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The metamorphic rocks of Nederland and the origin of life

Brian Alers, PGeo.
Posted 1/15/25

NEDERLAND - The bedrock that underlies Nederland contains evidence of ancient submarine hot springs, known as black smokers, 1.7-2.2 billion years ago. During the earliest beginnings of the earth, the first strains of bacteria flourished around...

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The metamorphic rocks of Nederland and the origin of life

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NEDERLAND - The bedrock that underlies Nederland contains evidence of ancient submarine hot springs, known as black smokers, 1.7-2.2 billion years ago.

During the earliest beginnings of the earth, the first strains of bacteria flourished around submarine hot springs. The lower temperature portions of these submarine hot springs and seepages focused a strong chemical disequilibrium on the ocean floor that played an important role in the emergence of life.

These concentrated chemical reactions provided a substrate for primitive bacteria to form without sunlight or oxygen. Conditions suitable for the reduction of CO2 and for the synthesis of organic molecules to form on site.

In Nederland, a complex group of metamorphic rocks lie below Pre-Wisconsin and Early Pleistocene-aged (75,000 to 11,000 years ago) glacial gravel cover. Metamorphic rocks are changed rocks – in this case, ancient island-arc related sedimentary, volcanic and igneous rocks that were heated and deformed to become metamorphic rocks sometime between 1.8-1.66 billion years ago when these ancient island-arc related rocks were smashed up against the 2.3-billion-year-old super continent of Colombia or Nuna that presently lies north of the Colorado-Wyoming border.

Imagine present day island arcs like Japan and Indonesia being smashed against Southwest Asia. 

The bulk of these metamorphic rocks are called gneiss (with a silent “g,” they are pronounced “nice”).

The obvious layering (foliation) you can see in these metamorphic rocks often represents the original layering of these rocks before metamorphism. The dark colored layers are mica (biotite) rich rocks that were once sediments; the more massive black (hornblende) rich rocks were once Hawaiian type basaltic lava flows; the lighter colored layers are feldspar (microcline) rich rocks that were once felsic volcanic flows and water-laid ash fall tuffs.

This rock package was intruded by igneous granitic intrusive rocks during metamorphism.   

Ogden Tweto and Josiah Spurr, some of the first geologists to visit Colorado 150 years ago. named this group of metamorphic rocks the Idaho Springs Formation. The Idaho Springs Formation is part of the Yavapai crustal province which underlies much of the southwestern United States and is found in the bottom of the Grand Canyon.

The early ocean was likely to have been partially vaporized many times by massive meteorite impacts in the first half a billion years or so of the Earth’s history.

At that time, the sun had only about 70% of its present luminosity and the UV flux was an order of magnitude higher due to the absence of an ozone layer. These conditions allowed the solar wind to blow away all the primary atmosphere that was degassing through volcanoes or introduced by micrometeorites and comets. What little atmosphere that was trapped gravitationally contained little oxygen and was known as the “volatisphere.”  

The continents started to form approximately 3.8 billion years ago. With no landmasses to speak of, the first continental crust was highly radioactive, hot, pliable, and much too weak to stack up above sea level and form landmasses.

Primitive oceans would have been turbulent places. Without the stabilizing effects of landmasses, the physical and chemical environment would have been highly turbulent and changeable. Such hostile conditions were far too unstable to support the “warm little pond” favored by Darwin as the cradle of life.

It seems likely that if delicate simple organic molecules, the building blocks of life, were delivered by micrometeorites and comet impacts, they would have had a hard time surviving on the early surface of the Earth.  

The Earth’s heat production for the first few billion years was more than five times present production. Given these high temperatures and rates of magma generation, the ocean floor was an important site of hot springs activity.

During the Late-Archean age, 2.8-3.0 billion years ago, hot spring activity is estimated to be three times what it is today. Lower temperature springs and seepages would have been widespread on the flanks of mid-ocean ridges and in the quieter conditions of the deep ocean floor on the early surface of the Earth.  

Modern sea floor exploration has shown that submarine hot springs are black smokers. Evidence of black smokers can be found in the Idaho Springs Formation in Colorado.

The black smoke expelled by submarine hot springs contains the metals zinc, copper, lead, silver, gold, and sulfur. Upon cooling, the metals settle on the sea floor in thin layers. In this case, the metamorphism of these metal-rich layers formed a rare zincian spinel mineral called gahnite.

At least 24 occurrences of zincian spinel (gahnite) occur in the metamorphic rocks of the central Rocky Mountains of Colorado. Three of these occurrences are found near Evergreen.

The widespread distribution of gahnite in the Idaho Springs Formation of north-central Colorado is second in regional extent only to the well-known gahnite horizons in the world class Broken Hill mineral deposits of the Curnamona Province of N.S.W. Australia. 

This interpretation is supported by the tight stratigraphic control of the gahnite-bearing horizons, interpreted metarhyolite host rocks, lithogeochemistry, zinc, copper, lead, silver, gold, and sulfur proportions, trace element contents, and the intimate relationship of metamorphic minerals representing syngenetic hydrothermal alteration to metal content.

References:

Kleinhans, L, Alers, B., James, L., Piper, J., Fisher, L., (2022), Three Precambrian Zincian Spinel Occurrences in the Central Colorado Front Range (CCFR).

Characteristics and Relationships Potentially Bearing on their Genesis and Metallogeny, Proceedings: Geological Society of America Annual Conference, 2022, Denver CO.

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