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The natrocarbonatites of Oldoinyo Lengai, Tanzania, are unique in magmatic petrology. The historical activity of Oldoinyo Lengai has seen changes from nephelinitic to natrocarbonatitic character of the emitted magmas. Since 1983 the activity was characterized by the effusion of fluid natrocarbonatite lava from which we have collected and analyzed fresh samples in the summit crater from 1988 to 2007...
We document the first-known Mesoproterozoic ophiolite from the southwestern part of the Amazon craton, corresponding to the Trincheira Complex of Calymmian age, and propose a tectonic model that explains many previously enigmatic features of the Precambrian history of this key craton, and discuss its role in the reconstruction of the Columbia supercontinent. The complex comprises extrusive rocks (fine-grained...
Studies on modern oceanic lithosphere and ophiolites have revealed high degrees of chemical and isotopic heterogeneity in the mantle, as well as isotopic contrasts between mantle and crust. These features cannot be explained just by simple extraction of partial melt, but require considerably more complex petrogenetic processes. Here we present an overview of the present knowledge on isotopic heterogeneities...
We describe the whole-rock geochemistry, biotite Ar–Ar and zircon U–Pb geochronology, and in situ Hf–O isotopic compositions of the Linzhi two-mica granitoid in the southeastern Lhasa terrane. The granitoids are calc-alkaline to high-K calc-alkaline in composition, and they have geochemical affinities with adakites. The whole-rock geochemistry, with high SiO 2 and Al 2 O 3 ...
The basal units of the allochthonous complexes of NW Iberia are formed by thick metasedimentary rock sequences intruded by granitoids, ranging in composition from calc-alkaline (c. 493Ma) to minor alkaline–peralkaline massifs (c. 475–470Ma), and mafic rocks. The granitoids were transformed into variably deformed othogneisses and the associated mafic rocks were transformed into amphibolites, blueschists...
TTGs (tonalite–trondhjemite–granodiorite) are one of the archetypical lithologies of Archaean cratons. Since their original description in the 1970s, they have been the subject of many studies and discussions relating to Archaean geology. In this paper, we review the ideas, concepts and arguments brought forward in these 40years, and try to address some open questions — both old and new.The late 1960s...
This study focuses on age and evolution of the Oligocene quartz latite of the Rogozna Mts. (Central Balkan Peninsula), in order to better understand the link between magmatism and formation of Pb–Zn±Ag mineralization. New 40 Ar/ 39 Ar biotite and amphibole plateau ages suggest that the Rogozna Mts. quartz latite originated through a continuous volcanic episode from 27.3±0.1 to 29.5±0...
The Late Neoproterozoic Greendale Complex, located within the Avalon terrane of Nova Scotia, is a suite of appinitic rocks ranging from ultramafic to felsic in composition that were intruded during regional ensialic arc magmatism and crystallized at shallow crustal levels under conditions of high pH 2 O. Amphibole is the dominant mafic mineral in ultramafic to mafic rocks and displays the...
Identification of the Mesoproterozoic A-type Jining granite and granite porphyry, which with abundant coeval mafic dike sills and volcanic rocks on the northern margin of the Precambrian North China Craton (NCC), may suggest intraplate extension of Columbia supercontinent. Major and trace elements of the Jining granite show an affinity to A-type granites, and may reflect an intraplate rift setting...
New in situ Lu–Hf data on zircons from GSWA geochronology samples has provided a unique isotopic dataset with a high temporal resolution for the Murchison Domain of the Yilgarn Craton in Western Australia. These data identify extended periods of juvenile mantle input (positive εHf values) into the crust firstly at c. 2980Ma and then from c. 2820Ma to c. 2640Ma with significant pulses of crustal recycling...
Size frequency distributions are the principal tool for predicting the macro-diamond grade of new kimberlite discoveries, based on micro-diamonds (i.e., diamond ≤0.5mm) recovered from small exploration samples. Lognormal size frequency distributions – as observed for the Artemisia kimberlite (Slave Craton, Canada) – suggest a common source for micro- and macro-diamonds recovered from single samples,...
The Alborz Magmatic Assemblage (AMA) is an Eocene volcanic complex in northern Iran, and is situated at the site of the closure of the Tethyan basin. The magmatic rocks of the Alborz assemblage exhibit a distinct progression in style, from shallow submarine explosive eruptions to more effusive sub-aerial eruptions. Their chemical compositions indicate that they belong to the high-K calc‐alkaline (shoshonitic)...
The 2200–1880Ma igneous rocks in the central and eastern parts of the North China Craton (NCC) constitute a new Hengling magmatic belt (HMB), which includes the ~2147Ma Hengling mafic sill/dyke swarm, the ~2060Ma Yixingzhai mafic dyke swarm, and the ~1973Ma Xiwangshan mafic dyke swarm. The three swarms are contiguous and have experienced variable degrees of metamorphism from greenschist to low amphibolite...
Structural characterization of silicate melts and aqueous fluids equilibrated at pressures and temperatures corresponding to the Earth's interior requires measurements in-situ while the samples are at the pressure and temperature of interest. To this end, structure and structure–property relations of melts and coexisting fluids in silicate-COH systems have been determined at temperatures up to 1000°C...
Jeju Island is the emergent portion of a basaltic volcanic field developed over the last c. 1.8Ma on continental crust. Initial volcanism comprised dispersed, small-volume (<0.01km 3 ) alkali basaltic eruptions that incrementally constructed a tuff pile. Lavas and scoria from continuing small-scaled monogenetic volcanism capped this foundation. From c. 0.4Ma large-volume (>1km 3...
Hydrothermal alteration resulting in albitization and quartz dissolution has been identified in Paleoproterozoic metagranites down to −1000m elevation at Forsmark, Sweden. The alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository. In general, albitization occurs extensively, but it is also observed locally...
The 16.4Ma old Bogács Ignimbrite, located south of the Bükk Mountains, northern Hungary, was formed during a silicic ignimbrite flare-up in the Pannonian Basin that occurred from 20Ma to 13Ma. It comprises two main units, a lower, variably welded pumiceous and an upper, scoriaceous pyroclastic flow unit. Bulk chemistry of the juvenile clasts indicates a gradual change of geochemical character with...
Magma differentiation processes that take place in conduits delivering basaltic magmas to the Earth's surface are still poorly understood. To get new insights into this problem we have studied in detail the whole-rock geochemistry of a section across a dolerite dyke (21m thick) and three sections across its narrow apophysis (69cm, 29cm and 17cm thick) from the Russian Fennoscandian Shield. The dyke...
The Inner Mongolia Suture Zone (IMSZ, incorporating the Khondalite Belt) forms part of an accretionary orogen developed during the Paleoproterozoic collision between the Yinshan Block and Ordos Blocks within the North China Craton (NCC). The granulites within the IMSZ are characterized by high-temperature (HT) to ultrahigh-temperature (UHT) metamorphism with diagnostic mineral assemblages for UHT...
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