Petrochemistry of Kimberlites, Lamproites and Diamonds in India

大约四千年前，印度首次发现了钻石。许多世界上最著名的钻石(Great Mogul、Orloff、Shah、Darya-i-Noor、Regent、Nizam)以及许多臭名昭著的钻石(如Hope、Koh-i-Noor)都是从南部安德拉邦Krishna河岸的冲积沉积物中找到的。就大小和透明度而言，这些钻石和许多其他非凡钻石的主要来源尚未找到。与世界各地钻石矿藏的地质背景一样，印度的钻石也位于克拉通和移动皮带上。两个著名的钻石区是Majhgawan(自公元13世纪以来就被称为Majhgawan)和Wajrakarur，这是邦德尔坎克拉顿(中央邦)的一个运营中的矿山，以及安德拉邦达瓦尔克拉通的Wajrakarur。这两个地区的侵入岩年龄都是元古代的，大约1.1Ga的年龄与南非的Premier Kimberlite(库利南钻石的来源，已报道的最大钻石)和澳大利亚的Argyle Lamproite(世界上最大的钻石生产商，每年超过40Mcts)相似。这两个地点，以及非洲中部和巴西的元古界冲积沉积物，位于重建的罗迪尼亚超大陆的主要线状构造上。这被解释为与羽流有关。在过去的十年里，印度发现了50多个新的侵入体，这些古老的克拉通是研究地幔状态及其与地壳(TTG)演化关系的重要新实验室。印度的钻石寄主岩石既不是经典的金伯利岩，也不是传统的钾镁质岩石，而且被不同地描述为既有金伯利岩(矿物学)，也有钾镁质(地球化学)亲和力。这是地幔岩石化学面临的重大新挑战。许多侵入体具丰富的地幔包体，有的强烈榴辉岩，有的以橄榄岩为主，两者都将为研究次克拉通岩石圈龙骨的成分和热状态提供新的见解。印度的地球物理地图绘制得很好，地幔数据库将提供一套独立的约束条件来模拟地幔深处。将对来自32个侵入体的地幔样本进行显微镜研究，并使用电子微束和X射线荧光技术进行分析，以分别获得矿物和大块岩石成分。钻石的形态将通过立体和扫描电子显微镜，以及拉曼和红外光谱进行检查。这些数据将为印度首次对元古界地幔侵入岩进行全面研究。不仅在印度，而且在罗迪尼亚钻石矿藏的更广泛背景下，预计将有重大的新见解和重要的新解释。

HaggertyEAR-0106187Diamonds were first discovered in India some four millinnia ago. Many of the world's most famous diamonds (Great Mogul, Orloff, Shah, Darya-i-Noor, Regent, Nizam), as well as many infamous stones (e.g. Hope, Koh-i-Noor), were recovered from alluvial deposits on the banks of the Krishna River in the southern state of Andra Pradesh. The primary sources of these and many other extraordinary diamonds, in terms of size and clarity, have not been located. In common with the geological setting of diamond deposits worldwide, diamonds in India are also on cratons and in mobile belts. The two prominent diamond districts are Majhgawan (known since the 13th C), which is an operating mine in the Bundelkand Craton (Madhya Pradesh), and Wajrakarur in the Dharwar Craton of Andra Pradesh. The ages of intrusions in both districts are Proterozoic, and at about 1.1 Ga are similar in age to the Premier kimberlite (source of the Cullinan, the largest diamond diamond ever reported) in South Africa, and the Argyle lamproite (the world's largest producer, over 40 M cts/yr) in Australia. These two sites, along with Proterozoic alluvial deposits in central Africa and Brazil, lie along major lineaments in the reconstructed supercontinent of Rodinia. This is interpreted to be plume related. With over 50 new intrusives discovered in India over the past decade, these ancient cratons are an important new laboratory to study the state of the mantle, and its evolutionary relation the crust (TTG). The diamond host rocks in India are neither classical kimberlites nor conventional lamproites and are variously described as having both kimberlitic (mineralogically), and lamproitic (geochemically) affinities. This is a significant new challenge in mantle petrochemistry. Many intrusions have abundant mantle xenoliths, some are intensely eclogitic, and others are dominantly peridotitic, and both will provide new insights to compositions and thermal states of subcratonic lithospheric keels. India is well mapped geophysically and the mantle data base will provide an independent set of constraints to model the deep mantle. Mantle samples from 32 intrusions will be studied microscopically and analysed using electron microbeam and x-ray fluoresence techniques to obtain mineral and bulk rock compositions, respectively. Diamond morphologies will be examined by stereo- and scanning electron microscopy, and by Raman and infrared spectroscopy. These data will provide the first comprehensive study of Proterozoic mantle intrusives in India. Significant new insights are predicted and important new interpretations are anticipated, not only in India but in the broader context of diamond deposits in Rodinia.