Type of EarthCache: Metamorphic Feature
Introduction
CH-GM Road as in the title of this EarthCache is the abbreviation of Cameron Highlands-Gua Musang Road which is a newly constructed road between Cameron Highlands in Pahang and Gua Musang in Kelantan (Figure 1). The road crosses the so called Bentong-Raub Suture which here is at least 18 km wide (Tjia & Syed Sheikh, 1996).
Figure 1. Location of Serpentinite: CH-GM Road EarthCache and geological map of Bentong-Raub Suture (modified after Metcalfe, 2000). The newly constructed road is not shown in the map.
Geology of CH-GM Road in the Bentong-Raub Suture
The Bentong-Raub Suture (Figure 1) represents the Palaeo-Tethys (ancient ocean) in Peninsular Malaysia. It is a southwards extension of the Nan-Uttaradit and Sra Kaeo sutures of Thailand (Hutchison, 2009). The suture zone contains oceanic ribbon chert that has been dated by radiolarian ranging in age from Upper Devonian to Upper Permian (Metcalfe, 1999). Graptolites in the associated states of the Tuan Estate south of Karak are dated Lower Devonian (Jones, 1970). Limestone clasts in mélange are of Lower and Upper Permian age. The Palaeo-Tethys therefore opened in the Lower Devonian, caused by separation of Sibumasu from Gondwanaland, and closed in the Triassic, caused by the Indosinian orogenic collision with the Indochina Block that was earlier sutured to Eurasia.
The western margin of the CH-GM Road is of Main Range granite and the eastern margin of bedded chert. On the west, the granite injects into phyllite-schist that is a common rock type. Tjia and Syed Sheik (1996) have mapped several thick zones of tuffaceous olistostrome and mélange. There is a small serpentinite lens. From west to east, there are at least seven tectonic units. A complete unit comprises a systematic sequence of phyllite and schist, olistostrome with or without a massive mudstone interval, and bedded chert. These packages are stacked with a NW-SE strike with steep to moderate dips towards the NE (Hutchison, 2009).
Serpentinite: CH-GM Road
At the EarthCache site, the CH-GM Road cuts across one of the serpentinite lens in the Bentong-Raub Suture. The identification of the serpentinite at this road cut is the exercise of this EarthCache.
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, i.e. a hydration and metamorphic transformation of ultramafic rocks from the Earth's mantle. The alteration is particularly important at the sea floor at tectonic plate boundaries. Samples of the oceanic crust and uppermost mantle from ocean basins document that ultramafic rocks there commonly contain abundant serpentine. Hence the occurrence of serpentinite is associated with oceanic crust and uppermost mantle environment (Wikipedia, 2012o).
Serpentinite is dark green to yellow-green colour often streaked or shot through with veins of other colors. Rock tends to be soft (H=3-5), and have a greasy or silky feel, especially on smooth flat surfaces. Luster tends to be dull or waxy. Once one becomes familiar with the rock it is distinctive and easy to recognize, but it is the “feel” of it that is most indicative. Note that there is no texture to the rock, no foliation or grains present. (Fichter, 2010).
Their olive green color and smooth or scaly appearance is the basis of the name from the Latin serpentinus, meaning "serpent rock". The product of weathering of serpentinite are unusually high in clay soils that are toxic to many plants, because of high levels of nickel, chromium, and cobalt; growth of many plants is also inhibited by low levels of potassium and phosphorus and a low ratio of calcium/magnesium. The flora is generally very distinctive, with specialised, slow-growing species. Areas of serpentine-derived soil will show as strips of shrubland and open, scattered small trees within otherwise forested areas; these areas are called serpentine barrens (Wikipedia, 2012j).
How to claim this EarthCache?
1. At the listed coordinates examine the serpentinite road cut.
2. Send us an email with the text "Serpentinite" on the first line, with answers to the following questions.
A. Describe the colour and appearance of the serpentinite rocks.
B. Describe the physical structure of the serpentinite exposure. Is the serpentinite body massive or fractured?
C. Describe the degree of weathering of the serpentinite exposure. Have the top or certain part of the serpentinite body weathered into soil?
3. Log your find, sharing your experiences and compulsory photos (to prove you were there)*
Glossary
1. Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color (from white to black), but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements present in the rock, and both red and green are most often related to traces of iron (in its oxidized and reduced forms respectively) (Wikipedia, 2012a).
2. Foliation is a term that refers to preferred orientation of minerals within a rock. It is common to rocks affected by regional metamorphic compression typical of orogenic belts. The foliation typically forms at right angles to the minimum principal strain direction. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and gneiss. The slatey cleavage typical of slate is due to the preferred orientation of microscopic phyllosilicate crystals. In gneiss the foliation is more typically represented by compositional banding due to segregation of mineral phases. Foliated rock is also known as S-tectonite in sheared rock masses (Wikipedia, 2012b).
3. Gondwanaland (now called Gondwana), was the southernmost of two supercontinents (the other being Laurasia – the northernmost) that later became parts of the Pangaea supercontinent. Gondwana is believed to have sutured between ca. 570 and 510 Mya, thus joining East Gondwana to West Gondwana. It includes most of the landmasses in today's Southern Hemisphere, including Antarctica, South America, Africa, Madagascar and the Australian continent, as well as the Arabian Peninsula and the Indian subcontinent, which have now moved entirely into the Northern Hemisphere (Wikipedia, 2012c).
4. Graptolites are fossil colonial animals known chiefly from the Upper Cambrian through the Lower Carboniferous (Mississippian). The name graptolite comes from the Greek graptos, meaning "written", and lithos, meaning "rock", as many graptolite fossils resemble hieroglyphs written on the rock (Wikipedia, 2012d).
5. Luster is a description of the way light interacts with the surface of a mineral, crystal, or rock. The word traces its origins back to the Latin lux, meaning "light", and generally implies radiance, gloss, or brilliance. A range of terms are used to describe luster. Many terms refer to materials having similar lusters, such as earthy, metallic, greasy, and silky. Similarly, the term vitreous (derived from the Latin for glass, vitrum) refers to a glassy luster (Wikipedia, 2012e).
6. A mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically consists of a jumble of large blocks of varied lithologies. Large-scale melanges formed in active continental margin settings generally consist of altered oceanic crustal material and blocks of continental slope sediments in a sheared mudstone matrix. The mixing mechanisms in such settings may include tectonic shearing forces, ductile flow of a water-charged or deformable matrix (such as serpentinite), sedimentary action (such as slumping, gravity-flow, and olistostromal action), or some combination of these. Some larger blocks of rock may be as much as 1 kilometre (0.62 mi) across. Smaller-scale localized mélanges may also occur in shear or fault zones, where coherent rock has been disrupted and mixed by shearing forces (Wikipedia, 2012f).
7. An olistostrome is a sedimentary deposit composed of a chaotic mass of heterogeneous material, such as blocks and mud, known as olistoliths, that accumulates as a semifluid body by submarine gravity sliding or slumping of the unconsolidated sediments. It is a mappable stratigraphic unit which lacks true bedding, but is intercalated amongst normal bedding sequences, as in the Tertiary basin of central Sicily. The term olistostrome is derived from the Greek olistomai (to slide) and stroma (accumulation). Olistostromes are mélanges formed by gravitational sliding under water and accumulation of flow as a semi fluid body with no bedding (Wikipedia, 2012g).
8. Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradation in the degree of metamorphism between slate and mica schist. Minute crystals of graphite, sericite, or chlorite impart a silky, sometimes golden sheen to the surfaces of cleavage (or schistosity). Phyllite is formed from the continued metamorphism of slate (Wikipedia, 2012h).
9. Schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. By definition, schist contains more than 50% platy and elongated minerals, often finely interleaved with quartz and feldspar. Schist is often garnetiferous (Wikipedia, 2012i).
10. The serpentine group describes a group of common rock-forming hydrous magnesium iron phyllosilicate ((Mg, Fe)3Si2O5(OH)4) minerals; they may contain minor amounts of other elements including chromium, manganese, cobalt and nickel. There are three important mineral polymorphs of serpentine: antigorite, chrysotile and lizardite. They have their origins in metamorphic alterations of olivine and pyroxene. Alterations may be incomplete, causing physical properties of serpentines to vary widely. All serpentine minerals are microcrystalline and massive in habit, never being found as single crystals. Most serpentines are opaque to translucent, light (specific gravity between 2.2–2.9), soft (hardness 2.5–4), infusible and susceptible to acids. The colour ranges from blackish to brown, olive-green to yellowish green, and grey to white. Luster may be vitreous, greasy, waxy, or silky. They are often splotchy or veined. Many are intergrown with other minerals, such as calcite and dolomite. Many types of serpentine have been used for jewellery and hardstone carving, sometimes under the name false jade or Teton jade (Wikipedia, 2012j).
11. Sibumasu (a tectonic block) is an acronym coined by Metcalfe (1984), constructed from Si (Sino = China), bu (Burma), ma (Malay Peninsular = Shan-Thai of western Thailand and western Peninsular Malaysia) and su (Sumatra).
12. In structural geology, a suture is a joining together along a major fault zone, of separate terranes, tectonic units that have different plate tectonic, metamorphic and paleogeographic histories. The suture is often represented on the surface by an orogen or mountain range. The term was borrowed from surgery where it describes the sewing together of two pieces of tissue. In plate tectonics, sutures are seen as the remains of subduction zones, and the terranes that are joined together are interpreted as fragments of different palaeocontinents or tectonic plates. Outcrops of sutures can vary in width from a few hundred meters to a couple of kilometers. They can be networks of mylonitic shear zones or brittle fault zones, but are usually both. Sutures are usually associated with igneous intrusions and tectonic lenses with varying kinds of lithologies from plutonic rocks to ophiolitic fragments (Wikipedia, 2012k).
13. Texture in geology refers to the physical appearance or character of a rock, such as grain size, shape, arrangement, and pattern at both the megascopic or microscopic surface feature level. This includes the geometric aspects and relations amongst the component particles or crystals which is called the crystallographic texture or preferred orientation. The term microstructure is preferred by some petrographers. Textures can be quantified in many ways. The most common parameter is the crystal size distribution (Wikipedia, 2012l).
14. Tuff (from the Italian tufo) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered tuffaceous (Wikipedia, 2012m).
15. Ultramafic rocks (also referred to as ultrabasic rocks) are igneous and meta-igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). The Earth's mantle is composed of ultramafic rocks namely dunites, peridotites and pyroxenites (Wikipedia, 2012n).
References
1 Fichter, L.S., 2010. Serpentinite #1 [online]. Available from http://csmres.jmu.edu/geollab/Fichter/MetaRx/Rocks/serpentinite1.html [accessed on 2011]. 2 Hutchison, C.S., 2009. Bentong-Raub Suture. In: Hutchison, C.S. & Tan, D.N.K. (eds.), 2009. Geology of Peninsular Malaysia. UM & GSM, Kuala Lumpur, Malaysia, pp 43-53. 3 Jones, C.R., 1970. On a Lower Devonian fauna from Pahang, West Malaysia. Geological Society of Malaysia Bulletin, 3, 63-75. 4 Metcalfe, I., 1984. Stratigraphy, paleontology and palaeogeography of the Carboniferous of Southeast Asia. Memoire de la societe geologique de France, 147, 107-118. 5 Metcalfe, I., 1999. The Palaeo-Tethys in East Asia. Geological Society of Malaysia Bulletin, 43, 131-143. 6 Metcalfe, I., 2000. The Bentong-Raub suture zone. Journal of Asian Earth Sciences, 18, 691-712. 7 Tjia, H.D. and Syed Sheikh Almashoor, 1996. The Bentong suture in southwest Kelantan, Peninsular Malaysia. Geological Society of Malaysia Bulletin, 39, 195-211. 8 Wikipedia, 2012a. Chert [online]. Available from http://en.wikipedia.org/wiki/Chert [accessed on 19 Aug 2012]. 9 Wikipedia, 2012b. Foliation (geology) [online]. Available from http://en.wikipedia.org/wiki/Foliation_(geology) [accessed on 20 Aug 2012]. 10 Wikipedia, 2012c. Gondwana [online]. Available from http://en.wikipedia.org/wiki/Gondwana [accessed on 20 Aug 2012]. 11 Wikipedia, 2012e Lustre (mineralogy) [online]. Available from http://en.wikipedia.org/wiki/Lustre_(mineralogy) [accessed on 20 Aug 2012]. 12 Wikipedia, 2012d. Graptolithina [online]. Available from http://en.wikipedia.org/wiki/Graptolithinia [accessed on 19 Aug 2012]. 13 Wikipedia, 2012f. Mélange [online]. Available from http://en.wikipedia.org/wiki/ Mélange [accessed on 19 Aug 2012]. 14 Wikipedia, 2012g. Olistostrome [online]. Available from http://en.wikipedia.org/wiki/Olistostrome [accessed on 19 Aug 2012]. 15 Wikipedia, 2012h. Phyllite [online]. Available from http://en.wikipedia.org/wiki/Phyllite [accessed on 19 Aug 2012]. 16 Wikipedia, 2012i. Schist [online]. Available from http://en.wikipedia.org/wiki/Schist [accessed on 19 Aug 2012]. 17 Wikipedia, 2012j. Serpentine group [online]. Available from http://en.wikipedia.org/wiki/Serpentine_group [accessed on 19 Aug 2012]. 18 Wikipedia, 2012k. Suture (geology) [online]. Available from http://en.wikipedia.org/wiki/Suture_(geology) [accessed on 19 Aug 2012]. 19 Wikipedia, 2012l. Texture (geology) [online]. Available from http://en.wikipedia.org/wiki/Texture_(geology) [accessed on 20 Aug 2012]. 20 Wikipedia, 2012m. Tuff [online]. Available from http://en.wikipedia.org/wiki/Tuff [accessed on 19 Aug 2012]. 21 Wikipedia, 2012n. Ultramafic rock [online]. Available from http://en.wikipedia.org/wiki/Ultramafic_rock [accessed on 20 Aug 2012]. 22 Wikipedia, 2012o. Serpentinite [online]. Available from http://en.wikipedia.org/wiki/Serpentinite [accessed on 19 Aug 2012].
Finding the answers to an EarthCache can often be challenging, and many people tend to shy away from these caches because of this. However, it is my opinion that geocaching is also meant to be a fun family experience that simply aims to introduce interesting and unique locations such as this one. Flexibility on logging requirements, however, can only be applied if it can be established that you have actually taken the time to visit the site. For this reason, a proper log describing your adventure accompanied by a good number of photos would be much appreciated.
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