Torres del Paine vs. Split Mountain — 2 — Split Mountain
Before comparing Split Mountain to Torres del Paine, a bit about Split Mountain itself. Split (4287 m, 14,064’) is a well-known “fourteener” in California—a peak over 14,000’ (4267 m) tall. It is a dominant peak along the stretch of the Sierra Nevada south of Bishop and lies south of the Palisades group of fourteeners. John Bartley, Kevin Mahan, and I described the geology of the Split Mountain area in a 2012 paper in Geosphere:
There are four main units in the area:
Metamorphosed sandstones, shales, and limestones from a late Proterozoic and Cambrian marine shelf sequence; these are correlative with the Cambrian Campito and Poleta Formations;
Jurassic leucogranite of the Red Mountain Creek pluton;
Dark gray Tinemaha Granodiorite, dated at 165 Ma; and
Dikes of the ~150 Ma Independence dike swarm, which cut all the units above.
To geologists of a certain age Split Mountain was made famous by the magnificent 1966 book Geology Illustrated by John Shelton. This book was essentially an introductory geology book centered around aerial photos that Shelton, a pilot, had taken.
Title page of Geology Illustrated
Shelton used his photo of Split Mountain to illustrate the concept of a “roof pendant”, a place where the roof of a great batholithic cauldron sagged down into the magma below. Regardless of the merits of the term, it is also a great photo of a pluton roof, and more subtly, of a pluton floor.
Shelton’s photo of Split Mountain, looking northwest over Mather Pass and Palisade Creek. This photo must have been taken from an altitude of 16,000’ or more.
Split Mountain is easily viewed from Highway 395 about 20 km south of the town of Big Pine. In morning light, the granite, overlying brown metamorphic rocks, and dark gray granodiorite that overlies everything are clearly visible.
Sierran range front, looking west in morning light, from Highway 395 south of the Poverty Hills. White leucogranite is overlain by dark brown metasedimentary rocks that are in turn overlain on Split Mountain by dark gray granodiorite. It’s a twofer—a pluton roof and a pluton floor in one photo. Split Mountain is the large peak on the right with its characteristic V notch, and the minor peak on the left, at the end of a long aréte composed of metasedimentary rocks, is Cardinal Peak.
Aerial photos of show the relationships of the plutonic rocks to their wall rocks in detail. I piloted a Cessna 152 past this area several times, and up to the cliff faces once. It took the better part of an hour to get the Cessna up to about 12,000’. The following air photos were taken by both me and by John Bartley, who was the passenger. The stall warning horn was going off intermittently the whole time, which only added to the excitement (we were safe, with several thousand feet of air beneath us).
Panorama of the aréte running from Cardinal Peak (left) north toward Split Mountain. Highly jointed and locally iron-stained leucogranite is overlain by brown metasandstone correlative with the Cambrian Campito Formation, with a bit of greenish Cambrian Poleta Formation atop Cardinal Peak.
Cardinal Peak. Abundant NW-striking dikes are evident in the leucogranite, but these cut the brown metamorphic rocks as well. The cirque on the right is occupied by rock glaciers.
Closeup of the Cardinal-Split aréte. Layering in the metasedimentary rocks is subparallel to the roof contact, and dikes of granite cut these roof rocks. Here and elsewhere there is no sign of any blocks of the roof rocks within the granite.
Here is a ground-based photo of the back side of this aréte, where Cardinal Lake lies:
Late-afternoon light on the east side of the Cardinal-Split aréte. Abundant mafic and intermediate dikes of the Independence swarm cut both the leucogranite and the capping metamorphic rocks. Summit of Cardinal Peak, with its cap of Poleta Formation, at left.
Although Split Mountain is best known as an illustration of a pluton roof, a pluton floor is clearly visible on the peak itself. The metamorphic rocks are squeezed between leucogranite below and mafic granodiorite above, and this relationship extends over several square km.
Aerial view of Split Mountain from ~4000 m altitude, looking northwest. Leucogranite, locally stained deep orange, underlies dark brown metaclastic and buff metacarbonate rocks. These are in turn overlain by dark gray Jurassic Tinemaha Granodiorite. In Shelton’s black-and-white photograph the metamorphic rocks and granodiorite are barely distinguishable. Nevertheless, this is an excellent example of a flat-lying pluton floor that extends over several square km in this area (Bartley et al., 2012). Intermediate and mafic dikes cut through all the units. These are locally up to 10 m thick, and are highly composite.