp and narrow.⁴⁰Ar–³⁹Ar dating and paleomagnetism show that the high-Ti dolerites were emplaced at 53–52 Ma (most likely during C23r) and hence surprisingly postdate the main flood volcanism by 2–5 Ma and the inception of seafloor spreading between Greenland and Europe by 1–2 Ma. The formation of tholeiitic and alkaline magmas emplaced into the Jameson Land Basin corroborates to the importance of post-breakup magmatism along the East Greenland volcanic rifted margin. Upwelling of the ancestral Iceland mantle plume under central Greenland at 53–52 Ma (rather than under the active rift), perhaps accompanied by a failed attempt to shift the rift zone westward towards the plume axis, may have triggered post-breakup continental magmatism of the Jameson Land Basin and the inner Scoresby Sund region, along preexisting structural lineaments.     

Volcanogenic tonsteins from tertiary coal measures,East Kalimantan,Indonesia

Laterally persistent tonsteins, up to 30 cm thick, occur in coal seams and associated sediments in the Tertiary Kutei Basin of East Kalimantan, Indonesia, where Neogene strata which form a generally eastward-prograding, marginal-marine to fluvio-deltaic sequence, are disposed in a north-northeast to south-southwest striking fold belt, centred on Samarinda. Eight tonsteins have so far been recorded in the middle to upper Miocene of the Badak syncline, some 40 km south-southwest of Samarinda, and range from tonsteins in the strict sense (kaolinite-mudstones of wide stratigraphical extent) including graupen and kristall varieties, to smectite-mudstones. They may pass laterally into each other. Most contain pyroclasts in varying stages of alteration and are regarded as volcanogenic. Primary textures include microscopic vitroclastic aggregates completely argillised to smectite, graded crystal-tuffs with abundant sanidine, glass shards and secondary vermiform kaolinite crystals, and argillised lithic tuffs. Texturally and compositionally these Tertiary tonsteins are closely similar to European Carboniferous tonsteins and this strengthens the conclusion of a volcanogenic origin even where pyroclastic textures have been removed through alteration. The East Kalimantan tonsteins are of economic and stratigraphic significance in providing distinctive horizons which have proved useful in aiding correlation of boreholes drilled in a coal-resource project in this area.     

Pyroxenite xenoliths and clinopyroxene megacrysts from the Cenozoic Jbel Saghro Volcanic Field (Anti-Atlas,Morocco): Petrography,mineral chemistry and equilibration conditions

A suite of mafic pyroxenite xenoliths and clinopyroxene megacrysts was brought to the surface by Cenozoic nephelinites of the Jbel Saghro Volcanic Field (Anti-Atlas, Morocco). The large population of samples was subdivided into five groups: (i) clinopyroxenites sensu stricto; (ii) olivine clinopyroxenites; (iii) mica-bearing clinopyroxenites; (iv) kaersutite-bearing clinopyroxenites; (v) clinopyroxene megacrysts. These xenoliths display a cumulate texture (adcumulate, heteradcumulate with poikilitic clinopyroxene including olivine). The clinopyroxenes have the composition of augite and show an appreciable variation of MgO (7.02–14.80 wt.%), TiO₂ (0.58–5.76 wt.%) and Al₂O₃ (2.81–12.38 wt.%) contents in grains. The clinopyroxenes are characterized by convex upward chondrite-normalized REE patterns, they display very similar trace element compositions with low contents of incompatible elements such as Rb (0−0.9 ppm), Ba (0.1–8.3 ppm), Th (0.1−0.3 ppm), U (0.01−0.04 ppm) and Nb (1.3–3.2 ppm). REE contents of the calculated melts in equilibrium with the clinopyroxene megacrysts and clinopyroxene from pyroxenite xenoliths are similar to those of the nephelinites exposed in Jbel Saghro. Crystallization temperatures of pyroxenite xenoliths and clinopyroxene megacrysts range from 950 °C to 1150 °C. Clinopyroxene barometry yielded pressure of crystallization ranging from 0.4 to 0.8 GPa for pyroxenite xenoliths and 0.3 to 0.7 GPa for clinopyroxene megacrysts. This pressure range is in agreement with pyroxenite xenoliths and clinopyroxene megacrysts being crystallized from their parental melts at the lower and upper crust.