scholarly journals The Alkaline Lamprophyres of the Dolomitic Area (Southern Alps, Italy): Markers of the Late Triassic Change from Orogenic-like to Anorogenic Magmatism

2019 ◽  
Vol 60 (6) ◽  
pp. 1263-1298 ◽  
Author(s):  
Federico Casetta ◽  
Ryan B Ickert ◽  
Darren F Mark ◽  
Costanza Bonadiman ◽  
Pier Paolo Giacomoni ◽  
...  

AbstractWe present the first complete petrological, geochemical and geochronological characterization of the oldest lamprophyric rocks in Italy, which crop out around Predazzo (Dolomitic Area), with the aim of deciphering their relationship with Triassic magmatic events across the whole of the Southern Alps. Their Mg# of between 37 and 70, together with their trace element contents, suggests that fractional crystallization was the main process responsible for their differentiation, together with small-scale mixing, as evidenced by some complex amphibole textures. Moreover, the occurrence of primary carbonate ocelli suggests an intimate association between the alkaline lamprophyric magmas and a carbonatitic melt. 40Ar/39Ar data show that the lamprophyres were emplaced at 219·22 ± 0·73 Ma (2σ; full systematic uncertainties), around 20 Myr after the high-K calc-alkaline to shoshonitic, short-lived, Ladinian (237–238 Ma) magmatic event of the Dolomitic Area. Their trace element and Sr–Nd isotopic signatures (87Sr/86Sri = 0·7033–0·7040; 143Nd/144Ndi = 0·51260–0·51265) are probably related to a garnet–amphibole-bearing lithosphere interacting with an asthenospheric component, significantly more depleted than the mantle source of the high-K calc-alkaline to shoshonitic magmas. These features suggest that the Predazzo lamprophyres belong to the same alkaline–carbonatitic magmatic event that intruded the mantle beneath the Southern Alps (e.g. Finero peridotite) between 190 and 225 Ma. In this scenario, the Predazzo lamprophyres cannot be considered as a late-stage pulse of the orogenic-like Ladinian magmatism of the Dolomitic Area, but most probably represent a petrological bridge to the opening of the Alpine Tethys.

Lithos ◽  
1998 ◽  
Vol 45 (1-4) ◽  
pp. 329-348 ◽  
Author(s):  
A. Rottura ◽  
G.M. Bargossi ◽  
A. Caggianelli ◽  
A. Del Moro ◽  
D. Visonà ◽  
...  

2011 ◽  
Vol 182 (6) ◽  
pp. 467-477 ◽  
Author(s):  
Céline Ducassou ◽  
Marc Poujol ◽  
Erwan Hallot ◽  
Olivier Bruguier ◽  
Michel Ballevre

Abstract The late stages of the Variscan orogeny in western and central Europe are characterized by the emplacement of numerous Carboniferous granitic intrusions. In the southern part of the Armorican massif, volcanic and plutonic rocks occur within the Carboniferous series of the Ancenis basin. Chemical analyses indicate that they belong to the same magmatic high-K calc-alkaline association of peraluminous composition, which likely derives from crustal melting of an igneous source. A LA-ICPMS U-Pb/zircon age of 319.3 ± 3.1 Ma dates, for the first time, this magmatic event and, by there, constrains the maximum age of both the end of the sedimentation and the northward tilting of the sediments in the Ancenis basin. This magmatic event is coeval with the sedimentation of the coal-bearing Namurian basins located along the Nort-sur-Erdre fault. These intrusions are interpreted as the feeding conduits of the volcano-sedimentary layers encountered in these basins. This would imply a minimal dextral displacement of ca. 20–25 km along the Nort-sur-Erdre fault.


Author(s):  
Qigui Mao ◽  
Songjian Ao ◽  
Brian F. Windley ◽  
Zhiyong Zhang ◽  
Miao Sang ◽  
...  

To constrain the closure mechanism and time of the Paleo-Asian Ocean, we report new geochronological and geochemical data for Triassic granites along a NW−SE corridor from Eastern Tianshan to Beishan, NW China. Seven granites have U-Pb ages that young southwards from 245 Ma to 234 Ma in the Kanguer accretionary complex, to 237 Ma to 234 Ma in the eastern Central Tianshan block, to 229 Ma to 223 Ma in the Liuyuan accretionary complex. Granites in the Kanguer accretionary complex formed by fractional crystallization and are peraluminous, high-K, calc-alkaline, and crust-derived. They have very low MgO (Mg# = 6−9), Cr, and Ni contents, and their high εNd(t) (+3.40) and εHf(t) (+4.49 to +11.91) isotopes indicate that the Dananhu arc crust was juvenile. The Huaniushan pluton in the Liuyuan accretionary complex displays the geochemical signatures of both A1- and A2-type granites (Y/Nb = 0.32−3.39). All other granites in the Central Tianshan block and Liuyuan accretionary complex are aluminous A2-types with high K2O+Na2O, Al, rare earth elements (REE), Zr+Nb+Y, Ga, Fe/Mg, and Y/Nb and remarkable depletions of Eu, Ba, Nb, Ta, Sr, P, and Ti. They have a broad range of MgO (Mg# = 9−59), Cr, and Ni contents, Isr (0.70741−0.70945) values, negative εNd (t) (−2.98 to −1.14), and low to moderate εHf(t) (−1.22 to +7.78), which suggests a mixture of mantle and crustal components. These 245−223 Ma granitoids show marked Nb-Ta depletions that point to a subduction origin. Notable enrichments in Nd-Hf isotopes of Late Triassic granites are likely an indication of collision. Integration with previous data enables us to conclude that the delamination of an oceanic slab and mantle upwelling induced partial melting of thickened arc crust during a tectonic transition from a multiple supra-subduction margin to a collisional setting in the Late Triassic.


2018 ◽  
Vol 55 (5) ◽  
pp. 475-489 ◽  
Author(s):  
Yong Zhang ◽  
Jing-Gui Sun ◽  
Shu-Wen Xing ◽  
Zeng-Jie Zhang

The Lesser Xing’an Range is located in the eastern segment of the Central Asian Orogenic Belt. It hosts an important polymetallic metallogenic belt that contains more than 20 large- to small-scale porphyry Mo, epithermal Au, and skarn Fe-polymetallic deposits. The Cuihongshan Fe-polymetallic deposit is one of the largest polymetallic deposits in northeastern China. To better understand the formation of the Cuihongshan Fe-polymetallic deposit, we investigated the geological characteristics of the Cuihongshan deposit and applied geochemistry and geochronology to constrain the timing of the mineralization, and characteristics of the magmas. Zircon U–Pb dating of the alkali-feldspar granite and monzogranite yielded weighted mean 206Pb/238U ages of 495 ± 1.6 and 203 ± 1 Ma, respectively. Re–Os dating on molybdenite yielded an isochron age of 203.2 ± 1.4 Ma, and 40Ar/39Ar dating on phlogopite yielded an age of 203.4 ± 1.3 Ma. These data suggest that mineralization occurred during the Late Triassic, and is closely related with the monzogranite emplacement. These rocks belong to the high-K calc-alkaline and subalkaline series, are enriched in Rb, U, and Th, are depleted in Nb, Ta, and Ti, and show strong Eu anomalies, implying that they are A-type post-orogenic rocks. The Cuihongshan Fe-polymetallic formation is possibly related to an extensional environment resulting from the final closure of the Paleo-Asian Ocean.


Author(s):  
Cheng-Hong Chen ◽  
Wayne Lin ◽  
Hsueh-Yu Lu ◽  
Chi-Yu Lee ◽  
Jung-Li Tien ◽  
...  

The Late Yanshanian Orogeny (130-90 Ma) encompasses an important Mesozoic magmatic event in the crustal evolution of SE China. Products of post-orogenic magmatism, widely distributed in the eastern part of Zhejiang and Fujian provinces known as the Southeast Coast Magmatic Belt (SCMB), are dominated by large amounts of slightly Nb and Ta depleted, high-K calc-alkaline granites (I-type) and small amounts of strongly Ba, Sr, Eu, Ti and P depleted, metaluminous granites (A-type). 40Ar/39Ar dating from amphiboles suggests that emplacement of A-type granites mostly postdates (94-90 Ma) the intrusion of voluminous I-type granitoids (110-99 Ma). Using the Al-in-amphibole geobarometer, I-type suites were estimated to have been emplaced at shallow depths (5-7 km). Along with the fact that A-type granites are phyric or miarolitic in texture, it can be concluded that all these post-orogenic suites in the SCMB belong to shallow intrusives. They have also undergone a rapid cooling (higher than 100°C/Ma at T > 300 °C) as indicated by the thermochronology of hornblende, biotite and K-feldspar; therefore, generation of A-type granites from I-type magmas through fractional crystallisation would be a difficult process. Alternatively, their geochemical characteristics are attributed to partial melting in the residual lower crust under an elevated geothermal environment. On the other hand, I-type magmas are considered to be middle-crust-derived melts largely modified with mantle-derived melts that had been depleted with Nb and Ta by earlier tectonic processes. Such a tectonic environment is explained by the underplating of basaltic magmas, most probably due to lithospheric delamination taking place at c. 110 Ma, which marks the beginning of the postorogenic episode in this area. Numerical modelling for a heat source provided by the underplating of basaltic magma supports such a proposition.


Author(s):  
Mbaihoudou Diontar ◽  
Jean Claude Doumnang ◽  
Maurice Kwékam ◽  
Zagalo Al-hadj Hamid ◽  
Armand Kagou Dongmo ◽  
...  

Major and trace element data were used to constrain the nature and origin of the Bitkine gabbro-diorite magma.The gabbro-diorites of Bitkine within the Guéra Massif, and associated microgranular enclaves consist of plagioclase, k-feldspar, clinopyroxene, amphibole, biotite and quartz. Gabbro-diorites and enclaves are basic to intermediate rocks. They are high-K magnesian calc-alkaline with shoshonite affinity. ΣREE range from 132 to 436 ppm in gabbro-diorites, while they are from 134 to 207 ppm in enclaves. LREE are weakly enriched compared to HREE (La/Yb)N = (12.23 -41.40) and (6.20-31.86) respectively in gabbro-diorites and enclaves. These rocks show a weak negative anomaly in europium (Eu/Eu* = 0.78-1.07). They are rich in Ba and Sr, and show negative anomalies in Nb, Ta and Ti. The Nb/Ta, Rb/Cs and Ba/Nb ratios of the Bitkine gabbro-diorites and their enclaves indicate that they are derived from mantle magma modified by subducted fluids. This magma during its evolution by fractional crystallization was contaminated by crustal materials.


2001 ◽  
Vol 28 (1) ◽  
pp. 155-157
Author(s):  
Elias Samankassou ◽  
M. Bernecker ◽  
Erik Flügel

2017 ◽  
Vol 34 (1) ◽  
pp. 45 ◽  
Author(s):  
Elizard González-Becuar ◽  
Efrén Pérez-Segura ◽  
Ricardo Vega-Granillo ◽  
Luigi Solari ◽  
Carlos Manuel González-León ◽  
...  

Plutonic rocks of the Puerta del Sol area, in central Sonora, represent the extension to the south of the El Jaralito batholith, and are part of the footwall of the Sierra Mazatán metamorphic core complex, whose low-angle detachment fault bounds the outcrops of plutonic rocks to the west. Plutons in the area record the magmatic evolution of the Laramide arc and the Oligo-Miocene syn-extensional plutonism in Sonora. The basement of the area is composed by the ca. 1.68 Ga El Palofierral orthogneiss that is part of the Caborca block. The Laramide plutons include the El Gato diorite (71.29 ± 0.45 Ma, U-Pb), the El Pajarito granite (67.9 ± 0.43 Ma, U-Pb), and the Puerta del Sol granodiorite (49.1 ± 0.46 Ma, U-Pb). The younger El Oquimonis granite (41.78 ± 0.32 Ma, U-Pb) is considered part of the scarce magmatism that in Sonora records a transition to the Sierra Madre Occidental magmatic event. The syn-extensional plutons are the El Garambullo gabbro (19.83 ± 0.18 Ma, U-Pb) and the Las Mayitas granodiorite (19.2 ± 1.2 Ma, K-Ar). A migmatitic event that affected the El Palofierral orthogneiss, El Gato diorite, and El Pajarito granite between ca. 68 and 59 Ma might be related to the emplacement of the El Pajarito granite. The plutons are metaluminous to slightly peraluminous, with the exception of El Oquimonis granite, which is a peraluminous two-mica, garnet-bearing granite. They are mostly high-K calc-alkaline with nearly uniform chondrite-normalized REE and primitive-mantle normalized multielemental patterns that are characteristic of continental margin arcs and resemble patterns reported for other Laramide granites of Sonora. The Laramide and syn-extensional plutons also have Sr, Nd and Pb isotopic ratios that plot within the fields reported for Laramide granites emplaced in the Caborca terrane in northwestern and central Sonora. Nevertheless, and despite their geochemical affinity to continental magmatic arcs, the El Garambullo gabbro and Las Mayitas granodiorite are syn-extensional plutons that were emplaced at ca. 20 Ma during development of the Sierra Mazatán metamorphic core complex. The 40Ar/39Ar and K-Ar ages obtained for the El Palofierral orthogneiss, the Puerta del Sol granodiorite, the El Oquimonis granite, and the El Garambullo gabbro range from 26.3 ± 0.6 to 17.4 ± 1.0 Ma and are considered cooling ages associated with the exhumation of the metamorphic core complex.


2021 ◽  
pp. 1-22
Author(s):  
Jia-Hao Jing ◽  
Hao Yang ◽  
Wen-Chun Ge ◽  
Yu Dong ◽  
Zheng Ji ◽  
...  

Abstract Late Mesozoic igneous rocks are important for deciphering the Mesozoic tectonic setting of NE China. In this paper, we present whole-rock geochemical data, zircon U–Pb ages and Lu–Hf isotope data for Early Cretaceous volcanic rocks from the Tulihe area of the northern Great Xing’an Range (GXR), with the aim of evaluating the petrogenesis and genetic relationships of these rocks, inferring crust–mantle interactions and better constraining extension-related geodynamic processes in the GXR. Zircon U–Pb ages indicate that the rhyolites and trachytic volcanic rocks formed during late Early Cretaceous time (c. 130–126 Ma). Geochemically, the highly fractionated I-type rhyolites exhibit high-K calc-alkaline, metaluminous to weakly peraluminous characteristics. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depleted in high-field-strength elements (HFSEs), with their magmatic zircons ϵHf(t) values ranging from +4.1 to +9.0. These features suggest that the rhyolites were derived from the partial melting of a dominantly juvenile, K-rich basaltic lower crust. The trachytic volcanic rocks are high-K calc-alkaline series and exhibit metaluminous characteristics. They have a wide range of zircon ϵHf(t) values (−17.8 to +12.9), indicating that these trachytic volcanic rocks originated from a dominantly lithospheric-mantle source with the involvement of asthenospheric mantle materials, and subsequently underwent extensive assimilation and fractional crystallization processes. Combining our results and the spatiotemporal migration of the late Early Cretaceous magmatic events, we propose that intense Early Cretaceous crust–mantle interaction took place within the northern GXR, and possibly the whole of NE China, and that it was related to the upwelling of asthenospheric mantle induced by rollback of the Palaeo-Pacific flat-subducting slab.


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