An appraisal of Archaean supracrustal sequences in Chitradurga Schist Belt, Western Dharwar Craton, Southern India
An appraisal of Archaean supracrustal sequences in Chitradurga Schist Belt, Western Dharwar Craton, Southern India
复制标题
DOI：
10.1016/j.precamres.2012.04.006
复制
发表时间：
2013-04
影响因子：
3.8
通讯作者：
T. Hokada;K. Horie;M. Satish-Kumar;Y. Ueno;A. Nasheeth;Kaoru Mishima;K. Shiraishi
中科院分区：
文献类型：
--
作者：
T. Hokada;K. Horie;M. Satish-Kumar;Y. Ueno;A. Nasheeth;Kaoru Mishima;K. Shiraishi
本文根据原岩、可能的沉积时间和变质事件沿着变质条件，重新评价了西达尔瓦尔邦奇特拉杜尔加片岩带的中生代变质沉积序列。现有的地质和地层的限制和我们的实地观察表明，最古老的表壳序列的Szurr组，这是发生在半岛片麻岩的飞地，是由下Bababudan和上Chitradurga组组成的Dharwar超群覆盖。奇特拉杜尔加片岩带各地层单位变质条件不同，其中奇特拉杜尔加群变质条件差异最为显著。下组为黑云母-白云母级变质，上组为绿泥-白云母级变质。离子探针分析碎屑锆石U-Pb年龄表明，最年轻的原岩岩浆年龄为3.14Ga，最年轻的原岩岩浆年龄为3.22-2.92Ga，分别代表了Bababudan群和Chitradurga群下单元沉积的最老年龄界限。Chitradurga片岩带上部单元的沉积年龄可由变流纹岩的2.68Ga岩浆锆石年龄和上覆砂岩的2.63Ga岩浆碎屑锆石年龄来确定，它们明显比下部单元年轻。独居石U-Th-Pb年龄在Chitradurga群的下单元和上单元都是相似的。2.4Ga），但明显比基础的Bababudan和Sadur群年轻（2.4Ga）。3.1Ga）。结合锆石和独居石的数据意味着连续或复合的中太古代-新太古代表壳序列的Chitradurga群一起变质在最新的太古代-早元古代。这些区域变质年龄在下伏的Bababudan群和Songur群以及基底半岛片麻岩中没有检测到。对比沉积和变质历史连贯的中太古代和新太古代地层在Chitradurga片岩带具有重要意义的比较与完善的沉积序列的皮尔巴拉和Kaapvaal的类似年龄。达尔瓦尔超群的原岩和变质年龄，与印度、马达加斯加和东南极洲周围的侏罗纪火山的类似信息相比，证明了可能的侏罗纪联系，并提供了从深到浅的侏罗纪地壳形成的线索。
Archaean metasedimentary sequences of the Chitradurga Schist Belt in Western Dharwar Craton were reassessed in terms of their protoliths, potential timing of deposition and metamorphic events along with metamorphic conditions. Existing geological and stratigraphic constraints and our field observations suggest that the oldest supracrustal sequence of the Sargur Group, which occurs as enclaves in Peninsular Gneiss, is overlain by the Dharwar Supergroup consisting of lower Bababudan and upper Chitradurga Groups. In the Chitradurga Schist Belt, the metamorphic conditions of each stratigraphic unit are distinct, with most prominent difference observed in the Chitradurga Group. The lower unit of this group are metamorphosed under biotite-muscovite grade, whereas the upper unit at chlorite-muscovite grade. Detrital zircon U–Pb dates obtained by ion microprobe analyses suggest 3.14Ga and 3.22–2.92Ga for the youngest protolith's magmatic ages, which constrain the oldest age limit of deposition of Bababudan Group and Lower Unit of Chitradurga Group, respectively. The depositional age of Upper Unit of Chitradurga Schist Belt can be bracketed by 2.68Ga magmatic zircon ages from meta-rhyolite and 2.63Ga magmatic detrital zircon age of the overlying sandstone that are significantly younger than the Lower Unit. Monazite U–Th–Pb ages are similar for both Lower and Upper Units of the Chitradurga Group (∼c. 2.4Ga) but are significantly younger than those of the underlying Bababudan and Sargur Groups (∼c. 3.1Ga). Combined zircon and monazite data imply that the continuous or composite Mesoarchaean-Neoarchaean supracrustal sequences of the Chitradurga Group are metamorphosed together at the latest Archaean-early Proterozoic. These regional metamorphic ages are not detected in the underlying Bababudan and Sargur Groups, as well as the basement Peninsular Gneiss. Contrasting depositional and metamorphic history in coherent Mesoarchaean and Neoarchaean strata in the Chitradurga Schist Belt have important implications for the comparison with the well-established sedimentary sequences of similar ages in the Pilbara and Kaapvaal cratons. The protolith and metamorphic ages of the Dharwar Supergroup, when compared with available similar information from the surrounding Archaean cratons in India, Madagascar, and East Antarctica, testify the probable Archaean connection, and give clues to the formation of deep to shallow Archaean crust.