Tektites in Cretaceous‐Tertiary boundary rocks on Haiti and their bearing on the Alvarez Impact Extinction Hypothesis
Tektites in Cretaceous‐Tertiary boundary rocks on Haiti and their bearing on the Alvarez Impact Extinction Hypothesis
复制标题
海地白垩纪-第三纪边界岩中的玻璃陨石及其对阿尔瓦雷斯撞击灭绝假说的影响
DOI：
10.1029/91je02249
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发表时间：
1991
影响因子：
--
通讯作者：
G. Izett
中科院分区：
文献类型：
--
作者：
G. Izett
遗迹玻璃陨石与铂族金属丰度异常和薄泥灰岩层中的冲击矿物有关，该薄泥灰岩层标志着海地的 K-T 边界。这三种撞击产生的材料在精确的 K-T 边界处的存在极大地加强了阿尔瓦雷斯撞击灭绝假说。玻璃陨石存在于蒙脱石小球中，其具有典型的玻璃陨石外部形状。它们的化学和物理性质与其他玻陨石类别大致相似，只是海地玻陨石的 Si 含量较低，而 Fe、Ca 和 Na 含量较高。平均而言，它们比其他玻璃陨石组含有更多的 Sc、V、Cu、Zn、Ga、Sr、Sn 和 Ba，以及更少的 Cr、Ni、Co、B、Mn 和 Hf。玻璃陨石中稀土元素（REE）的含量表明它们的原始材料不是熔化的镁铁质或超镁铁质洋壳；相反，它们是具有大量安山岩成分的沉积矿床。稀有玻璃陨石含有异常高含量的 CaO (∼20%) 和 S (0.4%)，这些数据表明一些目标材料由 CaSO4 组成。硬石膏层出现在两个候选撞击点（希克苏鲁伯和曼森）的地下。玻璃陨石的 Sm-Nd 同位素数据表明，熔化的前体沉积物很可能沉积在 -400 m.y 以下。晚白垩纪和志留纪之间。主要的化学变化伴随着玻璃到蒙皂石的成岩变化。海地玻璃陨石是K-T边界岩石中第一个有数据记录的撞击产物，玻璃的40Ar-39Ar年龄表明K-T边界和撞击事件同时发生在64.5±0.1 Ma。
Relic tektites are associated with a Pt-group metal abundance anomaly and shocked minerals in a thin marl bed that marks the K-T boundary on Haiti. The presence of these three impact-produced materials at the precise K-T boundary enormously strengthens the Alvarez impact extinction hypothesis. The tektites occur in smectite spherules that have external shapes typical of tektites. Their chemical and physical properties are broadly similar to those of other tektite groups, except that the Haitian tektites have lower Si and higher Fe, Ca, and Na. On average, they contain more Sc, V, Cu, Zn, Ga, Sr, Sn, and Ba and less Cr, Ni, Co, B, Mn, and Hf than Other tektite groups. Amounts of rare earth elements (REE) in the tektites indicate that their progenitor materials were not melted mafic or ultramafic oceanic crust; rather they were sedimentary deposits having a bulk composition of andesite. Rare tektites contain unusually high amounts of CaO (∼20%) and S (0.4%), and these data suggest that some target materials consisted of CaSO4. Anhydrite beds occur in the subsurface at two candidate impact sites (Chicxulub and Manson). Sm-Nd isotopic data for the tektites indicate that the melted precursor sediments were most likely deposited less than −400 m.y. between the Late Cretaceous and Silurian periods. Major chemical changes accompanied the diagenetic change of glass to smectite. The Haitian tektites are the first datable impact products in K-T boundary rocks, and 40Ar-39Ar ages of the glass show that the K-T boundary and impact event are coeval at 64.5±0.1 Ma.