14.1: Paleogeography and Tectonics of the Cenozoic
- Page ID
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)During the Cenozoic, the plates moved the continents into more familiar positions, with the most significant change being the closure of the Tethys Sea through continental collisions that built mountains, such as the Alps, the Zagros, and the Himalayas, the latter of which began about 57 million years ago and continues to this day. This closed off the Atlantic from the Indian Ocean, causing the rearrangement of global ocean circulation patterns.
Figure \(\PageIndex{1}\): The closure of the Tethys Sea during the Cenozoic. Dan.palcu, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons.Perhaps the most significant tectonic event to occur in the Cenozoic regarding North America was the transformation of the west coast of California from a convergent boundary subduction zone to a transform boundary. Subduction along the western margin of the United States had occurred throughout the Mesozoic and into the Cenozoic. The video below is an animation of the last 38 million years of movement in western North America. Note that after the mid-ocean ridge is subducted, the convergent boundary becomes a transform boundary, and continental rifting begins.
Near the end of the Mesozoic and into the Cenozoic, the Laramide Orogeny built mountains hundreds of miles east of the active western margin of the North American continent. This is attributed to "flat-slab" subduction and the oceanic Farallon Plate being young and close to its spreading center.
Figure \(\PageIndex{2}\): Shallow subduction during the Laramide Orogeny; public domain (USGS)Flat-slab subduction happened when the rate of subduction was faster than the spreading of the seafloor between the Farallon and the Pacific plates. Eventually, because the rate of seafloor spreading couldn't keep up with the rate of subduction, the mid-ocean ridge itself was subducted, causing the relative motion along the plate boundary to change from convergent to transform. The transform boundary became the San Andreas Fault System.
As the San Andreas grew, it caused east-west-directed extensional forces to spread over the western United States, creating the Basin and Range province. The transform fault has shifted position over the last 18 million years, twisting the mountains around Los Angeles; new faults in the southeastern California deserts may become future San Andreas-style faults.
As subduction ceased, the nearly horizontal Farallon slab of oceanic crust began to sink into the mantle, allowing asthenosphere material to rise around it and magma to rise to Earth's surface. This volcanic event is known as the Oligocene ignimbrite flare-up, one of the most significant periods of volcanism in history, including the largest single confirmed eruption, the 5,000 cubic-kilometer Fish Canyon Tuff.
Figure \(\PageIndex{4}\): From Humphreys, 1995. Volcanic activity happened with the double-dashed line. The numbers associated with the solid black lines indicate the timing and location of volcanic activity.- Laramide Orogeny - a major mountain‑building event that affected western North America from roughly 80 to 40 million years ago
- San Andreas Fault System - a series of faults that mark the transform plate boundary that accommodates horizontal motion between the Pacific Plate and the North American Plate