Temat: mafic microgranular enclaves - Katalog OPAC zbiorów

Skocz do pozycji: 1.

Tytuł:: Geochemical and fractal analysis of enclaves in the Dehe-Bala intrusion, (Northwestern Iran) : a new concept to the interpretation of crust-mantle interaction process
Autorzy:: Gharamohammadi, Zeynab
Kananian, Ali
Eliassi, Mohsen
Powiązania:: https://bibliotekanauki.pl/articles/2058583.pdf
Data publikacji:: 2019
Wydawca:: Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
Tematy:: Dehe-Bala Granodiorites
DBG
mafic microgranular enclaves
MMEs
magma mixing
fractal dimension of enclaves
Opis:: The Dehe-Bala intrusion is one of the remarkable intrusions of granodiorite rocks with I-type affinity and abundant mafic microgranular enclaves (MMEs) in the Buin Zahra area, Qazvin, Iran. The MMEs, composed of diorite and quartz-monzodiorites, are haphazardly widespread in the granodiorites. The Dehe-Bala Granodiorites (DBG) usually are characterized by high contents of SiO2 (64.2-66.9), Na2O (3-3.23), K2O (3.49-4), Mg# 4.84 and Th/Ta ratio (≈7.9). In comparison to the DBG, the MMEs can be distinguished by their lower value of SiO2 (52.8-58.2), K2O (1.4-3.8) and higher Mg# (0.4-0.46). All these characteristics show a different composition of the DBG and MMEs, more importantly, can argue in favor of a magma mixing/mingling origin in the DBG. The enrichment in total REEs and HFSEs in the MMEs clearly reflects a marked diffusional process from the felsic to mafic magma that could have been achieved by chemical exchange during the magma mixing/mingling process. The fractal dimensions (Dbox) of MMEs differ from 1.14 to 1.29 with the highest frequency at 1.29. The textural heterogeneity and geochemical features combined with high Dbox values in the MMEs compared with the DBG show lower degrees of mixing/mingling between mantle-derived mafic and lower crust-derived felsic magmas.
Źródło:: Geological Quarterly; 2019, 63, 3; 505--521
1641-7291
Pojawia się w:: Geological Quarterly
Dostawca treści:: Biblioteka Nauki

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Tytuł:: Petrology and geochemistry of granitoids and their mafic micogranular enclaves (MME) in marginal part of the Małopolska Block (S Poland)
Autorzy:: Wolska, Anna
Powiązania:: https://bibliotekanauki.pl/articles/127582.pdf
Data publikacji:: 2012
Wydawca:: Polskie Towarzystwo Mineralogiczne
Tematy:: the Małopolska Block (MB)
host granodiorites (HG)
mafic microgranular enclaves (MME)
Q-diorites
tonalites
mixing
mingling
hybridisation process
Opis:: Granitic plutons (the Dolina Będkowska valley and Pilica area) were found in a few boreholes in the Małopolska Block (MB). These granitic rocks may represent apical parts (apophyses) of a great magmatic bodies (batholiths) located in deeper level of the Ediacaran/Paleozoic basement. They are described as ‘stitching intrusions’, generated during/after collision in Carboniferous/Permian period (~300 Ma) between the Upper Silesian Block (USB) and the Małopolska Block (MB). These rocks are fresh, unaltered granodiorites that are pale grey in colour. They have holocrystalline, medium- to coarse-grained structure and massive texture. For the first time, several mafic microgranular enclaves (MME), varying in size and colour, were found in the granodioritic host (HG). The occurrence of MME in the host granodioritic rocks is evidence of a mingling process between mafic and felsic magmas. The MME are pale/dark grey in colour, fine-grained rocks with ‘porphyritic’ textures. They consist of large megacrysts/xenocrysts of plagioclase, quartz, alkali feldspars and the fine-grained groundmass of pseudo-doleritic textures (lath-shaped plagioclases, blade-shaped amphiboles/biotites). According to their modal/mineral composition, they represent Q-diorites and tonalites. The MME, similar to the host granodiorites (HG), are I-type rocks, exhibit high Na2O content >3.2 wt%; normative diopside or normative corundum occurs (mainly <1%). They are metaluminous to slightly peraluminous (ASI <1.1) and have calc-alkaline, medium-K to high-K character. They generally belong to magnesian series (#Mg=0.20-0.40) and have low agpaitic index (<0.87). They are low evolved magmatic rocks. The rocks studied are enriched in LREEs (La, Ce, Sm) compared to HREEs. The Eu* negative anomaly and high Sr contents point to varying degrees of plagioclase fractionation connected to the mixing process rather than simple fractional crystallization. Both rocks studied (HG and MME) are characterized by a high content of LILEs (K, Ba, Rb) in normalized patterns and a low HFS/LIL elements ratio (Ta, Nb)/(K, Rb, La). The projection points of the rocks studied plot in different fields of various petrochemical diagrams: mainly in the arc granites that are rare in the pre-collisional granites as well as the syn-subductional to post-collisional granites fields. For the first time, inner textures in rock-forming minerals related to mixing processes are described both in the granodioritic host (HG) and in the MME. Mantled boxy cellular plagioclase megacrysts with ‘old cores’ of labradorite composition, and amphibole aggregates with titanite and opaque minerals, represent peritectic rather than primary residual minerals. The plagioclase, quartz and alkali feldspar megacrysts/xenocrysts were mechanically transferred from the granodioritic host (HG) to MME. The presence of lath-shaped plagioclases, blade-shaped amphiboles/biotites and acicular-shaped apatites in the groundmass of the MME is evidence of undercooling of hot mafic blobs in a relatively cold granodioritic magma chamber. The MME were hybridized by leucocratic melt squeezed from the granodioritic magma in a later stage of the mixing process (quartz and alkali crystals in the interstices in the MME groundmass). In the granodiorites (HG), the spike and spongy cellular zones as well as biotite/amphibole zones in plagioclase megacrysts are connected to the mixing process. Both of the rocks studied are characterized by different amounts of major elements (SiO2, Na2O and K2O), trace elements (Ni, Cr, V, Ti and P), #Mg and modified alkali–lime index (MALI) that is related to their origins from different sources. On the other hand, they have similar chondrite-normalized patterns (for trace elements and REE), LILEs contents (Sr, Ba, Rb), aluminum saturation index (ASI) and isotopic signatures (high 86Sr/87Sr(0.079-0.713) and low 143Nd/144Nd (0.512) values but lower than in continental crust), which are evidence of the strong hybridisation of mafic enclaves by the granodioritic host magma. The parental rocks of both rocks studied have a similar mafic signature but were generated in different sources: the host granodiorites (HG) magma in lower continental crust rocks, and the MME magma in enriched upper mantle. The MME crystallized from strongly hybridized magma of intermediate compositions (Q-diorite, tonalite) rather than from primary mafic magma. The host granodiorites (HG) originated from completely homogenized crustal granodioritic magma which inherited its geochemical signature from ancient arc-rocks in a subduction-related setting.
Źródło:: Mineralogia; 2012, 43, 1/2; 3-127
1899-8291
1899-8526
Pojawia się w:: Mineralogia
Dostawca treści:: Biblioteka Nauki

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