The ultramafic dikes in the Tarim large igneous province(Tarim LIP), exposed in the Xiaohaizi area in the northwestern Tarim Basin of northwestern China, have porphyritic textures, and the olivine and clinopyroxene are as the major phenocryst phases. The groundmass therein consists of clinopyroxene, plagioclase and Fe-Ti oxides, with the cryptocrystalline texture. The olivine phenocrysts in one typical ultramafic dike have Fo(Mg/(Mg+Fe)) numbers ranging from 73 to 85, which are not in equilibrium with the olivine(Mg# of 89) from the host rock crystalized. Combined with microscope observation, both the olivine and clinopyroxene phenocrysts as well as some Fe-Ti oxides in the ultramafic rock are accounted as cumulates. The liquid(parental magma) composition of SiO_2 of 45.00 wt.%–48.82 wt.%, MgO of 9.93 wt.%– 18.56 wt.%, FeO of 5.85 wt.%–14.17 wt.%, CaO of 7.54 wt.%–11.52 wt.%, Al_2O_3 of 8.70 wt.%–11.62 wt.% and TiO_2 of 0.00 wt.%–3.43 wt.% in the Xiaohaizi ultramafic rock was estimated by mass balance, and the results show a reasonable liquid proportion in the cumulate-bearing ultramafic dike(ca. 45%–60% in the whole rock). The estimated parental magma composition corresponds to a melting temperature of 1 300–1 550 oC, which is equal or higher than those of a normal asthenosphere mantle, supporting the involvement of a mantle plume. Combined with other previous studies, an evolution model for the formation processes of the Xiaohaizi ultramafic dike of the Tarim LIP is proposed.
New geochemical and geochronological data of two types of granites,which are located in Yandangshan area,southeastern Zhejiang Province,were presented to constrain their magma condition,origin and the genetic relationship between them.The SHRIMP zircon U-Pb dating of Dongshan and Hesheng granite in Yandangshan area shows that they were formed at 114±1 and 103±2 Ma,respectively.Samples from the Dongshan granite have high Si O2(76.4 wt.%–76.9 wt.%)and total alkaline(K2O+Na2O=8.35 wt.%–8.47 wt.%)contents,but low Fe OT(0.89 wt.%–1.15 wt.%),Mg O(0.21 wt.%–0.22wt.%),and Ca O(0.24 wt.%–0.34 wt.%)contents and high A/CNK(~1.1)values,belonging to the peraluminous and magnesian granite.The Hesheng granite has high Si O2(72.2 wt.%–77.5 wt.%),total alkaline(K2O+Na2O=8.05 wt.%–9.41 wt.%)and Fe OT contents(1.20–2.06),and high A/CNK values(1.0–1.1),but low in Mg O(0.12 wt.%–0.29 wt.%)and Ca O(0.24 wt.%–0.34 wt.%)contents.Samples from the Hesheng granite also have high Fe OT/Mg O(6.9–10.0)and 10 000×Ga/Al(2.6–3.4)ratios similar to the ferroan/A-type granite.All the samples are enriched in LREE but have produced negative Eu anomalies(Eu/Eu*Dongshan=0.45–0.47;Eu/Eu*Hesheng=0.17–0.55),Ba,Nb,and Ta,while the REE contents of the ferroan/A-type granite(Hesheng)are higher than that of the magnesian granite(Dongshan).The(87Sr/86Sr)i value of the magnesian granite is slightly higher than that of the ferroan/A-type granite and itsεNd(t)value(-6.8)is lower than the latter(-6.0–-5.9).In addition,theεHf(t)value(-11.8–-4.2)of magnesian granite is also lower than that of the ferroan/A-type granite(-8.3–-2.0),indicating that there may be more mantle-derived components in the source area of the ferroan/A-type granite.Zircon saturation thermometer(TZr)and Ti-in-zircon thermometer(TZircon)are used to estimate the temperature of the magma source,and the results show that the magma temperature of the magnesian granite(average TZr=798oC;average TZircon=792oC)is lower than that of the ferroan/A-type granite(aver
