Pt Reyes' Pre-Cretaceous Metamorphic Rocks

These rocks are the oldest rocks found on the Pt. Reyes Peninsula. Originally formed as muddy, sandy and limy sediments these rocks were likely shales, sandstones and limestones prior to their heating and alteration.   Metamorphosed by the invasion of granitic rocks they are currently schists, quartzites and marbles. Exposures of these rocks are quite limited however, Chicken Ranch Beach and other Tomales Bay shoreline exposures have interesting exposures of these rocks. Inclusions and small masses of highly altered metamorphics are found in the dominantly granitic exposures found at McClures Beach.

The Geologic Map Description

From Galloway: the "pkm"  rocks of Pt. Reyes include: Shist, micaceous quartzite, calc-hornfels, and graphitic marble locally containing scheelite and occur mainly as relatively small inclusions in granitic rock.

From Clark and Blake:  Metamorphic rocks -- Mica schist, impure quartzite, calc-hornfels, and graphitic marble locally containing scheelite occur as inclusions and small roof pendants in the granodiorite and granite of Inverness Ridge.  Garnet- and sillimanite-bearing quartzofeldspathic gneiss and granofels form a septum at McClures Beach between the tonalite of Tomales Point and the granodiorite and granite of Inverness Ridge (Ross, 1977, 978).  Although Cretaceous granitic rocks intrude these metasedimentary rocks, their age is uncertain but is probably Mesozoic or Paleozoic.



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