Developing Heavy Stable Isotopes for Provenance of Turquoise, Metals and Glass

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。在美国国家科学基金会（National Science Foundation）的支持下，亚利桑那大学（University of Arizona）的一个跨学科团队将极大地扩展正在进行的工作，以确定(1)美国西南部和墨西哥北部绿松石的来源；(2)北美天然铜的来源；(3)北非和西非的铜资源；(4)非洲穆斯林时代的玻璃贸易珠。该小组由一名考古学家（大卫·基利克）、两名地球化学家（华金·鲁伊斯和约翰·切斯利）和三名研究生（托马斯·芬恩、丽莎·莫洛夫斯基和艾莉森·锡伯杜）组成。过去社会高度重视的一些无机材料在地质上是稀缺的，而且在地球表面分布不均匀。例如，美索不达米亚和西非萨赫勒地区都很少有铜矿，因此这些地区的人口必须通过长途贸易获得他们所消耗的几乎所有铜。绿松石只在半干旱地区的铜矿矿床周围形成，但通常在当地没有资源的地区的考古遗址中发现，如美索不达米亚和墨西哥中部。因此，这些材料（以及其他材料，如黑曜石、锡和玉石）是遥远地区之间史前接触的程度、持续时间和规模的潜在有价值的指标。只有将考古文物的化学或矿物成分与这些材料的特定地质来源的成分（物源分析领域）相匹配，才能获得远距离交换的实际证据。必要的第一步是证明这些材料的所有潜在来源实际上可以根据化学或矿物学证据彼此区分开来。最常用于物源分析的方法（微量元素比、光学岩石学和x射线衍射）不太可能完全成功地区分铜和绿松石矿床，它们是铜矿物和宿主岩石高度可变的集合体。这项研究将依赖于铅和锶同位素比例的测量。这些同位素的比例在特定矿床中的变化比微量元素的比例要小，不会因风化或冶炼而改变，并且通常与区域地质过程有关（例如，从地体中组合出次大陆）。在某些情况下，铜同位素比率也将用作第三条证据线。这些研究的更广泛影响将取决于实证结果。如果能成功地区分出绿松石的来源，考古学家将有一种强有力的新方法来研究墨西哥和美国西南部之间的史前相互作用。同样，如果西非考古遗址中铜合金和玻璃珠的地质来源能够从同位素和化学成分中可靠地推断出来，考古学家将能够详细研究穆斯林世界和撒哈拉以南非洲之间早期接触的历史——考虑到今天非洲三分之一的人口是穆斯林，这是一个非常受欢迎的话题。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).With the support of the National Science Foundation, an interdisiplinary team at the University of Arizona will greatly expand work in progress on characterizing (1) sources of turquoise in the southwestern USA and northern Mexico; (2) sources of native copper in north America; (3) sources of copper in North and West Africa; and (4) glass trade beads of the Muslim era in Africa. The team consists of an archaeologist (David Killick), two geochemists (Joaquin Ruiz and John Chesley) and three graduate students (Thomas Fenn, Lisa Molofsky and Alyson Thibodeau).Some of the inorganic materials that were highly valued by past societies are both geologically scarce and unevenly distributed across the earth's surface. For example, Mesopotamia and the West African Sahel both have few copper ore deposits, and thus the populations of these regions had to obtain almost all of the copper that they consumed through long-distance trade. Turquoise only forms around copper ore deposits in semi-arid areas, but is often recovered from archaeological sites in regions where there are no local sources, such as Mesopotamia and central Mexico. These materials (and others, like obsidian, tin and jade) are therefore potentially valuable indicators of the extent, duration and scale of prehistoric contacts between distant regions. Actual proof of long-distance exchange can only be obtained by matching the chemical or mineralogical composition of archaeological artefacts to the composition of specific geological sources of these materials (the field of provenance analysis). A necessary first step is to demonstrate that all potential sources of these materials can in fact be distinguished from each other on chemical or mineralogical evidence. The methods most commonly employed for provenance analysis (trace element ratios, optical petrography and x-ray diffraction) are not likely to be fully successful in distinguishing copper and turquoise deposits, which are highly variable aggregates of copper minerals and host rocks. This study will rely instead upon the measurement of isotopic ratios of lead and strontium. Ratios of these isotopes are less variable within particular deposits than are trace element ratios, are not altered by weathering or smelting, and can often be related to regional geological processes (e.g. the assembly of subcontinents from terranes). Copper isotope ratios will also be used as a third line of evidence in some cases.The broader impacts of these studies will depend upon the empirical findings. If turquoise sources can be successfully discriminated from each other, archaeologists will have a powerful new way of investigating prehistoric interaction between Mexico and the southwestern USA. Similarly, if the geological sources of copper alloys and glass beads in archaeological sites in West Africa can be reliably inferred from isotopic and chemical composition, archaeologists will be able to study in some detail the early history of contacts between the Muslim world and sub-Saharan Africa - a topic of very wide popular interest, given that one-third of the population of Africa today are Muslims.