Petrogenesis and tectonic implications of the Balong intermediate dyke swarms in East Kunlun Paleo-Tethyan orogenic belt
Dyke swarms are an important"probe"to study the tectonic evolution of orogenic belts and the growth mechanism of continental crust.Herein,we present petrological,geochronological and geochemical studies on the Balong intermediate dyke swarms in East Kunlun Paleo-Tethyan orogenic belt,to unravel their petrogenesis and its implications for the evolution of Paleo-Tethyan Orogeny.The studied Balong intermediate dyke swarms are mainly composed of diorite porphyrite with zircon U-Pb ages of 250.2±1.3 Ma.They have SiO2 contents ranging from 52.8% to 59.6%,total alkali(K2O+Na2O)contents ranging from 3.98% to 6.25%,Mg#values of 24 to 46,and aluminum saturation indices ranging from 0.91 to 0.98,belonging to the high-K calc-alkaline,metaluminous rock series.The samples exhibit significantly fractionation between LREE and HREE with(La/Yb)N ratios of 5.44～7.76,and they show unobvious Eu anomalies(δEu=0.91～1.11).They are enriched in large-ion lithophile elements but depleted in high-field-strength elements with significant negative Nb and Ta anomalies.Petrogenesis study shows that the early Triassic Balong intermediate dyke swarms are mainly derived from partial melting of ancient mafic crust with a certain degree of crust-mantle magma mixing.In combination with regional geology data,this study proposes that the studied intermediate dyke swarms are generated in Paleo-Tethyan oceanic subduction-related continental arc setting,and the reworking of continental arc crust followed by crust-mantle mixing is the key model of growth and evolutionary of continental ancient crust during East Kunlun Paleo-Tethyan orogeny.
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