Petrologic evolution of Pre-Unzen and Unzen magma chambers beneath the Shimabara Peninsula, Kyushu, Japan: Evidence from petrography and bulk rock chemistry

2005 ◽  
Vol 39 (3) ◽  
pp. 241-256 ◽  
Author(s):  
Takeshi Sugimoto ◽  
Hidemi Ishibashi ◽  
Sadatsugu Wakamatsu ◽  
Takeru Yanagi
Keyword(s):  
Bulk Rock ◽  
Magma Chambers ◽  
Bulk Rock Chemistry

40Ar/39Ar ages and bulk-rock chemistry of the lower submarine units of the central and western Aleutian Arc

Lithos ◽  
2021 ◽  
pp. 106147
Author(s):  
Rachel Bezard ◽  
Kaj Hoernle ◽  
Jörg A. Pfänder ◽  
Brian Jicha ◽  
Reinhard Werner ◽  
...  
Keyword(s):  
Bulk Rock ◽  
Aleutian Arc ◽  
Bulk Rock Chemistry

scholarly journals Mineralogy and Geochemistry of Nephrite Jade from Yinggelike Deposit, Altyn Tagh (Xinjiang, NW China)

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 418 ◽  
Author(s):  
Ying Jiang ◽  
Guanghai Shi ◽  
Liguo Xu ◽  
Xinling Li
Keyword(s):  
Mass Spectrometry ◽  
Inductively Coupled Plasma ◽  
Isotope Ratio Mass Spectrometry ◽  
Field Investigation ◽  
Bulk Rock ◽  
Dolomitic Marble ◽  
Nw China ◽  
Altyn Tagh ◽  
Bulk Rock Chemistry ◽  
Geochemical Studies

The historic Yinggelike nephrite jade deposit in the Altyn Tagh Mountains (Xinjiang, NW China) is renowned for its gem-quality nephrite with its characteristic light-yellow to greenish-yellow hue. Despite the extraordinary gemological quality and commercial significance of the Yinggelike nephrite, little work has been done on this nephrite deposit, due to its geographic remoteness and inaccessibility. This contribution presents the first systematic mineralogical and geochemical studies on the Yinggelike nephrite deposit. Electron probe microanalysis, X-ray fluorescence (XRF) spectrometry, inductively coupled plasma mass spectrometry (ICP-MS) and isotope ratio mass spectrometry were used to measure the mineralogy, bulk-rock chemistry and stable (O and H) isotopes characteristics of samples from Yinggelike. Field investigation shows that the Yinggelike nephrite orebody occurs in the dolomitic marble near the intruding granitoids. Petrographic studies and EMPA data indicate that the nephrite is mainly composed of fine-grained tremolite, with accessory pargasite, diopside, epidote, allanite, prehnite, andesine, titanite, zircon, and calcite. Geochemical studies show that all nephrite samples have low bulk-rock Fe/(Fe + Mg) values (0.02–0.05), as well as low Cr (0.81–34.68 ppm), Co (1.10–2.91 ppm), and Ni (0.52–20.15 ppm) contents. Chondrite-normalized REE patterns of most samples exhibit strong to moderate negative Eu anomalies (0.04–0.67), moderate LREE enrichments, nearly flat HREE patterns, and low ΣREE contents (2.16–11.25 ppm). The nephrite samples have δ18O and δD values of 5.3 to 7.4‰ and –74.9 to –86.7‰, respectively. The mineralogy, bulk-rock chemistry, and O–H isotope characteristics are consistent with the dolomite-related nephrite classification. Based on mineral paragenetic relationships, three possible mineral crystallization stages are recognized: (1) diopside formed by prograde metasomatism; (2) nephrite jade formed by retrograde metasomatism and replacement of Stage I anhydrous minerals; (3) hydrothermal alteration after the nephrite formation. Features of transition metal contents indicate that the color of the Yinggelike nephrite is likely to be controlled by the Fe2+, Fe3+, and Mn. Yellowish color is related to Mn and especially Fe3+, while greenish color is related to Fe2+. Our new mineralogical and geochemical results on the Yinggelike nephrite provide better constraints on the formation of other nephrite deposits in the Altyn Tagh Mountains, and can facilitate future nephrite prospecting and research in the region.

scholarly journals Multi-stage serpentinization of ultramafic rocks in the Manlay Ophiolite, southern Mongolia

2021 ◽  
Vol 26 (53) ◽  
pp. 1-17
Author(s):  
Nomuulin Amarbayar ◽  
Noriyoshi Tsuchiya ◽  
Otgonbayar Dandar ◽  
Atsushi Okamoto ◽  
Masaoki Uno ◽  
...  
Keyword(s):  
Mineral Chemistry ◽  
Ultramafic Rocks ◽  
Bulk Rock ◽  
Fluid Infiltration ◽  
Multi Stage ◽  
Central Asian ◽  
Bulk Rock Chemistry ◽  
Three Stages ◽  
Arc Setting ◽  
Global Cycle

Serpentinization of ultramafic rocks in ophiolites is key to understanding the global cycle of elements and changes in the physical properties of lithospheric mantle. Mongolia, a central part of the Central Asian Orogenic Belt (CAOB), contains numerous ophiolite complexes, but the metamorphism of ultramafic rocks in these ophiolites has been little studied. Here we present the results of our study of the serpentinization of an ultramafic body in the Manlay Ophiolite, southern Mongolia. The ultramafic rocks were completely serpentinized, and no relics of olivine or orthopyroxene were found. The composition of Cr-spinels [Mg# = Mg/(Mg + Fe2+) = 0.54 and Cr# = Cr/(Cr + Al) = 0.56] and the bulk rock chemistry (Mg/Si = 1.21–1.24 and Al/Si < 0.018) of the serpentinites indicate their origin from a fore-arc setting. Lizardite occurs in the cores and rims of mesh texture (Mg# = 0.97) and chrysotile is found in various occurrences, including in bastite (Mg# = 0.95), mesh cores (Mg# = 0.92), mesh rims (Mg# = 0.96), and later-stage large veins (Mg# = 0.94). The presence of lizardite and chrysotile and the absence of antigorite suggests low-temperature serpentinization (<300 °C). The lack of brucite in the serpentinites implies infiltration of the ultramafic rocks of the Manlay Ophiolite by Si-rich fluids. Based on microtextures and mineral chemistry, the serpentinization of the ultramafic rocks in the Manlay Ophiolite took place in three stages: (1) replacement of olivine by lizardite, (2) chrysotile formation (bastite) after orthopyroxene and as a replacement of relics of olivine, and (3) the development of veins of chrysotile that cut across all previous textures. The complex texture of the serpentinites in the Manlay Ophiolite indicates multiple stages of fluid infiltration into the ultramafic parts of these ophiolites in southern Mongolia and the CAOB.

Extension of the melilite-carbonatite province in the Apennines of Italy: the kamafugite of Grotta del Cervo, Abruzzo

2002 ◽  
Vol 66 (4) ◽  
pp. 555-574 ◽  
Author(s):  
F. Stoppa ◽  
A. R. Woolley ◽  
A. Cundari
Keyword(s):  
Trace Element ◽  
Volcanic Field ◽  
Igneous Rocks ◽  
Bulk Rock ◽  
The West ◽  
Pyroclastic Rocks ◽  
Ultramafic Xenoliths ◽  
Bulk Rock Chemistry ◽  
Italian Apennines

AbstractA new occurrence of a rare kamafugite near L'Aquila, Abruzzo, is described in detail to characterize its paragenesis and to establish possible genetic links with similar alkaline mafic igneous rocks from the Oricola-Camerata Nuova (OC) volcanic field, ˜20 km to the west. Both occurrences belong to the Umbria-Latium-Ultralkaline-District (ULUD), an igneous district represented by rare kamafugites and carbonatites and distinct from the much more voluminous Roman Region (RR) rocks. The new kamafugite was found in a cave known as Grotta del Cervo (GC), associated with epiclastic and pyroclastic rocks. In the latter, lapilli ash tuff, welded lapilli, ultramafic xenoliths, cognate lithics and pelletal lapilli have been identified. The mineralogy of the welded lapilli comprises, in order of decreasing abundance, diopside, leucite, haüyne, Mg-mica, andraditic garnet, apatite, magnetite, kalsilite and olivine. The rock is carbonate-free. Based on bulk-rock chemistry it is classified as a kamafugite, closely approaching the composition of ULUD kamafugites, according to Sahama's (1974) criteria. Separate lapilli ash tuff, characterized by the same silicate mineralogy as that of the welded lapilli, plus modal carbonate exceeding 10 wt.%, is classified as a carbonatitic kamafugite. Bulk-rock and trace-element compositions confirm that the Grotta del Cervo rocks closely approach the ULUD analogues.The Grotta del Cervo occurrence partially fills the geographical and compositional gap between ULUD rocks and the rocks from the Vulture Complex, also a carbonatite and melilitite locality ˜200 km south of GC, and adds considerably to the bulk of kamafugitic and related rocks lying along the Italian Apennines. The petrogenesis of these kamafugites rocks is discussed and possible mineralogical similarities with the Roman Region rocks are highlighted.

scholarly journals Conditions and timing of low-pressure – high-temperature metamorphism in the Montresor Belt, Rae Province, Nunavut

2019 ◽  
Vol 56 (6) ◽  
pp. 654-671
Author(s):  
Carolyn Dziawa ◽  
Fred Gaidies ◽  
John Percival
Keyword(s):  
White Mica ◽  
Age Dating ◽  
Bulk Rock ◽  
Prograde Metamorphism ◽  
Bulk Rock Chemistry ◽  
T Path ◽  
Temperature Time ◽  
High Bulk ◽  
High Temperature Metamorphism

Pressure–temperature–time (P–T–t) estimates for the Montresor Belt, obtained using phase equilibria and geospeedometry modelling integrated with in situ U–Th–Pb monazite geochronology, shed new light on the tectonometamorphic effects of the Snowbird phase of the Trans-Hudson orogeny. Typical metapelitic assemblages of the lower Montresor group consist of white mica, biotite, plagioclase, quartz, and andalusite, which in some rocks is partly or completely pseudomorphed by white mica. The observed assemblages reflect peak P–T conditions centring at approximately 575 °C and 3 kbar. Rocks with high bulk Fe/Mg contents contain compositionally zoned garnet, permitting the addition of further constraints on the conditions of metamorphism in the Montresor Belt: Core compositions of earliest-grown garnets indicate initial garnet crystallization at approximately 535 °C and 2.3 kbar, suggesting a nearly isobaric P–T path of prograde metamorphism with a gradient of approximately 50 °C·kbar–1. Chemical age-dating of monazite inclusions in garnet yields ages of ca. 1870 ± 9 to 1837 ± 9 Ma. Retrograde, pseudomorphic andalusite replacement by white mica at approximately 540 °C is inferred to have been controlled by variations in bulk rock chemistry. Morphologically corroded and chemically heterogeneous monazite adjacent to white mica pseudomorphs suggests that andalusite replacement took place at ca. 1792 ± 10 Ma, possibly associated with extension and movement along the detachment fault separating the upper and lower Montresor groups. Simulations of diffusion across chlorite- and biotite-filled cracks in garnet assumed to be coeval with andalusite replacement suggest that the rocks have experienced the retrograde event for at least 20 My.

The Highwood Mountains potassic igneous province, Montana: mineral fractionation trends and magmatic processes revisited

2012 ◽  
Vol 76 (4) ◽  
pp. 1005-1051 ◽  
Author(s):  
C. M. B. Henderson ◽  
F. R. Richardson ◽  
J. M. Charnock
Keyword(s):  
Major Element ◽  
Magma Mixing ◽  
Alkali Feldspar ◽  
Bulk Rock ◽  
Magma Chambers ◽  
Igneous Province ◽  
Rock Analysis ◽  
Volatile Loss ◽  
Primary Magmas ◽  
Alkali Feldspars

AbstractPotassium-rich mafic dykes and lavas from the Highwood Mountains Igneous Province, USA were studied by electron-microprobe and bulk-rock analysis. For the mafic phonolites, compositional trends for olivine and augite phenocrysts and groundmass biotite, alkali feldspar and titanomagnetites are presented and substitution mechanisms discussed. Phenocrysts of biotite and augite in the minettes are also characterized, together with groundmass alkali feldspar and titanomagnetite. The alkali feldspars and biotites are commonly enriched in Ba. Olivine, clinopyroxene and biotite phenocrysts are generally quite magnesium-rich, which is consistent with the primitive natures of the least evolved rocks.Bulk-rock major-element compositions are combined with modal and microprobe data for the principal phenocrysts to calculate model residual liquid compositions for mafic phonolites, minettes and a syenitic rock. On the basis of phase-equilibria, it is suggested that the main controls of differentiation are polybaric involving crystallization during transport of primary magmas from the mantle for the minettes, and low-pressure differentiation for the mafic phonolites. Whereas magma mixing might have contributed to petrogenesis, many of the disequilibrium features exhibited by clinopyroxene and biotite phenocrysts can also be attributed to pre-existing phenocrysts undergoing decompression melting during magma uprise from its mantle source, followed by rapid crystal growth and episodic volatile loss in sub-volcanic magma chambers.

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