Adakite-like granitoids of Songkultau: A relic of juvenile Cambrian arc in Kyrgyz Tien Shan

The early Paleozoic Terskey Suture zone, located in the southern part of Northern Tien Shan domain Kyrgyzstan, comprises tectonic slivers dismembered ophiolites and associated primitive volcanics deep-marine sediments. In Lake Songkul area, early-middle Cambrian pillow basalts are crosscut by Songkultau intrusion coarse-grained gneissose quartz diorites tonalites with geochemical characteristics typical for high-SiO2 adakites (SiO2 ?> ?56 ?wt.%, Al2O3 ?15 Na2O ?3.5 ?wt.% high Sr/Y La/Yb ratios). granitoids have positive initial ?Nd (+3.8 to +6.4) ?Hf (+12.3 +13.5) values indicating derivation from sources MORB-like isotopic signature. Volcanic formations, surrounding intrusion, affinities varying ocean floor island arc series. This rock assemblage is interpreted as a relic an early–middle where adakite-like were derived partial melting young hot subducted oceanic crust. An age 505 ?Ma, obtained shows that subduction under continued until middle Cambrian. complexes obducted onto domain, Andean type continental magmatic developed Ordovician. Formation was accompanied uplift, erosion deposition coarse clastic A depositional ca. 470 Ma, gravellites agreement timing lower Ordovician conglomerates elsewhere Shan, corresponds main phase magmatism. association formations constitute represent juvenile substantial size identified so far within predominantly crustal-derived terranes Shan. On regional scale this can be compared arcs Kazakhstan, Gorny Altai Mongolia.