DEFECTS OF MAGMA FORMATION ANALYSIS

2021 ◽  
pp. 3-17
Author(s):  
V. L. Khomichev ◽  
◽  
N. E. Egorova ◽  
Keyword(s):  
Igneous Rocks ◽  
Soviet Science ◽  
Great Achievement ◽  
Magmatic Rocks ◽  
Sayan Region ◽  
Yenisey Ridge ◽  
Natural Communities

The formation analysis of igneous rocks is a great achievement of the Soviet science in terms of classifying natural communities of magmatic rocks for the purpose of forecasting and prospecting of associated deposits. But due to the complexity of the problem itself, the uncertainty of boundaries between formational types in the practice of geological works, there are numerous defects that were clearly observed during the regional and interregional correlation of magmatic complexes of the Altai-Sayan region and Yenisey Ridge. The reasons and consequences of these defects, ways of their correction are analyzed.

scholarly journals Geochemistry of Nb and Та in magmatic rocks of the Ukrainian Shield

2020 ◽  
Vol 41 ◽  
pp. 12-31
Author(s):  
S.G. Kryvdik ◽  
◽  
O.V Dubyna ◽  
◽  
Keyword(s):  
Igneous Rocks ◽  
Ukrainian Shield ◽  
Geochemical Data ◽  
Alkaline Rocks ◽  
Magmatic Rocks ◽  
Azov Sea ◽  
Continental Rifts ◽  
Alkaline Feldspar ◽  
High Concentrations ◽  
Almost All

It was made an attempt to generalize geochemical data of Nb and Ta concentration in the most common igneous rocks of the Ukrainian Shield (USh). In the majority of widely distributed rocks of the USh (normal and subalkaline granitoids) the Nb and Ta concentration are similar to upper crust but lower the accepted Clark value for acidic rocks. In the more differentiated rapakivi granites concentrations of these elements reach or exceed the Clark’s concentrations (up to 35 ppm). Only highly differentiated alkaline rocks and alkaline feldspar granites (Perga, Kamiani mogyly, Ruska Poliana massifs) have high Nb concentrations (up to 800, 120 and 370 ppm, respectively). Medium rocks of the normal range are the least geochemically studied and typically are characterized low Nb and Ta concentrations. Almost all gabbroids as well as their metamorphosed analogues in the greenstone structures, are characterized by very low Nb (and Ta) concentration (two or more orders of magnitude) compared with Clark’s values for basic rocks (20 ppm Nb and 0.48 ppm Ta) according to A.P. Vinogradov. Against this background, increased of Nb and Ta concentration is observed in the main rocks of anorthosite-rapakivi-granite plutons. Howover even in these rocks concentration of these elements rarely reach or does not achieve the values which are typical for subalkaline and alkaline basalts of continental rifts. The regional heterogeneity in Nb and Ta distribution is observed in alkaline rocks of different composition: in the Azov Sea region these rocks are characterized by high concentrations, while in the western part of the USh the content of these elements is extremely low. The increased concentration of these elements is also revealed in kimberlites from the Azov Sea region and the Kyrovohrad megablock of the USh. The authors give some considerations and assumptions about the dependence on geochemical features of the Precambrian igneous rocks of the USh from the geodynamic conditions of their formation.

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.

scholarly journals Early Tertiary flood basalts from Hareøen and western Nûgssuaq, West Greenland

1976 ◽  
Vol 120 ◽  
pp. 1-36
Author(s):  
N Hald
Keyword(s):  
Thin Layers ◽  
Igneous Rocks ◽  
Chemical Analyses ◽  
Flood Basalts ◽  
The West ◽  
West Greenland ◽  
Basaltic Rocks ◽  
Magmatic Rocks ◽  
Incompatible Elements ◽  
Early Tertiary

In central West Greenland flood basalts were erupted in the Early Tertiary. On Hareøen and western Nûgssuaq the upper part of the volcanic sequence predominates reaching a thickness of more than 3 km. In these two areas tholeiitic, olivine porphyritic basalts and picritic basalts are followed by tholeiitic basalts with plagioclase as the dominant phenocryst. The content of incompatible elements in the plagioclase porphyritic basalts is low in the early stages, as is the case in most of the older olivine porphyritic lavas in the province; however, after a pause in the volcanic activity, the concentration of these elements is increased by a factor of 3-6. A few thin layers of peralkaline, rhyolitic tuffs are found in the upper part of the plagioclase porphyritic sequence. The tholeiitic lavas are intruded by dykes. Most of these are petrographically the equivalent of the extrusive rocks, but dykes of transitional olivine basalts are presumed to represent a younger magmatic episode from which no lavas are known. The youngest igneous rocks in the area – and perhaps the youngest lavas in all of the West Greenland basalt province – are olivine porphyritic, alumina enriched transitional basalts deposited unconformably on the tholeiitic sequence on Hareøen. Forty-three new chemical analyses of the magmatic rocks are presented as well as micro-probe data on phenocryst and groundmass phases. The diversity of basaltic rocks cannot be explained by low pressure crystal fractionation alone, and it is suggested that the chemical evolution of the lavas and dyke rocks reflect chemical variations in batches of olivine rich magmas injected into the crust from the mantle.

scholarly journals Ocean Drilling Program (ODP) off South-East Greenland: formation of a volcanic rifted margin

1993 ◽  
Vol 159 ◽  
pp. 69-73
Author(s):  
H.C Larsen
Keyword(s):  
Continental Shelf ◽  
Tectonic Setting ◽  
Igneous Rocks ◽  
Plate Tectonic ◽  
Ocean Drilling Program ◽  
Skaergaard Intrusion ◽  
East Greenland ◽  
Ocean Drilling ◽  
Magmatic Rocks ◽  
Rifted Margin

The exposures of the Tertiary igneous rocks along the East Greenland coast (Fig. I) have attracted the attention or earth scientists for more than half a century (Wager, 1934; Wager & Deer 1938). However, most of the work has concentrated on the petrological and mineralogical aspects of the magmatic rocks (e.g. Skaergaard intrusion). With a few exceptions, such as Brooks (1973). Nielsen (1978). H. C. Larsen (1978), Branks (1979), Myers (1980) and Nielsen & Branks (1981). Relatively little attention has been given to the tectonic and plate tectonic setting. mainly because the plate tectonic paradigm did not become accepted until 30 years after Wager and Deer's revolutionary work. Furthermore, the tectonic context of the coastal exposures first becomes really striking when seen together with the geology and structure of the adjacent continental shelf and slope (H.C. Larsen, 1990).

Kimberlites: From Deep Earth to Diamond Mines

Elements ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 377-380 ◽  
Author(s):  
Andrea Giuliani ◽  
D. Graham Pearson
Keyword(s):  
Trace Elements ◽  
Igneous Rocks ◽  
Continental Lithosphere ◽  
Rich Picture ◽  
Magmatic Rocks ◽  
Current Thinking ◽  
Deep Earth ◽  
Low Volume ◽  
Incompatible Trace Elements ◽  
Composite Pipes

Kimberlites are rare, enigmatic, low-volume igneous rocks. They are highly enriched in magnesium, volatiles (CO2 and H2O) and incompatible trace elements and are thought to be the most deeply derived (&gt;150 km) magmatic rocks on Earth. Kimberlites occur in ancient and thick continental lithosphere, forming intrusive sheets and composite pipes, commonly in clusters. Despite their rarity, kimberlites have attracted considerable attention because they entrain not only abundant mantle fragments but also diamonds, which can provide a uniquely rich picture of the deep Earth. This issue summarises current thinking on kimberlite petrology, geochemistry, and volcanology and outlines the outstanding questions on the genesis of kimberlites and associated diamond mines.

scholarly journals The Paleogene ophiolite conundrum of the Iran–Iraq border region

2020 ◽  
Vol 177 (5) ◽  
pp. 955-964 ◽  
Author(s):  
Hadi Shafaii Moghadam ◽  
Qiu-Li Li ◽  
Robert J. Stern ◽  
Massimo Chiaradia ◽  
Orhan Karsli ◽  
...  
Keyword(s):  
Analytical Procedure ◽  
Rift Zone ◽  
Border Region ◽  
Igneous Rocks ◽  
Bulk Rock ◽  
Geochronological Data ◽  
Content Type ◽  
Magmatic Rocks ◽  
Supplementary Material ◽  
Extreme Extension

New and compiled geochemical, isotopic and geochronological data allow us to propose a new explanation for Paleogene oceanic magmatic rocks along the Iran–Iraq border. These rocks are represented by a thick pile (>1000 m) of pillow lavas and pelagic sediments and underlying plutonic rocks. These are sometimes argued to represent a Paleogene ophiolite but there are no associated mantle rocks. Integrated zircon U–Pb ages, bulk rock major and trace element and radiogenic isotope data indicate that these rocks are more likely related to forearc rifting due to extreme extension during Late Paleogene time which also triggered high-flux magmatism in the Urumieh–Dokhtar Magmatic Belt and exhumation of core complexes in Iran. These observations are most consistent with formation of the Paleogene oceanic igneous rocks in a >220 km long forearc rift zone.Supplementary material: Detailed analytical procedure and tables S1 to S6 are available at: https://doi.org/10.6084/m9.figshare.c.4972994

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.

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