Geochemical constraints on source region of Cretaceous/Tertiary impact glasses
Geochemical constraints on source region of Cretaceous/Tertiary impact glasses
复制标题
白垩纪/第三纪撞击玻璃来源区的地球化学限制
作者：
H. Sigurdsson;H. Sigurdsson;P. Bonté;L. Turpin;M. Chaussidon;N. Métrich;M. Steinberg;P. Pradel;S. D’Hondt
在海地的Beloc，50厘米厚的白垩纪/第三纪边界层含有直径为1-8毫米的黑色玻璃小球，这些小球被认为是大陆地壳撞击融合的产物。钙黄色玻璃（高达30重量% CaO）在一些黑色玻璃球上形成涂层并在其中形成条纹，并归因于富含碳酸盐的沉积物1或富含有机物或黄铁矿石灰石2的熔融。在这里，我们提出了新的微量元素和稳定的和放射性同位素数据表明，钙玻璃是来自安山组成的大陆地壳，而高钙玻璃熔融形成的富钙长石沉积物。在1，200 - 1，400 °C下用蒸发岩和安山岩进行的熔化实验证实了这一点，这些实验近似地再现了高钙玻璃。合成高钙玻璃中硫含量随温度的变化表明，海地玻璃的形成温度为1，300 °C。从海地玻璃的地球化学特征推断出的撞击地点的地质情况与在墨西哥白垩纪蒸发岩矿床中发现的180公里长的希克苏鲁布结构中发现的岩性相匹配。钙玻璃中的高硫含量表明，撞击可能产生了大量的二氧化硫排放到大气中，导致短期的全球变冷。
THE 50-cm-thick Cretaceous/Tertiary boundary layer at Beloc in Haiti contains spherules of silicic black glass, 1–8 mm in diameter, which have been attributed to impact fusion of continental crust1. Calcic yellow glass (up to 30 wt% CaO) forms a coating on and streaks within some black glass spherules, and has been attributed to melting of carbonate-rich sediment1, or organic-rich or pyritic limestone2. Here we present new trace-element and stable and radiogenic isotope data which show that the silicic glass is derived from continental crust of andesitic composition, whereas the high-Ca glass formed by melting of evaporite-rich sediment. This is confirmed by melting experiments with evaporite and andesite at 1,200–1,400 °C, which approximately reproduce the high-Ca glass. The temperature-dependent variation of sulphur content in synthetic high-Ca glasses indicates a formation temperature of 1,300 °C for the Haiti glasses. The geology of the impact site inferred from the geochemistry of the Haiti glasses matches the lithologies found in the 180-km Chicxulub structure, which occurs in Cretaceous evaporite deposits in Mexico. The high sulphur content of the calcic glasses suggests that the impact may have generated significant emissions of sulphur dioxide to the atmosphere, causing short-term global cooling.