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The Igaliko Nepheline-Syenite Complex of Gardar age (1300-1120 Ma) includes carbonatite, lamprophyre, basalt, trachybasalt, phonolite and rhyolite dykes. The relationship of carbonatite magma to the other magma types in this area is not immediately obvious. Field, geochemical and petrological studies suggest three equally acceptable models for the evolution of the carbonatites. Here we present...
Minor magmatic intrusions (dykes and explosion pipes) of lamprophyric and carbonatitic compositions occur on several islands in the Gulf of Kandalaksha (White Sea, Kola Peninsula, Russia). The lamprophyre dykes yielded K-Ar ages of 368 ± 15 Ma and 360 ± 16 Ma, similar to the majority of alkaline rocks from the Kola Alkaline Province. Mineralogical data (presence of perovskite and sodalite, absence...
Plate reconstructions at 30 Ma place northeastern Brazil over the Fernando de Noronha hotspot, presently ~250 km offshore northeastern Brazil. Tertiary basaltic centers in northeastern Brazil may therefore be products of the Fernando de Noronha hotspot. We examined alkalic basalt from seven ~30-13 Ma old centers in Rio Grande do Norte and Pernambuco states to assess this possible link. Compositions...
Subsequent to high-pressure and temperature metamorphism of the axial zone of the Variscan foldbelt in central Europe at ca. 340 to 330 Ma, formation of lamprophyre dikes during transtensional tectonics may be viewed as the beginning of the post-collisional stage of the orogeny. We report the results of 40 Ar/ 39 Ar mica dating, major and trace element data, and isotope compositions...
The Tabar-Lihir-Tanga-Feni (TLTF) volcanic island chain occurs in a zone of lithospheric extension superimposed on a post-collisonal tectonic setting along the Pacific and Indo-Australian plates northeast of Papua New Guinea. We present geochemical and Sr, Nd, and Pb isotope data for volcanic rocks from these islands and three recently discovered seamounts located at Lihir island. Major element data...
Tonalitic, granodioritic and monzogranitic enclaves occur in the Hercynian peraluminous porphyritic biotite granite and biotite-muscovite granite from the Nelas region. Some variation diagrams show linear trends, but others show dispersion. The enclaves generally have closely similar isotopic signatures to those of the host granites. They contain xenocrystic plagioclase with the same composition as...
To test existing lateral accretion models for the Archean Kaapvaal Craton in South Africa, metapelites and leucocratic granitoids from two different provinces, the granulite facies Southern Marginal Zone of the Limpopo Belt and the northern part of the adjacent greenschist to amphibolite facies Kaapvaal Craton, have been studied. Both provinces resemble each other in terms of isotope and trace element...
Voluminous late Mesoproterozoic monzonite through granite of the Vernon Supersuite underlies an area of approximately 1300 km 2 in the Highlands of northern New Jersey. The Vernon Supersuite consists of hastingsite+/-biotite-bearing granitoids of the Byram Intrusive Suite (BIS) and hedenbergite-bearing granitoids of the Lake Hopatcong Intrusive Suite (LHIS). These rocks have similar major...
The Arkhangelsk kimberlite province (AKP) is situated in the north of the Baltic Shield within the buried southeastern portion of the Kola-Kuloi craton. It forms part of the extensive Devonian magmatic event of the northern Baltic Shield and Kola Peninsula. Two main groups of kimberlites can be distinguished within the province: (1) kimberlites from the diamondiferous Zolotitsa field that have geochemical...
Fenitization in granodioritic rocks has been investigated taking the Iivaara alkaline complex (Finland) as a case study. Five main fenitization reactions responsible for the transition from a granodioritic precursor mineral assemblage to a syenitic or even cancrinite-syenitic mineral assemblage of the fenites are set up. An assessment of element transfer and volume change associated with each of these...
The Cowra Granodiorite is a relatively mafic, enclave-rich, S-type pluton in the Lachlan Fold Belt, which has been cited as a type example of a restitic origin for all varieties of enclaves in Lachlan Fold Belt S-type granites. Microgranitoid enclaves from the pluton are subordinate to metasedimentary varieties and can be subdivided into two groups according to their mafic mineral assemblage: pyroxene...
This study reports new geochemical and Sr-Nd-Pb isotopic data for Miocene to Quaternary basaltic to andesitic, dacitic, and rhyolitic volcanic rocks from the Huichapan caldera, located in the central part of the Mexican Volcanic Belt (MVB). The initial Sr and Nd isotopic ratios, except for one rhyolite, range as follows: 87 Sr/ 86 Sr 0.70357-0.70498 and 143...
In northern Algeria, the coastal area displays a very variegated magmatism of Miocene age, extending E-W over 900 km with a width of less than 50 km. This magmatism includes both plutonic and volcanic massifs containing basic, intermediate to acidic rock types. Two groups may be identified on the basis of the chemistry and mineralogy. The first group has a calc-alkaline metaluminous chemistry and...
Igneous rocks exposed on Electric Peak and Sepulcher Mountain represent the preserved intrusive and extrusive components of an early Eocene, calc-alkaline eruptive center in the Absaroka Volcanic Province (AVP) of Montana and Wyoming, USA. The Electric Peak stock has an outcrop area of ~1 km 2 and consists of six discrete phases ranging in composition from quartz diorite to granite, representing...
In Venezuela, kimberlites have so far only been found in the Guaniamo region, where they occur as high diamond grade sheets in massive to steeply foliated Paleoproterozoic granitoid rocks. The emplacement age of the Guaniamo kimberlites is 712±6 Ma, i.e., Neoproterozoic. The Guaniamo kimberlites contain a high abundance of mantle minerals, with greater than 30% olivine macrocrysts. The principal kimberlite...
We have obtained major and trace element data for a suite of rocks emplaced over an area of ∼45,000 km2 in the Eastern Goldfields Province (EGP), Yilgarn Craton, that are petrographically and mineralogically described as kimberlites, melnoites and carbonatites. Kimberlites dominate the rock types found in the west whereas carbonatites and melnoites are common in the east. Compatible element data from...
Eclogites from the Earth's mantle found in kimberlites provide important information on craton formation and ancient geodynamic processes because such eclogites are mostly Archean in age. They have equilibrated over a range of temperatures and pressures throughout the subcratonic mantle and some are diamond-bearing. Most mantle eclogites are bimineralic (omphacite and garnet) rarely with accessory...
The Quaternary Acatlán Volcanic Field (AVF) is located at the western edge of the Trans-Mexican Volcanic Belt (TMVB). This region is related to the subduction of the Pacific Cocos and Rivera plates beneath the North American plate since the late Miocene. AVF rocks are products of Pleistocene volcanic activity and include lava flows, domes, erupted basaltic andesite, trachyandesite, trachydacite, and...
The overwhelming part of the continental crust in the high-grade part of the Damara orogen of Namibia consists of S-type granites, metasedimentary rocks and migmatites. At Oetmoed (central Damara orogen) two different S-type granites occur. Their negative ε Nd values (−3.3 to −5.9), moderately high initial 87 Sr/ 86 Sr ratios (0.714–0.731), moderately high 206 Pb/ ...
Earth sciences deal with physical entities spanning 15 orders of magnitude, from nanometer (crystal lattice unit cells) to megameter (faults and orogens). The understanding of megameter-scale processes is greatly improved by the study of the nanometer-scale processes: the growth of crystals, their deformation under shear, and the transport of isotopes used for dating.From a physical point of view,...
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