scholarly journals Geoquímica das Rochas Máficas Toleíticas da Suíte Pós-Colisional Paulo Lopes, Neoproterozóico do Sul do Brasil

2005 ◽  
Vol 32 (2) ◽  
pp. 69 ◽  
Author(s):  
LUANA MOREIRA FLORISBAL ◽  
LAURO NARDI ◽  
MARIA DE FÁTIMA BITENCOURT ◽  
LEANDRO MENEZES BETIOLLO
Keyword(s):  
Coarse Grained ◽  
Main Body ◽  
Chronological Order ◽  
Orientation Field ◽  
Rapid Crystallization ◽  
Magmatic Rocks ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
Basic Rocks

The Paulo Lopes Suite (SPL), composed of the Paulo Lopes Granite (GPL), Garopaba Granitoids (GG) and Silveira Gabbro (GS), is an association of contemporaneous acid and basic rocks, comprising monzo and syenogranites associated to basic dikes, with abundant mafic microgranular enclaves, interpreted as co-mingling products. The contacts between the granitoids and the basic rocks are evidences of coeval and interactive magmas. The Silveira Gabbro occurs in the study area as a main body and several narrow dikes of NNE orientation. Field relations define a chronological order of magmatic events, where the GPL is the first magmatic pulse and, while steel partially crystallized, was intruded by mingled magmas, represented by the GG and the GS. The basic components are medium-grained, equigranular rocks, with subophitic and ophitic textures. The centre of the main body contains medium- to coarse-grained, equigranular rocks, where agglomerates of early-formed clinopyroxene and plagioclase crystals are found. In the chilled margins, they are microporphyritc rocks of aphanitic groundmass, indicative of rapid crystallization. The Silveira Gabbro rocks are composed of labradorite-andesine, orthopyroxene, augite, pigeonite, olivine (occasionally serpentinized), Fe-hornblende and magnesian hornblende, red biotite, magnetite, ilmenite, apatite, and baddeleyite. The composition is tholeiitic, similar to the high-Ti-P basalts of the Serra Geral Formation. Their high contents of K, Rb, Sr and Ba, as well as negative anomalies of Nb and Ta in multielemental diagrams are similar to the ones observed in magmatic rocks from mature arcs or post-collisional environments. The Neoproterozoic basic rocks may be discriminated from the ones belonging to the Cretaceous Serra Geral Formation by their higher contents of alcalis, Cs, U, Th, and by their fractionated REEpatterns, expressed in the La/LuN ratio. The associated granitoids are structural and compositionally compatible with the ones found in post collisional settings, which indicates that the SPL magmatism developed in such environment.

Ferromagnesian silicate association in S-type granites: the Darongshan granitic complex (Guangxi, South China)

2008 ◽  
Vol 179 (1) ◽  
pp. 13-27 ◽  
Author(s):  
Bernard Charoy ◽  
Pierre Barbey
Keyword(s):  
South China ◽  
Granulite Facies ◽  
Coarse Grained ◽  
Magma Ascent ◽  
Granulite Facies Metamorphism ◽  
Rock Types ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
Type Granite ◽  
Granite Complex

Abstract The late Indosinian Darongshan granite complex (Guangxi Province, South China) consists mainly of three plutons (Taima, Jiuzhou and Darongshan), with coarse-grained to subvolcanic rock types. There is a rough mineral evolution from the western to the eastern part of the complex, with ferromagnesian magmatic silicates sequentially distributed : Opx+Crd±Bt (Taima), Opx+Grt+Bt+Crd (Jiuzhou) and Bt+Crd (Darongshan). Restitic, cumulative or xenocrystic minerals (mainly Crd with fibrolite+spinel inclusions, Grt and probably Opx in some cases) are also encountered. Mineralogical, chemical and isotopic compositions of the granites suggest that the three plutons derive from a source dominated by a reduced, immature greywacke-psammite series, which has experienced high-amphibolite to granulite-facies metamorphism. This S-type granite complex is considered to result from various degrees of melting at different crustal levels by biotite dehydration-melting in a high T (800° to 950°C), low P (400–600 MPa) metamorphic environment. Abundant granulite-facies metasedimentary enclaves with refractory compositions are considered as xenoliths entrapped during magma ascent. The presence of scarce mafic microgranular enclaves and the high temperatures needed for melting could suggest that heat may have been partly contributed by mantle-derived magmas.

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.

Hydrous mafic-ultramafic intrusives in a nascent arc (Massif du Sud, New Caledonia ophiolite).

2021 ◽  
Author(s):  
Arianna Secchiari ◽  
Alessandra Montanini ◽  
Dominique Cluzel ◽  
Elisa Ferrari
Keyword(s):  
Trace Element ◽  
Transition Zone ◽  
New Caledonia ◽  
Incompatible Trace Element ◽  
Coarse Grained ◽  
Main Body ◽  
Distinctive Features ◽  
First Occurrence ◽  
Ultramafic Cumulate ◽  
Compositional Variability

&lt;p&gt;The New Caledonia ophiolite hosts one of most complete sections of a nascent arc, representing an excellent natural laboratory for investigating the origin and the evolution of subduction systems. The sequence, originated during the onset of the Eocene subduction [1, 2], is composed of ultra-depleted forearc harzburgites [3] overlain by a dunite-dominated transition zone (500m thick), in turn overtopped by mafic-ultramafic cumulate lenses. The ultramafic rocks of the transition zone (mainly dunites and wehrlites) most likely resulted from melt-peridotite reactions involving primitive arc tholeiites and boninitic magmas [2]. By contrast, dunite-pyroxenite and gabbronorite cumulates derive from H&lt;sub&gt;2&lt;/sub&gt;O-poor depleted melts transitional between boninites and arc-tholeiites [2, 4].&lt;/p&gt;&lt;p&gt;In this contribution, we report the first occurrence of amphibole-bearing ultramafic lithologies in the New Caledonia arc sequence. Our study deals with a petrological and geochemical characterisation of a 2.5km x 5km composite, roughly snowball-shaped, intrusive body, consisting of pyroxenite, dunite, wehrlite, hornblendite and associated mafic-ultramafic, locally sheared, dikes from the Plum area (Massif du Sud). &amp;#160;The pyroxenite component, which forms the core of the intrusion, consists of coarse-grained websterites, mainly composed of weakly oriented orthopyroxene (~ 30-75 vol.%) and clinopyroxene (~ 20-40 vol.%), with variable amounts of edenitic amphibole (~ 2-30 vol.%). The amphibole generally occurs as poikilitic crystals or develops as coronas on pyroxenes. Highly calcic plagioclase (An= 83-96 mol %) is scarce in the pyroxenite body (~ 2 vol. %), but more abundant in the associated dikes (~ 10-50 vol.%). Clinopyroxene shows variable Mg# (0.82-0.92) and low Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3 &lt;/sub&gt;(0.99-2.00 wt%). Likewise, amphibole yields high Mg# (0.712-0.865). Estimated equilibrium temperatures based on conventional pyroxene thermometry range between 870-970&amp;#176;C, whereas amphibole-plagioclase pairs provide slightly lower values (800-910 &amp;#176;C).&lt;/p&gt;&lt;p&gt;Whole rocks have moderately high Mg# (71-82) and REE concentrations one to five times chondritic values. The websterites of the main body show LREE-depleted (La&lt;sub&gt;N&lt;/sub&gt;/Nd&lt;sub&gt;N&lt;/sub&gt; = 0.5-0.8), weakly concave downward patterns, with flat HREE segments (Lu&lt;sub&gt;N&lt;/sub&gt;/Tm&lt;sub&gt;N&lt;/sub&gt; = 1.1-1.3). The mafic-ultramafic dikes display similar patterns, bearing depleted to flat LREE segments (La&lt;sub&gt;N&lt;/sub&gt;/Nd&lt;sub&gt;N&lt;/sub&gt; = 0.6-1) and positive Eu anomalies. For all the investigated lithologies, extended trace element diagrams indicate enrichments for FME (i.e. Rb, Ba, U) and Th, coupled to Zr-Hf depletion. Strong Sr positive spikes are only observed for the crosscutting dikes, while the pyroxenite body yields Sr negative anomalies.&lt;/p&gt;&lt;p&gt;Geochemical modelling shows that the putative liquids in equilibrium with the websterites have intermediate Mg# (57&amp;#8211;63) and incompatible trace element patterns sharing remarkable similarities with the New Caledonia CE-boninites [5]. However, they significantly differ from the equilibrium melts reported for the other intrusive rocks of the sequence [1, 4], suggesting greater compositional variability for the liquids ascending into the Moho transition zone and lower crust. Our results support the notion that petrological and geochemical heterogeneity of magmatic products may be distinctive features of subduction infancy.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;[1] Marchesi et al., Chem. Geol., 2009, 266, 171-186.&lt;/p&gt;&lt;p&gt;[2] Pirard et al., J. Petrol., 2013, 54, 1759&amp;#8211;1792.&lt;/p&gt;&lt;p&gt;[3] Secchiari et al., Geosc. Front., 2020, 11(1), 37&amp;#8211;55.&lt;/p&gt;&lt;p&gt;[4] Secchiari et al., Contrib. Mineral. Petrol.,&amp;#160;2018,&amp;#160;173(8),&amp;#160;66.&lt;/p&gt;&lt;p&gt;[5] Cluzel et al., Lithos, 2016, 260,&amp;#160;429&amp;#8211;442.&lt;/p&gt;

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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