OFİYOLİT KUŞAKLARINDA SERPANTİNLEŞME VE DOĞAL HİDROJEN OLUŞUMU
Jeolojik ortamlarda doğal hidrojen oluşumu çeşitli süreçler yoluyla gerçekleşir, ancak en önemli ve yaygın olarak incelenen mekanizma, Dünya'nın mantosundan türetilen ultramafik kayaları içeren bir su-kaya reaksiyonu olan serpantinizasyondur.
Peridotit, dunit ve harzburJit gibi bu kayalar, olivin ve piroksen gibi demir içeren mineraller bakımından zengindir. Su, bu kayalara kırıklar ve faylar yoluyla nüfuz ettiğinde, mineral yapısındaki demir (Fe²⁺) ile reaksiyona girer. Bu reaksiyon, demiri demir (Fe³⁺)'e oksitlerken su moleküllerini indirger ve hidrojen gazı üretimine yol açar. Aynı zamanda, orijinal mineraller serpantin, manyetit ve brusit gibi yeni fazlara dönüşür.
Bu süreç tipik olarak yaklaşık 200 ile 320°C arasındaki sıcaklıklarda gerçekleşir, ancak basınca, sıvı bileşimine ve kaya kimyasına bağlı olarak daha geniş bir aralıkta da gerçekleşebilir. En önemli faktör, hem reaktif demirin hem de dolaşan suyun bulunabilirliğidir; bunlardan herhangi biri olmadan hidrojen üretimi sınırlıdır. Daha da önemlisi, serpantinleşme, taze kaya yüzeyleri açıkta kaldığı ve sıvı akışı devam ettiği sürece devam edebilir; bu da hidrojen üretiminin tek seferlik bir olaydan ziyade sürekli bir süreç olabileceği anlamına gelir.
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Serpantinitler ve Serpantin Oluşumu
Serpantin mineralleri, peridotit , dunit ve diğer ultramafik kayaçların hidrotermal metamorfizmaya uğradığı yerlerde oluşur. Ultramafik kayaçlar Dünya yüzeyinde nadirdir, ancak okyanus kabuğunun tabanı ile üst manto arasındaki sınır olan okyanus moho'sunda bol miktarda bulunur.
Okyanus plakasının mantoya doğru itildiği yakınsak levha sınırlarında başkalaşıma uğrarlar . Bu süreçte hidrotermal metamorfizmaya maruz kalırlar. Bu işlem için su kaynağı, okyanus levhasının kaya ve tortullarında bulunan deniz suyudur.
Hidrotermal metamorfizma sırasında, olivin ve piroksen mineralleri serpantin minerallerine dönüşür veya serpantin mineralleriyle yer değiştirir. Burada oluşan metamorfik kayaların bazıları neredeyse tamamen serpantin minerallerinden oluşmaktadır. Bu serpantin bakımından zengin kayalar "serpentinitler" olarak bilinir.
Dünya yüzeyinin geniş alanları serpantinitlerle kaplıdır. Bu alanlar, günümüzdeki veya geçmişteki yakınsak levha sınırlarının yakınında bulunur. Bunlar, okyanus levhasının kalıntılarının yüzeye çıktığı yerlerdir. Levhanın kalıntı kısmı ya karaya doğru itilmiş, bir kara kütlesinin kenarına eklenmiş ya da yükselme ve derin aşınma sonucu yüzeye çıkmıştır.
Okyanus plakasının bu açıkta kalan bölgeleri ofiyolit olarak bilinir. Bunlar genellikle manyetit , kromit , krizopraz , yeşim taşı ve serpantin gibi değerli minerallerin kaynağıdır.
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NATURAL HYDROGEN.. BENEFIT OF SERPENTINIZATION..
Natural hydrogen—often called geologic hydrogen, “white hydrogen,” or sometimes “gold hydrogen”—refers to molecular hydrogen gas (H₂) that is generated and stored within the Earth’s crust through natural geological processes, without the need for industrial conversion of hydrocarbons or water electrolysis. Unlike engineered hydrogen types such as blue or green hydrogen, natural hydrogen is not manufactured; it already exists in subsurface systems, sometimes accumulating in volumes comparable to conventional natural gas reservoirs. Its growing importance lies in the possibility that it could serve as a low-carbon, potentially renewable energy resource, depending on how it is generated and replenished underground. Hydrogen is the simplest and lightest element, consisting of two hydrogen atoms bonded together, and its physical properties—low density, high diffusivity, and high energy per unit mass—strongly influence how it behaves in geological environments. Historically, natural hydrogen was largely overlooked because exploration efforts were focused on hydrocarbons, and hydrogen was often treated as a minor or incidental gas. However, recent discoveries of hydrogen-rich fields, along with improved understanding of subsurface geochemistry, have shifted attention toward hydrogen as a primary exploration target in its own right.
The formation of natural hydrogen in geological settings occurs through several processes, but the most significant and widely studied mechanism is serpentinization, a water–rock reaction involving ultramafic rocks derived from the Earth’s mantle. These rocks, such as peridotite, dunite, and harzburgite, are rich in iron-bearing minerals like olivine and pyroxene. When water penetrates these rocks through fractures and faults, it reacts with ferrous iron (Fe²⁺) in the mineral structure. This reaction oxidizes iron to ferric iron (Fe³⁺) while reducing water molecules, leading to the production of hydrogen gas. At the same time, the original minerals are transformed into new phases such as serpentine, magnetite, and brucite. This process typically occurs at temperatures between roughly 200 and 320°C, although it can happen over a broader range depending on pressure, fluid composition, and rock chemistry. The key factor is the availability of both reactive iron and circulating water; without either, hydrogen generation is limited. Importantly, serpentinization can continue as long as fresh rock surfaces are exposed and fluid flow persists, meaning that hydrogen generation can be ongoing rather than a one-time event.
Beyond serpentinization, other geological processes can also generate natural hydrogen, although they are generally less dominant. These include radiolysis of water, where natural radioactive decay splits water molecules into hydrogen and oxygen; thermal decomposition of organic matter at high temperatures; and reactions involving reduced gases in deep crustal or mantle environments. In some cases, hydrogen may also be produced during tectonic deformation, where mechanical stress and fracturing facilitate chemical reactions and fluid circulation. However, serpentinization remains the most efficient and volumetrically significant mechanism because it directly involves large volumes of ultramafic rock and can operate over geological timescales.
Once generated, hydrogen does not simply remain in place; it migrates through the subsurface in a manner similar to natural gas, although its smaller molecular size and higher mobility make its behavior more complex. Migration occurs primarily through faults, fractures, and porous rock layers, driven by buoyancy and pressure gradients. Because hydrogen is much lighter than other gases, it tends to move upward rapidly, and if no trapping mechanism is present, it may escape to the surface as seepage. Indeed, natural hydrogen seeps have been observed in various parts of the world, providing direct evidence of active subsurface systems. For hydrogen to accumulate in economically significant quantities, a complete geological system is required, analogous to a petroleum system.
The concept of natural hydrogen as an energy resource is still emerging, but it has already demonstrated significant potential through real-world examples and ongoing exploration efforts. One of the most notable cases is a hydrogen field in Mali, where high-purity hydrogen has been produced from shallow wells and used for electricity generation. This discovery has challenged the traditional assumption that hydrogen cannot accumulate in large volumes and has sparked renewed interest in exploring similar systems globally. The key advantage of natural hydrogen lies in its low production cost potential, since it does not require energy-intensive processing to create the gas. Instead, the primary challenge is geological: identifying locations where hydrogen is both generated and effectively trapped. This shifts the focus from chemical engineering to subsurface exploration, requiring integration of geology, geophysics, and geochemistry. As research advances, natural hydrogen is increasingly viewed as part of a broader transition toward cleaner energy systems. While uncertainties remain—particularly regarding resource size, recharge rates, and long-term sustainability—the fundamental processes that generate hydrogen in the Earth are well understood. This makes natural hydrogen not just a theoretical concept, but a credible and potentially transformative energy resource rooted in the dynamics of the planet itself.
aZRUL aMIR (azgeos@gmail.com)
https://www.linkedin.com/pulse/natural-hydrogen-benefit-serpentinization-m-azrul-amir-mausimm-uohac/
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