Sheeted dykes in Kandra ophiolite complex, Nellore schist belt, Andhra Pradesh — Vestiges of Precambrian oceanic crust

Abstract

Extensive field and petrological studies carried out in Kandra ophiolite complex (KOC) in the southern part of Nellore schist belt (NSB) revealed the existence of sheeted dykes in Kandra-Kondakuru-Gollapalli section. The sheeted dykes occur in the northern part of the complex and compositionally vary from medium-grained dolerites showing typical sub-ophitic texture to diabase dykes that are extremely fine grained aphanitic to fine-grained cryptocrystalline parallel basic dykes (varying in width from 4 cm to 1.25 m). These dykes show chilled margins on either side with the host dykes into which these are intruded. Veins of oceanic plagiogranite (0.5 x 5 m) are noticed in a major sheeted dyke. Occurrence of oceanic plagiogranite as ovoid / semicircular patches of 6 cm diameter resembling "immiscible droplets" within basic dykes is also noticed. The southern part of the complex is made of a major NW-SE trending cumulus gabbro that grades into olivine gabbronorite in its eastern part. The southern gabbros represent the plutonic component and form the deeper part of the complex. In this paper an attempt has been made to present the field, petrographic and mineral chemistry account of various lithounits that constitute the Kandra ophiolite complex in a succinct manner.

New SHRIMP Age and Microstructures from a Deformed A-Type Granite, Kanigiri, Southern India: Constraining the Hiatus between Orogenic Closure and Postorogenic Rifting

“…Among the ophiolite remnants, the 1900 Ma KOC occurs in the southern part of the NSB, with imbricate thrust slices documented around Kandra and Gurramkonda hosting hornblende metagabbros, thick massive to pillowed metabasalts, sheeted metadolerite dikes, and thin metapelite and metapsammite horizons intercalated with metabasalt (Sesha Sai 2009;Vijaya Kumar et al 2010;Saha 2011). On the basis of detailed geochemistry and a lithological association similar to that of deformed remnants of ocean plate stratigraphy, the KOC is interpreted as an oceanic backarc subtype of subduction-related ophiolite (Saha 2011;Saha et al 2015).…”

The Chimalpahad anorthosite Complex and associated basaltic amphibolites, Nellore Schist Belt, India: Magma chamber and roof of a Proterozoic island arc

“…The presence of ophiolitic rocks on the western border of the Eastern Ghats Belt (Dharma Rao and Reddy, 2009;Sesha Sai, 2009;Vijaya Kumar et al, 2010) indicates an active convergent margin, which developed as a result of westward subduction and accretion before final collision with the Dharwar craton (Dharma .…”

“…Symbols as in Fig. 8. ophiolite with sheeted dolerite dykes (Sesha Sai, 2009;Vijaya Kumar et al, 2010). Thus, several lines of evidence suggest that the NSB has a long history of subduction-accretion processes at an active plate margin, and may be comparable with the Japanese Islands that have a 500 Ma history of subduction-accretion (Isozaki et al, 2010).…”

Dismembered ophiolites in Paleoproterozoic nappe complexes of Kandra and Gurramkonda, South India

“…The metabasalts, interstratified sedimentary rocks, sheeted basalt to dolerite dykes and hornblende metagabbros are outcropped intermittently within a narrow (c. 2.5 km  10 km) WNW trending strip around Kandra and Arimanupadu villages. The rock association outcropped around Kandra has been variously named as Kandra volcanics (Roy, 1956), Kandra igneous complex (Nagaraja Rao et al, 1991;Rao, 1992), Kandra ophiolite complex (Vijaya Kumar et al, 2010) or Kandra nappe complex (Saha, 2010 (Rao, 1992;Sesha Sai, 2009;Vijaya Kumar et al, 2010) show a southern metagabbro with small patches of ultramafic rocks (talc-chlorite schists of Vijaya Kumar et al, 2010) and a northern sheeted dyke unit with patches of quartzite and conglomerates. These two units are surrounded by metabasalts belonging to the supposedly older (Neoarchean) components of the Nellore schist belt (Ravikant, 2010).…”