| Kangdian geo-axis in the western margin of the Yangtze, is a special geologicalunit, showing a long, unique platform base trending north-south, in the west, is theIndosinian fold belt which was formed after Paleotethys sea closed, in the east, is theplatform covered by Sinian to Cenozoic system. Kangdian geo-axis exposed extensiveoutcrops of metamorphic-migmatized complex rocks, known as Kangding group.Kangding group is generally considered the oldest, a complex combination of rocks,showing the dome-like distribution in Kangding, Luding, Shimian, Mianning, Xichang,Panzhihua, Yuanmou area etc., approximately3540km2. As an important part of thepre-Cambrian strata of the western margin of the Yangtze, the research on rockcomposition, geological evolution, origin and age assignment of Kangding group havebeen a focus, but also a difficulty.There are big arguments about the complex rocks in origin of "magma ", or"migmatized ", or metamorphic, other magmatic intrusions-mixing rock and so.Meanwhile, in the view of "migmatized group", there are also different ideas thatformed by intrusive rock juice or place melting-metasomatic causes. This graduationthesis discussed the petrology, geochemistry and geochronology, the origin of thecomplex rocks and the relationship with uranium mineralization in the DaTian complex,achieved the following understanding.（1）The rock of DaTian quartz diorite complex in the northern DaTian,commonly shown a directional distribution of plagioclases and amphiboles, noobviously intrusive contact interface with country rocks, no condensation-coolingmargin and no obviously fractional crystallization, so that it was considered as an originof migmatization.（2）The lithology of the DaTian migmatite was controlled by initialmetamorphic rocks, such as the hornblende plagioclase migmatitic rock was formedfrom amphibolites which derived from mafic volcanic rocks, and also the biotite-plagioclase migmatitic rock from clastic sedimentary rocks or felsic volcanics. Thereare a large number of metasomatic structures, such as plagioclase were replaced byquartz, new plagioclase feldspar replaced elder ones and K-feldspar, biotite replacedhornblende etc., and also residual structure, myrmekitic quartz structure and so. （3）Usually migmatite rocks show a contacting with gradual transition betweenleucosomes and melanosomes, and a large number of residual bodies (Relicts) withroughly direction of its long axis, parallel to the metatexite veins, minerals foliations,gneissosity and regional structural trends. Some residual bodies are of distinctmutations boundaries, some are blurred, occasionally can see some directional coarseminerals cutting the residual bodies, about characteristics are interpreted the migmatitesto have in situ formed.（4）Geochemical characteristics of major elements of the migmatites show thatSiO2content is53%to69%, the individual reached to85.24%; Rittman index δmajority is less than3.3, similar to aluminum-rich calc-alkaline rocks; Na2O+K2Ohighest up to8.61%, and Na2O content greater than K2O. That is recorded a type ofalkali (sodium) rich migmatites.According to the pattern of REE and Eu anomalies, the migmatites can be dividedinto two categories. One is an anatexite type with ΣREE (108.99~1118.13)×10-6,(La/Yb)N1.60to54.29, significantly negative Eu anomaly. Some inherited characteristicsof metamorphic rocks, developed in the primary stage of anatexis, and some are resultof melt fraction in the advanced stage of deep source, the melt was migrated. Someindustrial ores of Uranium occurred in this anatexite rocks, indicate that uraniummineralization may be associated with the hydrothermal flow in migmatization,uranium enriched in migmatization, and the migamtitation has played a significant rolein promoting the overall uranium to a high background values,or ores exited locally.Another rocks with lower ΣREE of44.62~146.15×10-6,and (La/Yb)Nof22.77~35.72, significant positive Eu anomaly, low Y content, the uranium content of lessthan2×10-6etc., are interpreted to have formed in diatexitic stage. the rock was in meltstateTrace elements of the migmatie show that enriched in LILE, K, Rb, Th and Pb,etc, and high field strength elements Zr, Hf,as well as heavy rare earth elements Y, Yb,relatively lower of V, Cr, Co, Ni. In the Rb-Y+Nb discrimination diagrams for tectonicenvironment, the migmatite rocks are plotted within a mixed volcanic arc granite,which Indicates that the migmatite have been formed in volcanic island arcenvironment.（5）The data using zircon U–Pb age, combined with the geological setting, thispaper argued that metamorphic rocks in Kangdian geo-axis have been formed in the lateArchean-Proterozoic, the migmatites have been formed in740~930Ma, duringJinning orogeny period.（6）various features fully illustrated that DaTian migmatites are formed byanatexis with in-situ or semi-situ nature. Migmatization processed uraniumre-activation, migration, enrichment and mineralization in favorable locations. |
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