scholarly journals Textural Relations of Lamprophyric Mafic Microgranular Enclaves and Petrological Implications for the Genesis of Potassic Syenitic Magmas: the example of Piquiri Syenite, southern Brazil

2002 ◽  
Vol 29 (2) ◽  
pp. 21 ◽  
Author(s):  
JORGE PLÁ CID ◽  
LAURO VALENTIM STOLL NARDI ◽  
PERE ENRIQUE GISBERT
Keyword(s):  
Alkali Feldspar ◽  
Textural Features ◽  
Southern Brazil ◽  
Mineral Phase ◽  
Mineral Phases ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
Textural Relationship ◽  
Important Evidence ◽  
Liquidus Temperatures

The Neoproterozoic Piquiri Syenite exhibits a large amount of mafic microgranular enclaves (MME) with elliptical-shape and millimeter to centimeter-size dimensions. These enclaves were originated by co-mingling of minettetype lamprophyre and potassic syenite magmas, producing the typical textural features of quenched magmas. They show elongated crystals of diopside and Mg-biotite, and acicular apatite. Early crystallized phases are represented by the same minerals, which occur as phenocrysts (diopside + Mg-biotite) and euhedral smaller crystals (apatite). The textural relationship and the identification of mineral phases as K-clinopyroxene and pyrope in the MME, suggest that mingling started at mantle conditions, when lamprophyric and syenitic magmas were near crystal-free and close to liquidus temperatures. The absence of syenite xenocrysts and chilled-margins in MME, are consistent with the high temperature of co-mingling. Alkali feldspar laths that poikilitically enclose quenched phases, represent late-magmatic mineral phase. The Piquiri Syenite MME represent a quite rare example of co-mingling between lamprophyre and intermediate magmas, and represents important evidence for the genesis of potassic silica-saturated magmas at mantle conditions.

scholarly journals Petrology of Gameleira potassic lamprophyres, São Francisco Craton

2012 ◽  
Vol 84 (2) ◽  
pp. 377-398 ◽  
Author(s):  
Jorge Plá Cid ◽  
Cristiani S. Campos ◽  
Lauro V.S. Nardi ◽  
Luana Florisbal
Keyword(s):  
High Growth ◽  
Alkali Feldspar ◽  
High Growth Rate ◽  
Alkaline Magmatism ◽  
Mantle Heterogeneities ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
Liquid Chemical ◽  
Reverse Zoning ◽  
Basic Rocks

Gameleira lamprophyres are dykes and mafic microgranular enclaves associated with the shoshonitic Gameleira monzonite. This association belongs to the Paleoproterozoic alkaline magmatism from Serrinha nucleus, northeast Brazil. The liquidus paragenesis is diopside, pargasite, apatite and mica. Reverse zoning was identified in the groundmass alkali feldspar and was related to the undercooling of lamprophyric magma during the emplacement, with high growth rate of pargasite/edenite inducing disequilibrium between feldspars and liquid. Chemical data indicate that the lamprophyres are basic rocks (SiO2 < 48 wt%), with alkaline character (Na2O + K2O > 3 wt%) and potassic signature (K2O/Na2O ≈ 2). High contents of MgO and Cr are consistent with a signature of a primary liquid, and such concentrations, as well as Al, K, P, Ba, Ni- and light rare earth elements, are consistent with an olivine-free metasomatic mantle source enriched in amphibole, clinopyroxene and apatite. By contrast, the ultrapotassic lamprophyres from Morro do Afonso, contemporaneous alkaline ultrapotassic magmatism in Serrinha nucleus, were probably produced by melting of a clinopyroxene-phlogopite-apatite enriched-source. The identification of different mineral paragenesis in the source of potassic and ultrapotassic lamprophyres from Serrinha nucleus can contribute to the understanding of the mantle heterogeneities and tectonic evolution of this region.

Automated mineral analysis in TASK8

1990 ◽  
Vol 48 (2) ◽  
pp. 212-213
Author(s):  
William F. Chambers ◽  
Arthur A. Chodos ◽  
Roland C. Hagan
Keyword(s):  
National Laboratory ◽  
Control Program ◽  
Mineral Analysis ◽  
Alamos National Laboratory ◽  
Mineral Phase ◽  
Los Alamos National Laboratory ◽  
California Institute Of Technology ◽  
Mineral Phases ◽  
Letter Code ◽  
Institute Of Technology

TASK8 was designed as an electron microprobe control program with maximum flexibility and versatility, lending itself to a wide variety of applications. While using TASKS in the microprobe laboratory of the Los Alamos National Laboratory, we decided to incorporate the capability of using subroutines which perform specific end-member calculations for nearly any type of mineral phase that might be analyzed in the laboratory. This procedure minimizes the need for post-processing of the data to perform such calculations as element ratios or end-member or formula proportions. It also allows real time assessment of each data point.The use of unique “mineral codes” to specify the list of elements to be measured and the type of calculation to perform on the results was first used in the microprobe laboratory at the California Institute of Technology to optimize the analysis of mineral phases. This approach was used to create a series of subroutines in TASK8 which are called by a three letter code.

The role of shallow open system processes in the evolution of South Tepeldag Pluton (NW Turkey): insights and constraints from thermodynamic modelling

2021 ◽  
Author(s):  
Tunahan Arık ◽  
Ömer Kamacı ◽  
Işıl Nur Güraslan ◽  
Şafak Altunkaynak
Keyword(s):  
Fractional Crystallization ◽  
Open System ◽  
Suture Zone ◽  
Thermodynamic Simulations ◽  
Nw Turkey ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
Ophiolitic Rocks ◽  
Compositional Variations ◽  
Spider Diagrams

&lt;p&gt;Eocene granitoids in NW Anatolia occurred following the continental collision between Sakarya Continent and Tauride-Anatolide Platform and mark the onset of post-collisional magmatism in the region. One of the representative members of the Eocene granitoids, the Tepelda&amp;#287; pluton crops out as two isolated granitic bodies and is intruded into the Cretaceous blueschist assemblages (Kocasu formation) and ophiolitic rocks within the Izmir-Ankara-Erzincan suture zone (IAESZ). South Tepelda&amp;#287; pluton (STP) is composed mainly of granodiorite with subordinate quartz diorite, which show transitional contacts. Aplitic dykes crosscut the pluton as well as the country rocks. STP includes a number of mafic microgranular enclaves (MME) of gabbro/diorite composition.&lt;/p&gt;&lt;p&gt;Geochemically, STP shows distinct I-type affinity with a metaluminous to slightly peraluminous (ASI &amp;#8804;1.02) nature. The samples are medium-K to high-K calc-alkaline in character. They exhibit depletion in HFSE (Ti, Hf, Zr, Nb and Ta) compared to large ion lithophile elements (Rb, Ba, Th, U, K) and presents negative Nb, P, Ti anomalies. STP displays slight negative Eu anomalies (Eu/Eu* = 0.7&amp;#8211;1.2), enrichment in LREE and flat HREE patterns in chondrite-normalized spider diagrams. MELTS modeling (with initial parameters of 1&amp;#8211;3 kbar pressure, 2&amp;#8211;3% water and QFM-NNO oxygen fugacity buffers) indicate that compositional variations in STP samples can be interpreted as a result of open system processes (assimilation fractional crystallization) rather than a reflection of fractional crystallization in the upper crustal magma chamber. All thermodynamic simulations dictate a crustal assimilation, especially in the late stages of the magmatic process, with a MgO, Na&lt;sub&gt;2&lt;/sub&gt;O and Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-rich assimilant similar to the suture zone (IAESZ) rocks.&lt;/p&gt;

Insights into granite petrogenesis from quantitative assessment of the field distribution of enclaves, xenoliths and K-feldspar megacrysts in the Monte Capanne pluton, Italy

2008 ◽  
Vol 72 (4) ◽  
pp. 925-940 ◽  
Author(s):  
D. Gagnevin ◽  
J. S. Daly ◽  
G. Poli
Keyword(s):  
Field Study ◽  
Magma Chamber ◽  
Late Stage ◽  
Field Data ◽  
Quantitative Assessment ◽  
Mafic Magma ◽  
Crustal Assimilation ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
Quantitative Analyses

AbstractA detailed field study to determine quantitatively the distribution of K-feldspar megacrysts, mafic microgranular enclaves (MME) and metasedimentary xenoliths has been carried out in the Monte Capanne pluton (Elba, Italy) with a view to evaluating the utility of this approach to petrogenetic investigations. Mafic microgranular enclaves are inferred to result from interactions between mafic and felsic magmas, while xenoliths attest to crustal assimilation occurring in the Monte Capanne magma chamber. In particular, we emphasize, based on our field data, that both processes are intimately linked, such that xenolith dissolution during assimilation was triggered by replenishment with hot mafic magma. It is suggested that the previously defined ‘San Piero’ and ‘San Francesco’ facies do not differ substantially, and are thus amalgamated and renamed as the ‘Pomonte’ facies. Results also indicate that the abundance of K-feldspar megacrysts is positively correlated with the volumetric abundance of MME in the Sant’ Andrea facies, which we link to a recharging, mingling and textural coarsening event that occurred at a rather late stage of magma-chamber evolution prior to emplacement. This study demonstrates how petrogenetic processes can be deciphered by detailed field quantitative analyses of granite-forming components, thus complementing geochemical investigations.

Anisian granodiorites and mafic microgranular enclaves in the eastern Kunlun Orogen, NW China: Insights into closure of the eastern Paleo–Tethys

2020 ◽  
Vol 55 (9) ◽  
pp. 6487-6507
Author(s):  
Yanjun Li ◽  
Junhao Wei ◽  
M. Santosh ◽  
Huan Li ◽  
Huiwen Liu ◽  
...  
Keyword(s):  
Nw China ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves
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