The Palaeoproterozoic Birimian Supergroup of the West African Craton (WAC) consists of volcanic belts composed predominantly of basaltic and andesitic rocks and intervening sedimentary basins composed predominantly of wackes and argillites. Mafic metavolcanic rocks and granitoid-hosted enclaves from the Palaeoproterozoic Lawra Belt of Ghana were analysed for geochemical and Sr–Nd isotopic data to constrain the geological evolution of the southeastern part of the WAC. The metavolcanic rocks display mainly tholeiitic signatures, whereas the enclaves show calc-alkaline signatures. The high SiO2 contents (48.6–68.9 wt%) of the enclaves are suggestive of their evolved character. The high Th/Yb values of the samples relative to that of the mantle array may indicate derivation of their respective magmas from subduction-modified source(s). The rocks show positive εNd values of +0.79 to +2.86 (metavolcanic rocks) and +0.79 to +1.82 (enclaves). These signatures and their Nd model ages (TDM2) of 2.31–2.47 Ga (metavolcanic rocks) and 2.39–2.47 Ga (enclaves) suggest they were probably derived from juvenile mantle-derived protoliths, with possible input of subducted pre-Birimian (Archean?) rocks in their source(s). Their positive Ba–Th and negative Nb–Ta, Zr–Hf and Ti anomalies may indicate their formation through subduction-related magmatism consistent with an arc setting. We propose that the metavolcanic rocks and enclaves from the Lawra Belt formed in a similar island-arc setting. We infer that the granitoids developed through variable degrees of mixing/mingling between basic magma and granitic melt during subduction, when blobs of basic to intermediate parental magma became trapped in the granitic magma to form the enclaves.

The Tengchong Block within the Sanjiang Tethys belt in the southeastern part of the Tibetan plateau experienced a widespread intrusion of a felsic magmatic suite of granites in its central domain during Late Cretaceous times. Here, we investigate the Guyong and Xiaolonghe plutons from this suite in terms of their petrological, geochemical, and Sr–Nd, zircon U–Pb and Lu–Hf–O isotopic features to gain insights into the evolution of the Neo-Tethys. The Guyong pluton (76 Ma) is composed of metaluminous monzogranites, and the Xiaolonghe pluton (76 Ma) is composed of metaluminous to peraluminous medium- and fine-grained syenogranite. A systematic decrease in Eu, Ba, Sr, P and Ti concentrations; a decrease in Zr/Hf and LREE/HREE ratios; and an increase in the Rb/Ba and Ta/Nb ratios from the Guyong to Xiaolonghe plutons suggest fractional crystallization of biotite, plagioclase, K-feldspar, apatite, ilmenite and titanite. They also show the characteristics of I-type granites. The negative zircon εHf(t) isotopic values (−10.04 to −5.22) and high δ18O values (6.69 to 8.58 ‰) and the negative whole-rock εNd(t) isotopic values (−9.7 to −10.1) and high initial 87Sr/86Sr ratios (0.7098–0.7099) of the Guyong monzogranite suggest that these rocks were generated by partial melting of the Precambrian basement without mantle input. The zircon εHf(t) isotopic values (−10.63 to −3.04) and δ18O values (6.54 to 8.69 ‰) of the Xiaolonghe syenogranite are similar to the features of the Guyong monzogranite, and this similarity suggests a cogenetic nature and magma derivation from the lower crust that is composed of both metasedimentary and meta-igneous rocks. The Xiaolonghe fine-grained syenogranite shows an obvious rare earth element tetrad effect and lower Nb/Ta ratios, which indicate its productive nature with respect to ore formation. In fact, we discuss that the Sn mineralization in the region was possible due to Sn being scavenged from these rocks by exsolved hydrothermal fluids. We correlate the Late Cretaceous magmatism in the central Tengchong Block with the northward subduction of the Neo-Tethys beneath the Burma–Tengchong Block.

In the Variscan fold belt of Morocco, the Jebilet massif is characterized by Palaeozoic metasedimentary rocks intruded by syntectonic magmatism that includes an ultramafic–granitoid bimodal association and peraluminous granodiorites emplaced c. 330 Ma, intruded by younger leucogranites c. 300 Ma. The mafic–ultramafic rocks belong to a tholeiitic series, and display chemical and isotopic signatures consistent with mixing between mantle-derived and crust-derived magmas or assimilation and fractional crystallization. The granites within the bimodal association are mainly metaluminous to weakly peraluminous microgranites that show characteristics of A2-type granites. The peraluminous, calc-alkaline series consists mainly of cordierite-bearing granodiorites enclosing magmatic microgranular enclaves and pelitic xenoliths. Detailed element and isotope data suggest that the alkaline and the peraluminous granitoids were formed in the shallow crust (<30 km) by partial melting of tonalitic sources at high temperatures (up to 900°C) and by partial melting of metasedimentary protoliths at relatively low temperatures (c. 750°C), respectively. Mixing between the coeval mantle-derived and crust-derived magmas contributed to the large variation of initial εNd values and initial Sr isotopic ratios observed in the granitoids. Further contamination occurred by wall-rock assimilation during ascent of the granodioritic plutons to the upper crust. The ultramafic–granitoid association has been intruded by leucogranites that have high initial Sr isotopic ratios and low initial εNd values, indicating a purely crustal origin. The heating events that caused emplacement of the Jebilet magmatism are related to cessation of continental subduction and convective erosion/thinning of the lithospheric mantle during plate convergence.

In Northeast China, large volumes of Mesozoic–Cenozoic igneous rocks have developed as a result of long-lasting subduction of the palaeo-Pacific and Pacific plates beneath the eastern Eurasian continent. Previous studies have convincingly confirmed the presence of depleted mantle (DM), FOcal ZOne (FOZO) mantle and enriched mantle 1 (EM1) end-members; the enriched mantle 2 (EM2) end-member is probably present but it has been poorly constrained. The Late Cretaceous Shuangyashan suite, comprising a monzogabbro and diorite–porphyrite stocks and their cumulate hornblendite enclaves, from the Shuangyashan coal basin, Northeast China, is characterized by high initial 87Sr/86Sr (0.70922–0.71095) and low initial 143Nd/144Nd ratios (0.51221–0.51238) at 98 Ma. Their occurrence demonstrates that EM2 is present in the lithospheric mantle of Northeast China and its formation may be related to recycled continental material in a subduction setting.