The standard explanation for this pattern, based on ideas put forward by geophysicist J. Tuzo Wilson in 1963, is that the islands record motion of the Pacific plate over a volcanic hot-spot [see "Hot Spots on the Earth's Surface," by Kevin C. Burke and J. Tuzo Wilson; SCIENTIFIC AMERICAN, August 1976]. The hotspot can be thought of as a candle within the earth whose flame burns through the crust, pumping lava to the surface and building an island. The ever moving plate pulls the island off the hotspot, the hotspot generates a new island, and the cycle continues. Together the hotspot and plate tectonics produce islands like an assembly line.

In 1971 Jason Morgan of Princeton University went a step further. He proposed that the "candle" was the molten tip of a plume of hot rock rising from deep within the earth's mantle. Pinned down in the planet's interior, the hotspot itself did not move; only the plate did. In this view, the Hawaiian hotspot has remained at a latitude of about 19 degrees north, while the Pacific plate has moved northwest at about 10 centimeters a year. The great bend in the hotspot's track suggests that the direction of plate motion suddenly changed some 47 million years ago.

How come in these two sentences, the author is using past and present tense? I'm very confused. Blue color for present and red for past right? Can someone explain to this to me please.
The -ing words are untensed participles. You should discount those completely, as they don't carry any tense.

The whole article is in the past tense except the part where the reader is asked to imagine a situation by way of explanation of a geologic principle. The actions described in this imaginary scenario did not actually occur in the real world in the same way the other events mentioned in the article, so the past tense is not used for that explanatory scenario.

Once you understand this simple difference, there is no need for any confusion. Emotion: smile

"Pinned down" is another one which gets exempted from a tense designation.
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based on ideas put forward by geophysicist J..- BASED is in the past participle.

Ths ING verbs, have no tense, they're in the participle.

while the Pacific plate has moved - PRESENT PERFECT

The main Idea of the text is in the past, however, it's ok sometimes to use the simple present to refer to an action that happened in the past. We see that many times specially in headlines.
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