The Wajrakarur Kimberlite Field (WKF) on the Eastern Dharwar Craton in southern India hosts several occurrences of Mesoproterozoic kimberlites, lamproites and ultramafic lamprophyres, for which mantle-derived xenoliths are rare and only poorly preserved. The general paucity of mantle cargo has hampered the investigation of the nature and evolution of the continental lithospheric mantle (CLM) beneath cratonic southern India. We present a comprehensive study of the major and trace element compositions of clinopyroxene and garnet xenocrysts recovered from heavy mineral concentrates for three c.1·1 Ga old WKF kimberlite pipes (P7, P9, P10), with the goal to improve our understanding of the cratonic mantle architecture and its evolution beneath southern India. The pressure-temperature conditions recorded by peridotitic clinopyroxene xenocrysts, estimated using single-pyroxene thermobarometry, suggest a relatively moderate cratonic mantle geotherm of 40 mW/m² at 1·1 Ga. Reconstruction of the vertical distribution of clinopyroxene and garnet xenocrysts, combined with some rare mantle xenoliths data, reveals a compositionally layered CLM structure. Two main lithological horizons are identified and denoted as layer A (∼80–145 km depth) and layer B (∼160–190 km depth). Layer A is dominated by depleted lherzolite with subordinate amounts of pyroxenite, whereas layer B comprises mainly refertilised and Ti-metasomatized peridotite. Harzburgite occurs as a minor lithology in both layers. Eclogite stringers occur within the lower portion of layer A and at the bottom of layer B near the lithosphere–asthenosphere boundary at 1·1 Ga. Refertilisation of layer B is marked by garnet compositions with enrichment in Ca, Ti, Fe, Zr and LREE, although Y is depleted compared to garnet in layer A. Garnet trace element systematics such as Zr/Hf and Ti/Eu indicate that both kimberlitic and carbonatitic melts have interacted with and compositionally overprinted layer B. Progressive changes in the REE systematics of garnet grains with depth record an upward percolation of a continuously evolving metasomatic agent. The intervening zone between layers A and B at ∼145–160 km depth is characterized by a general paucity of garnet. This ‘garnet-paucity’ zone and an overlying type II clinopyroxene-bearing zone (∼115–145 km) appear to be rich in hydrous mineral assemblages of the MARID- or PIC kind. The composite horizon between ∼115–160 km depth may represent the product of intensive melt/rock interaction by which former garnet was largely reacted out and new metasomatic phases such as type II clinopyroxene and phlogopite plus amphibole were introduced. By analogy with better-studied cratons, this ‘metasomatic horizon’ may be a petrological manifestation of a former mid-lithospheric discontinuity at 1·1 Ga. Importantly, the depth interval of the present-day lithosphere–asthenosphere boundary beneath Peninsular India as detected in seismic surveys coincides with this heavily overprinted metasomatic horizon, which suggests that post-1·1 Ga delamination of cratonic mantle lithosphere progressed all the way to mid-lithospheric depth. This finding implies that strongly overprinted metasomatic layers, such as the ‘garnet-paucity’ zone beneath the Dharwar craton, present structural zones of weakness that aid lithosphere detachment and foundering in response to plate tectonic stresses.

中文翻译：

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金伯利岩中的Clinopyroxene和石榴石地幔货物作为Dharwar Craton建筑和地热的探源，对印度南部下的1·1 Ga岩石圈减薄事件有影响

印度南部东部达沃克拉通的Wajrakarur金伯利岩田（WKF）拥有数次中元古代的金伯利岩，红铁矿和超镁铁质的煌斑岩，其中地幔衍生的异岩很罕见，而且保存得很差。地幔货物的普遍匮乏妨碍了对印度南部克拉通以下的岩石圈地幔（CLM）的性质和演化的研究。我们目前单斜辉石和石榴石捕虏晶的主要和微量元素组成的综合研究，从沉重的精矿回收3个Ç.1·1 Ga旧的WKF金伯利岩管（P7，P9，P10），目的是增进我们对印度南部克拉通地幔构造及其演化的了解。用单次rox热气压计估计的橄榄石化次生辉石异种晶记录的压力-温度条件表明，一个相对中等的克拉通地幔地热为40 mW / m ^2。在1·1 Ga处进行的井斜辉石和石榴石异晶的垂直分布重建，再结合一些罕见的地幔异岩数据，揭示了组成分层的CLM结构。确定了两个主要的岩性层位，分别表示为A层（约80-145 km深度）和B层（约160-190 km深度）。A层主要由贫化的锂铁矿和次要数量的黄铁矿组成，而B层则主要包含经精炼和Ti变质的橄榄岩。Harzburgite在两层中均以次要的岩性出现。榴辉岩出现在A层的下部和B层的底部，在1·1 Ga附近的岩石圈-软流层边界。B层的可利用性由富含Ca，Ti，Fe，Zr和LREE的石榴石成分来标记。 ，尽管与A层中的石榴石相比，Y耗尽了。石榴石微量元素系统（如Zr / Hf和Ti / Eu）表明金伯利岩和碳酸盐熔体都与B层相互作用并组成叠印层。石榴石晶粒REE系统中随着深度的逐渐变化记录了不断演化的交代剂向上渗透。A和B层之间的深度约为145-160 km的区域具有石榴石的一般稀疏性。这个“石榴石稀少”区和上覆的Ⅱ型斜柏基带（约115-145 km）似乎富含MARID或PIC类型的含水矿物组合。约115-160 km深度之间的复合层可能代表了强烈的熔体/岩石相互作用，由此使以前的石榴石发生了很大的反应，并引入了新的交代相，如II型斜ino，金云母和闪石。与研究更好的克拉通类比，这种“变质层”可能是前岩石圈中部在1·1 Ga处的不连续性的岩石学表现。重要的是，目前印度半岛下方岩石圈-软流圈边界的深度间隔已被检测到在地震勘测中，与这个重叠的超自然界层层相吻合，这表明克拉通地幔岩石圈的1·1 Ga后分层一直发展到中岩层深度。这一发现暗示着强烈叠印的交代层，