Petrogenises of Triassic gabbroic and basaltic rocks from Chukotka, NE Russia: Eastern end of the ‘arc–type’ Siberian LIP?

Abstract

The Triassic gabbroic intrusions and associated basaltic lavas from Chukotka are mainly tholeiitic with both ocean island basalt (OIB) and island arc basalt (IAB)-type geochemical signatures. Mg-number [Mg# = 100 × Mg/(Mg + Fe 2+ )] is around 40 for OIB-type gabbros, ranges from 48 to 66 for IAB-type hornblende-rich gabbros, and 43 to 65 for IAB-type basaltic rocks (ankaramites, lamprophyres, pyroxene-phyric basalts and hornblende-phyric basaltic andesite). TiO 2 contents of the IAB-type gabbros and basaltic rocks are low (<2 wt%), but are high in OIB-type gabbros (4.3-5.3 wt%). OIB-type gabbros are typically enriched in FeO * (16-18 wt%) as compared to IAB-type gabbros (10-14 wt%) and IAB-type lavas (ankaramites,~10 wt%; lamprophyres,~14; pyroxene-phyric basalt, 11 wt% and basaltic andesite, 9-10 wt. %). In the primitive mantle normalized trace element patterns, IAB-type basalts and gabbros are characterized by depletion in HFSE (Nb, Ta, Zr and Hf ) and enrichment in LILE. OIB-type gabbros can be distinguished from the rests by the absence of HFSE depletion, with strong negative Sr anomaly. The positive Ti anomaly in the OIB-type gabbros can be attributed to high content of ilmenite in these rocks. Trace element characteristics of IAB-type gabbroic rocks and basalts are compatible with their magmas derived from subduction influenced melts, whereas OIB-type gabbros show within-plate geochemical characteristics. IAB-type gabbros and basaltic rocks display similar geochemical features to the low-Ti Nadezhdinsky suit (Noril'sk region) and Bel'kov dolerite (New Siberian Islands) of the Siberian large igneous province (LIP) in view of HFSE depletion and high H 2 O content of the magma to crystallize abundant hornblende not only in gabbros but also as phenocrysts in basalts. The Triassic gabbroic and basaltic rocks of both OIB and IAB types may as a whole represents the eastern end of the Siberian LIP.

Geochemical constraints on the origin and tectonic setting of Chargar intrusions in the Alborz orogenic belt, NW Iran

“…It seems that the gabbroic intrusions could be the cumulative parts of the magma chamber for the Chargar intrusions. Such cumulative assemblages imply post-collisional transtensional movements (Desta et al 2015). Furthermore, the positive Eu anomaly is attributed to the mixing of a mantle component with crustal melts (Mazzucchelli et al 1992).…”

“…A pronounced negative Zr anomaly for the Chargar samples is pointing out of a subduction setting (Wang et al 2013). Characteristics of some gabbroic samples which show weak positive Eu anomaly in the chondrite-normalized REE pattern and the weak positive Ti anomaly in the primitive mantle-normalized spider diagram (figure 12a) reflect the abundance of cumulative plagioclase (Bau 1991) and presence of ilmenite or titanomagnetite (Desta et al 2015). According to Zheng (2012), positive Pb anomalies on a primitive mantle-normalized spider diagram (Sun and McDonough 1989) are ascribed to mantle wedge metasomatism in subduction zones by continental crust sediments and also attributed to the continental contamination (Kamber et al 2002) (figure 12a).…”

Contrasting geological background based on the geochemistry of the mafic metamorphic rocks in central Dronning Maud Land

“…The fields for the Siberian large igneous province (LIP) (from Desta et al . 2015 and references therein); Ethiopian LIP (Beccaluva et al . 2009); Kamchatka arc (Churikova et al .…”

Petrogenesis of Miocene igneous rocks in the Tafresh area (central Urumieh‐Dokhtar magmatic arc, Iran): Insights into mantle sources and geodynamic processes

“…In the latter diagrams, a positive Ti anomaly (as observed in gabbroic dikes) suggests that residual orthopyroxene controls partitioning, and a negative Ti anomaly is related to abundance of clinopyroxene (Rampone, Bottazzi, & Ottolini, 1991; Salters, Longhi, & Bizimis, 2002; Salters & Hart, 1989). Alternatively, a high modal proportion of Fe–Ti oxides (ilmenite, titanomagnetite) could produce high Ti in gabbroic dikes (Desta et al, 2015).…”