Эрдэмтэд Онтонг Жава тэгш өндөрлөгийн доорх далайн хавтангийн бүтэц, химийн найрлагад галт уулын идэвхжил хэрхэн нөлөөлснийг тогтоов.
Номхон далайн баруун хэсэгт орших Онтонг Жава тэгш өндөрлөг нь 110-120 сая жилийн өмнө болсон галт уулын асар том дэлбэрэлтийн улмаас үүсжээ. Окаямагийн Шинжлэх ухааны их сургуулийн багш Азуса Шито тэргүүтэй судлаачид далайн ёроолын сейсмик долгионыг (Po болон So долгион) ашиглан энэхүү өндөрлөгийн доорх тектоникийн хавтангийн нууцлаг бүтцийг судлав. Судалгаагаар галт уулын дэлбэрэлт нь зөвхөн гадаргуу дээр лаав хуримтлуулаад зогсохгүй, хавтангийн дотоод бүтцийг өөрчилж, гүн гүнзгий сорви үлдээдэг болохыг тогтоожээ.
Сейсмик долгионы хурд болон хүч сулрах байдалд хийсэн шинжилгээгээр тус бүсэд босоо чиглэлийн магмын сувгууд болон хэвтээ давхаргууд хосолсон нарийн бүтэц илэрсэн байна. Энэ нь эртний магмын урсгал хавтангийн давхаргыг нэвтлэн, “дайк” буюу магмын сувгуудын сүлжээг үүсгэснийг нотолж байна. Судлаачдын үзэж буйгаар, термохимийн мантийн урсгалаас гарсан магма нь хүрээлэн буй чулуулагтай харилцан үйлчилж, химийн найрлагыг нь өөрчилсөн “дахин үржил” (refertilization) хэмээх үйл явц явагджээ.
Энэхүү ололт нь галт уулын асар том муж үүсэх явцад дэлхийн царцдас болон мантийн дотоод бүтэц хэрхэн өөрчлөгддөгийг илүү тодорхой болгов. Ингэснээр эрдэмтэд далайн ёроолын галт уулын үйл ажиллагаа нь зөвхөн гадаргын хэлбэрт нөлөөлөөд зогсохгүй, сая сая жилийн турш хадгалагдан үлддэг гүнзгий өөрчлөлтүүдийг хавтан дотор үүсгэдэг болохыг баталлаа.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
One of Earth’s largest volcanic events did far more than create the Ontong Java Plateau beneath the Pacific Ocean. Scientists have found that the eruption also changed the structure and chemistry of the oceanic plate buried below it.
The discovery shows that giant volcanic events can leave behind deep geological scars. Instead of simply covering the seafloor with layers of lava, massive amounts of magma can travel through existing plates and transform them from within.
The Ontong Java Plateau (OJP) is the largest oceanic plateau on Earth. Located in the western Pacific Ocean, it formed around 110 to 120 million years ago during an enormous period of submarine volcanism that produced one of the greatest volcanic outpourings in Earth’s history.
The event has long interested scientists because of its possible impact on the planet’s environment. Researchers have suggested that the huge amount of volcanic material released during this period may have affected ocean chemistry, climate conditions, and marine ecosystems.
A team led by Lecturer Azusa Shito from Okayama University of Science, together with Associate Professor Akira Ishikawa from the Institute of Science Tokyo and Professor Masako Yoshikawa from Hiroshima University, looked beneath the plateau to understand what happened inside the oceanic plate itself.
Something Unusual Is Hiding Beneath The Ocean Floor
To explore the hidden interior of the plate, the researchers studied high-frequency seismic signals called Po and So waves. These waves move through oceanic plates and can reveal underground features based on changes in their speed and strength.
The study published in Geophysical Research Letters found that the seismic behavior beneath the Ontong Java Plateau was different from what scientists usually see in oceanic plates. Po waves moved through the region relatively well, while So waves became much weaker.
This difference pointed to a complicated structure beneath the plateau. Instead of a simple series of layers, the plate appeared to contain horizontal layers cut by many vertical features created by ancient magma movement.
The data came from ocean bottom seismometers placed around the plateau and instruments installed on nearby islands. By studying the way the waves traveled, the researchers were able to identify the structures hidden deep below the ocean floor.
Earth’s Hidden Magma Network
The researchers found evidence of large groups of vertical intrusions called dike swarms. These structures form when molten rock forces its way through cracks before cooling and becoming solid.
The discovery suggests that magma from deep inside Earth pushed through the existing oceanic plate during the formation of the Ontong Java Plateau. The volcanic activity was not limited to the surface; it created a network of pathways inside the plate.
The team found that the combination of horizontal layers and vertical magma channels explains the unusual seismic signals recorded around the plateau. Some wave types could travel through the layered structure, while others were disrupted by the vertical intrusions.
The findings provide a new look at how giant volcanic provinces are built. The eruption created a huge underwater plateau while also leaving behind a complex internal structure that remains preserved millions of years later.
Magma Changed The Rocks Beneath The Plateau
The researchers also found that seismic waves traveled more slowly beneath the Ontong Java Plateau compared with normal oceanic plates. This suggested that the rocks below the plateau had been modified.
The team found that the unusual wave speeds could not be explained only by fractures. The researchers propose that magma from a thermochemical mantle plume interacted with the surrounding mantle rock and changed its chemical composition through a process called refertilization.
Refertilization happens when magma adds chemical components back into mantle rocks that previously lost them during partial melting. This process changes the minerals inside the rocks and can affect their physical properties.
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