scholarly journals Emplacement and crustal contamination of the peridotites in the Ivrea-zone

2019 ◽  
Keyword(s):  
Crustal Contamination ◽  
Ivrea Zone

Synthetic seismic reflection profile through the Ivrea zone–Serie dei Laghi continental crustal section, northwestern Italy

Geology ◽  
1999 ◽  
Vol 27 (1) ◽  
pp. 79 ◽  
Author(s):  
Ernest H. Rutter ◽  
Jalal Khazanehdari ◽  
Katharine H. Brodie ◽  
Derek J. Blundell ◽  
David A. Waltham
Keyword(s):  
Seismic Reflection ◽  
Seismic Reflection Profile ◽  
Reflection Profile ◽  
Ivrea Zone

Geochemistry of bimodal amphibolitic—felsic gneiss complexes from eastern Massif Central, France

1995 ◽  
Vol 132 (3) ◽  
pp. 321-337 ◽  
Author(s):  
Bernard Briand ◽  
Jean-Luc Bouchardon ◽  
Houssa Ouali ◽  
Michel Piboule ◽  
Paul Capiez
Keyword(s):  
Crustal Contamination ◽  
Igneous Rocks ◽  
Chemical Characteristics ◽  
Continental Margins ◽  
High Grade ◽  
Transitional Stage ◽  
Crust Formation ◽  
Massif Central ◽  
Mantle Sources ◽  
Two Populations

AbstractHigh-grade basic and acidic meta-igneous rocks are widespread in the bimodal amphibolitic—felsic gneiss complexes, which are characteristic formations of the ‘Middle Allochthonous Unit’ from eastern and southern French Massif Central. The metabasites from the Lyonnais and Doux complexes are chemically diverse and range from N-MORB type tholeiitic to transitional types. The two populations are not related by fractional crystallization or crustal contamination processes and their chemical characteristics reflect differences in their mantle sources. An ensialic setting is supported by the crustally-derived character of some of the associated felsic rocks, but the presence of N-MORB-type metabasites argues for an extensional environment. This bimodal association compares well with the magmatism of rifted continental margins and may reflect a transitional stage between continental rifting and oceanic crust formation during the Cambro-Ordovician spreading event.

The petrological and geochemical study of granitoid rocks from Mashhad area, Iran: Evidence for the Late Triassic Collisional Belt Northeast of Iran

2021 ◽  
Author(s):  
Banafsheh Vahdati ◽  
Seyed Ahmad Mazaheri
Keyword(s):  
Subduction Zones ◽  
Tectonic Setting ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Late Triassic ◽  
Common Belief ◽  
Thrust Tectonics ◽  
Wide Range ◽  
Lree Enrichment ◽  
Granitoid Rocks

<p>Mashhad granitoid complex is part of the northern slope of the Binalood Structural Zone (BSZ), Northeast of Iran, which is composed of granitoids and metamorphic rocks. This research presents new petrological and geochemical whole-rock major and trace elements analyses in order to determine the origin of granitoid rocks from Mashhad area. Field and petrographic observations indicate that these granitoid rocks have a wide range of lithological compositions and they are categorized into intermediate to felsic intrusive rocks (SiO<sub>2</sub>: 57.62-74.39 Wt.%). Qartzdiorite, tonalite, granodiorite and monzogranite are common granitoids with intrusive pegmatite and aplitic dikes and veins intruding them. Based on geochemical analyses, the granitoid rocks are calc-alkaline in nature and they are mostly peraluminous. On geochemical variation diagrams (major and minor oxides versus silica) Na<sub>2</sub>O and K<sub>2</sub>O show a positive correlation with silica while Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, CaO, Fe<sub>2</sub>O<sub>3</sub>, and MgO show a negative trend. Therefore fractional crystallization played a considerable role in the evolution of Mashhad granitoids. Based on the spider diagrams, there are enrichments in LILE and depletion in HFSE. Low degrees of melting or crustal contamination may be responsible for LILE enrichment. Elements such as Pb, Sm, Dy and Rb are enriched, while Ba, Sr, Nd, Zr, P, Ti and Yb (in monzogranites) are all depleted. LREE enrichment and HREE depletion are observed in all samples on the Chondrite-normalized REE diagram. Similar trends may be evidence for the granitoids to have the same origin. Besides, LREE enrichment relative to HREE in some samples can indicate the presence of garnet in their source rock. Negative anomalies of Eu and Yb are observed in monzogranites. Our results show that Mashhad granitoid rocks are orogenic related and tectonic discrimination diagrams mostly indicate its syn-to-post collisional tectonic setting. No negative Nb anomaly compared with MORB seems to be an indication of non-subduction zone related magma formation. According to the theory of thrust tectonics of the Binalood region, the oceanic lithosphere of the Palo-Tethys has subducted under the Turan microplate. Since the Mashhad granitoid outcrops are settled on the Iranian plate, this is far from common belief that these granitoid rocks are related to the subduction zones and the continental arcs. The western Mashhad granitoids show more mafic characteristics and are possibly crystallized from a magma with sedimentary and igneous origin. Thus, Western granitoid outcrops in Mashhad are probably hybrid type and other granitoid rocks, S and SE Mashhad are S-type. Evidences suggest that these continental collision granitoid rocks are associated with the late stages of the collision between the Iranian and the Turan microplates during the Paleo-Tethys Ocean closure which occurred in the Late Triassic.</p>

Variable modes of formation for tonalite-trondhjemite-granodiorite-diorite (TTG)-related porphyry-type Cu ± Au deposits in the Neoarchean southern Abitibi subprovince (Canada): Evidence from petrochronology and oxybarometry

2021 ◽  
Author(s):  
Xuyang Meng ◽  
Jeremy P Richards ◽  
Daniel J Kontak ◽  
Adam C Simon ◽  
Jackie M Kleinsasser ◽  
...  
Keyword(s):  
Crustal Contamination ◽  
Edge Structure ◽  
Isotopic Signatures ◽  
Porphyry Cu ◽  
Abitibi Subprovince ◽  
Local Restriction ◽  
Fractionation Trend ◽  
Magma Crystallization ◽  
X Ray Absorption

Abstract Most known porphyry Cu ± Au deposits are associated with moderately oxidized and sulfur-rich, calc-alkaline to mildly alkalic arc-related magmas in the Phanerozoic. In contrast, sodium-enriched tonalite-trondhjemite-granodiorite-diorite (TTG) magmas predominant in the Archean are hypothesized to be unoxidized and sulfur-poor, which together preclude porphyry Cu deposit formation. Here, we test this hypothesis by interrogating the causative magmas for the ~2.7 Ga TTG-related Côté Gold, St-Jude, and Clifford porphyry-type Cu ± Au deposit settings in the Neoarchean southern Abitibi subprovince. New and previously published geochronological results constrain the age of emplacement of the causative magmas at ~2.74 Ga, ~2.70 Ga, and ~2.69 Ga, respectively. The dioritic and trondhjemitic magmas associated with Côté Gold and St-Jude evolved along a plagioclase-dominated fractionation trend, in contrast to amphibole-dominated fractionation for tonalitic magma at Clifford. Analyses of zircon grains from the Côté Gold, St-Jude, and Clifford igneous rocks yielded εHf(t) ± SD values of 4.5 ± 0.3, 4.2 ± 0.6, and 4.3 ± 0.4, and δ18O ± SD values of 5.40 ± 0.11 ‰, 3.91 ± 0.13 ‰, and 4.83 ± 0.12 ‰, respectively. These isotopic signatures indicate that although these magmas are mantle-sourced with minimal crustal contamination, for the St-Jude and Clifford settings the magmas or their sources may have undergone variable alteration by heated seawater or meteoric fluids. Primary barometric minerals (i.e., zircon, amphibole, apatite, and magnetite-ilmenite) that survived variable alteration and metamorphism (up to greenschist facies) were used for estimating fO2 of the causative magmas. Estimation of magmatic fO2 values, reported relative to the fayalite-magnetite-quartz buffer as ΔFMQ, using zircon geochemistry indicate that the fO2 values of the St-Jude, Côté Gold, and Clifford magmas increase from ΔFMQ -0.3 ± 0.6, ΔFMQ +0.8 ± 0.4, to ΔFMQ +1.2 ± 0.4, respectively. In contrast, amphibole chemistry yielded systematically higher fO2 values of ΔFMQ +1.6 ± 0.3 and ΔFMQ +2.6 ± 0.1 for Côté Gold and Clifford, respectively, which are consistent with previous studies that indicate amphibole may overestimate the fO2 of intrusive rocks by up to one log unit. Micro X-ray absorption near edge structure (μ-XANES) spectrometric determination of sulfur (i.e., S6+/ΣS) in primary apatite yielded ≥ΔFMQ -0.3 and ΔFMQ +1.4–1.8 for the St-Jude and Clifford, respectively. The magnetite-ilmenite mineral pairs from the Clifford tonalite yielded ΔFMQ +3.3 ± 1.3 at equilibrium temperatures of 634 ± 21 °C, recording the redox state of the late stage of magma crystallization. Electron probe microanalyses revealed that apatite grains from Clifford are enriched in S (up to 0.1 wt. %) relative to those of Côté Gold and St-Jude (below the detection limit), which is attributed to either relatively oxidized or sulfur-rich features of the Clifford tonalite. We interpret these results to indicate the deposits at Côté Gold and Clifford formed from mildly (~ΔFMQ +0.8 ± 0.4) to moderately (~ΔFMQ +1.5) oxidized magmas where voluminous early sulfide saturation was probably limited, whereas the St-Jude deposit represents a rare case whereby the ingress of externally derived hydrothermal fluids facilitated metal fertility in a relatively reduced magma chamber (~ΔFMQ +0). Furthermore, we conclude that variable modes of formation for these deposits and, in addition, the apparent rarity of porphyry-type Cu-Au deposits in the Archean may be attributed to either local restriction of favorable metallogenic conditions, and/or preservation, or an exploration bias.

Genesis of the Wuxing Pt–Pd-rich Cu–Ni sulfide deposit in the eastern Central Asian Orogenic Belt: evidences from geochronology, elemental geochemistry, and Sr–Nd–Hf isotopic data

2019 ◽  
Vol 56 (4) ◽  
pp. 380-398 ◽  
Author(s):  
Jing-gui Sun ◽  
Yun-peng He ◽  
Ji-long Han ◽  
Zhong-yu Wang
Keyword(s):  
Crustal Contamination ◽  
Early Period ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Geochemical Data ◽  
Sulfide Deposit ◽  
Late Period ◽  
Enriched Mantle ◽  
Central Asian ◽  
T Values

The Wuxing Pt–Pd-rich Cu–Ni sulfide deposit in Heilongjiang Province, Northeast China, is located to the northeast of the Dunhua–Mishan fracture of the eastern Central Asian Orogenic Belt. The mafic–ultramafic complex consist of early-period hornblende–olivine pyroxenite, diopsidite, and hornblende pyroxenite and late-period gabbro and diabase units. An early-period hornblende pyroxenite yielded a zircon U–Pb age of 208.2 ± 2.6 Ma and a late-period diabase yielded a U–Pb age of 205.6 ± 1.1 Ma, with zircon εHf(t) values of +1.24 to +8.13. The early- and late-period lithofacies are relatively enriched in LILE (Rb, Ba, and Sr) and LREE, and variably depleted in HFSE (Nb, Ta). The whole-rock and single-mineral analyses of the early-period lithofacies yield (87Sr/86Sr)i ratios of 0.7055–0.7083 and εNd(t) ratios of −7.98–+3.10. These geochemical data suggest that the parental magmas of the Wuxing complex are high-Mg subalkaline basaltic in nature and were derived from an enriched mantle source. The magmas chamber formed after the injection of magma into the crust along with crustal contamination, producing early crystalline minerals and ore-bearing magmas. The rupturing of the magma chamber released evolved magmas, which then ascended and generated Pt–Pd-bearing lithofacies and Cu–Ni sulfide orebodies by fractional crystallization, accumulation, and liquation. During the late period, the residual magma invaded the early lithofacies and Cu–Ni orebodies. The fluids exsolved from the gabbroic magmas concentrated the mineralized metal elements and enhanced the precipitation of Pt–Pd-bearing veinlet-disseminated orebodies and Pt–Pd–Cu–Ni orebodies.

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