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It remains uncertain whether a stagnant slab in the mantle transition zone can affect the asthenospheric mantle beyond its leading edge. To address this question, we investigated Cenozoic alkaline basalts from the Dariganga volcanic field (DVF) in southeastern Mongolia. The DVF is located west of North–South Gravity Lineament (NSGL) in Eastern China, which is spatially coincident with the seismically detected stagnant Pacific slab front. Basalts from the DVF consist of nephelinite, basanite and alkali olivine basalt. These rocks have relatively high Nb/U (average = 58) and Nb/La (>1) ratios and radiogenic Nd–Hf isotopic compositions. They also have high Ca/Al (0.60–1.13), Zn/FeT (13.5–16.5), and FeO/MnO (77–112) ratios as well as low δ26Mg (−0.42‰ to −0.26‰) values, reflecting an asthenospheric mantle source modified by carbonated eclogite‐derived melts. Pb–Nd–Hf isotope characteristics indicate that the carbonated eclogite‐derived melts likely originated from the stagnant Pacific slab. Although Cenozoic basalts from both the east of the NSGL (ENSGL) and DVF domains exhibit light δ26Mg values, basalts from the ENSGL nevertheless have lower δ26Mg values than those in the DVF domain. This suggests a gradual westward decline in the amount of carbonated melts/fluids derived from the stagnant Pacific slab. This variation trend, combined with a more fertile and oxidized asthenospheric mantle toward the ENSGL, indicates that the stagnant slab has affected the mantle and created a compositional aureole beyond its leading edge, which substantially contributed to the formation of the alkaline basalts in the DVF. Plain Language Summary: Subducted slabs can exert a profound influence on overlying mantle domains. However, it remains uncertain whether material from a stagnant subducted slab in the mantle transition zone can influence the mantle domain beyond its leading edge and contribute to the formation of alkaline basalts. This article presents a study on Cenozoic alkaline basalts in SE Mongolia, which lie west of the North–South Gravity Lineament, beyond the leading edge of the stagnant Pacific slab. The Cenozoic alkaline basalts in SE Mongolia are characterized by relatively high Ca/Al, Nb/U and Nb/La ratios. They also show depletion in Pb–Zr–Hf and have radiogenic Nd–Hf and relatively light Mg isotopic compositions, which is consistent with their origination from an asthenospheric mantle source modified by carbonated eclogite‐derived melts. Radiogenic isotopic compositions suggest that the carbonated melts were likely derived from the stagnant Pacific slab. Furthermore, there is a westward decline in signals of carbonated melts/fluids derived from the stagnant Pacific slab. These findings suggest that the stagnant Pacific slab has influenced the mantle domain beyond its front edge, leading to a differential modification of the asthenospheric mantle and the formation of intraplate alkaline basalts in the Dariganga volcanic field. Key Points: The Cenozoic alkaline basalts in Dariganga were sourced from asthenospheric mantle modified by carbonated eclogite‐derived meltsThe carbonated eclogite‐derived melts were derived from the subducted Pacific slab that stagnated in the mantle transitional zoneThe influence of the carbonated melts/fluids waned westward, resulting in a compositional aureole across the North–South Gravity Lineament [ABSTRACT FROM AUTHOR]

Archean to Palaeoproterozoic basement rocks exposed in the Dunhuang block in NW China were affected by Palaeozoic crustal reworking, as constrained by previous zircon U–Pb geochronological investigations. However, relationships between the Palaeozoic metamorphic ages, P–T evolution and deformational history of the region remain ambiguous. In order to address this issue, P–T–t–D paths of paragneisses from the basement of the Hongliuxia belt in the southern Dunhuang block were investigated. Inclusions in garnet and kyanite from the paragneisses are considered as vestiges of Palaeozoic M1 metamorphism corresponding to initiation of the prograde evolution. The earliest continuous metamorphic fabric is an originally steep N–S striking foliation S2. This fabric was reworked by vertical folds F3 associated with the development of a ubiquitous steep, mainly south‐dipping, E‐W striking axial planar foliation S3. The S2 foliation in paragneisses is mainly associated with Grt–St–Ky–Sil–Bt–Ms–Pl–Qz–Rt assemblages in samples from the western domain and with Grt–Ky–Sil–Bt–Kfs–Pl–Qz–Rt assemblages in samples from the northeastern domain of the Hongliuxia belt. The S3 foliation is associated with Grt–Sil–St–Bt–Ms–Pl–Qz–Ilm assemblages in the western domain and with Grt–Sil–Bt–Ms–Pl–Qz–Kfs–Ilm assemblages in the northeastern domain, followed by growth of chlorite in both domains. Early prograde stage (M1) from 4.0–6.5 kbar and 540–560°C to metamorphic peak (M2a) at 9–10 kbar and ~650–675°C is mainly recorded by paragneisses from the western domain. Subsequent decompression is initially accompanied by heating (M2b) constrained to 6.5–7 kbar and 675–710°C in the western domain, and to 6–6.5 kbar and ~730°C in the northeastern domain, followed by cooling (M3) through 4–6.5 kbar and 550–650°C till late chloritization (late M3). In situ U–Pb dating of monazite combined with monazite trace‐element compositions suggests that prograde evolution (M1) most likely started at c. 406 Ma, peak‐P conditions (M2a) were reached at 400–394 Ma, decompression associated with heating (M2b) took place at 393–391 Ma, and cooling (M3) during exhumation probably lasted from 380 to 354 Ma. The prograde metamorphism probably reflects burial during underthrusting of neighbouring continental basement (the Alxa block or an equivalent) below the Dunhuang block. This event culminated in pure shear thickening (D2a) of the whole supra‐subduction margin followed by minor heating and exhumation (D2b). The D3‐M3 event is interpreted as reflecting exhumation during orthogonal shortening of the system, possibly in response to an independent orogenic cycle. Combined with the available regional data, this study reveals the existence of a complex tectono‐metamorphic evolution for the Dunhuang block characterized by two distinct orogenic phases with (i) the thickening of a previously thinned arc‐back‐arc crust recorded in the northern and central belts at 420–410 Ma in the pro‐wedge side of the active margin (Sanweishan phase), followed by (ii) the 410–390 Ma thickening in the retro‐wedge side (Hongliuxia phase). Such a tectonic evolution of the whole Dunhuang block resembles Andean‐type migration of crustal thickening from the convergent front to hinterlands. The D3‐M3 event, potentially responsible for the juxtaposition of rocks from different geological occurrences and depths, is seemingly independent from this Andean‐type orogenic cycle. [ABSTRACT FROM AUTHOR]

New geochronological and geochemical data were presented for the Early Carboniferous basaltic to andesitic volcanic rocks and Late Carboniferous granitic intrusions in the Aqishan–Yamansu Belt of Eastern Tianshan, NW China. Zircon U–Pb dating indicates that the andesite and granite were emplaced at 330 Ma and 321 Ma, respectively. The andesitic rocks of the Yamansu Formation (FM) display subalkaline to calc-alkaline characteristics with moderate SiO2, relatively high Mg# values, and low Cr, Co and Ni, indicating an origin from mantle-derived melts. Their relatively low εNd(t) values (–0.02 ~ +0.61) and old TDM ages (TDM = 1.39–1.40 Ga) suggest a mantle source with addition of old crustal materials. Their high Rb/Y and Ba/La, low Nb/Y and Th/Yb ratios elucidate that the magma sources were probably metasomatized by slab-derived fluids. Besides, the high Th and low Ce/Th and Ba/Th ratios of the andesites suggest a contribution from subducted sediment–derived melts. Integrated with the depletion in high field strength elements and enrichment in light rare earth elements (LREEs), we suggest that the Yamansu andesites were formed by partial melting of relatively enriched mantle wedge metasomatized by both subducted sediment-derived melts and fluids. The basalts of the Tugutublak Formation (TF) have high MgO, Mg# (56–58) and εNd(t) (+5.9 ~ +6.3) values with enriched in LREEs and depleted in Nb–Ta–Ti anomalies, implying an arc setting. Their high Ba/Th, Ba/La and low Th/Ta, Th/Yb ratios suggest that the slab-derived fluids were involved. The basaltic andesites of the TF have higher SiO2, lower Mg# (48–50), Cr, Ni and εNd(t) (+1.21) values than the basalts of this formation, indicating that they were evolved from the basaltic magma. Therefore, the Carboniferous volcanic rocks in this study indicate that the Aqishan–Yamansu Belt was in a subduction background. The granites intruding into the TF show typical characteristics of I-type granite. Their highly positive εHf(t) values (+14 ~ +17) suggest a significant contribution from juvenile basaltic lower crust. Moreover, changes in the Dy/Yb and Ho/Yb ratios of Late Paleozoic felsic igneous rocks in the Aqishan–Yamansu Belt imply that the crust underwent four periods of thickening and thinning, which were likely triggered by the variation of subduction angles. [ABSTRACT FROM AUTHOR]