海拉尔盆地基底晚古生代adakite的发现及其地质意义

海拉尔盆地的前中生代基底隶属中亚造山带东段的兴蒙造山带。 在盆地基底地层中发现了具有adakite成分特征的粗面安山岩、英安岩和闪长玢岩。 这些火成岩与晚古生代沉积地层交互或伴生, 共同构成晚中生代裂陷盆地的基底。 地球化学研究表明, 这些火成岩基本上属于高钾钙碱性和准铝质岩石系列, 具有高SiO₂和Al₂O₃含量, 高Sr、Sr/Y和La/Yb值, 富集轻稀土(LREE), 亏损重稀土(HREE)、Y和高场强元素(HFSE),Eu表现弱的负异常或轻微的正异常, 相容元素Mg、Cr和Ni含量低, 这些特征与增厚下地壳部分熔融成因的adakite非常相似, 而明显不同于典型的由俯冲洋壳熔融形成的adakite。 样品的(⁸⁷Sr/⁸⁶Sr)_i值基本一致,为0.7041, (¹⁴³Nd/¹⁴⁴Nd)_i值为0.51243~0.51247, ε_Nd (t)为正值(+3.7~+4.5), 显示其岩浆源区可能源于弱亏损地幔, 或亏损地幔受到地壳物质混染。 本文认为海拉尔地区晚古生代adakite型岩浆很可能是由当时新底侵的玄武质下地壳在角闪岩相向榴辉岩相过度或榴辉岩相条件下部分熔融形成。 这些adakite岩石的出现反映了兴蒙造山带晚古生代受到了古亚洲洋的俯冲消减引起的强烈的地幔玄武质岩浆底侵作用, 并由此导致地壳垂向上显著的增生加厚过程。     

Toxicity of ammonia to surf clam (Spisula solidissima) larvae in saltwater and sediment elutriates

Ammonia is a natural component of sediments and has been identified as a common contributor to toxicity in marine sediment, elutriate and porewater testing. In our study, the role of ammonia as a possible toxicant in sediment toxicity tests was evaluated using larvae of the surf clam, Spisula solidissima. Elutriates were prepared and tested using six baseline sediment samples. Ammonia was then purged from aliquots of the baseline sediment samples prior to elutriate preparation. Finally, ammonia was spiked into aliquots of the purged elutriates to mimic ammonia concentrations measured in the baseline elutriates. Toxicity was present in all of the baseline samples and was removed in the ammonia purged samples. In most cases, toxicity was comparable in the ammonia spiked samples to levels measured in the baseline samples. Water only toxicity tests revealed that larvae of the surf clam are one of the more ammonia sensitive marine species. The LC50 for survival was 10.6?mg/L total ammonia (.53?mg/L unionized ammonia) and the EC50 for shell development was 2.35?mg/L total ammonia (.12?mg/L unionized ammonia). Toxicity endpoints calculated from the water only ammonia toxicity test were good predictors of effects observed in the sediment elutriate tests.