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Genesis of the Late Archean granitoids of the northern part of the Dharwar foreland (Dharwar Craton), south India – Insights from field, crystal size distribution, thermobarometry, microgeochemical and bulk-rock geochemical studies
Geochemistry ( IF 3.7 ) Pub Date : 2020-10-18 , DOI: 10.1016/j.chemer.2020.125688
Chandan K. Boraiaha , Annappa G. Ugarkar , Jayant K. Padhi , Rashmi Chandan , Mallappa V. Kallapur

An intrusive granitoid pluton into TTG-Dharwar Supergroup greenstone sequence is being reported for the first time from the Dharwar Foreland region. Based on field and petrographic characteristics, these granitoids are classified as - quartz-monzodiorites and granites. Occasional mafic bodies of dioritic-granodioritic composition with size ranging from small microgranular magmatic enclaves to bodies of several centimeters are common in these granitoids.

The granitoids are devoid of any crystal-plastic fabric as well as high-strain characteristics. The textural (CSD) studies indicate that the quartz-monzodiorites are derived from magma mixing whereas the granites are derived from equilibrium crystallization of the magma derived from the reworking of quartz-monzodiorites. The P-T estimates indicate that the quartz-monzodiorites were crystallized at higher temperature (>950 °C) and pressure (3.09–4.36 kbar) conditions in a reducing environment at mid-crustal levels. However, the granites indicate lower temperature (<750 °C) and pressure (0.89–1.88 kbar) conditions of crystallization in an oxidizing environment at shallow-crustal levels. The bulk rock chemical characteristics indicate that the quartz-monzodiorites were derived from the melt generated by the mixing of two melts - a melt derived from the differentiation of sanukitoids senso lato (s.l.) and a melt derived from the partial melting of TTG. On the other hand, reworking of the hot crystallizing quartz-monzodiorite due to its rapid upliftment to shallow crustal levels resulted in a decompression melting which gave rise to granitic melts.

The relative age of the Dharwad granitoids is estimated to be ∼2580–2560 Ma and unlike the other older granitoids (> 2.61 Ga) reported from the northern part of the Shimoga greenstone belt, the studied granitoids marks the final stage of cratonization in the Foreland region.



中文翻译:

印度南部达瓦尔前陆北部(达瓦尔克拉通)晚期太古宙花岗岩的成因–田野,晶体大小分布,热压计,微地球化学和块状岩石地球化学研究的真知灼见

从Dharwar前陆地区首次报道了侵入TTG-Dharwar Supergroup绿岩序列的侵入性花岗岩类岩体。根据田野和岩石学特征,这些花岗岩类被分类为-石英单闪闪石和花岗岩。在这些花岗岩类中,偶数-粒-粒-粒岩组成的基性镁铁质岩体的大小从小型微颗粒岩浆飞地到几厘米的岩体都很普遍。

花岗岩没有任何晶体塑料织物,也没有高应变特性。质地(CSD)研究表明,石英-单闪长岩是从岩浆混合中衍生出来的,而花岗岩则是从石英-单闪长石的返工中产生的岩浆的平衡结晶中衍生出来的。PT估计值表明,在中等地壳水平的还原性环境中,石英-单闪闪石在较高的温度(> 950°C)和压力(3.09-4.36 kbar)的条件下结晶。然而,花岗岩表明在浅地壳水平的氧化环境中较低的结晶温度(<750°C)和压力(0.89-1.88 kbar)。块岩的化学特征表明,石英单闪闪岩是由两种熔体混合产生的熔体产生的,熔体是指由薄壳类千寿树(sukitoids senso lato)(s1)的分化产生的熔体,而熔体是由TTG的部分熔解产生的。另一方面,由于热结晶的石英单闪闪石迅速上升到浅地壳水平而进行的返工导致减压熔融,从而产生了花岗岩熔体。

Dharwad花岗岩的相对年龄估计为〜2580–2560 Ma,与Shimoga绿岩带北部报道的其他较老的花岗岩(> 2.61 Ga)不同,研究的花岗岩标志着前陆克拉通化的最后阶段地区。

更新日期:2020-10-18
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