Magma Signatures in the Terceira Rift Azores: a melt inclusion study

The Terceira Rift (TR) is a 550km long ESE trending line of volcanic reliefs (Graciosa Island, Terceira Island, D. João de Castro Bank, S. Miguel Island) alternating with deep basins (e.g. E of Terceira, Hirondelle) that define the plate boundary between the European and African plates on the Azores plateau [1]. Seismic tomography suggests that the Azores plume is centered NE of Terceira supplying upwelling plume material SW of Terceira (e. g. Faial) [2]. Melt inclusions (MI) are small portions of melt trapped during crystal growth. Their study allows the characterization of the composition of primary melts, mantle heterogeneity, magma sources and timescales. This study presents the first ge ochemical dataset of olivine - hosted unexposed MI sampled from submarine and subaereal lavas along the TR. Plots of incompatible trace element ratios (Fig.1) confirm the presence of distinct mantle signatures showing a mixing trend between two end-members that represent extreme topographic domains: Terceira and Hirondelle Basin. These findings will be discussed considering recent geophysical and geochemical data obtained in the area

Mesélj nekem! Játssz velünk!

Balassi-füzetek 4–5. Maróti Orsolya – Sipos Linda MESÉLJ NEKEM! Balassi Intézet, Budapest, 64. p. Bándli Judit – Gordos Katalin – Maróti Orsolya JÁTSSZ VELÜNK! Balassi Intézet, Budapest, 63. p

Importance of Parking Afforestation with its Impact on the Local Microclimate

In urban areas, trees are generally not in the best conditions. This is particularly true for car parks near shopping centres. Paving, traffic, small tree pits and chemical pollutants do not let the roots grow properly. Also, vehicles can cause harm to the tree’s roots through compaction and the tree’s trunk, therefore the most valuable part of trees – the crown – cannot reach its expected size (Jim 1993). In addition, weakness pests, pathogens can appear more easily. This is particularly true in parking lots especially in front of malls, where maintenance would be the responsibility of the company. The solution is to pay regular attention and to ensure stricter compliance with the law, but without improving the conditions in which trees are located, we will not be able to make a significant difference. Of the innovative solutions available on the market, based on foreign experience and numerous publications the suspended pavement system is the best solution. Although it requires a large financial outlay, the results show that it is definitely worth the investment. Because in a loose medium with a healthy soil life, protected from the compaction and vibrations provided by the root cell, the tree will grow much faster, become larger and healthier without changing the structure of the car park, thus the ecosystem services of the parking lot and human wellbeing will be much better (Ulrich 1991). The difference between the current and potential condition of the trees in the car park was examined by making an environmental model. This showed that larger, healthier trees can reduce the predicted mean vote (human thermal comfort) by 20-24 °C in the summer. In our study, we present further assessments and solutions that provide tangible evidence of the need to make our busy environment more liveable. A nice, well-maintained car park with shade and green vegetation provides a more pleasant environment for shoppers who prefer to spend time in or around the shop (Wolf 2003)

Evolution of Mafic Alkaline Melts Crystallized in the Uppermost Lithospheric Mantle: a Melt Inclusion Study of Olivine-Clinopyroxenite Xenoliths, Northern Hungary

Olivine-clinopyroxenite xenoliths exhumed in alkali basalts (sensu lato) in the Nógrád-Gömör Volcanic Field (NGVF), northern Hungary, contain abundant silicate melt inclusions. Geothermobarometric calculations indicate that these xenoliths crystallized as cumulates in the upper mantle near the Moho. These cumulate xenoliths are considered to represent a period of Moho underplating by mafic alkaline magmas prior to the onset of Late Tertiary alkaline volcanism in the Carpathian-Pannonian region. The major and trace element compositions of silicate melt inclusions in olivine display an evolutionary trend characterized by a strong decrease in CaO/Al2O3. The parental melt of the cumulates was a basanite formed by low-degree (∼ 2%) partial melting of a garnet peridotite source. The compositional trend of the silicate melt inclusions, textural features, and modelling with pMELTS show that the parental melt evolved by major clinopyroxene and minor olivine crystallization followed by the appearance of amphibole simultaneously with significant resorption of the earlier clinopyroxene and olivine. The resulting residual melt was highly enriched in Al2O3, alkalis and most incompatible trace elements. This type of melt is likely to infiltrate and react with surrounding mantle peridotite as a metasomatic agent. It might also form high-pressure pegmatite-like bodies in the mantle that might be the source of the amphibole and sanidine megacrysts also found in the alkali basalts of the NGVF. Preferential remelting of the later-formed (i.e. lower temperature) mineral assemblage (amphibole, sanidine, residual glass) might have significantly contaminated the host alkaline mafic lavas, increasing their Al2O3 and total alkali contents and, therefore, reducing their MgO, FeO and CaO conten

Copper partitioning between silicate melts and amphibole: Experimental insight into magma evolution leading to porphyry copper ore formation

AbstractA series of piston cylinder experiments were conducted to determine the partition coefficient of Cu between amphibole and andesitic to rhyolitic silicate melts. The experiments were run at T=740–990°C, P=0.7GPa, oxygen fugacity (fO2) ranging from that of the Ni-NiO buffer (NNO) to 2.3 log units higher (NNO+2.3 and dissolved water in variable concentrations (under-saturated to saturated conditions). Fixed metal activities were imposed by using Au97Cu3 and Au92Cu8 alloy capsules, which allowed simultaneously determination of Cu solubility. Our data demonstrate that Cu solubilities in both the silicate melt and amphibole decrease with decreasing temperature. The solubility of Cu decreases by a factor of 6 from 990 to 740°C in equilibrium with andesitic to rhyolitic melt compositions. The average amphibole/silicate melt partition coefficient of Cu [DCu (amph/melt)] is 0.066±0.006, and is essentially constant without showing any correlation with silicate melt composition, dissolved water concentration, temperature or fO2.The low DCu (amph/melt) value suggests that amphibole crystallizing at any stage of calc-alkaline magma evolution is unable to scavenge a significant fraction of the initially available Cu from the melt. However, DCu (amph/melt) is high enough to yield precisely measurable Cu concentrations in natural amphiboles. As DCu (amph/melt) results constant along the liquid line of descent of calc-alkaline magmas, amphibole compositions may thus be used as a proxy to monitor the evolution of the Cu concentration in the silicate melt (not the bulk magma if sulfide is present). This may be useful for understanding the metallogenic evolution of intrusive rocks, in which silicate melt inclusions in minerals are generally absent. As most porphyry-type Cu ore deposits are associated with upper crustal intrusions, in-situ microanalysis of inclusion-free amphiboles in such rocks may help understand ore genesis and might also be used in mineral exploration to assess the fertility of prospective magmatic systems

A Quartz-bearing Orthopyroxene-rich Websterite Xenolith from the Pannonian Basin, Western Hungary: Evidence for Release of Quartz-saturated Melts from a Subducted Slab

An unusual quartz-bearing orthopyroxene-rich websterite xenolith has been found in an alkali basaltic tuff at Szigliget, Bakony-Balaton Highland Volcanic Field (BBHVF), western Hungary. Ortho- and clinopyroxenes are enriched in light rare earth elements (LREE), middle REE and Ni, and depleted in Nb, Ta, Sr and Ti compared with ortho- and clinopyroxenes occurring in either peridotite or lower crustal granulite xenoliths from the BBHVF. Both ortho- and clinopyroxenes in the xenolith contain primary and secondary silicate melt inclusions, and needle-shaped or rounded quartz inclusions. The melt inclusions are rich in SiO2 and alkalis and poor in MgO, FeO and CaO. They are strongly enriched in LREE and large ion lithophile elements, and display negative Nb, Ta and Sr anomalies, and slightly positive Pb anomalies. The xenolith is interpreted to represent a fragment of an orthopyroxene-rich body that crystallized in the upper mantle from a hybrid melt that formed by interaction of mantle peridotite with a quartz-saturated silicate melt that was released from a subducted oceanic slab. Although the exact composition of the slab melt cannot be determined, model calculations on major and trace elements suggest involvement of a metasedimentary componen