BULLETIN Relation between texture and chemical composition of peridotite xenoliths and its implications : An example from Wangqing, Jilin Province XU Yigang Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. Guangzhou 510640, China Abstract Spinel peridotite xenoliths from Wangqing. NE China exhibit correlative variations in texture, temperature, geochem- istry and radiogenic isotopes. This suggests that the Wangqing xenoliths may come from a mantle d i a ~ i r . It is possible that the fer- tile and undeformed lhemlites were situated in the interior of the diapir, whereas the refractory and deformed hanburgites and clinopyroxene-poor lherwlites were within the diapiric flanks. Keywords: peridotite xenoliths, texture, geochemistry, Wangqing. PERIDOTITE'S texture may record the deformation history in the upper mantle, while their geochemical composition can be related to diverse mantle processes such as depletion, enrichment and subsolidus reequilibration. Previous studies were commonly focused on either of these two aspects. In fact, the rela- tionship between texture and chemistry of peridotites can be used to assess the nature of processes opera- tive in the upper mantle"'. Therefore, it is of importance to integrate both textural and geochemical data of xenoliths in order to better constrain the evolution of the mantle. With this strategy, we have under- taken a petrological and geochemical investigation on a suite of spinel peridotite xenoliths from Wavqing, NE China. The texture of these xenoliths includes coarse-grained protogranular (grain size > 4 mm) , transitional and tabular granuloblastics (about 1 rnm) . Twenty of them were selected for electron micro- probe analysis. A subset of ten was then analysed for bulk rock major element composition, rare earth ele- ment (REE) contents in clinopyroxene (cpx) and Sr-Nd isotopic ratios of cpx. The main petrological and geochemical characteristics of the samples analysed are listed in table 1. Table 1 Petrological and geochemical characteristics of peridotite xenoliths from Wangqing Sample Rock type Cpx( %) GO(%) MgO( %) (LdYb).,, s7~r/s6Sr 143Nd/14'Nd Protogranular W- 1 lherz W-37 lhcrz Transitional W-6 lherz W-11 Iherz W-77 lherz Granuloblastic W-5 harz W-13 ham W-20 lherz W-21 lhen W-22 harz 2.5 0.65 45.40 7.42 0.703 831 f 12 0.512 780 f 5 cpx, Clinopyroxene; Iherz, Iherzolite; ham, harzburgite. Whole rock major element compositions. REE contents in clinopy- roxene and Sr-Nd isotopic ratios were measured at Isotopic Laboratory of University of London using XRF, IDMS and TIMS meth- ods. 1 Relationship between texture and chemistry of peridotite xenoliths 1.1 Correlation between mineral chemistry and textural variation Figure l(a) illustrates a correlation between Al content of orthopyroxene (opx) and Cr/(Cr + Al) of coexisting spinel. The latter is a good indicator of degree of partial melting, while the former is related to both melting degree and equilibrium temperature. The variations of A1 content within individual grains and between grains are presented as vertical tie lines. It is noted that ( i ) Al content in opx decreases* Chinese Science Bulletin Vol .43 No. 10 May 1998 837