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Mesozoic mafic dikes are widely distributed in Luxi (Mengyin and Zichuan) and Jiaodong regions of the Shandong Peninsula, China, providing an opportunity of investigating the nature of the lost lithospheric mantle beneath the North China Craton (NCC). The mafic dikes are characterized by strong depletion in high field strength elements (HFSE), enrichment in light rare earth elements (LREE), highly variable Th/U ratios, high initial ( 87 Sr/ 86 Sr) i (0.7050-0.7099) and negative ε Nd (T) (-6.0 to -17.6). They were derived from melting of metasomatized portions of the subcontinental lithospheric mantle, followed by fractionation of clinopyroxenes. The similarity in Nd isotopic compositions between the Mengyin gabbro dikes and the Paleozoic peridotite xenoliths suggests that ancient lithospheric mantle was still retained at 120 Ma below Mengyin, although the ancient lithospheric mantle in many other places beneath NCC had been severely modified. There might be multiple enrichment events in the lithospheric mantle. An early-stage (before or during Paleozoic) rutilerich metasomatism affected the lithospheric mantle below Mengyin, Jiaodong and Zichuan. Since then, the lithospheric mantle beneath Mengyin was isolated. A late-stage metasomatism by silicate melts modified the lithospheric mantle beneath Jiaodong and Zichuan but not Mengyin. The removal of the enriched lithospheric mantle and the generation of the mafic dikes may be mainly related to the convective overturn accompanying Jurassic-Cretaceous subduction of the paleoPacific plate.

Geochemical and Sr–Nd–Pb isotopic data are presented for volcanic rocks from Zougouyouchaco (30.5 Ma) and Dogai Coring (39.7 Ma) of the southern and middle Qiangtang block in northern Tibet. The volcanic rocks are high-K calc-alkaline trachyandesites and dacites, with SiO2 contents ranging from 58.5 to 67.1 wt % The rocks are enriched in light REE (LREE) and contain high Sr (649 to 986 ppm) and relatively low Yb (0.8 to 1.2 ppm) and Y (9.5 to 16.6 ppm) contents, resulting in high La/Yb (29–58) and Sr/Y (43–92) ratios, as well as relatively high MgO contents and Mg no., similar to the compositions of adakites formed by slab melting in subduction zones. However, the adakitic rocks in the Qiangtang block are characterized by relatively low εNd(t) values (−3.8 to −5.0) and highly radiogenic Sr ((87Sr/86Sr)i=0.706–0.708), which are inconsistent with an origin by slab melting. The geochemistry and tectonics indicate that the adakitic volcanic rocks were most likely derived from partial melting of delaminated lower continental crust. As the pristine adakitic melts rose, they interacted with the surrounding mantle peridotite, elevating their MgO values and Mg numbers.

Cretaceous mafic dykes in Fujian province, SE China provide an opportunity to examine the nature of their mantle source and the secular evolution of the Mesozoic lithospheric mantle beneath SE China. The mafic rocks have SiO2 ranging from 47.42 to 55.40 wt %, Al2O3 from 14.0 wt % to 20.4 wt %, CaO from 4.09 to 11.7 wt % and total alkaline (K2O+Na2O) from 2.15 wt % to 6.59 wt %. Two types are recognized based on their REE and primitive mantle-normalized trace element patterns. Type-A is the dominant Mesozoic mafic rock type in SE China and is characterized by enrichment of light rare earth elements (LREE) ((La/Yb)n = 2.85–19.0) and arc-like trace element geochemistry. Type-P has relatively flat REE patterns ((La/Yb)n = 1.68–3.43) and primitive mantle-like trace element patterns except for enrichment of Rb, Ba and Pb. Type-A samples show EMII signatures on the Sr-Nd isotopic diagram, whereas type-P rocks have high initial 143Nd/144Nd ratios (0.5126–0.5128) relative to the type-A rocks (143Nd/144Nd = 0.5124–0.5127). The type-A rocks have 207Pb/204Pb ranging from 15.47 to 15.67 and 206Pb/204Pb from 18.26 to 18.52. All the type-A rocks show a negative correlation between 143Nd/144Nd and 206Pb/204Pb ratios and a positive relationship between 87Sr/86Sr and 206Pb/204Pb ratios, indicating mixing of a depleted mantle source and an EMII component. Geochemical modelling shows that the parental magmas were formed by 5–15 % partial melting of a spinel lherzolite, and contaminated by less than 1 % melt derived from subducted sediment. The type-P magmas were derived from a mantle source unmodified by subduction components. The wide distribution of type-A dykes in SE China suggests that subduction-modified lithospheric mantle was extensive beneath the Cathaysia Block. Geochemical differences between Mesozoic and Cenozoic mafic rocks indicate that lithospheric thinning beneath SE China occurred in two episodes: firstly by heterogeneous modification by subducted components in early Mesozoic times, and later by chemical–mechanical erosion related to convective upwelling of the asthenosphere during Cenozoic times.

Major-and trace-element data for Mesozoic mafic dikes from Fujian Province, Southeast China, provide insights into the nature of their mantle source and evolution of the lithospheric mantle beneath the Cathaysian block. These dikes are alkali to subalkali in composition, and are characterized by high Al 2 O 3 (14.0-20.4 wt%) and moderate CaO (4.09-12.7 wt%) compared to Cenozoic basalts in the same region. In primitive mantle-normalized plots, they are enriched in LREE and LILE, and depleted in HFSE (Nb and Ta), with positive Pb and negative Ti anomalies. They are divided into two types, based on their REE contents: type 1 had low total REE (53.8-145.5 ppm) with relatively flat chondrite-normalized patterns [(La/Yb) n =1.68-4.65], whereas type 2 has much higher total REE (63-247 ppm) with LREE enrichment [(La/Yb) n = 4.63-19]. Zr/Y ratios show a good correlation with Y in the type 1 dikes, but not in the type 2 varieties. Rocks in both groups experienced modest crustal contamination. All have slightly higher Pb isotopic ratios than the associated Cenozoic basalts, suggesting that the Mesozoic dikes were derived from a mantle source that had been modified by subducted materials (fluid + sediment). Type 1 dikes are believed to have been derived from garnet-spinel lherzolite, whereas type 2 dikes were probably derived from spinelor spinel-plagioclase lherzolite. Both mantle sources were compositionally heterogeneous and they experienced different degrees of depletion. Asthenospheric upwelling provides a possible mechanism for lithosphere thinning and extension, leading to emplacement of the dikes.

Abstract– The Grove Mountains (GRV) 021663 meteorite was collected from the Grove Mountains region of Antarctica. The meteorite is composed primarily of olivine (Fa5.4), orthopyroxene (Fs4.7Wo3.0), chromian diopside (En53.6Fs2.4Wo44), troilite, kamacite, and plagioclase (Ab74.5Or4An21.5). Minor phases include schreibersite and K‐feldspar. The meteorite is highly weathered (W3) and weakly shocked (S2). We determine a whole rock oxygen isotopic composition of δ18O = 7.50‰, δ17O = 3.52‰. Comparisons of these data with other primitive achondrites have resulted in the reclassification of this meteorite as a member of the winonaite group. The occurrences of troilite, metal, and schreibersite in GRV 021663 indicate that these minerals were once completely molten. Euhedral inclusions of pyroxene within plagioclase further suggest that these may have crystallized from a silicate melt, while the depletion of plagioclase, metal, and troilite indicates that GRV 021663 could represent a residuum following partial melting on its parent asteroid. Trace element distributions in silicate minerals do not, however, confirm this scenario. As with other winonaite meteorites, the formation of GRV 021663 probably relates to brecciation and mixing of heterogeneous lithologies, followed by varying degrees of thermal metamorphism on the parent body asteroid. Peak metamorphic conditions may have resulted in localized partial melting of metal and silicate mineralogies, but our data are not conclusive.