Late Cretaceous tectono–magmatic event in Songliao Basin, NE China: New insights from mafic dyke geochronology and geochemistry analysis

Abstract

The ages and source of Late Cretaceous mafic dolerite dykes of the Songliao Basin were determined using geochronological, geochemical, zircon Hf, whole‐rock Sr–Nd isotopic, and zircon fission tract. The results show that (a) petrographic data reveal doleritic, poikiloblastic textures, and amygdale structures of the dolerite dykes. (b) LA‐MC‐ICP‐MS U–Pb analysis of zircons yielded an age of 70.0 ± 3.0 Ma of one of these mafic dykes in agreement with the zircon fission track age (69–68 Ma) of host rocks within uncertainty, placing them within the Late Cretaceous. (c) Geochemical researches indicate that the dykes are classified as the alkaline and tholeiitic series according to their major elements and characterized by high Na2O (2.79–4.89 wt.%), TiO2 (1.63–2.71 wt.%), and low K2O (0.46–2.45 wt.%). And they have enrichment of incompatible elements (e.g., K, Ti, Rb, Ba, Th, U, Nb, Ta, and REEs), high Rb/Sr (0.026–0.066), LaN/YbN (3.83–15.93), near‐chondritic HREEs ([Gd/Yb]N = 1.78–3.37), low Sm/Nd (0.202–0.282) ratios, and with negligible Eu anomalies (Eu/Eu* = 0.98–1.06). The dykes contain relatively low amounts of radiogenic Sr, as shown by (87Sr/86Sr)i values (0.7037–0.7045), and have positive values of εNd(t) (3.66–5.40) and εHf (t) (2.66–7.45), suggesting that the mafic dykes have been derived from partial melting of the depleted lithospheric mantle and contaminated by crust in the source region and formed in back‐arc rift settings caused by the subduction of the Pacific Oceanic Plate. All the above indicate large‐scale extensional event in Songliao Basin NE China at about 70 Ma.

Micro-XRF Analysis On The Relationship Between Pyrite And Uranium Mineralization In Sandstone-Hosted Uranium Deposits

“…The Songliao Basin was in the stage of extensional fault depression and basin formation during the Early Cretaceous period, which was the period of sedimentation and diagenesis of the surrounding rock. 19 The enrichment of Fe was due to the humid and warm environment of the Early Cretaceous, which led to the mudstone deposited in the basin being rich in organic carbon debris, Fe 2+ , and other reducing substances. 20 In the Late Cretaceous, the Songliao Basin comprehensively suffered from compression and uplift, and the tectonic movement exposed the strata to the surface.…”

Petrogenetic Constraints of Early Cenozoic Mafic Rocks in the Southwest Songliao Basin, NE China: Implications for the Genesis of Sandstone-Hosted Qianjiadian Uranium Deposits

“…Plots of (a) Na2O+K2O vs. SiO2 (after Irvine and Baragar [47]), (b) Zr/(TiO2 × 10 −4 ) vs. Nb/Y (after Winchester and Floyd [48]), (c) K2O (wt.%) versus Na2O (wt.%) [49], and (d) TFeO-Na2O+K2O-MgO triangular diagram, the boundary line between alkaline series and the tholeiitic series after Irvine and Baragar [47], A = Na2O + K2O (wt.%); F = T FeO (wt.%); M = MgO (wt.%). The chemical data for the alkaline basalts of Shuangliao [46], Tholeiitic basaltic rock of Qianjaidian areas [37], and potassium basalts of Greater Khingan Range [49] are shown for comparison.…”

“…In addition, the samples of AB group show positive Nb-Ta anomalies, which are similar to oceanic island basalt (OIB) (Figure 8b), whereas the TB samples display lower abundances of most trace elements similar to those of enriched mid-oceanic ridge basalt (E-MORB). The chemical data for the alkaline basalts of Shuangliao [46], Tholeiitic basaltic rock of Qianjaidian areas [37], and potassium basalts of Greater Khingan Range [49] are shown for comparison.…”

“…Based on whole-rock Ar-Ar dating, Xia et al [15] proposed that the diabase dikes were emplaced at 49.5 ± 5 Ma. However, LA-ICP-MS analysis of zircons from mafic dike in Baixingtu ore deposit yielded an age of 70.0 ± 3.0 Ma [37]. Therefore, detailed geochronology and geochemistry of the mafic rocks could provide important information for regional tectonic evolution of the basin.…”