Mineral chemistry, petrology and geochemistry of the Sebago granite-pegmatite system, southern Maine, USA

The Colli Albani volcano is an ultrapotassic caldera complex located 30 km to the SE of Rome and has displayed a wide range of eruptive behaviors, ranging from effusive activity to highly explosive and large volume eruptions (up to 63 km3 dense rock equivalent per eruption) despite its mafic nature.We combine physical volcanology, petrology, and geochemistry to focus on the mildly explosive to effusive products of two sections (Tuscolo and Artemisio) which are located on opposite sides of the main caldera and stratigraphically between the last large ignimbrite, Villa Senni. The target of this study is to identify the processes responsible for the transition from the smaller explosions to the larger caldera-forming ignimbrite eruptions, and eventually trace how the magmatic system rebuilds in the interim.Whole rock analyses, mineral chemistry, and petrography of fall deposits from both field localities are compared with an existing dataset for the Villa Senni ignimbrites. We will use unsupervised and supervised machine learning approaches to identify similarities and differences between large caldera-forming eruptions and mild-explosive to effusive activity and identify the processes modulating the transition between these two behaviours.

Download Full-text

Geodynamic constraints deciphered from the petrology and geochemistry of the Late Cretaceous granitoids from Anafi island (Cyclades - Greece)

10.5194/egusphere-egu21-3522 ◽

2021 ◽

Author(s):

Petros Koutsovitis ◽

Konstantinos Soukis ◽

Panagiotis Voudouris ◽

Stylianos Lozios ◽

Theodoros Ntaﬂos ◽

...

Keyword(s):

Late Cretaceous ◽

Mineral Chemistry ◽

Crustal Assimilation ◽

Corner Flow ◽

Granitoid Magma ◽

Thrust Sheets ◽

Petrology And Geochemistry ◽

Crystallization Conditions ◽

Structural Levels ◽

Temperature Crystallization

In the Aegean region (Cyclades - Greece), the island of Anafi island comprises Late Cretaceous intermediate and felsic granitoids that intruded within exhumed HT/LP metamorphic sequences that include amphibolites, serpentinites and metasediments. The granitoids correspond to I-type arc-related rocks with calc-alkaline geochemical affinities. Variations in their petrography mineral chemistry and geochemical features are attributed to magma differentiation with removal of plagioclase and/or K-feldspar, but also amphibole and biotite. Differentiation processes of the upwelling granitoid magma included fractional crystallization accompanied with crustal assimilation, pointing to interaction with the overriding continental crust. Mineral chemistry and geochemical results display that the Anafi granitoids are highly comparable with the Late Cretaceous granitoids of East Crete and Donousa island suggesting that this magmatic activity was not a local event. Geothermometric results show relatively moderate temperature crystallization conditions (~790 &#176;C) for the compositionally intermediate granitoids, which are and lower for the felsic granitoids (~630 &#176;C). Geobarometric calculations suggest shallow intrusion conditions (~2.0-6.5 kbar), which corresponds to a depth of crystallization of ~12 &#177; 4 km.The thrust sheets that overly the flysch constitute a subducted and metamorphosed oceanic sequence, that after the intrusion of the granitoids was exhumed from the Late Cretaceous to the Late Oligocene. These metamorphic units likely represent a part of the Pindos - CBU domain that was subducted at an earlier pre-Campanian stage. In the hydrated mantle wedge, incorporation of shallow level granitoids within metamorphic units was likely facilitated via corner flow intrusion mechanisms. Ongoing underplating of subducted material gradually brought the granitoids along with the host units to shallow structural levels and on top of the parautochtonous flysch.

Download Full-text

Two types of gabbroic xenoliths from rhyolite dominated Niijima volcano, northern part of Izu-Bonin arc: petrological and geochemical constraints

Open Geosciences ◽

10.1515/geo-2017-0001 ◽

2017 ◽

Vol 9 (1) ◽

pp. 1-12 ◽

Cited By ~ 1

Author(s):

Yoji Arakawa ◽

Daisuke Endo ◽

Kei Ikehata ◽

Junya Oshika ◽

Taro Shinmura ◽

...

Keyword(s):

Basaltic Magma ◽

Olivine Basalt ◽

Mineral Chemistry ◽

Central Japan ◽

Volcanic Arc ◽

Andesitic Magma ◽

Petrology And Geochemistry ◽

Different Origins ◽

Geochemical Constraints

AbstractWe examined the petrography, petrology, and geochemistry of two types of gabbroic xenoliths (A- and B-type xenoliths) in olivine basalt and biotite rhyolite units among the dominantly rhyolitic rocks in Niijima volcano, northern Izu-Bonin volcanic arc, central Japan. A-type gabbroic xenoliths consisting of plagioclase, clinopyroxene, and orthopyroxene with an adcumulate texture were found in both olivine basalt and biotite rhyolite units, and B-type gabbroic xenoliths consisting of plagioclase and amphibole with an orthocumulate texture were found only in biotite rhyolite units. Geothermal- and barometricmodelling based on mineral chemistry indicated that the A-type gabbro formed at higher temperatures (899–955°C) and pressures (3.6–5.9 kbar) than the B-type gabbro (687–824°C and 0.8–3.6 kbar). These findings and whole-rock chemistry suggest different parental magmas for the two types of gabbro. The A-type gabbro was likely formed from basaltic magma, whereas the B-type gabbro was likely formed from an intermediate (andesitic) magma. The gabbroic xenoliths in erupted products at Niijima volcano indicate the presence of mafic to intermediate cumulate bodies of different origins at relatively shallower levels beneath the dominantly rhyolitic volcano.

Download Full-text

The mineral chemistry of gahnite, garnet and columbite-group minerals (CGM): Implications for genesis and evolution of the Kenticha Rare-element granite-pegmatite, Adola, Ethiopia

Journal of African Earth Sciences ◽

10.1016/j.jafrearsci.2019.103691 ◽

2020 ◽

Vol 162 ◽

pp. 103691

Author(s):

Barsisa Bekele ◽

Amit Kumar Sen

Keyword(s):

Mineral Chemistry ◽

Rare Element ◽

Granite Pegmatite

Download Full-text

Phosphate Mineral Associations from the Tres Arroyos Aplite-Pegmatites (Badajoz, Spain): Petrography, Mineral Chemistry, and Petrogenetic Implications

The Canadian Mineralogist ◽

10.3749/canmin.1900102 ◽

2021 ◽

Author(s):

Idoia Garate-Olave ◽

Encarnación Roda-Robles ◽

Pedro Pablo Gil-Crespo ◽

Alfonso Pesquera

Keyword(s):

Mineral Chemistry ◽

Chemical Compositions ◽

Granite Pegmatite ◽

System P ◽

Phosphate Mineral ◽

Mineral Associations ◽

Low Degree ◽

History Of ◽

Granitic Batholith ◽

Tres Arroyos

ABSTRACT In the Tres Arroyos granite-pegmatite system (Badajoz, Spain) a zoned aplite-pegmatite field occurs, with poorly evolved, intermediate, and Li-rich dikes intruded into metasediments, close to the contact with the Nisa-Alburquerque granitic batholith. A large variety of Fe-Mn phosphate minerals occur in the poorly evolved aplite-pegmatites; Al-phosphates occur mainly in the intermediate and Li-rich dikes. The Fe/(Fe + Mn) ratio of the Fe-Mn phosphates is the highest reported for aplite-pegmatite fields in the Central Iberian Zone, suggesting a low degree of fractionation for the poorly evolved aplite-pegmatites that host these minerals. In contrast, the high F contents observed in crystals of the amblygonite–montebrasite series from the intermediate and Li-rich aplite-pegmatites indicates a higher fractionation degree for these dikes. The relatively common occurrence of phosphate minerals in the three types of aplite-pegmatites from Tres Arroyos attests to a significant availability of P in the pegmatitic melt. In this granite pegmatite system, P first started behaving as a compatible element, thus favoring the crystallization of discrete phosphates, during the crystallization of the poorly evolved aplite-pegmatites. In more fractionated melts, where Fe-Mn-(Mg) contents were extremely depleted, P was still available, allowing the crystallization of the Al-phosphates, mainly of the amblygonite–montebrasite series, in the more evolved intermediate and Li-rich aplite-pegmatites. Subsolidus replacement of the early phosphate phases, such as those of the amblygonite–montebrasite series, by lacroixite, together with the presence of late Ca- and Sr-bearing phosphates such as jahnsite-(CaMnFe), whiteite-(CaFeMg), mitridatite, and goyazite, attest to a high activity of metasomatic fluids in the Tres Arroyos granite-pegmatite system. Consequently, variations in the phosphate mineral associations and in their chemical compositions reflect well the fractional crystallization processes suffered by the pegmatitic melts from the poorly evolved up to the Li-rich dikes, as well as the subsolidus history of the Tres Arroyos system.

Download Full-text