The Solonker zone, extending from Solonker to Sonidzuoqi and Xilinhot in northern Inner Mongolia, China, has been considered as the suture between the Manchurides and Altaids. Two magmatic belts have been recognized along the suture zone: an older, variably deformed arc-related magmatic belt represented by the Baolidao magma suite, and a younger, collisional granite belt, represented by the Halatu plutons. The Baolidao suite is composed of gabbroic diorite, quartz diorite, tonalite and granodiorite. Hornblende is present in all rock types. The Halatu plutons consist mainly of two-mica adamellite and subordinate granodiorite and leucogranite. Hornblende is absent in all rock types. The bulk of Baolidao rocks were emplaced at ca. 310 Ma (zircon 206Pb/238U age). They are metaluminous to weakly peraluminous and possess high Na2O/K2O ratios from 2 to 10. They have no Eu anomalies in the REE patterns but show strong positive Sr anomalies in the primitive-mantle-normalized spidergrams. In contrast, the Halatu granites were formed at ≈230 Ma based on a whole-rock Rb-Sr isochron. They are weakly metaluminous to peraluminous and have rather uniform chemical compositions. In comparison with the Baolidao magma suite, they have much lower contents of FeO, MgO, CaO, TiO2, Cr, V and Sr, but are richer in SiO2, K2O and Rb. They also exhibit distinct negative Sr, P, Ti and Nb anomalies in the spidergrams and signi®cant negative Eu anomalies in the REE patterns, a feature typical of crustal melts. The most primitive rock type of the Baolidao suite (gabbroic diorite) has ISr=0.7052 and eNd(T)=+2.4; whereas the other rock types show small variations in both ISr (0.7056-0.7059) and eNd(T) (+0.7 to-0.1). Geochemical modelling suggests that the gabbroic diorite was derived from a metasomatized upper mantle and the other rock types were generated from the gabbroic diorite magma by fractional crystallization coupled with assimilation of older crustal material (AFC), and followed by hornblende-dominated fractionation in a closed system. The Halatu granites exhibit a range of ISr (0.7048-0.7063) and eNd(T) (+1.0 to -2.2). They were derived from sources dominated by young mantle-derived rocks with variable amounts of ancient continental crust. The largely juvenile isotopic signature for both the Baolidao suite and Halatu granites indicates a significant addition of new continental crust in northern Inner Mongolia.

A geochemical and isotopic study was carried out for three Mesozoic intrusive suites (the Xishu, Wu'an and Hongshan suites) from the North China Craton (NCC) to understand their genesis and geodynamic implications. The Xishu andWu'an suites are gabbroic to monzonitic in composition. They share many common geochemical features like high Mg# and minor to positive Eu anomalies in REE patterns. Initial Nd-Sr isotopic compositions for Xishu suite are eNd(135 Ma)= 12.3 to 16.9 and mostly ISr= 0.7056-0.7071; whereas those for Wu'an suite are slightly different. Pb isotopic ratios for Xishu suite are (206Pb/204Pb)i =16.92-17.3, (207Pb/204Pb)i= 15.32-15.42, (208Pb/204Pb)i=37.16-37.63, which are slightly higher than for Wu'an suite. The Xishu-Wu'an complexes are considered to originate from partial melting of an EM1-type mantle source, followed by significant contamination of lower crustal components. The Hongshan suite (mainly syenite and granite) shows distinctly higher eNd(135 Ma) values (8 to 11) and slightly higher Pb isotopic ratios than the Xishu-Wu'an suites. It was formed via fractionation of a separate parental magma that also originated from the EM1-type mantle source, with incorporation of a small amount of lower crustal components. Partial melting of the mantle sources took place in a back-arc extensional regime that is related to the subduction of the paleo-Pacific slab beneath the NCC.

We report elemental and Nd-Sr isotopic data for two coeval postcollisional magmatic suites (300 Ma), the Miaogou and Karamay suites, from West Junggar foldbelt (NW China), aiming to determine their source regions and implications for continental growth. The Miaogou rocks, monzonitic to granitic in composition, show low Mg# (0.30) and depletion of HFSE, and are highly depleted in isotopic compositions, with ISr ranging from 0.7035 to 0.7045, Nd(300 Ma) from +8.4 to +6.6 and young Nd model ages (0.37-0.70 Ga) that coincide with the ages of the ophiolites in the area. These features suggest that the Miaogou rocks were derived essentially by partial melting of a juvenile basaltic lower crust formed in the early to middle Palaeozoic. The Karamay suite contains a variety of rock types from gabbroic diorite to granite. These rocks show enrichment of LREE and LILE and depletion of HFSE, and have chemical composition (e.g., Mg#=0.63-0.41) rather different from the Miaogou suite, though isotopically they are indistinguishable. This suggests that the parental magma of the Karamay suite originated from melting of a young lithospheric mantle that had previously been metasomatized during the Palaeozoic subduction. The West Junggar magmatic rocks represent production of juvenile continental crust in the Phanerozoic, triggered by upwelling of asthenophere in an extensional regime. The basement beneath the area is dominated by "trapped" Palaeozoic arc series and oceanic crust.

The post-collisional magmatism of the Junggar Terrane is characterized by intrusion of large amounts of granitoids and minor basic/ultrabasic rocks. The granitoids comprise two magmatic suites: calc-alkaline and alkaline, which were emplaced contemporaneously at about 294Ma. The calc-alkaline rocks are typically sodium-rich (Na2O/K2O=1.1-3.5) and metaluminous (A/NK.1.0, A/CNK=0.78-1.04). They show mildly fractionated REE patterns ((La/Yb)N, 15) and spidergrams with strong depletion of Nb, Ti and, to a lesser extent, Sr. The alkaline granites have high contents of SiO2 (75-78%), alkalis, Nb, HREE, Y, Sn, F and high FeO/MgO ratios and huge Sr and Eu depletion in the spidergrams. Moreover, they display characteristic tetrad REE patterns and non-CHARAC trace element behaviour. The two rock suites have similar initial Nd and Sr isotopic compositions, with 1Nd

Voluminous felsic rocks (mainly monzonitic) and coeval mafic rocks (mainly monzogabbro-diorites) were emplaced in the Taihang-Yanshan orogen of eastern North China craton in Mesozoic time. The monzogabbro-diorites have high Sr (mostly. 1300ppm) and low ENd(t) values (9.5 to 15), indicating a long-term incompatible element enriched subcontinental lithospheric mantle source for their genesis. The monzonitic rocks show elemental geochemistry (e.g. high Sr, and REE patterns) and isotopic compositions similar to the monzogabbro-diorites, which leaves little doubt that the two rock suites share a similar origin. These mafic and felsic rocks thus represent a significant addition of juvenile continental crust from an enriched lithospheric mantle source in the Mesozoic, and their generation via melting of enriched portions of the subcontinental lithospheric mantle is probably an important mechanism responsible for the lithosphere thinning beneath eastern North China craton.