The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
Although diamonds of eclogitic paragenesis are commonly encountered in the productions of many Southern Africa kimberlites, the nature and evolution of the protolith to eclogitic diamonds are still poorly understood. There is some evidence that these protoliths (and possibly also the diamonds) may be related to subduction of oceanic crust, although this is not a universally accepted view. In order...
The identification of a fossil arc–trench system from the ophiolite-decorated Solonker suture zone in the southernmost Central Asian Orogenic Belt (CAOB) enables us to constrain the timing of pre-subduction extension (ca. 299–290Ma), subduction initiation (ca. 294–280Ma), ridge–trench collision (ca. 281–273Ma) and slab break-off (ca. 255–248Ma) in the Permian. A fraction of proto-arc crust (ca. 45km...
Neoproterozoic continental growth in the Saharan Metacraton in central North Sudan is marked by juvenile A-type magmatism (the Jebel Arusa and Jebel Sherif ring complexes). Chemical features are characteristic of within plate (A-type) magmatism marked by Y/Nb ratios >1.2 typical of the A2 group. Zircon U–Pb analyses yield an age of 707±19Ma for the Jebel Arusa complex and an age of 718±18Ma for...
Textural and chemical variations of juvenile clasts are widely observed in pyroclastic deposits. In particular, the co-existence of whitish, pumiceous, and dark grey, scoriaceous, juvenile clasts has been observed in many eruptive units of well-known volcanoes (i.e., Somma–Vesuvius, Vulsini, Colli Albani, Stromboli). Here we report the example of the Tufo Giallo della Via Tiberina (TGVT) pyroclastic...
Throughout the Cenozoic, post-collisional potassic volcanism has been widespread in the Tibetan Plateau, but Holocene (<10ka) volcanism is rare and has only been reported from three volcanoes near Tengchong (Yunnan Province, China) within the southeastern Tibetan Plateau. Some of the Holocene volcanic rocks are differentiated lavas with SiO 2 contents of 58wt.% and contain zircon crystals...
Major-element, trace-element and O-isotope analyses were carried out for garnetiferous Ti–clinohumite rocks and eclogites from the Kumdy Kol area, as well as talc–kyanite–phengite–almandine schists (previously named as whiteschists) and eclogites from the Kulet area of the Kokchetav ultrahigh-pressure (UHP) terrane, to explore their possible origins. Both garnetiferous Ti–clinohumite rocks and talc–kyanite–phengite–almandine...
Pb isotopic data are presented for hybrid rocks formed by mingling between mantle-derived tholeiitic magma of the Eocene Miki Fjord macrodike (East Greenland) and melt derived from the adjacent Precambrian basement. Bulk mixing and AFC processes between end-members readily identified in the field fail to model the Pb isotope systematics. Selective contamination during diffusional exchange, which can...
Carbonatites are known to contain the highest concentrations of rare-earth elements (REE) among all igneous rocks. The REE distribution of carbonatites is commonly believed to be controlled by that of the rock-forming Ca minerals (i.e., calcite, dolomite, and ankerite) and apatite because of their high modal content and tolerance for the substitution of Ca by light REE (LREE). Contrary to this conjecture,...
We present major and trace element data of olivine (Fo 86–91 ) — hosted melt inclusions from five Island Arc Basalt (IAB) lavas from Marsili seamount, a large volcano in the active Marsili back-arc basin of the Southern Tyrrhenian. The geochemical composition of this suite of melt inclusions varies widely, extending the range of variation of the host lavas and providing further insights into...
The Qinling molybdenum belt is a prominent metallogenic structure in central China hosting several significant porphyry- and porphyry–skarn-type deposits. The Huanglongpu Mo deposit in the north-western part of the belt is unique in that it is associated with carbonatite dykes, rather than felsic magmatism. The carbonatites are composed largely of Sr–Mn-rich calcite and characterized by high concentrations...
We determined plagioclase-melt partition coefficients for 18 elements by performing controlled cooling rate, 1-atmosphere experiments using both natural and synthetic basaltic (51wt.% SiO 2 ) and basaltic andesite (56wt.% SiO 2 ) powders in a vertical quench furnace. The experiments produced An 69 to An 87 composition plagioclase. Three starting powders were Gorda Ridge...
The Lower to Middle Jurassic Mudurnu formation of the Sakarya Zone (Northern Turkey) was deposited in an extensional basin. This unit crops out along the southern Pontide range and consists of marine sedimentary rocks including debris flows, lignite-bearing clastic rocks and Ammonitico Rosso horizons alternating with mafic and felsic volcanic and volcaniclastic rocks. Magmatic rocks of the Mudurnu...
Oldoinyo Lengai and the volcanic centres of the Lake Natron–Engaruka province contain melilite as a widespread mineral. Extraordinarily Na–Al-rich melilites (up to 6wt.% Na 2 O and 9wt.% Al 2 O 3 ) from recent explosive eruptions are among the most Na-rich ever reported. Their unusual mineral composition leads to optical properties with vivid birefringence colours of 2nd order...
Abundant mantle xenoliths are found in widespread undersaturated Cenozoic basaltic rocks in Northeastern Tasmania and comprise lavas, dykes, plugs and diatremes. The basanites and nephelinites, include primitive magmas (11–14wt.% MgO) with OIB-like geochemical features. Trace element and Pb– and Sr–Nd isotope data suggest that they were generated by mixing of melts derived from low degree (<5%)...
The Tianshan rodingite was formed from eclogite tectonically included in ultramafic rocks of the Changawuzi ophiolite in the southwestern Tianshan, China. Rodingites derived from eclogite contain a mineral assemblage of prehnite, clinozoisite, hydrogrossular, diopside, vesuvianite, chlorite and minor zircon. Pervasive rodingitization took place during exhumation of the subducted slab under conditions...
The Llano Uplift of central Texas is a gentle structural dome exposing ∼1370 to 1230Ma metaigneous and metasedimentary rocks of Grenville affinity along the southern margin of Laurentia. The metamorphic rocks were subsequently intruded by ∼1119 to 1070Ma late syn- to post-tectonic granites collectively known as the Town Mountain Granite (TMG). The eastern most of the TMG, the Marble Falls (MF), Kingsland...
The compositional variation of clinopyroxene and the partitioning of major elements between clinopyroxene and melt are estimated as a function of the cooling rate. Clinopyroxenes were crystallized under variable cooling regimes (15, 9.4, 3, 2.1, and 0.5°C/min from 1250 down to 1000°C) and at isothermal conditions of 1000°C from a basaltic composition at a pressure of 500MPa under anhydrous and hydrous...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.