Mike Searle

Research Interests

(1) SW England Tectonics and Structure

1.1. Cornubian Granite batholith, Dartmoor to Land’s End.

The Variscan granites of SW England are Permian (295-275 Ma) S-type granites containing tourmaline, lithium micas, rare topaz and are pervasively mineralised with tin (cassiterite) tungsten (wolframite), copper (chalcopyrite, bornite), arsenic (arsenopyrite) and zinc (sphalerite) mineralised lodes. We are working on all the main Cornubian granite plutons, and their metamorphic aureoles, especially on the Land’s End, Cligga Head, Tregonning, Carnmenellis, and St. Austell plutons, combining geology and geophysics (gravity, seismic, bathymetry, topography) to determine the shape, structure, and emplacement mechanism of the granite batholith.

1.2. Lizard Ophiolite Cornwall, the metamorphic sole, and Kennack gneiss.

The Devonian Lizard ophiolite complex in Cornwall is the largest exposed ophiolite in the Variscan orogenic belt and contains an almost complete section from mantle peridotites (lherzolites, harzburgites), Moho transition zone, crustal gabbros, up to the sheeted dykes. It has an extensive metamorphic sole around the base consisting of amphibolites, and greenschist facies assemblages, and an enigmatic sequence of granitoids around the base (Kennack gneiss). Our project involves field structural mapping, thermobarometry, geochemistry, and U-Pb zircon dating in order to unravel the origin and emplacement history of the Lizard complex.

1.3. Lundy granite, Bristol channel.

Lundy Island in the Bristol Channel is an anomalous peraluminous granite intrusion of similar mineralogy (quartz + plagioclase + K-feldspar + biotite ± garnet ± topaz) and mineralisation (tin, tungsten) as the Permian Cornubian granites, but has a U-Pb zircon age of 59.8 ± 0.4 Ma making it related to the British Cenozoic Igneous Province, and not to the Permian granites of Devon and Cornwall. The similarity of mineralogy and composition is the result of melting similar source rocks at different times.

(2) Oman – United Arab Emirates ophiolite

2.1. Semail Ophiolite, Oman - United Arab Emirates (UAE) Mountains; origin and emplacement of the ophiolite, and Structural evolution.

The 96-95 Ma Semail ophiolite (Oman and UAE) is the largest, best exposed and most extensively studied ophiolite complex on Earth. Our project involves large scale structural mapping, microstructural analysis, thermobarometry, and detailed U-Pb dating of zircon from gabbros, and the amphibolite metamorphic sole. Geological studies are complimented by geophysical studies involving seismic imaging, gravity and magnetic profiles, and receiver functions, in collaboration with Khalifa University, Abu Dhabi.

2.2. Metamorphic Sole of the Semail ophiolite, Oman and UAE.

The metamorphic sole of the Semail ophiolite consists of an inverted profile the base of the ophiolite through garnet + clinopyroxene amphibolites (granulite facies), epidote amphibolites and greenschist facies meta-cherts and meta-carbonates. Peak PT conditions of formation are 700-900ºC, and 11-13 kbar, equivalent to ~40 km depth in a subduction zone beneath the Semail ophiolite. Synchronous U-Pb zircon ages from the ophiolite and the sole confirm a supra-subduction zone origin of the ophiolite. Our project involves large scale mapping, construction of balanced and restored cross-sections, microstructural analysis, thermobarometry, and detailed U-Pb and Sm-Nd dating of zircon, rutile and garnet, from about 15 localities along the mountain belt.

2.3. High-Pressure metamorphism, Saih Hatat; As Sifah eclogites, north Oman

In the As Sifah region of northern Oman a high-pressure belt, consisting of eclogites (20-23 kbar), blueschists (10-12 kbar) and extensive carpholite-bearing rocks (7-8 kbar) records the attempted subduction of the leading margin of the Arabian continental plate beneath the Semail Ophiolite during the later stages of ophiolite obduction. PT conditions 2.0 GPa and 550 – 600ºC record ultra-high pressure metamorphism at depths >100 km during the period ~81 – 77 Ma. Our project involves detailed mapping, micro-structural fabric analysis, combined with thermobarometry, and geochronology (U-Pb zircon, rutile) and Sm-Nd garnet).

2.4. Geology and geophysics of the Straits of Hormuz syntaxis, Musandam, Oman

The northern part of the Oman-UAE Mountains in the Musandam peninsula records a transition from Late Cretaceous ophiolite obduction tectonic regime in the SE to an early continent-continent collision along the Zagros Mountains in southern Iran. Our project involves detailed field mapping, surface structural mapping, and structural interpretation of the deep crust from seismic and well data, thermobarometry of the Bani Hamid granulites, and U-Pb dating.

(3) Himalaya

3.1. Structural, metamorphic and magmatic evolution of the Zanskar Himalaya (NW India)

The collision of India with Asia and closing of the intervening NeoTethys ocean at ca 50 Ma resulted in crustal shortening and thickening along the Indian plate margin. Obduction of the Spontang ophiolite onto the north Indian plate margin preceded continental collision. Deformation propagated south (or SW) from the Tethyan Himalaya to the Greater Himalaya with time, culminating in kyanite grade regional metamorphism between ~45-35 Ma, and sillimanite grade regional metamorphism from ~35-12 Ma. At the highest temperatures, partial melting of pelitic gneisses resulted in migmatisation and formation of the classic Himalayan leucogranites with widespread magmatic tourmaline, garnet, biotite, muscovite, and rare andalusite and cordierite-bearing leucogranites. The Zanskar Himalaya has the greatest extent of kyanite grade metamorphism and field mapping along the Suru Valley shows large-scale recumbent folding and deep thrusting.

3.2. Structural, metamorphic and magmatic evolution of the Nepal Himalaya.

The Nepal Himalaya shows spectacular exposures of kyanite and sillimanite gneisses, migmatites and large leucogranites, emplaced as giant sill complexes along the top of the Greater Himalayan Slab, bounded above by a low-angle normal fault. the South Tibetan Detachment. Our project involves detailed regional mapping in the Annapurna – Manaslu Himalaya, the Langtang valley, around the Everest – Makalu region in both Nepal and south Tibet, combined with thermobarometry, metamorphic modelling, and U-Pb dating of zircons and monazites.

3.3. 25th April 2015 Gorkha earthquake, Nepal

The 25th April 2015 Gorkha earthquake (magnitude 7.8) in Nepal ruptured the Main Himalayan Thrust (MHT) for ~140 km from the epicenter north of Gorkha, eastwards towards the Mount Everest region. The earthquake nucleated at a depth of ~15-18 km, but did not rupture to the surface. Our project used geodetic measurements of surface displacement to determine about 1 meter of uplift of the mountains north of the Kathmandu valley, and 0.6 meter of subsidence in the Everest region, showing a northward tilt of the Himalaya during the earthquake. Our data suggest the earthquake ruptured above a ramp in the MHT. We link geological studies of the Cenozoic evolution of the Nepal Himalaya with the active tectonics and earthquake record.

3.4. Quaternary metamorphism and melting, Nanga Parbat, Pakistan.

The western Himalayan syntaxis is centered on the mountain of Nanga Parbat (8126 meters) in the Pakistan Himalaya and exposes high-grade sillimanite and cordierite-bearing gneisses and migmatites intruded by tourmaline, muscovite and garnet-bearing leucogranites. Our project combines monazite petrochronology with thermal modelling to evaluate the roles of crustal melting, surface denudation, and tectonics in processes of ultra-fast exhumation of deeply buried rocks. We determined a pulse of ultra-fast exhumation (9-13 mm/year) that began ~1 million years ago, and was preceded by a slower, but still rapid exhumation (2-5 mm/year). These rocks are the youngest crustal melt granites anywhere in the World and record the highest exhumation rates.

(4) Kohistan, Karakoram, Pamir ranges, central Asia

The Kohistan Island arc (Jurassic to Eocene) was a major intra-oceanic arc within NeoTethys between the Indian plate to the south and the Asian plate to the north. It comprises lower crust ultramafic rocks (Sapat complex), and HP garnet granulites (Jijal complex), gabbro-norites (Chilas complex) with amphibolites (Kamila amphibolites) and upper crustal arc volcanics, intruded by granites and granodiorites of the Late Cretaceous to Eocene Kohistan – Ladakh – Gangdese granites. The Karakoram terrane located along the southern margin of the Asian plate, includes the southern Karakoram metamorphic complex, the Miocene Baltoro granite batholith and the northern Karakoram - southern Pamir sedimentary zone. Our project involves regional field mapping, structural analysis, petrology, thermobarometry, metamorphic modelling and U-Pb zircon geochronology, with the aim of unravelling the tectonic evolution of the Asian plate during and after the India-Asia collision.

(5) Tibet – structure, metamorphism, magmatism, and tectonics

Strike-slip faults in Tibet and SE Asia are key to the interpretation of the continental extrusion of Tibet hypothesis. We are studying the geology of the Lhasa Block, the southern margin of the Asian plate, and the major strike-slips involved in eastward extrusion, particularly the Karakoram fault, SW Tibet and Ladakh, the Red River fault, Yunnan and north Vietnam, the Xianshui-he fault in Eastern Tibet, and the Sagaing fault in Myanmar. These projects all involve field mapping, structural mapping, combined with U-Th-Pb geochronology, with the aim of determining the amount of geological offsets and timing of slip along these faults.

(6) South-East Asia

6.1. Burmese Jade mines Belt, Myanmar

The Hpakan – Taw Maw region of northern Myanmar hosts extensive deposits of World-class Jade, including jadeitites, rare Cr-rich jadeite (mawsitsit), Cr-rich clinopyroxene (kosmochlore) and albitite. This project studies ophiolites around Lake Indawgyi and samples from the Jade Mines. Our U-Pb zircon age from gabbros associated with the Jade Mines peridotites (169.71 ± 1.3 Ma) correlates well with similar un-metamorphosed ophiolites along the Myitkyina ophiolite belt (173 Ma). This project intends to fingerprint Burmese jade using petrology, Electron microprobe analyses, geochemistry, isotopes and LA-ICPMS.

6.2. Mogok metamorphic complex, Myanmar

The Mogok metamorphic belt in Myanmar (Burma) extends for 1000 km from the East Himalayan syntaxis south to the Andaman Sea, in Myanmar. It consists dominantly of high-grade marbles which host the World’s best quality rubies, skarn deposits which host blue sapphires, and many other rare gems. Syenites and charnokites form sheet-like intrusions into the marbles and have three different age groups, Jurassic (170-168 Ma), late Cretaceous – Paleocene (68-63 Ma) and late Eocene-Oligocene (44-21 Ma). Our project involves mapping, petrology, thermobarometry, and U-Pb zircon and titanite dating around many of the ruby-sapphire mines in the Mogok region.

6.3. Ophiolite belts of the Indo-Burman ranges, Myanmar, and Andaman Islands

The Indo-Burma ranges along the western border of Myanmar show extensive, highly deformed Triassic turbidites (Pane Caung Fm.), and four ophiolite complexes, with the Kaleymo ophiolite having an Early Cretaceous age similar to ophiolites along the Indus-Tsangpo suture zone in Tibet, and the Nagaland ophiolite in NE India. Our project involves, structural mapping, biostratigraphy, detrital zircon dating, and tectonic interpretation of the eastern margin of the indenting Indian plate. This suture zone extends south to the Andaman Islands where we have also studied the ophiolite, and the forearc region to the active volcanic arc (Barren Island volcano).

6.4. Tin granites of Malaysia, Thailand, and Myanmar

The South Myanmar – Thailand (Phuket Island) – west Malaysia Main Range province consists of biotite-K-feldspar (± garnet, ± tourmaline) S-type granites, which are associated with the World’s largest tin deposits in greisen-type veins. These granites result from crustal thickening following the collision of Sibumasu with Indo-China in the Triassic. Our project involves regional mapping, and sampling across the whole Malay peninsula for geochemistry, isotopes and U-Pb zircon dating.

(7) Aegean Islands, Greece

7.1. Metamorphic core complexes, Naxos and Ios Islands

The metamorphic core complexes of Naxos and Ios Islands are compressional in origin with high-grade kyanite- and sillimanite gneisses in the core and extensional faults around the margin. Older high-pressure blueschists and eclogites record an early subduction related metamorphism. ‘Extensional’ faults related to exhumation of blueschists, and exhumation of the regional Barrovian metamorphic core rocks occurred in a compressional setting. Only the last phase of low-angle normal faulting relates to regional Aegean Sea extension. Our project involves regional mapping, strain analysis, petrological modelling, thermobarometry, and U-Pb geochronology, with the aim of unravelling the tectonic evolution of the Aegean Orogeny.

7.2. Cycladic blueschist units, Tinos and eclogite metamorphism and structure, Syros, Naxos

The HP-LT rocks on Tinos Island include lawsonite- garnet- and glaucophane-bearing schists metamorphosed at 22-26 kbar and 490-520ºC. Eclogites containing aegirine omphacite and chromium-rich kosmochlore on Syros Island formed at pressure around 20-23 kbar. Exhumation of these HP rocks from the subduction zone occurred during the late stage of ophiolite emplacement, and assisted uplift of footwall rocks below a passive roof fault. Our project on Tinos and Syros Islands in the Aegean Sea involves regional mapping, detailed petrology, thermobarometry and metamorphic modelling, as well as U-Pb geochronology.

7.3. Tsniknias ophiolite, Tinos Island, and high-pressure metamorphism

The Tsniknias Island ophiolite is the best preserved obducted ophiolite in the Aegean Islands, and shows an amphibolite metamorphic sole accreted to the base of the harzburgite – lherzolite mantle sequence. The sole rocks comprise upper amphibolites and lower greenschist – blueschist facies meta-sediments. A plagiogranite intruded in the crustal sequence has a U-Pb zircon date of 161.9 ± 2.8 Ma. Partial melting occurred during subduction at ~ 74 Ma and the ophiolite was obducted some 90 m.y. after formation. Subduction beneath resulted in regional blueschist terrain exposed around the island of Tinos and HP eclogites on Syros Island.

7.4. I- and S-type granites on Tinos, Delos, Naxos islands

On the islands of Tinos, Delos, Mykonos, and Naxos in the Aegean Sea, Greece both hornblende, biotite bearing I-type granites and garnet + muscovite S-type granites occur together. U-Pb zircon ages suggest they formed simultaneously at ~15 – 14 Ma. The I-type granites are not related to Hellenic subduction but formed from dehydration melting of Variscan basement, whereas the S-type granites formed from muscovite-dehydration melting of a sedimentary protolith. Granite composition is related to different source rocks at different depths, at the same time. In this project we use field structural mapping, combined with major and trace-element geochemistry, Sr-Nd isotopes and U-Pb geochronology to constrain granite origin, and the tectonic evolution of the Aegean region.

(8) Geology of NW Scotland

8.1. Moine thrust belt, Loch Eriboll and Assynt Window

The Moine thrust belt in NW Scotland is the western margin of the Caledonian orogenic belt in Britain and is a classic fold-and-thrust belt that has been studied for more than100 years. New mapping in the Loch Eriboll and Assynt Window regions combined with restoration of balanced cross-sections has enabled a more detailed geometric analysis of the Moine thrust belt. The relationship of alkaline intrusions such as the Loch Ailsh syenites, Borralan intrusion and suite of lamprophyre dykes and sills, with thrusts enable us to constrain the sequence of thrusting in greater detail. Our project extends across the Northern Highlands with recent new work on the island of Mull constraining the P-T conditions and age of metamorphism of kyanite and sillimanite gneisses. We are also studying the relationships between the ~430-420 Ma ‘Newer granite’ suite with lamprophyre magmatism across the Northern Highlands and Grampian terranes.