Early Cretaceous A-type Rhyolite and Adakitic Lavas from the Songliao Basin, NE China: Magmatic Tracer of Paleo-Pacific Plate Roll-back
Abstract
Late Mesozoic igneous rocks in NE China were produced in an extensional setting; however, the timing and mechanism of lithospheric extension remain debated. We present LA-ICP-MS zircon U-Pb ages and geochemical data (major and trace element concentrations and Hf isotopic compositions) for Early Cretaceous adakitic lavas and A-type rhyolite from the Songliao Basin in NE China. The zircon U-Pb determinations on the adakitic lavas and A-type rhyolite yielded ages between 115 Ma and 102 Ma. Geochemically, the adakitic lavas are characterized by high Sr (515-1610 ppm), but low Y (0.98-17.58 ppm) and heavy rare earth element (HREE) contents, and thus have high Sr/Y (51-112) ratios. They are also exhibit high MgO (0.56-3.53 wt.%), Cr (15.7-87.3 ppm), and Ni (6.7-44.7 ppm) contents and Mg# (36-57) values, comparable with high-Mg adakitic rocks. The A-type rhyolite yields metaluminous to peraluminous (A/CNK = 0.98-1.35) compositions characterized by enrichment in alkalis, Ga, Zr, Nb and Y, depletion in Sr and P, and fractionated REE patterns with strongly negative Eu anomalies (Eu/Eu* = 0.05-0.77). Primary zircon grains from the analyzed samples yield positive ɛHf(t) values of +3.6 to +12.1 and juvenile two-stage model (TDM2) ages of 934-392 Ma. The adakitic lavas were likely generated by partial melting of delaminated lower continental crust and subsequent interaction with the mantle during ascent of the melt. In contrast, the A-type rhyolite was likely produced through partial melting of dehydrated charnockitic middle-lower crust. These data suggest that the adakitic lavas and A-type rhyolite formed in an extensional environment related to roll-back of the subducting Paleo-Pacific Plate. The upwelling of asthenospheric mantle and local delamination of the lithosphere, which were induced by rollback of the subducting Paleo-Pacific Plate, extended from the Great Xing'an Range southeastward through the Songliao Basin to eastern Heilongjiang and Jilin provinces, giving rise to the southeastward migration of lithospheric extension and extension-related volcanism after ca. 140 Ma.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T31C0316J
- Keywords:
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- 8102 Continental contractional orogenic belts and inversion tectonics;
- TECTONOPHYSICSDE: 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8149 Planetary tectonics;
- TECTONOPHYSICSDE: 8150 Plate boundary: general;
- TECTONOPHYSICS