Ugra stambham rock, Ahobilam
Nallamalla hills ner Srisailam"The Nallamalas (Telugu: నల్లమల్ల కొండలు) (also called the Nallamalla Range) are a section of the Eastern Ghats which stretch primarily over Kurnool, Mahabubnagar,Guntur, Prakasam and Kadapa districts of the state of Andhra Pradesh, India. They run in a nearly north-south alignment, parallel to the Coromandel Coast for close to 430 km between the rivers, Krishna and Pennar. Its northern boundaries are marked by the flat Palnadu basin while in the south it merges with the Tirupatihills. An extremely old system, the hills have been extensively weathered and eroded over the years."https://en.wikipedia.org/wiki/Nallamala_Hills
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Imaging mantle lithosphere for diamond prospecting in southeast India
Lithosphere, August 2013, v. 5, p. 331-342, first published on May 10, 2013, doi:10.1130/L269.1Imaging mantle lithosphere for diamond prospecting in southeast India
Abstract
An understanding of the tectonic makeup of an area through study of surface geological features, together with depth information on the nature of the underlying lithosphere, forms the key to diamond exploration strategy. Although diamonds have been reported from the Indian craton for many centuries, the search for their carrier rocks dates back only to the beginning of the twentieth century. This study focuses on a wide area in southeast India, parts of which are sources of both diamondiferous and nondiamondiferous kimberlites and lamproites. Using Ps (SV and SH) and Sp receiver functions, we recovered depth images of the lithospheric mantle beneath southeast India encompassing the Eastern Dharwar–Bastar cratons and the adjoining Eastern Ghats mobile belt. These images reveal the presence of two significant velocity anomalies of contrasting nature at different depths beneath the study region. High-velocity features are observed between 160 and 220 km depth (Lehmann discontinuity depth, or L-depth), and a complex low-velocity contrast layer is delineated at ∼80–100 km depth. Analyses of results from several other studies that include regional geology, geophysics, geochemistry, and geochronology allow us to infer that the positive velocity contrasts at L-depth represent preserved oceanic remnants of a ca. 1.6 Ga paleosubduction event in southeast India. Analysis of selected geothermobarometry data in conjunction with other evidence presented in this study indicates that the craton beneath southeast India is underlain by a thick lithospheric root/keel in excess of 200 km, suggesting an environment conducive to diamond stability. Consequently, we interpret the complex low-velocity contrast layer feature as a midlithospheric discontinuity and not a shallow lithosphere-asthenosphere boundary. The diamond formation potential of the area is discussed in light of a working model that incorporates the Mesoproterozoic paleosubduction scenario (ca. 1.6 Ma event) and subsequent kimberlite and/or lamproite intrusions. Wide regions covering the Godavari graben and adjoining areas are identified as potential zones for diamond exploration.
- Received 11 December 2012.
- Revision received 11 March 2013.
- Accepted 12 March 2013.
- © 2013 Geological Society of America
- http://lithosphere.gsapubs.org/content/5/4/331.abstract
Study finds new diamond mines
Picture for representational purpose only.
Hyderabad: New research has hinted at the possibility of a diamond seam in the Nallamala forest region in Andhra Pradesh and the Godavari Graben, one of the largest sedimentary basins in India. Scientists involved in the research also claimed to have found a new, cost-effective and quick search tool, using earthquake data, for identifying regions where diamonds could potentially occur.
Geoscientists from city-based CSIR National Geophysical Research Institute (NGRI) studied seismic data related to recent earthquakes retri-eved from seismological stations located at Hyderabad, Kadapa, Kothagudem and Dharwar. Geoscientists Dr Subrata Das Sharma and Dr Durbha Sai Ramesh published their findings in the latest issue of the journal Lithosphere.
Diamonds are generally formed inside the Earth at a depth of more than 150 km, and forge through the surface by rocks known as kimberlites and lamproites. Earlier studies had suggested that the Indian lithosphere is thin, but Dr Sharma and Dr Ramesh’s work suggests otherwise.
Areas identified for exploring diamonds
A study by geoscientists Dr Subrata Das Sharma and Dr Durbha Sai Ramesh claims that geothermal conditions are conducive for diamond stability. They have identified an area spread across two lakh square kilometres where there is a possibility of finding diamonds.
“There are several conditions required for the formation of diamonds, foremost among which are high pressure, high temperature and appropriate partial pressure of oxygen within the Earth’s mantle. Our findings suggest that these conditions are fulfilled in south-eastern India,” Dr Das Sharma said.
However, he cautioned that “we are only hinting at the possibility of a diamond field in the Nallamala forest region and the Godavari graben. New exploration strategies are essential. These are only potential areas.”
The Nallamala forest region is the largest untouched forest reserve in South India and is known to have rocks formed by large scale volcanic activity millions of years ago.
Geoscientists from city-based CSIR National Geophysical Research Institute (NGRI) studied seismic data related to recent earthquakes retri-eved from seismological stations located at Hyderabad, Kadapa, Kothagudem and Dharwar. Geoscientists Dr Subrata Das Sharma and Dr Durbha Sai Ramesh published their findings in the latest issue of the journal Lithosphere.
Diamonds are generally formed inside the Earth at a depth of more than 150 km, and forge through the surface by rocks known as kimberlites and lamproites. Earlier studies had suggested that the Indian lithosphere is thin, but Dr Sharma and Dr Ramesh’s work suggests otherwise.
Areas identified for exploring diamonds
A study by geoscientists Dr Subrata Das Sharma and Dr Durbha Sai Ramesh claims that geothermal conditions are conducive for diamond stability. They have identified an area spread across two lakh square kilometres where there is a possibility of finding diamonds.
“There are several conditions required for the formation of diamonds, foremost among which are high pressure, high temperature and appropriate partial pressure of oxygen within the Earth’s mantle. Our findings suggest that these conditions are fulfilled in south-eastern India,” Dr Das Sharma said.
However, he cautioned that “we are only hinting at the possibility of a diamond field in the Nallamala forest region and the Godavari graben. New exploration strategies are essential. These are only potential areas.”
The Nallamala forest region is the largest untouched forest reserve in South India and is known to have rocks formed by large scale volcanic activity millions of years ago.
The method used by Dr Das Sharma and Dr Ramesh could also be the quickest and most cost-effective for diamond exploration. Kimberlites and lamproites are extremely difficult to locate but the techniques by the NGRI geoscientists could be path-breaking for their pace and cost-effectiveness.
http://www.deccanchronicle.com/130816/news-current-affairs/article/study-finds-new-diamond-mines
India Sparkles with Promise of Diamonds, Study Finds
By Laura Poppick, Staff Writer | August 13, 2013 05:41pm ET
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Diamonds form deep within the Earth, and then travel to the surface within volcanic rocks, such as this kimberlite. |
India may contain a natural trove of diamonds previously overlooked by prospectors, new research shows.
Canada, Russia and southern Africa currently dominate the world diamond market. But, in recent years, geologists have debated whether southeast India could produce large quantities of diamonds as well. Now, research from a group of geologists at the National Geophysical Research Institute in Hyderabad, India, suggests that southeastern regions of the country do, in fact, contain the right ingredients for these gems to form in abundance. A report of their findings appeared earlier this month in the journal Lithosphere.
Diamonds form deep within the Earth's mantle and erupt to the surface within volcanic rocks called kimberlites and lamproites. The team discovered such diamond-bearing rocks by chance while conducting an unrelated geologic survey and decided to investigate the sites further as a side project.
"We thought that it may be a good idea to conduct further research on this crucial aspect to propose a suitable and cost-effective reconnaissance technique that can be deployed as a quick search tool over large areas for diamond prospecting," said geologist Subrata Das Sharma, an author on the paper. [Shine On: Photos of Dazzling Mineral Specimens]
Diamond-forming conditions
Instead of tediously searching an entire landscape for diamond-bearing rocks — which tend to crumble easily and are often difficult to identify — geologists have devised a variety of techniques to search for key diamond-forming conditions within the mantle, and then later explore promising areas on land.
These diamond-forming conditions include extremely high temperatures and pressures, found only in the deepest depths of theEarth's lithosphere — a region including the entire Earth's crust and the solid upper mantle that rests above the more molten lower mantle where crystals melt into magma.
Without the heat and pressure of the deep lithosphere, carbon — the only ingredient in diamonds — takes on the less valuable form of graphite.
The lithosphere varies in thickness across the planet, and does not always reach depths deep enough to facilitate diamond growth. Das Sharma and his team sought to find out how thick the lithosphere is under India, and did so by looking at seismic data collected during several relatively recent earthquakes. Since seismic waves travel at different speeds and amplitudes depending on the material they pass through, seismic data can reveal the transition from the hard upper mantle to the molten lower mantle, which is the lower boundary of the lithosphere.
Previous studies based on seismic data have suggested that southeastern India rests atop a thin portion of the lithosphere. But Das Sharma and his team reanalyzed related data using different techniques, and discovered a signal much deeper indicating the lithosphere reaches down far enough to facilitate diamond growth.
The team also examined existing analyses of the chemical composition of nearby rocks on the surface to further confirm that the temperature and pressure conditions would have been extreme enough to support diamond growth.
Indian diamond mining?
Ultimately, the researchers identified a region wider than 120,000 square miles (200,000 square kilometers) across southeastern India that could potentially contain diamond-bearing rocks.
These findings could lead to increased diamond mining in the country, but this will depend on the interests of mining companies, Das Sharma said.
"Diamond mining could become viable once an appropriate mining strategy is worked out," Das Sharma said. "This needs concerted efforts in field detection of generally obscured kimberlites and lamproites in a region." [Infographic: Tallest Mountain to Deepest Ocean Trench]
While the team's techniques are relatively quick and cheap, geologists elsewhere have developed other efficient methods for diamond prospecting as well. For example, some use electromagnetic tools that measure the conductivity of the mantle in search of carbon-rich areas (because carbon is highly conductive, or allows for the easy flow of electrons), while others use seismic imaging techniques that illustrate physical boundaries within the mantle.
Still, this new study demonstrates how to use effective and relatively cheap techniques that could help smooth the way for future diamond exploration programs around the world, according to Alan Jones, a geologist at the Dublin Institute for Advanced Studies in Ireland who was not involved in the study.
"This has really cleared up this Indian lithosphere issue," Jones told LiveScience. "In terms of global impact, I would say the paper is on part of the cutting edge along with other people's work."
The team members plan to share their results with the Indian government, and to continue honing their research methods to develop even more efficient diamond-hunting techniques.
http://www.livescience.com/
New Diamond Hope for Seemandhra in Nallamala Forests?
New research found diamond mines in in the Nallamala forest belt in Seemandhra region of Andhra Pradesh across the Godavari Graben, one of the largest sedimentary rock basins in India.
Geologists of CSIR National Geophysical Research Institute (NGRI), Hyderabad said they found new, cost-effective and quick search tool, using earthquake data, for identifying regions where diamonds could be mined.
Based on data collected from the recent earthquakes recorded in seismological stations located in Hyderabad, Kadapa, Kothagudem and Dharwar, Geoologists led by Subrata Das Sharma and Durbha Sai Ramesh published their research findings in the latest issue of the journal “Lithosphere”.
Diamonds are formed inside the Earth’s crest at a depth of more than 150 km, and forge through the surface by rocks known as kimberlites and lamproites.
Unlike the earlier studies, Sharma and ramesh suggest that the geothermal conditions in the region are conducive for diamond stability. The diamond mining will be possible over two lakh square kilometres, according to the study.
“There are several conditions required for the formation of diamonds, foremost among which are high pressure, high temperature and appropriate partial pressure of oxygen within the Earth’s mantle. Our findings suggest that these conditions are fulfilled in south-eastern India,” Das Sharma said.
However, he was quick to add:“we are only hinting at the possibility of a diamond field in the Nallamala forest region and the Godavari graben. New exploration strategies are essential. These are only potential areas.”
The Nallamala forest region is the largest untouched forest reserve in South India and is known to have rocks formed by large scale volcanic activity millions of years ago.
The method used by Sharma and Ramesh could lead to unearth diamonds quickly and in the most cost-effective manner. Kimberlites and lamproites are usually very difficult to locate diamonds but the techniques used by the NGRI geoscientists could replace earlier methods in diamond mining.