The correlation between lithium and magnesium in trioctahedral micas: Improved equations for Li2O estimation from MgO data

1999 ◽  
Vol 63 (1) ◽  
pp. 57-74 ◽  
Author(s):  
G. Tischendorf ◽  
H.-J. Förster ◽  
B. Gottesmann
Keyword(s):  
Lithium Concentration ◽  
Limited Range ◽  
Igneous Rocks ◽  
Alternative Methods ◽  
Metamorphic Rocks ◽  
Lithium Content ◽  
Magmatic Rocks ◽  
Major Disadvantage ◽  
Empirical Approaches

AbstractA major disadvantage of the electron microprobe is its inability to determine Li, which may make up an essential component in micaceous minerals. Correct classification of micas and proper calculation of their formulae require alternative methods. One of these is the indirect estimation of the lithium concentration by empirical approaches based on element correlations. Relationships between Li2O and SiO2 have long been used for this purpose; however, they are valid only for a limited range of mica compositions (i.e. Li-rich, Mg-poor varieties).In this paper we report the results from a renewed study of the correlation between Li2O and MgO contents in trioctahedral micas. It is demonstrated that the relations between both oxides are strongly dependent upon the geological environment in which the mica was formed. It is necessary to distinguish a ‘normal group’, which comprises micas from ‘common’ S- and I-type magmatic rocks and most metamorphic rocks , a ‘low Li-Mg group’, to which belong Fe-rich micas from non-alkaline rocks of A-type affinity, and a ‘high Li-Mg group’ which includes micas from either peraluminous or peralkaline igneous rocks and Mg-enriched wall-rocks. These wall rocks supplied additional magnesium to the mica-forming environment. We offer empirical expressions relating Li2O and MgO contents for these three types which, in many cases, allow a sufficiently good estimation of the lithium content in trioctahedral micas of widely varying compositions.

scholarly journals Petrogenesis and tectonic evolution of metaluminous sub-alkaline granitoids from the Takab Complex, NW Iran

2010 ◽  
Vol 148 (2) ◽  
pp. 250-268 ◽  
Author(s):  
ROBAB HAJIALIOGHLI ◽  
MOHSSEN MOAZZEN ◽  
AHMAD JAHANGIRI ◽  
ROLAND OBERHÄNSLI ◽  
BEATE MOCEK ◽  
...  
Keyword(s):  
Tectonic Evolution ◽  
Mineral Chemistry ◽  
Quartz Diorite ◽  
Igneous Rocks ◽  
Metamorphic Rocks ◽  
Crustal Melting ◽  
Calc Alkaline ◽  
Nw Iran ◽  
Magmatic Rocks ◽  
Crustal Origin

AbstractThe Takab complex is composed of a variety of metamorphic rocks including amphibolites, metapelites, mafic granulites, migmatites and meta-ultramafics, which are intruded by the granitoid. The granitoid magmatic activity occurred in relation to the subduction of the Neo-Tethys oceanic crust beneath the Iranian crust during Tertiary times. The granitoids are mainly granodiorite, quartz monzodiorite, monzonite and quartz diorite. Chemically, the magmatic rocks are characterized by ASI<1.04, AI<0.87 and high contents of CaO (up to ~14.5 wt%), which are consistent with the I-type magmatic series. Low FeOt/(FeOt+MgO) values (<0.75) as well as low Nb, Y and K2O contents of the investigated rocks resemble the calc-alkaline series. Low SiO2, K2O/Na2O and Al2O3 accompanied by high CaO and FeO contents indicate melting of metabasites as an appropriate source for the intrusions. Negative Ti and Nb anomalies verify a metaluminous crustal origin for the protoliths of the investigated igneous rocks. These are comparable with compositions of the associated mafic migmatites, in the Takab metamorphic complex, which originated from the partial melting of amphibolites. Therefore, crustal melting and a collision-related origin for the Takab calc-alkaline intrusions are proposed here on the basis of mineralogy and geochemical characteristics. The P–T evolution during magmatic crystallization and subsolidus cooling stages is determined by the study of mineral chemistry of the granodiorite and the quartz diorite. Magmatic crystallization pressure and temperature for the quartz-diorite and the granodiorite are estimated to be P~7.8±2.5 kbar, T~760±75°C and P~5±1 kbar, T~700°C, respectively. Subsolidus conditions are consistent with temperatures of ~620°C and ~600°C, and pressures of ~5 kbar and ~3.5 kbar for the quartz-diorite and the granodiorite, respectively.

Multidimensional classification of magma types for altered igneous rocks and application to their tectonomagmatic discrimination and igneous provenance of siliciclastic sediments

Lithos ◽  
2017 ◽  
Vol 278-281 ◽  
pp. 321-330 ◽  
Author(s):  
Surendra P. Verma ◽  
M. Abdelaly Rivera-Gómez ◽  
Lorena Díaz-González ◽  
Kailasa Pandarinath ◽  
Alejandra Amezcua-Valdez ◽  
...  
Keyword(s):  
Igneous Rocks ◽  
Siliciclastic Sediments

Revised stratigraphy of the Mesozoic rocks of southern Cyprus

1980 ◽  
Vol 117 (6) ◽  
pp. 547-563 ◽  
Author(s):  
R. E. Swarbrick ◽  
A. H. F. Robertson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Late Cretaceous ◽  
Sedimentary Cover ◽  
Igneous Rocks ◽  
Late Triassic ◽  
Metamorphic Rocks ◽  
Southern Cyprus

SummaryRecent resurgence of interest in the Mesozoic rocks of SW and southern Cyprus necessitates redefinition of the Mesozoic sedimentary and igneous rocks in line with modern stratigraphical convention. Two fundamentally different rocks associations are present, the Troodos Complex, not redefined, a portion of late Cretaceous oceanic crust, and the Mamonia Complex, the tectonically dismembered remnants of a Mesozoic continental margin. Based on earlier work, the Mamonia Complex is divided into two groups, each subdivided into a number of subsidiary formations and members. The Ayios Photios Group is wholly sedimentary, and records the evolution of a late Triassic to Cretaceous inactive continental margin. The Dhiarizos Group represents Triassic alkalic volcanism and sedimentation adjacent to a continental margin. Several other formations not included in the two groups comprise sedimentary mélange and metamorphic rocks. The Troodos Complex possesses an in situ late Cretaceous sedimentary cover which includes two formations of ferromanganiferous pelagic sediments, radiolarites and volcaniclastic sandstones. The overlying Cainozoic calcareous units are not redefined here.

scholarly journals Learn from every mistake! Hierarchical information combination in astronomy

2016 ◽  
Vol 12 (S325) ◽  
pp. 39-45 ◽  
Author(s):  
Maria Süveges ◽  
Sotiria Fotopoulou ◽  
Jean Coupon ◽  
Stéphane Paltani ◽  
Laurent Eyer ◽  
...  
Keyword(s):  
Big Data ◽  
Probability Distributions ◽  
Variable Stars ◽  
Alternative Methods ◽  
Photometric Redshift ◽  
Promising Tool ◽  
Combination Methods ◽  
General Improvement ◽  
Output Probability

AbstractThroughout the processing and analysis of survey data, a ubiquitous issue nowadays is that we are spoilt for choice when we need to select a methodology for some of its steps. The alternative methods usually fail and excel in different data regions, and have various advantages and drawbacks, so a combination that unites the strengths of all while suppressing the weaknesses is desirable. We propose to use a two-level hierarchy of learners. Its first level consists of training and applying the possible base methods on the first part of a known set. At the second level, we feed the output probability distributions from all base methods to a second learner trained on the remaining known objects. Using classification of variable stars and photometric redshift estimation as examples, we show that the hierarchical combination is capable of achieving general improvement over averaging-type combination methods, correcting systematics present in all base methods, is easy to train and apply, and thus, it is a promising tool in the astronomical “Big Data” era.

Gneiss, marbres, prasinites en coussins et polymetamorphisme dans la partie sud-occidentale du massif Dora-Maira (Alpes cottiennes piemontaises)

1961 ◽  
Vol S7-III (4) ◽  
pp. 345-354
Author(s):  
Andre Michard ◽  
P. Vialon
Keyword(s):  
White Mica ◽  
Igneous Rocks ◽  
Metamorphic Rocks ◽  
Retrograde Metamorphism ◽  
Po River ◽  
Alpine Metamorphism

Abstract Igneous rocks of the Dora-Maira massif in the Po river headwater region in the Cottian Alps of Piedmont, Italy, are surrounded, and in many places surmounted, by gneiss, marble, and other associated metamorphic rocks of controversial age. The evidence is considered conclusive that the age of the rocks ranges from Permo-Carboniferous to Triassic. Criteria for discrimination of successive periods of metamorphism, including retrograde metamorphism, are reviewed. Carbonatized rocks and phengitic conglomeratic quartzite serve as "metamorphic thermometers" useful locally for discriminating successive periods of metamorphism. Cataclastic effects are also useful for determining time relationships, as are also optical peculiarities of quartz, feldspar, white mica, and biotite in various rocks. It is concluded that the region has been subjected to two major periods of metamorphism, and that the Alpine metamorphism in general was less intensive, and in certain aspects was retrograde compared with the pre-Alpine metamorphism.

scholarly journals Suggestions regarding the Classification of the Igneous Rocks

1900 ◽  
Vol 8 (1) ◽  
pp. 1-31
Author(s):  
William H. Hobbs
Keyword(s):  
Igneous Rocks
Sign in / Sign up

Export Citation Format

Share Document